The multifunctional roles of vegetated strips around and within agricultural fields

The multifunctional roles of vegetated strips around and within agricultural fields Background: Agriculture can have substantial negative impacts on the environment. The establishment and man‑ agement of vegetated strips adjacent to farmed fields (including various field margins, buffer strips and hedgerows) are commonly advocated mitigation measures for these negative environmental impacts. However, it may be difficult to obtain reliable evidence on the effects of implementation and management of vegetated strips, even though a substantial body of evidence exists. We describe a systematic map of research relating to vegetated strips in boreo‑ temperate farming systems to answer the question: What evidence exists regarding the effects of field margins on nutrients, pollutants, socioeconomics, biodiversity, and soil retention in boreo‑ temperate systems? Methods: We searched 13 bibliographic databases, 1 search engine and 37 websites of stakeholder organisations using a predefined and tested search string focusing on a comprehensive list of English language vegetated strip synonyms. Searches in Danish, Finnish, Spanish, and Swedish were also conducted using web searches. We screened search results at title, abstract and full text levels, recording the number of studies deemed non‑ relevant (with reasons at full text). A systematic map database of meta‑ data (i.e. descriptive summary information about the settings and methods) for relevant studies was produced following full text assessment. The systematic map database is provided as an evidence atlas: interactive, web‑ based geographical information system. Results: Over 31,000 search results were identified, resulting in a total of 1072 relevant primary research studies and 130 evidence reviews. Articles used a variety of terminology to describe vegetated strips, with ‘field margin’, ‘hedge ‑ row’, ‘shelterbelt’ and ‘riparian buffer’ most common. The volume of primary research is increasing linearly year ‑ by‑ year, whilst the increase in reviews has tailed off in the last 10 years. The USA and UK were most frequently studied and reviewed. Arable systems were investigated in c. 70% of primary research but 50% of reviews. Some 50% of primary research vegetated strips were field edge and 25% riparian, whilst riparian and field edge strips were roughly equally the focus of around a half of all described strips in reviews. Terrestrial biodiversity, nutrients (nitrogen and phospho‑ rus) and soil/water loss or retention were the most commonly measured outcomes in primary studies and reviews, although some other outcomes were more common in reviews than research articles (e.g. pesticides). Conclusions: We identified substantial bodies of evidence on particular sets of related outcomes and ecosystem services, which constitute important knowledge clusters/synthesis gaps relating to: strip width, terrestrial biodiversity, nutrient retention, hydrological regimes, toxic substances, erosion protection, pests, carbon sequestration, and soil and biodiversity combined. We also identified key knowledge gaps relating to: climate regulation, freshwater biodi‑ versity, strip harvesting, cultural ecosystem services, long‑ term impacts, the relationship between pest populations and crop yield, fuel and fibre production, specific regions and countries (e.g. Russia and South America), and multi ‑ use *Correspondence: neal.haddaway@sei.org; neal_haddaway@hotmail.com Mistra Council for Evidence‑Based Environmental Management (EviEM), Stockholm Environment Institute, Box 24218, 10451 Stockholm, Sweden Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Haddaway et al. Environ Evid (2018) 7:14 Page 2 of 43 vegetated strips. This systematic map is an important step in identifying what research has been done to date, and what primary and secondary research is needed as the next step for this topic. Keywords: Vegetative strip, Hedgerow, Beetlebank, Riparian buffer, Buffer strip, Filter strip, Buffer, Agri‑ environment, Agricultural policy, Mitigation, Agricultural pollution, Agricultural management Background fixtures in agricultural landscapes, and the interventions The ecological impacts of agricultural intensification must therefore be in place for longer than 12 months (see and change in Europe since the Second World War are inclusion criteria for further details). well documented and affect both agricultural areas and Vegetated strips may have a multi-functionality that their surrounding systems [1]. Biodiversity, air and water covers a range of processes, including protection of quality and soil structure of ecological systems have all water quality in surface waters and soil conservation of been affected [2]. Well-documented impacts of agricul - slopes, habitat improvement, biodiversity, shading, car- tural development include: widespread negative effects bon sequestration, flow capture, biomass production, of the application of nutrients in fertilisers (mineral and landscape diversity, and societal services [10]. These pro - organic) and agro-chemicals on soil, and surface and cesses occur through a set of pathways that impact socio- ground water quality [3]; emission of N O as a potent economic and environmental outcomes (Fig. 2). greenhouse gas [4]; negative effects of pesticides on non- target invertebrate species [5], birds [6] and biological Vegetated strips, water flow and sediment control potential [7]; and loss of ecological heterogeneity Many of the ecosystem services provided by some veg- at multiple spatial and temporal scales [8]. The establish - etated strips exist because of a reduction in water flow ment and management of vegetated strips (including field that occurs due to soil properties induced by the strip margins, buffer strips and hedgerows) are key mitigation and the presence of roots and above-ground vegetation. measures for these negative environmental impacts [9]. As surface runoff passes across field margins, the veloc - ity of shallow uniform flow tends to decrease in response Definition of vegetated strips to the type and density of strip vegetation as well as any Here, we define vegetated strips as any vegetated area set- decrease in slope. This reduction in flow velocity allows aside from the main cropping regime within or around a suspended sediment to be deposited, which decreases field, and installed for the purposes of benefiting native the transport of sediment and sorbed nutrients and biota, water and air quality, socio-economics, and yield. other contaminants beyond the strip. Strips with per- Examples of such interventions include: hedgerows, ennial vegetation, such as grasses, trees and/or shrubs, field margins, buffer strips, beetlebanks and shelterbelts can counter soil erosion via filtration of larger sediment (Fig. 1). For the purposes of this review, we focus on those particles [11, 12], and by increasing soil stability through interventions that are permanent or semi-permanent increased root density [13]. The reduction in flow veloc - ity also provides potential for infiltration of water into the strip, decreasing the total volume of runoff water and the associated load of dissolved contaminants; this process is controlled by the infiltration capacity of the soil and vegetated strips are known to modify this soil parameter relative to adjacent agricultural land [14]. The effective - ness of vegetated strips in reducing sediment transport off-site is known to vary with the ratio of runoff area to the area of the strip [15] as well as with other factors including soil type, topography, soil–water management (such as drainage pipes), land use, rainfall intensity and antecedent moisture conditions [16]. For instance, heavy rainfall may cause fast preferential flow where nutrients and pollutants readily flow from the soil surface through macropores, cracks and root channels into drainage Fig. 1 Illustration of the variety of vegetated strips used within pipes, particularly in dry clay soils [17]. In addition to soil and around fields. Interventions include: in‑field strips such as beetlebanks, hedgerows, forested shelterbelts, shrubs, grassy strips, cracking, high water repellence of old vegetated strips and wildflower margins. Illustration: Gunilla Hagström/Form Nation with a mossy soil surface may enhance preferential flow Haddaway et al. Environ Evid (2018) 7:14 Page 3 of 43 Fig. 2 Conceptual model of pathways to impact for vegetated strips within or around fields. Illustration: Neal Haddaway or surface runoff thus increasing the potential for erosion margin are one of the most commonly applied manage- on steep slopes under dry soil conditions [18]. In these ment measures, and are mainly designed and imple- kinds of situations, vegetated strips are not effective in mented to control sediment, phosphorus, nitrogen and retaining soluble or particle bound nutrients. Any condi- pesticide losses to off-site surface waters [23, 24]. They tion that promotes the formation of channel flow (rather have been shown to be highly efficient for reducing nutri - than sheet runoff) will reduce the flow reduction and ent runoff from farmed fields in a wide range of climatic sediment capture [e.g. 19]. This can be associated with regions across the world [19, 25]. Vegetated strips in steepness of slope, local topography and/or intensity of riparian zones can also remove nitrogen in proximity to rainfall. Gully formation caused by concentrated flows in watercourses, particularly subsurface nitrogen, although agricultural fields can be hindered by grassed waterways. their effectiveness appears to be less than for sediment The grassed waterway outlet is kept wide and shallow to or sediment bound contaminants [26]. The efficiency slow the velocity of water and spread the flows evenly of vegetated strips in reducing dissolved phosphorus before entering a vegetated strip [20]. Similarly, the bene- is dependent on the dynamic equilibrium between soil ficial flow reduction properties of vegetated strips can be and dissolved phosphorus. Phosphorus is adsorbed by negated where the strip occurs on steep ditch banks. In soil when the phosphorus concentration in soil water such cases, the design of ditch banks or implementation is higher than the equilibrium level and vice versa [27]. of two-stage ditches may improve planting of banks and Generally, the effectiveness of vegetated strips in con - flow reduction properties. trolling transport of soluble contaminants is less than for strongly-sorbed chemicals because the reduction Vegetated strip effects on nutrients and other in water transfer across the buffer is generally smaller contaminants than the reduction in sediment transfer [28]. There is Nutrients and pesticides are amongst the most important also potential for dissolved contaminants infiltrating pressures on aquatic ecosystems, where excess inputs into the margin to reach surface water subsequently via may deteriorate ecosystem integrity and/or threaten subsurface drains and/or shallow groundwater. In some drinking water resources [21, 22]. Even strongly-sorbed circumstances, vegetated strips may change from a nutri- compounds, including faecal pathogens from livestock ent trap into a nutrient source. For example, phosphorus or slurry fertiliser applications, can harm surface water may be desorbed from the deposited soil particles and quality through runoff. Vegetated strips at the field soil surface or liberated from the frost-broken plant cells Haddaway et al. Environ Evid (2018) 7:14 Page 4 of 43 in vegetated strips during heavy rainfall events or spring semi-natural landscapes [48]. Finally, vegetated strips runoff [19, 29]. To cycle the nutrients assimilated by the around and within fields may also impact on crop pro - plants, vegetation in vegetated strips should be harvested duction. Field margins can support beneficial inverte - and plant waste removed from strips [29]. brates such as natural enemies of pest invertebrates, but Where contaminants may be emitted to the air, as for also may harbour weeds, pests and diseases (e.g. viruses), pesticide spraying, vegetated strips have a dual function- which could potentially create a conflict between crop ality in increasing the distance between the emission production and biodiversity conservation [9, 49, 50]. source and vulnerable habitats such as surface waters Increased habitat heterogeneity may also have negative or non-crop habitats, but also through the potential impacts on some migratory (grass-eating) species (e.g. for interception of spray drift. Finally, it is known that geese) or farmland species such as skylarks that rely on pharmaceuticals used in animal husbandry may also be the cropped area of large fields, for breeding and foraging important contaminants of terrestrial environments adja- [51, 52]. For these species, homogeneous environments, cent to agricultural fields [e.g. 30]. In such cases, veg - commonly considered to be the result of agricultural etated strips can again increase distance from source for development and intensification, may represent preferred operations such as spreading of manure and biosolids, as habitat equivalent to permanent grassland ecosystems in well as having potential for interception of airborne par- central and eastern Europe [53]. ticulates at time of spreading. Other effects Vegetated strip effects on biodiversity Depending on the nature of their management, vegetated The widespread loss of spatial landscape heterogene - strips can provide various other services. Some resources ity, associated with the cultivation of a few high yielding from vegetated strips can be harvested periodically, such crop types across large uniform fields [8], is often viewed as wood and fodder [23]. Strips are also used to provide as a key driver of biodiversity loss on arable land [31– nesting and foraging habitat for game bird populations 34]. Hence, the creation and management of vegetated [e.g. 54], although elevated mortality and nest predation strips such as field margins have the potential to restore can occur in these habitats [55, 56]. A less well-studied habitat diversity for the benefit of associated farmland aspect of vegetated strips is their potential to enhance biodiversity [35]. Hedgerows and other field margin veg - aesthetic values and perceived “naturalness” of agricul- etation types have been shown to affect the richness and tural landscapes, especially when vegetated with trees abundance of flora, invertebrates and birds [36–38]. For and/or shrubs and employed in areas where such features instance, grassy field margins have been shown to pro - are absent [23]. Similarly, other values may include amen- vide important refuge and food for invertebrates, mam- ity use of agricultural land, for example by horse riders. mals and birds [39, 40]. Yet, these effects may depend on landscape structure and regional levels of agricultural intensification [41]. As a result measures are sometimes Multipurpose vegetated strips and conflicting objectives implemented in landscapes where their effects are small One key question relating to vegetated strips as an or even negative for some species [42]. environmental intervention on farmland is how to eval- As vegetated strips comprise a variety of different veg - uate multifunctional effects; that is, impacts of single etation types that are managed for different purposes, strips on multiple outcomes. True evaluation for areas their effects on biodiversity and associated ecosys - larger than the plot-scale is difficult to undertake due to tem services may vary. For instance, pollinator habitat difficulties in having representative controls. One pos - enhancement in the form of hedgerows and flower-rich sibility to overcome large-scale evaluation problems is strips may contribute to yield on adjacent fields [43], but therefore upscaling of plot results and/or modelling, also overall biodiversity and biological control poten- and in both cases collection of data from experimental tial in the surrounding landscape [44]. Vegetated strips studies conducted around the world will be invaluable established using densely planted perennial grasses may as a baseline. In their review of the multifunctional role primarily benefit invertebrates for pest suppression [45], of vegetated strips on arable farms, Hackett and Law- but also increase the availability of suitable nesting sites rence [57] concluded that although different strip types for ground-foraging farmland birds on adjacent crop can produce multiple benefits, none can wholly provide fields [46]. At the regional scale these benefits may be for all environmental outcomes. One way to optimise particularly valuable in resource-poor landscapes [47]. multiple benefits from field margins at the field and In addition, both at local and regional scales, vegetated landscapes scale could therefore be to adjust manage- strips provide valuable linear habitats that may promote ment practices locally according to purpose. Cresswell connectivity between areas of non-agricultural land or et  al. [58] used systematic mapping to identify which Haddaway et al. Environ Evid (2018) 7:14 Page 5 of 43 Identification of the Topic and Stakeholder Engagement plant traits deliver different ecosystem services to help The topic was suggested at a general stakeholder meet - inform future plant community design of vegetative ing arranged by MISTRA EviEM on September 24th, strips. 2012. Suggestions for the topic were made by the Swed- In reality, many vegetated strips vary in their purpose, ish Board of Agriculture, the Swedish Environmental method of establishment and ongoing management. Protection Agency, the Swedish Ministry of the Envi- Common forms include those that are naturally regen- ronment, Svensk Sigill, Hushållningssällskapet, WWF, erated from unused farmland, those sown with grass and researchers from the Centre for Biodiversity and or wildflower mixes, those sown specifically for target the Department of Ecology at the Swedish University of organisms such as pollinators (nectar and pollen mixes) Agricultural Sciences. The focus and scope of the review or for wild birds (seed mixes), those that are annu- was narrowed and better defined during a specific stake - ally cultivated and those that are unmanaged [57]. The holder event on September 1st, 2015. Details of this specific design and management of a vegetated strip meeting and the modifications in scope are available may depend on the main reason for the intervention, on request. Stakeholders who attended this event were and the resultant efficacy for the different outcomes invited to comment on the draft protocol prior to sub- described above may vary accordingly. Wildflower mission for publication, although none did. Stakeholders strips, for example, are designed to benefit pollinators were not engaged during the conduct of the review. such as bees [39], whereas densely vegetated strips typi- cally established by sowing a mixture of perennial grass species adjacent to water courses, are primarily used to mitigate soil erosion [59] and reduce runoff of nutrients Objective of the review and agro-chemicals [60]. The access to foraging oppor - The aims of this review were to identify, collate, and tunities for insectivorous birds in strips designed for describe relevant published research relating to the effec - water protection may be substantially lower compared tiveness of vegetated strips in and around farmland for to strips planted with wildflower mixes [61] or naturally a wide variety of purposes, including but not limited to: regenerating strips on poor soils with a diverse seed the enhancement of biodiversity; the reduction of pesti- bank [40]. Accordingly, managing vegetated strips for cide and nutrient drift/runoff/leaching; the mitigation biodiversity or for diffuse pollution purposes may entail of soil loss; the reduction of pathogens and toxins; and, very different management practices, since retained socioeconomic values, such as provision of game habi- dissolved or particulate matter eventually accumulates tat and reduction of crop pests. The map is restricted in within the strip, which in turn may reduce the poten- geographical scope to boreal and temperate systems (see tial for biodiversity benefits. However, removal of plant inclusion criteria below), and this report is accompanied material from vegetated strips could help maintain by a searchable database describing the identified rel - long-term retaining capacity, avoiding their transfor- evant studies, and an evidence atlas, an interactive, web- mation into nutrient sources, and with simultaneous based geographical information system (GIS) displaying benefits of lower nutrient levels and/or sparser veg - the contents of the database. etation for wild flora and visual foragers such as birds [62]. An additional consideration in this context relates Primary Question: What evidence exists regard- to pollution swapping [63], where mitigation measures ing the effects of field margins for one pollutant cause an increase in another pollut- on nutrients, pollutants, socio- ant. In this way, vegetated strips for controlling nitro- economics, biodiversity, and soil gen leaching could lead to simultaneous transformation retention? of sediment-bound phosphorus into soluble reactive Secondary Question: To what extent has this research phosphorus. focused on multi-use vegetated Whilst a large volume of evidence is known to exist strips? on these varied impacts of vegetated strips around and Population: Boreo-temperate regions as within agricultural fields, and whilst various literature defined by the following Köp- reviews have sought to examine their impacts for specific pen–Geiger climate classification outcomes [e.g. 26, 64–66], no review has systematically zones [67]: Cfa, Cfb, Cfc, Csb, collated evidence on their impacts, certainly not across Csc, Dfa, Dfb, Dfc (see Fig. 3). multiple diverse outcomes. Here, we report on the results Intervention: Vegetated strip interventions of a comprehensive systematic mapping of all avail- around and within fields used for able evidence relating to the impacts of vegetated strips crop production (arable), grazing within and around fields in boreo-temperate regions. Haddaway et al. Environ Evid (2018) 7:14 Page 6 of 43 Main climates Precipitation Temperature World Map of Köppen−Geiger Climate Classification A: equatorial W: desert h: hot arid F: polar frost updated with CRU TS 2.1 temperature and VASClimO v1.1 precipitation data 1951 to 2000 B: arid S: steppe k: cold arid T: polar tundra C: warm temperate f: fully humid a: hot summer Af Am As Aw BWk BWh BSk BSh Cfa Cfb Cfc Csa Csb Csc Cwa D: snow s: summer dry b: warm summer E: polar w: winter dry c: cool summer m: monsoonal d: extremely continental Cwb Cwc Dfa Dfb Dfc Dfd Dsa Dsb Dsc Dsd Dwa Dwb Dwc Dwd EF ET 90 −160 −140 −120 −100−80 −60−40 −20 020406080100 120140 160 180 Resolution: 0.5 deg lat/lon Version of April 2006 80 80 ET EF 70 70 Dfd ET Dwd Dfc Dsc Dfc 60 60 Dfc Dwc Dfb 50 50 Dwb Dfb Dfa Cfb BSk Dwa Csb Dfa Csb BWk 40 40 Cfb Cfa Csa BSk Csa Cwa ET 30 30 Cfa BWh BSh Cwb BWh Cwa BWh BWh Csa BSh Aw 20 20 Aw Am Aw Am Aw Am BSh 10 10 Aw Cwb Af Am Aw Am 0 Af Af 0 Af As Am Af BWh Aw BSh −10 −10 Aw Aw Cwa Af Af BSh Aw −20 BSh −20 BWk Cwa Cfa BWh Cfa Cwb BWh BWk −30 −30 Cfb Cfa Csa Csb BSk Csb Csb Cfb Cfb −40 −40 Cfb BSk −50 −50 Cfc ET −60 −60 Kottek, M., J. Grieser, C. Beck, −70 −70 B. Rudolf, and F. Rubel, EF 2006: World Map of Köppen- http://gpcc.dwd.de Geiger Climate Classification −80 −80 http://koeppen-geiger.vu-wien.ac.at updated. Meteorol. Z., 15, 259-263. −90 −160 −140 −120 −100−80 −60−40 −20 020406080100 120140 160 180 Fig. 3 Map of Koppen Geiger climate zones (http://koepp en‑geige r.vu‑wien.ac.at/prese nt.htm) websites to our search strategy, including a database of and horticulture, orchards and review articles as an additional output, and our inability vineyards, where presence of a to screen and code a small number of articles in German vegetated strip or management and Swedish due to a change in availability of the Ger- of the strip is investigated. man and Swedish speaking review team member. Comparator: Before vegetated strip establish- ment, before a change in veg- Searches etated strip management (tem- Bibliographic databases poral comparisons); no vegetated The following bibliographic databases were searched for strip, different vegetated strip studies using English search terms (non-English arti- management, including strip cles, where present, are typically catalogued with English width (spatial comparisons); out- titles, abstracts and/or keywords): side a vegetated strip. Outcome: All and any outcomes were 1. Academic Search Premier (http://www.ebsco host. included iteratively as they com/acade mic/acade mic-searc h-premi er). are identified within the rel- 2. Agricola (http://agric ola.nal.usda.gov/). evant literature and were coded 3. AGRIS: agricultural database (FAO) (http://agris accordingly. .fao.org/agris -searc h/index .do). 4. Biosis Citations Index (http://wok.mimas .ac.uk/). 5. Directory of Open Access Journals (http://doaj. Methods org/). The methods described herein reflect those outlined in 6. PubMed/MEDLINE (http://www.ncbi.nlm.nih. the published protocol [68]. Our methods deviate from gov/pubme d). the protocol only in adding a number of organisational Haddaway et al. Environ Evid (2018) 7:14 Page 7 of 43 7. Scopus (http://www.scopu s.com/). OR “forest boundar*” OR “forested boundar*” OR “non- 8. Web of Science Core Collections (http://wok. cropped boundar*” OR “non-cropped boundar*” OR mimas .ac.uk/). “plant boundar*” OR “planted boundar*” OR “*flower 9. Zoological Record (http://thoms onreu ters.com/ boundar*” OR “wood boundar*” OR “wooded boundar*” pr o du ct s_s er v i c e s/s c ien c e/s c ien c e_pr o du ct s/a-z/ OR “woody boundar*” OR “herbacious boundar*” OR zoolo gical _recor d). “cultivated boundar*” OR “uncultivated boundar*” 10. JSTOR (http://www.jstor .org/). OR “bird cover boundar*” OR “grazed boundar*” OR 11. DART-Europe E thesis (http://www.dart-europ “weedy boundar*” OR “weeded boundar*” OR “peren- e.eu/basic -searc h.php). nial boundar*” OR “*grass buffer*” OR “grassed buffer*” 12. EThOS (British Library) (http://ethos .bl.uk/Home. OR “grassy buffer*” OR “managed buffer*” OR “ripar - do). ian buffer*” OR “sown buffer*” OR “uncropped buffer*” 13. Index to Theses Online (http://www.these s.com/). OR “un-cropped buffer*” OR “unmanaged buffer*” OR “unploughed buffer*” OR “un-ploughed buffer*” OR “veg - Search string etated buffer*” OR “vegetation buffer*” OR “vegetative The following search string was used as a basis for buffer*” OR “forest buffer*” OR “forested buffer*” OR “non - searches within each of the above databases and was cropped buffer*” OR “non-cropped buffer*” OR “plant adapted using database-specific syntax as appropriate buffer*” OR “planted buffer*” OR “*flower buffer*” OR (see Additional file  1). Searches in bibliographic data- “wood buffer*” OR “wooded buffer*” OR “woody buffer*” bases were performed on 13/11/15 and have not been OR “herbacious buffer*” OR “cultivated buffer*” OR updated during the conduct of the review. “uncultivated buffer*” OR “bird cover buffer*” OR “grazed (“*grass barrier*” OR “grassed barrier*” OR “grassy bar- buffer*” OR “weedy buffer*” OR “weeded buffer*” OR “per - rier*” OR “managed barrier*” OR “riparian barrier*” OR ennial buffer*” OR “*grass filter*” OR “grassed filter*” OR “sown barrier*” OR “uncropped barrier*” OR “un-cropped “grassy lter*” fi OR “managed lter*” fi OR “riparian filter*” barrier*” OR “unmanaged barrier*” OR “unploughed bar- OR “sown filter*” OR “uncropped filter*” OR “un-cropped rier*” OR “un-ploughed barrier*” OR “vegetated barrier*” lter*” OR “ fi unmanaged filter*” OR “unploughed filter*” OR “vegetation barrier*” OR “vegetative barrier*” OR OR “un-ploughed filter*” OR “vegetated filter*” OR “veg - “forest barrier*” OR “forested barrier*” OR “noncropped etation filter*” OR “vegetative filter*” OR “forest filter*” barrier*” OR “non-cropped barrier*” OR “plant barrier*” OR “forested filter*” OR “noncropped filter*” OR “non- OR “planted barrier*” OR “*flower barrier*” OR “wood cropped filter*” OR “plant filter*” OR “planted filter*” OR barrier*” OR “wooded barrier*” OR “woody barrier*” OR “*flower filter*” OR “wood filter*” OR “wooded filter*” OR “herbacious barrier*” OR “cultivated barrier*” OR “uncul- “woody filter*” OR “herbacious filter*” OR “cultivated fil - tivated barrier*” OR “bird cover barrier*” OR “grazed ter*” OR “uncultivated filter*” OR “bird cover filter*” OR barrier*” OR “weedy barrier*” OR “weeded barrier*” OR “grazed filter*” OR “weedy filter*” OR “weeded filter*” OR “perennial barrier*” OR “*grass border*” OR “grassed “perennial filter*” OR “*grass margin*” OR “grassed mar - border*” OR “grassy border*” OR “managed border*” OR gin*” OR “grassy margin*” OR “managed margin*” OR “riparian border*” OR “sown border*” OR “uncropped “riparian margin*” OR “sown margin*” OR “uncropped border*” OR “un-cropped border*” OR “unmanaged bor- margin*” OR “un-cropped margin*” OR “unmanaged der*” OR “unploughed border*” OR “un-ploughed border*” margin*” OR “unploughed margin*” OR “un-ploughed OR “vegetated border*” OR “vegetation border*” OR “veg- margin*” OR “vegetated margin*” OR “vegetation mar- etative border*” OR “forest border*” OR “forested border*” gin*” OR “vegetative margin*” OR “forest margin*” OR OR “noncropped border*” OR “non-cropped border*” OR “forested margin*” OR “noncropped margin*” OR “non- “plant border*” OR “planted border*” OR “*flower bor - cropped margin*” OR “plant margin*” OR “planted der*” OR “wood border*” OR “wooded border*” OR “woody margin*” OR “*flower margin*” OR “wood margin*” OR border*” OR “herbacious border*” OR “cultivated border*” “wooded margin*” OR “woody margin*” OR “herbacious OR “uncultivated border*” OR “bird cover border*” OR margin*” OR “cultivated margin*” OR “uncultivated “grazed border*” OR “weedy border*” OR “weeded bor- margin*” OR “bird cover margin*” OR “grazed margin*” der*” OR “perennial border*” OR “*grass boundar*” OR OR “weedy margin*” OR “weeded margin*” OR “peren- “grassed boundar*” OR “grassy boundar*” OR “managed nial margin*” OR “*grass strip*” OR “grassed strip*” OR boundar*” OR “riparian boundar*” OR “sown boundar*” “grassy strip*” OR “managed strip*” OR “riparian strip*” OR “uncropped boundar*” OR “un-cropped boundar*” OR “sown strip*” OR “uncropped strip*” OR “un-cropped OR “unmanaged boundar*” OR “unploughed boundar*” strip*” OR “unmanaged strip*” OR “unploughed strip*” OR “un-ploughed boundar*” OR “vegetated boundar*” OR “un-ploughed strip*” OR “vegetated strip*” OR “veg- OR “vegetation boundar*” OR “vegetative boundar*” etation strip*” OR “vegetative strip*” OR “forest strip*” OR Haddaway et al. Environ Evid (2018) 7:14 Page 8 of 43 “forested strip*” OR “noncropped strip*” OR “non-cropped agroecosystem* OR agricult* OR agronom* OR arable* OR strip*” OR “plant strip*” OR “planted strip*” OR “*flower crop* OR cultivat* OR farm* OR field* OR grassland* OR strip*” OR “wood strip*” OR “wooded strip*” OR “woody “grass land*” OR horticult* OR meadow* OR orchard* OR strip*” OR “herbacious strip*” OR “cultivated strip*” OR plantation* OR ranch* OR vineyard* OR pasture* OR cat- “uncultivated strip*” OR “bird cover strip*” OR “grazed tle* OR graz*). strip*” OR “weedy strip*” OR “weeded strip*” OR “per- Search terms were identified through a scoping pro - ennial strip*” OR “*grass zone*” OR “grassed zone*” OR cess. Firstly, we generated a list of 120 articles known by “grassy zone*” OR “managed zone*” OR “riparian zone*” the review authors to be relevant to the topic. The titles, OR “sown zone*” OR “uncropped zone*” OR “un-cropped keywords and abstracts were then subjected to textual zone*” OR “unmanaged zone*” OR “unploughed zone*” analysis to identify the most frequently occurring words. OR “un-ploughed zone*” OR “vegetated zone*” OR “veg- Key terms were then selected from this list and added to etation zone*” OR “vegetative zone*” OR “forest zone*” OR a pre-existing list generated by the review authors. Key “forested zone*” OR “noncropped zone*” OR “non-cropped terms were then used to probe the titles and keywords of zone*” OR “plant zone*” OR “planted zone*” OR “*flower articles in the above list to identify common co-locators zone*” OR “wood zone*” OR “wooded zone*” OR “woody (i.e. words located next to key terms in the text). Com- zone*” OR “herbacious zone*” OR “cultivated zone*” OR mon pairs (i.e. any pair of words that frequently occur “uncultivated zone*” OR “bird cover zone*” OR “grazed together in the corpus) were also identified. All key terms zone*” OR “weedy zone*” OR “weeded zone*” OR “peren- were then assembled and tested both individually and in nial zone*” OR “barrier strip*” OR “border strip*” OR combination. Terms that resulted in very large numbers “boundary buffer*” OR “boundary margin*” OR “bound - of results but that were also subjectively assessed as hav- ary strip*” OR “boundary management*” OR “field bor - ing low relevance (i.e. the terms ‘vfs’, ‘bz’, ‘bzs’, ‘fbz’) were der*” OR “field buffer*” OR “field margin*” OR “buffer excluded from the final search string. strip*” OR “buffer zone*” OR “filter strip*” OR “filter zone*” OR “managed edge*” OR “buffer management*” OR buff - Specialist searches erstrip* OR bufferzone* OR “cropland buffer*” OR “farm - Searches for grey literature were performed in two key land buffer*” OR “farmland margin*” OR “ditch bank*” ways (in addition to the searches as part of the biblio- OR “farm buffer*” OR “farm edge*” OR “farm interface*” graphic database searches above; i.e. thesis databases and OR “field bank*” OR “field boundary*” OR “field edge*” Scopus). OR “field interface*” OR “filter margin*” OR “filter strip*” Firstly, searches were conducted using an extensive OR filterstrip* OR “filter zone*” OR filterzone* OR “mar - (i.e. downloading and assessing the first 1000 results) gin strip*” OR beetlebank* OR “beetle bank*” OR “hedge title-only search of Google Scholar (https ://schol ar.googl row*” OR hedgerow* OR shelterbelt* OR “shelter belt*” OR e.ca/intl/en/schol ar/about .html), which has been proven “grassed waterway*” OR “grassed water way*” OR “grass to return a high percentage of grey literature (c. 37%; waterway*” OR “grass water way*” OR “grassy waterway*” [69]). Searches were conducted for a range of key inter- OR “grassy water way*” OR “vegetated waterway*” OR vention search terms that individually returned more “vegetated water way*” OR “vegetative waterway*” OR than 100 search results in Web of Science during scop- “vegetative water way*” OR “wind buffer*” OR “agrofor - ing. Details of these searches are provided in Additional estry buffer*” OR “conservation buffer*” OR “conservation file  1. Searches were performed in English, French, Span- headland*” OR “conservation head land*” OR “stream ish, Swedish, German, Finnish and Danish. Only the first border*” OR “stream barrier*” OR “stream buffer*” OR 1000 results are viewable within Google Scholar due to “stream margin*” OR “river border*” OR “river barrier*” restrictions in the search engine, but these records were OR “river buffer*” OR “river margin*” OR “waterway downloaded into a database for later screening using the border*” OR “waterway buffer*” OR “waterway mar - method outlined in Haddaway et al. [70]. gin*” OR “water way border*” OR “water way buffer*” Secondly, searches of 43 websites of key organisations OR “water way maring*” OR “countour strip*” OR “nec- were undertaken (see Table  1). For each of the websites, tar strip*” OR “widlife strip*” OR “wildlife corridor*” OR web scraping was employed where possible to search for “set-aside margin*” OR “set-aside border*” OR “set-aside key terms using the built-in search facility using the soft- buffer*” OR “setaside margin*” OR “setaside border*” OR ware Import.io (http://www.impor t.io). See Haddaway “setaside buffer*” OR “permanent strip*” OR “perma - et  al. [70] for a detailed description of the web-scraping nent margin*” OR “permanent border*” OR “permanent methods used. Where automatic web-scraping could not buffer*” OR “sterile strip*”) AND (“agro-ecosystem*” OR be used due to incompatibility with the website, searches Haddaway et al. Environ Evid (2018) 7:14 Page 9 of 43 Eligibility criteria were performed, and results recorded by hand using the built-in search facilities on each site. Additional file  2 outlines the terms used for each website. The results Eligible subjects: Boreo-temperate regions from all searches across all databases were combined into as defined by the follow - one database for each language and screened by a review ing Köppen-Geiger climate team member with relevant language expertise. classification zones [67]: Cfa [warm temperate]; Cfb and Cfc [maritime temper- Supplementary searches ate or oceanic]; Csb [dry The comprehensiveness of results of the above searches summer or Mediterranean]; was tested by comparing a predefined test list of 114 Csc [dry summer mari- studies against the combined results to ensure all of these time subalpine]; Dfa [hot relevant studies are found. This checking was performed summer continental]; Dfb iteratively at the start of the searching process. In addi- [warm summer continental tion, bibliographic checking was performed by screening or hemiboreal]; and, Dfc the reference lists of 96 relevant reviews that were iden- [continental subarctic or tified during screening of search results to retrieve any boreal (taiga)]. potentially relevant studies missed by the search strategy described above. Eligible interventions: Vegetated strip interven- Following feedback on our original search string, we tions in or around fields performed an additional search to include records men- used for arable, grazing tioning the term ‘riparian buffer’ in all bibliographic and horticulture, orchards databases. This supplementary search was conducted on and vineyards, where pres- 21/12/15. ence of a vegetated strip or management of the strip is Screening investigated. All articles identified through searching were screened Eligible comparators: Before vegetated strip for eligibility at title, abstract and then full text levels establishment, before a using predefined inclusion criteria (detailed below). Con - change in vegetated strip sistency in the application of the inclusion criteria was management (temporal tested by comparing agreement between two review- comparisons); no vegetated ers at title, abstract and full text level screening, using a strip, different vegetated subset of records. All disagreements were discussed. The strip management, includ- level of agreement was tested formally using a kappa test ing strip width (spatial [71], and where agreement score fell below 0.6, indicat- comparisons); outside a ing moderate agreement, a third reviewer was consulted vegetated strip. and a further set of records screened following discus- Eligible outcomes: Outcomes were included sion of disagreements. Consistency checking results were iteratively as they were as follows: title level, n = 149 kappa = 0.66; abstract level identified within the rel- first test, n = 200 kappa = 0.46; abstract level second test, evant literature and were n = 205 kappa = 0.82; full text level, n = 50 kappa = 0.62. coded accordingly. All Following abstract screening, potentially relevant stud- social and ecological out- ies were retrieved in full text. Unobtainable articles are comes were included, such listed in Additional file  3. All screened full texts that were as: terrestrial and aquatic excluded from the review are listed along with exclusion biodiversity (including con- reasons in Additional file 4. nectivity); nutrient runoff During screening, relevant reviews were placed into a or leaching; pesticide run- separate database for coding (see below). This coding of off, leaching or drift; soil reviews was restricted to English language reviews only, due to resource constraints. retention; socioeconomics. Haddaway et al. Environ Evid (2018) 7:14 Page 10 of 43 Table 1 List of organisational websites searched for evidence Organisation Website searched Aalto Universityhttp://www.otali b.fi/tkk/index ‑eng.html Aarhus University, Department of Agroecology http://agro.au.dk/en/ Adas http://www.adas.uk/ Alterra, Wageningen Universityhttp://www.wagen ingen ur.nl/en/Exper tise‑Servi ces/Resea rch‑Insti tutes /alter ra.htm ARTOhttps ://arto.linne anet.fi/vwebv /searc hBasi c?sk=fi_FI Arvalishttp://www.arval isins titut duveg etal.fr/index .html Columbia Basin Agricultural Research Centerhttp://cbarc .aes.orego nstat e.edu/long_term_pubs European Crop Protection Association http://www.ecpa.eu/ European Environment Agencyhttp://www.eea.europ a.eu/ European Soil Portalhttp://eusoi ls.jrc.ec.europ a.eu GRACEnet, USDA Agricultural Research Servicehttp://www.ars.usda.gov/resea rch/progr ams/progr ams.htm?np_code=212&docid =21223 Greppa Näringenhttp://www.grepp a.nu Hankehaavihttp://www.hanke haavi .fi/ Hydrotekniska Sällskapethttp://www.hydro tekni skasa llska pet.se/ INIAhttp://www.inia.es/IniaP ortal /verPr esent acion .actio n INRA http://www.inra.fr/ IRSTEAhttp://www.irste a.fr/accue il LUKEhttp://jukur i.luke.fi/ NABUhttps ://www.nabu.de/ National Farmers Unionhttp://www.nfuon line.com/home/ OPERAhttp://opera resea rch.eu/ Rothamsted Researchhttp://www.rotha msted .ac.uk/ RSPB http://www.rspb.org.uk/ SERA‑17http://sera1 7.org/ Soilservice http://www4.lu.se/o.o.i.s/26761 Swedish Board of Agriculturehttp://www.jordb ruksv erket .se Swedish Environmental Protection Agencyhttp://www.natur vards verke t.se Swedish University of Agricultural Sciences http://www.slu.se SYKEhttp://www.syke.fi/fi‑FI/Julka isut Theseushttps ://www.these us.fi/ UC Davis, Agricultural Sustainability Institutehttp://ltras .ucdav is.edu/ University of Copenhagenhttp://www.ku.dk/engli sh University of Illinois, Department of Crop Scienceshttp://crops ci.illin ois.edu/resea rch/morro w USDA Agricultural Research Servicehttp://www.ars.usda.gov/resea rch/progr ams/progr ams.htm?np_code=211&docid =22480 VIIKKIhttp://eviik ki.hulib .helsi nki.fi/ Wageningen Universityhttp://www.wagen ingen ur.nl/en/wagen ingen ‑unive rsity .htm World bankhttp://www.world bank.org/refer ence/ BioRxivhttp://biorx iv.org/ ArXivhttp://arxiv .org/ Nature Precedingshttp://prece dings .natur e.com/ Peer J Preprintshttps ://peerj .com/prepr ints/ Science paper onlinehttp://www.paper .edu.cn/en Research gatehttps ://www.resea rchga te.net/home Haddaway et al. Environ Evid (2018) 7:14 Page 11 of 43 Eligible types Primary research stud- appropriate, flagging up clearly unreliable research that of study design: ies involving field-based should be excluded from further synthesis, and serious deficiencies that should be pointed out in those studies experimental manipula- that remain in the map. tions and observations. Interventions must have been in place for 12 months Data coding strategy or more. Management Meta-data (i.e. descriptive data regarding the methods and interventions within fields setting of each study, provided as free text) were extracted that are applied to existing from included, relevant studies and entered into a search- crops (such as cover crops, able database: one database was produced for primary intercropping, etc.) were research studies and another for relevant reviews. The not considered. Further- database was populated with a number of variables, each more, only direct evidence given a category according to a predetermined strategy of the impacts of vegetated (also known as coding). This database forms one of the main outputs of the review and is supplied herein as a strips were included in the Additional files 1 , 2, 3, 4, 5, 6, 7, 8 and 9. During meta-data map: i.e. not indirect evi- extraction, each study will be assigned codes correspond- dence, such as the ability ing to the ecosystem services explicitly mentioned. The list of a border species grown of ecosystem services was adapted from Cork et  al. [72], elsewhere to alter an out- adding a code for ‘pest regulation’ as a regulating service. come. Modelling studies Consistency of data extraction across team mem- were included where they bers was assessed by double checking a subset of stud- provided primary data. ies between two reviewers (NRH and JE). Where Laboratory studies were meta-data were missing from articles this was stated as not included. Relevant “not reported”/“not stated”, since making efforts to obtain reviews and meta-analyses these data was not possible within the resources allocated were recorded in a separate to this project. database. Coding and meta-data was extracted for relevant Eligible languages: All languages were included reviews identified during screening using the schema where possible. Studies in provided in Additional File 5. This database is provided languages not able to be as an interactive, searchable database in a Additional files translated were included in 1, 2, 3, 4, 5, 6, 7, 8 and 9 (see "Results"). a separate supplementary database. Study mapping and presentation (narrative synthesis) Key variables were described in the form of tables and figures. Multiple variables were cross-tabulated in heat Efforts were made to ensure that authors of research maps that display the volume of evidence across two cat- studies included in this review were not involved in any egorical meta-data variables. In addition, we have sum- decisions regarding their own work. For Finnish studies, marised the relevant evidence identified in the form of an however, this was not possible, and JUK was involved in evidence atlas, an interactive geographical information screening a small number of studies for which she was system (GIS), that maps studies by their location across an author. Studies were further checked for relevance by a cartographical map. This evidence atlas is published on NRH following screening, however, and no articles were the EviEM website (http://www.eviem .se/en/proje cts/ included that did not meet the review’s inclusion criteria. Buffe r-strip s/). Knowledge gap and cluster identification Critical appraisal Knowledge gaps (subtopics that are un- or under-rep- Critical appraisal was not undertaken within this map, resented in the evidence base) and knowledge clusters since the measurement methods and study designs (subtopics with sufficient numbers of studies to allow varied substantially across different outcomes. A very meaningful synthesis) were identified by the review team basic quality assessment was conducted in the form of by cross-tabulating key meta-data variables in heat maps. a ‘free text’ meta-data variable where a brief description Specific, arbitrary cut-offs (described in the Results text of the study quality was made for some studies where Haddaway et al. Environ Evid (2018) 7:14 Page 12 of 43 and legends of each heat map in tables, below) were used Results to identify poorly studied topics. The team discussed all The mapping process knowledge gaps and clusters, including those that they Figure  4 displays the flow of articles and studies through felt were of key relevance to decision-makers and read- the systematic mapping process. From over 31,000 ers. No prioritisation was performed, and gaps and clus- search results there were 19,457 unique records that ters are displayed in order of the volume of evidence. were then screened on title, with 8094 abstracts screened Fig. 4 Flow diagram showing the flow of articles and studies through the systematic mapping process Haddaway et al. Environ Evid (2018) 7:14 Page 13 of 43 Fig. 5 Screenshot of the evidence atlas for the systematic review database of primary research studies in the next stage. Some 3000 articles remained for full Primary research studies text screening, although 1123 of these (37%) could not Vegetated strip terminology be found or accessed (see Additional file  3). A total of A wide variety of different terminology was used to 417 potentially relevant articles were added in for full describe vegetated strips across studies in the system- text screening from bibliographic checking, and from atic map (Fig.  6). The most commonly used terms were searches of Google Scholar and organisational websites. ‘field margin’ (n = 152), ‘hedgerow’ (n = 146), ‘shelter- Following full text screening, 1089 articles were excluded belt’ (n = 80), ‘riparian buffer’ (n = 73), and ‘buffer strip’ (see Additional file  4 for exclusion reasons). This left a (n = 55). Table 2 lists the terms that were used only once. final set of 1072 studies reporting primary data relevant In total, across the 1072 studies in the systematic map to the review in the systematic map database (see Addi- database there were 205 different terms relating to vege - tional file  6), and a further 130 review articles within the tated strips that were used a total of 1220 times (multiple review article database (see Additional file  7). Due to terms within some articles). In comparison, there were resource constraints, we were unable to screen German 360 search terms in our search string. However, of these, or Swedish articles at full text, which left 26 potentially only 84 search terms were represented in articles within relevant articles unscreened (see Additional file 8). the systematic map database. Thus, sources of articles other than the formalised database searches (i.e. biblio- Evidence atlas graphic searching) were a vital methodological addition We have produced an evidence atlas (see Fig.  5 for a to ensure we captured any article using some of the other screenshot and visit http://www.eviem .se/en/proje cts/ 121 terms and none of the 84 search term synonyms. Buffe r-strip s/) that displays the studies in the primary Additional file  9 includes a table of the primary vegetated research systematic map database visually on a carto- strip terms (first, main mention) used across different graphic map. This map is interactive and allows the user field study locations, indicating, for example, that ‘ripar - to search for specific evidence both using a visual interface ian buffer’ is most common for US studies (n = 52), whilst and a text search facility. A small number of studies (n = 8) ‘field margin’ is most common in the UK (n = 66). could not be displayed on the map because they lacked information about sample location (including country). Publications per year Figure 7 displays the number of relevant research studies published per year from within the systematic map data- base. Currently the publication rate is approximately 70 Haddaway et al. Environ Evid (2018) 7:14 Page 14 of 43 Fig. 6 Tree map of terminology used to describe vegetated strips in studies within the systematic map. Only showing terms used in 10 studies or more. Polygon area corresponds to the number of studies using the term Haddaway et al. Environ Evid (2018) 7:14 Page 15 of 43 Table 2 Vegetated strip terms used only once in primary studies within the systematic map database Agricultural buffer Forest margin Meadow strip Uncropped edge Agroforestry buffer strip Forest shelter belt Perennial filter strip Uncropped margin Agroforestry vegetated filter strip Forested buffer zone Perennial grass buffer Uncropped wildlife strip Arable margin Forested riparian buffer Perennial grass strip Uncultivated strip Barrier strip Forested riparian corridor Permanent vegetation strip Unploughed strip Biocorridor Forested strip Plant strip Upland habitat buffer Border crop Gamagrass strip Pond buffer Vegetated buffer system Border strip Game‑ cover strip Prairie edge Vegetated field border Border zone Grass bank Prairie filter strip Vegetated field margin Boundary strip Grass buffer zone Prairie strip Vegetated margin Conservation buffer strip Grass hedgerow Restored/natural riparian zone Vegetated riparian buffer Conservation strip Grass margin strip Retired pasture strip Vegetated strip Contour strip Grass vegetated filter strip Riparian conservation buffer Vegetated waterway Conventional hedgebank Grass waterway Riparian filter strip Vegetational corridor Cover strip Grass‑ wetland buffer Riparian forest buffer strip Vegetative barrier Crop margin Grassed channel Riparian margin Water margin Ditch slope Grassed strip Riparian vegetated buffer strip Watercourse margin Earth bank Grassy field boundary Riparian wood Weed border Fencerow Green fence Riparian woods Weedy field margin Field adjacent woodlot Headland Rose bush strip Wild bird mix Field bank Hedge and ditch Ruderal vegetation strip Within‑field refuge Field corner plantation Hedge bank Set‑aside Within‑field ridge Field strip Herbaceous border Shelter tree Wooded riparian strip Field windbreak Herbaceous buffer Sown patch Woodlot edge Field‑adjacent grassland strip Herbaceous field edge Sown weed strip Woody border Filter Herbaceous strip Streamside management zone Floral field margin Herbaceous vegetated strip Successional strip Flowering plant strip Improved field margin Successional weed strip Forest belt Insect border Switchgrass barrier Forest border Isolated hedge Switchgrass hedge Forest buffer Live fence Tree belt Forest edge Marginal grassland Tree row studies per year. Whilst many other systematic reviews the third highest number of studies was France, with 64 and maps have identified exponential growth in research studies. publications over recent decades [73–75], publication rates within the topic of this review appear to be more Study design linear, increasing from a minimum of approximately 5/ More studies were observational (i.e. quasi-experimental) year in 1990 at the rate of c. 2.7 studies per year from (n = 660) than manipulative (i.e. experimental) (n = 406), that point onwards. This suggests a more stable growth in with only six studies combining observation and manipu- research on the topic. lative designs. It is worth noting that reviewers identified a spectrum of study designs between purely observa- Study location tional studies and purely manipulative ones: these stud- Out of 1072 studies within the systematic map, the ies may have used observational methods to investigate majority of studies come from North America (n = 393, a prior manipulation. This was common in long-term 37%) (Fig.  8), with most of these coming from the USA experiments. (n = 341). Of these US studies, many were undertaken in Figure  9 shows the duration of studies included in the Iowa (n = 70), North Carolina (n = 40), Missouri (n = 33) systematic map database. Around two-thirds (n = 710) and Mississippi (n = 27) (Table 3). After the USA, the UK of studies were only 1 or 2 years in length, with very few was most commonly studied (n = 213). The country with Haddaway et al. Environ Evid (2018) 7:14 Page 16 of 43 Fig. 7 The number of research studies published per year in the systematic map database (Fig.  11). Some 344 studies investigated the impact of studies lasting longer than 10 years (n = 23). A large num- the presence of a strip or strip management relative to a ber of studies did not report their study length (n = 70). control site lacking a strip, or to the same system before Study spatial scale is shown in Fig.  10, showing that the change was put in place. A similar number of studies studies were fairly evenly distributed across plot-, field- (n = 329) investigated differences in outcomes resulting and regional-scales. Farm- and catchment-scale studies from strips of different vegetation. Only 5 studies failed were less common, with only a minor proportion not to describe the intervention in detail. describing the scale. However, the distinction between A large proportion of the evidence base did not catchment and regional is questionable. Following report the duration of the intervention (i.e. the time screening, reviewers noted that spatial scale was not easy period that the vegetated strip or management prac- to code and often overlapped. This may result in confu - tice was in place) (n = 592). Of those reporting dura- sion when (1) different levels of organisation are char - tion, a third of the studies were 10  years or less since acterised by a variety of processes that have their own establishment of the vegetated strip or strip manage- scales of space and time, (2) replication is low and plot ment (n = 366). The most common duration over size is large and (3) comparisons are made among sam- which strips or strip management were in place was ples that are not independent (i.e. pseudoreplication). 2 years (Fig. 12). The distinction between catchment and regional is there - fore unlikely to be a useful one. It was most common for measurements within studies Vegetated strip type, location and management to be conducted across two quarters (n = 392), followed by Field edge vegetated strips were most common only one quarter (n = 225). Considering the timings specif- (n = 651), followed by riparian strips (n = 304), and ically, measurements were most commonly taken over the very few within-field strips (n = 86) (Fig .  13). A total of spring and summer (Q2 [April–June] and Q3 [July–Sep- 96 studies did not report strip location: this was com- tember], n = 272), with studies spanning the whole year mon for studies examining strips as pollutant filters in a the next most common time period (n = 171) (Table 4). manipulative design, where the experimental filter trips were placed fully within a field. Grasses were the most common type of vegetation Interventions in strips (n = 530), followed by trees (n = 354) (Fig . 14). Most studies investigated the change in an outcome from Many other strips had a combination of vegetation or within a field into or across a vegetated strip (n = 472) Haddaway et al. Environ Evid (2018) 7:14 Page 17 of 43 Fig. 8 Number of studies per country in the systematic map database (grouped by continent) Haddaway et al. Environ Evid (2018) 7:14 Page 18 of 43 Table 3 Number of  studies per  US State in  the  systematic (n = 214), a lack of management (n = 110), and other map database less common practices (see Fig. 16). State Number of studies Measured outcomes and ecosystem services The most commonly measured outcome across the Iowa 70 evidence base was terrestrial biodiversity (in all cases North Carolina 40 some surrogate measure of biodiversity was used) Missouri 33 (n = 596), which was almost three times more com- Mississippi 27 mon than the second most common outcome, nitrogen Nebraska 19 nutrients (n = 201). Following this, over 100 studies Maryland 13 quantified the following outcomes: water loss/reten - Minnesota 12 tion (n = 183); phosphorus nutrients (n = 140); soil Oregon 11 chemical (n = 123) and physical (n = 107) characteris- Georgia 10 tics; and pest control (n = 104). Social impacts of veg- Michigan 10 etated strips were not commonly investigated: social, Wisconsin 9 n = 19; farming economics, n = 15; and, recreation, Illinois 8 n = 9 (Fig .  17). Table  5 displays the number of studies Virginia 8 in which multiple outcomes were reported together. California 6 Commonly co-occurring outcomes (i.e. n > 50 studies) Arkansas 5 were: biodiversity (terrestrial) and pest control (n = 61) New York 5 (although many pest control outcomes were also meas- Ohio 5 ures of diversity); nutrients N and nutrients P (n = 99); Washington 5 nutrients N and soil soil/sediment (chemical not N/P) Florida 4 (n = 75); nutrients N and water loss/retention (n = 86); Indiana 4 nutrients P and water loss/retention (n = 56); soil loss/ Kansas 4 retention and water loss/retention (n = 56); and, soil/ Kentucky 4 sediment (chemical, not N/P) and soil/sediment (physi- Texas 3 cal) (n = 53). Oklahoma 2 The most common groups of ecosystem services were Pennsylvania 2 regulating services (n = 1119), followed by supporting Colorado 1 services (n = 836) (Fig. 18). The most frequently reported Connecticut 1 single ecosystem service was biodiversity (n = 662), fol- Louisiana 1 lowed by pollution control (n = 313) and nutrient cycling Massachusetts 1 (n = 297). Under-reported ecosystem services were: all Nevada 1 provisioning services (food, fresh water, fibre and fuel, North Dakota 1 biochemical products, genetic materials); climate regula- South Dakota 1 tion; natural hazards; all cultural services (spiritual and Utah 1 inspirational, recreational, aesthetic, educational); and Vermont 1 pollination. It is worth noting, however, that some studies Multiple 8 may have focused on pollinators without describing them Not stated 5 as such, and this may result in under-representation of research on this topic. Figure 19 displays how studies of the various ecosystem other groups of plants (n = 295), perhaps indicating the services have increased in frequency over time. There are need for more specific coding. no clear trends, with all services increasing in representa- The majority of studies were performed in arable sys - tion over time in a similar way. tems (n = 738), followed by livestock (n = 351) (Fig . 15). Ecosystem services reported in studies differed Many studies did not describe the farming production depending on the location of the vegetated strip (Fig. 20), system (n = 168). with riparian strips more commonly associated with Management of strips was generally not described fresh water, fibre and fuel, hydrological regimes, pollu - across the evidence base (n = 513), but where descrip- tion control, erosion protection, nutrient cycling, and soil tions existed they related to sowing or planting of veg- formation services than average. Conversely, field margin etation in strips (n = 394), cutting of strip vegetation strips were more commonly associated with food, genetic Haddaway et al. Environ Evid (2018) 7:14 Page 19 of 43 Fig. 9 Study length for primary research included in the systematic map Fig. 10 Spatial scale of studies included in the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 20 of 43 Table 4 Study measurement quarter (a) Nothern Hemisphere (b) Southern Hemisphere Q1 Q2 Q3 Q4 # studies Q1 Q2 Q3 Q4 # studies 0 1 10 261 1 1 1 110 1 1 1 1 155 10 0 18 00 10 96 0 1 10 6 0 10 087 1 10 04 0 1 1 1730 00 14 00 1 1350 0 10 3 1 10 028 10 00 3 1 1 10 25 0 1 1 12 10 0 1240 0 1 11 00 0 116 1 1 10 1 0 10 1150 10 11 10 00 13 1 10 11 1 10 18 10 1 11 10 1 14 10 10 1 10 10 10 10 00 Totals 258 652 650 330 29 25 25 28 Not described 154 Not described17 The total number of studies performed across combinations of quarters (rows) and the total number of studies employing measurements within the quarter (columns) Q1, January–March; Q2, April–June; Q3, July–September; Q4, October–December. Data are separated for northern (a) and southern (b) hemispheres Fig. 11 Type of intervention investigated within studies in the systematic map database materials, pest regulation, spiritual and inspirational, rec- further synthesis in a meta-analysis or similar). There reational, aesthetic, biodiversity and pollination services may exist more, important knowledge gaps in the evi- than average. dence base for each country, but these other gaps would When comparing ecosystem services studies within reflect larger gaps in research across each country in each country (Table  6), some pairs of countries and ser- general. vices can be highlighted as knowledge gaps (underrep- Table  7 shows that different vegetated strip locations resented by primary studies) and some as synthesis gaps were the focus of different ecosystem service measure - or knowledge clusters (many studies, possibly permitting ments. Particularly noticeable is the high level of research Haddaway et al. Environ Evid (2018) 7:14 Page 21 of 43 Fig. 12 Intervention duration for studies in the systematic map database Fig. 13 Vegetated strip location in studies from within the systematic map database into biodiversity measurements in field edge vegetated expected focus on pollution control and nutrient cycling strips (and within field strips to a lesser extent), whilst in riparian strips. Research on pollination services and pest regulation in riparian strips is perhaps lacking. this is less common in riparian strips. There is also an Haddaway et al. Environ Evid (2018) 7:14 Page 22 of 43 Fig. 14 Vegetation described in strips from studies within the systematic map database Fig. 15 Farming production systems studied within the systematic map database The reviews Vegetated strip terminology A total of 130 reviews were identified through screen - Across the reviews, 153 different main terms (i.e. the ing. These are outlined in a reviews database that can be predominant term used in each review) were used found in Additional file 7. to describe vegetated strips (see Table  8). The most Haddaway et al. Environ Evid (2018) 7:14 Page 23 of 43 Fig. 16 Strip management in studies within the systematic map database Farming system frequently used term was shelterbelt (n = 19), followed Approximately half of the reviews referred to arable by field margin (n = 15), riparian buffer (n = 14), wind- farming systems (n = 63), with livestock farming being break (n = 14), and hedgerow (n = 13). the second most commonly studied system (n = 22); 55 reviews did not specify the system considered (Fig.  22). Publications per year Horticulture (n = 1), viticulture (n = 1), orchard fruit sys- The number of reviews has increased roughly linearly tems (n = 3) and grasslands (n = 3) were also represented. since the 1980s (Fig.  21), with around a third of these reviews published in the last 10  years (n = 43). The use Studied vegetated strips of individual terms varies over time (Table  9), with sev- Most reviews did not specify the vegetation type within eral terms clearly more historically used than others (i.e. the described strips (n = 74), but trees were most com- hedgerow, shelterbelt and windbreak) perhaps with some monly described (n = 38) (Fig.  23). The majority of of these also becoming less commonly used (i.e. shelter- reviews did not report management of strips (n = 105), belt and windbreak). with sowing and harvesting reported in 15 and 8 reviews, respectively (Fig.  24). The vegetated strips described in reviews were mostly riparian (n = 53) or at the field edge Review focus and type (n = 45), with a smaller number of in-field strips (n = 18) Of the 130 relevant reviews that we identified, the major - and 50 strips with no specified location. The interven - ity had a primary focus on vegetated strips (n = 84), tions most commonly described were the presence of whilst 46 reviews mentioned vegetated strips as a sec- vegetated strips (n = 114), with many studies examining ondary topic. Most reviews were not specific to a geo - the change in an outcome across the strip from within the graphical region (n = 99), with only 30 reviews focusing field to outside the strip (n = 82) (Fig.  25). Strip dimen- on specific locations or regions: the most frequently ref - sion (i.e. width) and vegetation type were also moderately erenced were the USA (n = 9) and UK (n = 4) (Table 10). common (n = 28 and 23, respectively). The vast majority of reviews were narrative (n = 107), with a small number of theses (n = 7), quantitative reviews (i.e. meta-analyses or similar) (n = 11), and Measured outcomes reviews that were to some extent systematic (i.e. a doc- Figure 26 displays the outcomes that were reported to be umented search and/or screening phase) (n = 7). One affected by vegetated strips. The most commonly meas - review was a quantitative systematic review and one was ured outcomes were nutrients (N), terrestrial biodiver- a quantitative narrative review. sity and nutrients (P) (n = 53, 52 and 52, respectively). Of Haddaway et al. Environ Evid (2018) 7:14 Page 24 of 43 Fig. 17 Measured outcomes in studies within the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 25 of 43 Table 5 Co-occurrence matrix, showing the number of studies in which outcomes were measured together Darker cells indicate a greater proportion of each row and column Comparing primary literature findings to review findings these, 19 reviews considered terrestrial biodiversity and Terminology both nutrients (N) and (P). Nutrients (N) and (P) were Across primary studies and reviews, the most common reported together in 44 reviews. Least commonly meas- terms were similar; the four terms ‘field margin’, ‘hedge - ured were impacts on soil physical characteristics (n = 2) row’, ‘shelterbelt’, and ‘riparian buffer’ were all in the five and recreation (n = 2), with social impacts, pathogens, most frequently cited terms for both databases. non-crop yield, physical habitat, water chemistry, light, greenhouse gasses, game species and genetically modi- Volume of evidence fied pollen being measured in fewer than 10 reviews each. The publication rate of primary studies and review arti - The most common ecosystem service described in cles is similar (Fig. 27), although there is a relative reduc- reviews was pollution control (n = 70), followed by tion in the number of reviews over the past 10  years, biodiversity (n = 51) and erosion protection (n = 47) whilst the number of primary research articles continues (Table  11). Cultural ecosystem services were poorly rep- to increase linearly. resented (n = 14 in total). Haddaway et al. Environ Evid (2018) 7:14 Page 26 of 43 Fig. 18 Ecosystem services reported within studies in the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 27 of 43 Fig. 19 Measured ecosystem services over time in studies within the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 28 of 43 Fig. 20 Ecosystem services reported for different strip locations in studies within the systematic map database Locations Strip type The most frequently investigated countries in primary Reviews did not often mention vegetation type, probably research were the USA and UK, and this pattern was because they included relevant studies with any vegeta- reflected in the subset of reviews that focused on a spe - tion type, whilst grasses were most commonly reported cific location. in primary studies. Strip management was infrequently described in both reviews and primary studies. Around Farming system half of vegetated strips in primary studies were field edge Approximately half of the reviews focused on arable and a quarter were riparian, whilst riparian and field farming, whilst this system was investigated in almost edge strips were roughly equally the focus of around a 70% of primary studies. half of all described strips in reviews. Strip presence and Haddaway et al. Environ Evid (2018) 7:14 Page 29 of 43 Table 6 Heat map showing the number of studies across all ecosystem services in each studied country County Grandtotal Argenna 2 010010010000000400 9 Australia 0100004630670000 11 03 41 Austria 000000010011000020 0 5 Belgium 0020002310130000 13 01 26 Brazil 0200000310030000102 12 Canada 3110138 20 60 1 18 2110 30 17 104 Chile 0000001100010000000 3 China 100001535013000020 4 25 Colombia 0000000000000000100 1 CzechRepublic 0000031010000000102 8 Denmark 010000153023000030 0 18 Equador 100000010001000000 1 4 Estonia 0010011500050000400 17 Finland 004001 16 24 41 1 21 3030 20 25 105 France 2200028 11 23 8121020 42 16 102 Germany 210000685 01050000 28 12 68 Hungary 000000101100000050 0 8 Ireland 0000000000100000 11 00 12 Italy 1510005 15 20 2120000 20 07 70 Japan 000000000010000010 0 2 Kenya0 00000121002000000 1 7 NewZealand 1210035710560000 13 05 49 Norway 000000022011000040 0 10 Poland 1100023300270100 24 25 51 Romania 010000111001000000 1 6 Russia 000000010004000020 4 11 Serbia 000000000000000010 0 1 Slovakia 000000110001000010 1 5 SouthAfrica0 00000010000000000 0 1 South Korea 000000000000000010 0 1 Spain 111001431004000090 0 25 SriLanka 1010000000000000000 2 Sweden 000001000010000094 0 15 Switzerland 200000010 1 19 0001 0 44 10 69 Taiwan 000010010001000000 0 3 TheNetherlands 1020005610670000 17 11 47 Turkey 000000000000000010 0 1 UK 32201 3 16 25 61 31 24 1610 191 11 4 328 USA 22 26 80 1 25 97 149 68 8 29 141 1230 135 5 79 799 Notstated 000000222020000040 1 13 Mulple 001001120023000071 2 20 GrandTotal 44 46 26 04 48 195313 11815133 2978 10 11 0662 30 1442104 Knowledge gaps (cells within with < 3 studies where (i) country (row) totals are > 50, AND (ii) where ecosystem service (column) totals are > 20) are indicated with a red border. Synthesis gaps/knowledge clusters (cells with > 14 studies) are indicated with pink highlighting and red text comparisons between strips and field environments were Measured outcomes the most common types of comparison in both primary Primary studies and reviews generally prioritised similar studies and reviews, whilst vegetation type was the focus sets of outcomes (i.e. terrestrial biodiversity, nitrogen and of around a quarter of primary studies, but only 17% of phosphorus nutrients, soil and water loss or retention). reviews. Some 22% of reviews focused on the impact of However, several outcomes, including wind, pesticides, vegetated strip width, whilst only 14% of primary studies and crop yield, were the focus of a substantial number of investigated this factor. reviews despite being relatively poorly represented in the primary literature. Overall there were 5.4 primary studies Food Freshwater Fiberand fuel Biochemicalproducts Genec materials Climate regulaon Hydrological regimes Polluon control Erosionprotecon Naturalhazards Pest regulaon Nutrient cycling Spiritualand inspiraonal Recreaonal Aesthec Educaonal Biodiversity Pollinaon Soil formaon Haddaway et al. Environ Evid (2018) 7:14 Page 30 of 43 Table 7 The number of studies for all ecosystem services across different types of vegetated strip Vegetated sp locaon Within field 93 54 11 21 24 61617224 11 5 Field edge 55 27 5158 85 83 1102 35 86 61 20 3111729 Riparian 72 1115 22 2169 54 47 179871915196 Notdescribed 15 2261 11 41 64 28 45 36 62 94 per review article identified and catalogued within this Most studies last only a few years and vegetated strips project. Figure 28 displays the primary study: review arti- or strip management were in place for a similar length of cle ratios for all reported outcomes. Studies with ratios time before being studied. Studies most commonly com- greater than the average indicate that further synthesis pared vegetated strips to conditions within a field, fol - may be a priority. Outcomes with lower ratios are not lowed by conditions in fields without strips or different necessarily well-synthesised, however, since the total strip vegetation. Field edge strips were most frequently number of primary studies measuring these outcomes studied, followed by riparian strips. Strip vegetation was may be low. most commonly grasses, then trees. The most common farming system studied was arable fields. The manage - Ecosystem services ment of strips was generally not described, but beyond The mean number of primary studies per review across planting or sowing to establish the strip, cutting was all ecosystem services was 6.6, with higher values the most common management practice that was men- (lower numbers of reviews relative to primary stud- tioned. Terrestrial biodiversity was the most frequently ies) for several regulating services (natural hazards, measured outcome, followed by nitrogen, water loss pest regulation, and nutrient cycling) and supporting and phosphorus, but a suite of other outcomes was also services (biodiversity and soil formation) (Table  11). reported in the evidence base. Across all outcomes, the Despite having more than the average number of most commonly identified ecosystem services related to primary studies per ecosystem service (x  ̄=  17.6), biodiversity, pollution control and nutrient cycling. hydrological regimes, pollution control, and erosion protection were relatively under-represented in terms Notable patterns across the evidence base of syntheses, representing a possible synthesis gap. It is notable that more than half of the studies in the pri- mary studies systematic map database originate from Discussion either the USA or the UK (38 and 16% of total studies, General observations regarding the evidence base respectively; Fig. 8). For comparison, Canada, France and We have found a substantial body of evidence investigat- Finland each contribute c. 5% of the total number of stud- ing and reviewing the various impacts of vegetated strips. ies, and no other countries contribute more than 3% of It seems that the publication rate of primary research the total. Research from the USA is itself strongly skewed, continues to increase, beyond that of synthetic research with 20% of studies undertaken in Iowa and a further that reviews this work. It is unsurprising that research on 30% in North Carolina, Missouri and Mississippi com- the topic continues to increase in popularity. Countries bined. The reasons and implications for these geographi - such as the UK, Denmark, The Netherlands, the USA, cal biases in the dataset are worthy of consideration in Sweden, and New Zealand, amongst others, are moving synthesising the data to inform policy. There is also geo - towards targeted regulation of nutrient losses from agri- graphical bias in the study of particular ecosystem ser- cultural fields. As a result, there is a strong incentive to vices (Table  6). Biodiversity is the most studied service understand how vegetated strips can be used to remove (31% of total studies) and there are marked variations N and P through both simple and more advanced tech- across the evidence base, with biodiversity investigated nologies, including saturated buffers, intelligent buffer in 17% of US studies, but in 58 and 64% of studies in the zones, etc. [31, 76]. UK and Switzerland, respectively. These differences most Soil formaon Pollinaon Biodiversity Educaonal Aesthec Recreaonal Spiritualand inspiraonal Nutrientcycling Pest regulaon Naturalhazards Erosion protecon Polluon control Hydrologicalregimes Climateregulaon Genec materials Biochemicalproducts Fibre andfuel Fresh water Food Haddaway et al. Environ Evid (2018) 7:14 Page 31 of 43 Table 8 Frequency of  main terms used to  describe protection is a particular focus for studies in China (20% vegetated strips in the reviews identified in our systematic of total studies compared to 6% for studies from all coun- map tries combined). Pest regulation is a particular focus in Switzerland (28% of total studies), and with a wide range Term Frequency of authors, this appears to be a specific concern in this Shelterbelt 19 country rather than disproportionate impact from a sin- Field margin 15 gle research group. Windbreak 14 Figure  16 shows that studies investigating certain Hedgerow 13 ecosystem services are often strongly associated with Riparian buffer 12 a specific type of vegetated strip. For example, studies Buffer zone 9 into effects on biodiversity, pest regulation and polli - Buffer strip 9 nation focus predominantly on strips at the field edge Vegetative filter strip 6 rather than either in-field or riparian strips. In contrast, Filter strip 4 studies into pollution control and nutrient cycling tend Riparian buffer strip 4 to consider riparian strips. There are very few studies Vegetated buffer strip 4 that consider more than one strip location (field mar - Pollen barrier 3 gin vs. in-field vs. riparian), so there is a strong possi - Shelter belt 3 bility that this association between ecosystem service Vegetative buffer 3 studied and strip type is influenced by existing practice Buffer 2 and concepts rather than clear evidence that a particu- Conservation buffer 2 lar strip location is optimal for a specific ecosystem Field boundary 2 service. In-field strips have been shown to be highly Grass buffer strip 2 effective in control of erosion and associated transport Riparian area 2 of pollution through inhibiting the formation of con- Riparian buffer zone 2 centrated flow pathways [80]; nevertheless, strips that Riparian zone 2 are studied for this purpose are overwhelmingly either Agricultural buffer 1 riparian or at the field edge (Fig.  16). Overall, there are Agroforestry buffer 1 very few studies that consider in-field vegetated strips, Flower strip 1 presumably because this is the most difficult strip type Grass buffer 1 for farmers to implement. Grassed buffer strip 1 Grassed waterway 1 Multifunctionality of vegetated strips Grassy field margin 1 The review has identified 30 different measured out - Herbaceous wind barrier 1 comes across 19 ecosystem services. Although vegetated Non‑ crop habitat 1 strips may be implemented for a specific function, their Non‑ crop strip 1 design and management may influence their ability to Refuge strip 1 support other ecosystem services [81]. Riparian forest buffer 1 In most cases, where authors studied multiple out- Riparian vegetative buffer strip 1 comes (Table  5), they were closely related; the most Stream buffer 1 common of these were the nutrients N and P (where 99 Vegetated buffer 1 studies reported on both), followed by N and water loss/ Vegetation border 1 retention (85 studies). Many pest control and pollina- Vegetation filter 1 tion outcomes (61 and 31 respectively) were reported Wildflower strip 1 together with biodiversity, but this is largely because Woody border 1 these outcomes, such as species abundance, are also a Grand total 151 feature of wider biodiversity. Studies that looked at more contrasting ecosystem services were less common, but biodiversity and nutrients were notably studied together likely relate to differences in national frameworks for the in a number of studies; nitrogen (24 studies) and phos- protection of biodiversity [77–79]. Studies of nutrient phorus (20 studies). Similarly, biodiversity was co-meas- cycling, hydrological regime, and pollution control were ured with a variety of soil outcomes. These studies often relatively evenly spread geographically, whereas erosion considered the soil or plant communities associated with Haddaway et al. Environ Evid (2018) 7:14 Page 32 of 43 Fig. 21 The number of reviews published by 5‑ year period soil or nutrient outcomes, but a few did consider wider representing a very sensitive approach. We also under- biodiversity, such as Stockan et al. [82], who studied car- took extensive bibliographic searching, screening the abid species together with outcomes related to soil and reference lists of almost 100 relevant literature reviews. water nutrients. This supplementary searching was vital to identify arti - The intensification and expansion of agriculture means cles that might have used other synonyms for buffer that both quantity and quality of off-crop habitats, such strips that were identified in the evidence base. However, as vegetated strips, are likely to be increasingly important there is a risk that some studies using less common syno- in supporting a wide variety of ecosystem services [83], nyms may have been missed from the database and bibli- and further primary studies into the value and enhance- ography searches. Future updates or amendments to this ment of multifunctional services offered by vegetative topic should integrate the synonyms that we identified strips would be useful. into new searches to minimise this risk. Additionally, our organisational website searches for grey literature were focused more on European contexts, Limitations of the systematic map given the experience of the review team. We did attempt We searched for evidence using a suite of synonyms to include non-European organisations, but future work for vegetated strips that included 360 search terms, of could direct effort particularly towards organisations in which only 84 were represented in the evidence base, Haddaway et al. Environ Evid (2018) 7:14 Page 33 of 43 Table 9 Trends in the use of vegetated strip terminology over time: (a) only years with publications reported, (b) 5-year periods (a) Year 1944 11 1954 1 1 1983 1 1 1984 1 1 2 1986 1 1 2 1988 1 5 1 8 15 1990 1 1 1991 1 1 1992 1 1 1993 1 1 1 3 1994 3 1 1 5 1995 1 1 2 1996 3 1 1 5 1997 1 1 1 1 4 1998 1 12 1999 1 1 1 1 1 1 1 1 8 2000 1 1 1 1 1 1 1 1 1 9 2001 1 1 1 3 2002 1 2 1 4 2003 1 1 1 3 2004 2 1 1 1 1 1 1 8 2005 1 1 3 1 1 1 1 1 1 11 2006 1 1 1 1 1 5 2007 1 1 2 2 2 1 9 2008 12 1 1 5 2009 1 1 1 2 1 1 7 2010 11 11 11 6 2011 1 1 1 1 1 5 2012 1 1 1 1 2 1 7 2013 1 1 2 1 2 7 2014 1 1 1 1 1 5 2015 1 1 1 3 Grand Total2 29 92 215413 11 1131 11 31 2124 21 12 319114 11 36 1141 151 (b) Period 1940-1944 11 1945-1949 1 1 1950-1954 0 1955-1959 0 1960-1964 0 1965-1969 0 1970-1974 0 1975-1979 0 1980-1984 1 2 3 1985-1989 1 6 2 8 17 1990-1994 3 1 2 1 1 1 1 1 11 1995-1999 1 4 2 2 1 1 1 1 1 2 1 3 1 21 2000-2004 1 1 2 2 4 1 2 1 1 2 1 1 2 1 1 1 1 1 1 27 2005-2009 21 22 61 11 12 15 11 31 12 21 37 2010-2014 12 21 21 41 24 11 13 21 130 2015-2019 1 1 1 3 Grand Total2 29 92 215413 11 1131 11 31 2124 21 12 319114 11 36 1141 151 Agricultural buffer Agricultural buffer Buffer Buffer Buffer strip Bufferstrip Buffer zone Bufferzone Conservaonbuffer Conserva on buffer Field boundary Fieldboundary Fieldmargin Fieldmargin Filter strip Filter strip Flower strip Flower strip Grass buffer strip Grass buffer strip Grassed buffer strip Grassed buffer strip Grassedwaterway Grassed waterway Grassy field margin Grassy field margin Hedgerow Hedgerow Herbaceous windbarrier Herbaceouswindbarrier Non-crop habitat Non-crop habitat Non-crop strip Non-crop strip Pollen barrier Pollen barrier Refuge strip Refugestrip Riparian area Riparian area Riparian buffer Riparian buffer Riparian bufferstrip Riparian buffer strip Riparian bufferzone Riparian buffer zone Riparian forest buffer Riparian forest buffer Riparian vegetave buffer strip Riparian vegeta vebuffer strip Riparian zone Riparian zone Shelterbelt Shelterbelt Shelterbelt Shelterbelt Stream buffer Stream buffer Vegetated buffer Vegetated buffer Vegetated buffer strip Vegetated buffer strip Vegetaon border Vegetaonborder Vegetaon filter Vegetaonfilter Vegetave buffer Vegetave buffer Vegetavefilter strip Vegetave filter strip Wildflower strip Wildflower strip Windbreak Windbreak Woodyborder Woodyborder GrandTotal Grand Total Haddaway et al. Environ Evid (2018) 7:14 Page 34 of 43 Table 10 Number of reviews focusing on specific regions several institutions, including Stockholm University and SLU, which are together relatively comprehensive, but Specific region Frequency evidently not completely so. Future work could attempt USA 6 to source these difficult to access articles. Piedmont‑ Coastal Plain, USA 1 Europe and USA 1 Limitations of the evidence base Virginia, USA 1 Missing meta-data was a consistent issue with a small UK 4 number of studies, even with basic information, such New Zealand 3 as the study country (n = 8). Occasionally high levels of Australia 3 missing meta-data at times reflect the study topics: for North America 2 example, 592 studies did not report the intervention Northern Europe 2 duration, but this is perhaps to be expected with field Poland 2 margins and hedgerows that may have been in place for Central and Northern Europe 1 extensive periods, and this information may be unavail- Europe and Mediterranean 1 able. Other meta-data is surprising in its absence: for Brittany, France 1 example, 99 studies did not report the type of strip veg- European Union 1 etation and 168 studies did not report the type of farming Sweden 1 system investigated. We echo previous calls for improved No region specified 99 reporting to facilitate synthesis and repeatability [e.g. 84, 85]. The publication rate of primary research studies on this the USA, where a great deal of evidence was identified by topic can perhaps be considered to deviate from common our work. patterns in other systematic reviews [e.g. 86] in that there Finally, we were unable to source 276 papers due to is an abrupt change in rate from the late 1980s and a a lack of subscription. We used subscriptions across steady, linear increase in papers thereafter. Other reviews Fig. 22 Farming systems described within relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 35 of 43 Fig. 23 Vegetated strip vegetation type within relevant reviews Fig. 24 Strip management described within relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 36 of 43 Fig. 25 Strip interventions described within relevant reviews suggest a more exponential growth rate. This difference features. This evidence base is vital for making the possibly reflects the fact that this topic is broader than best use of available evidence in national (and other) many other systematic reviews (and some maps) to date, policy-making. or that there was some shift in research funding during The expertise of the author team is European focused, the late 80 s that has remained in constant growth since. and as such we are unable to discuss in detail North American policy, and focus instead on EU policy, with Conclusions which we are most familiar. The experience from Den - Implications for policy, practice and research mark with the Buffer Zone Act adopted in 2011 that To date, the evidence bases used in national level pol- implemented 50,000 ha of 10 m wide mandatory buffer icy settings have often been drawn from national level strips along all watercourses and lakes is an illustrative research evidence, which can be restricted in nature, example of the need for reliably synthesised evidence showing only one or a limited number of outcomes or [87]. The Buffer Zone Act was revised after 3  years, ecosystem services and including a narrow set of con- halving the area of buffer strips following boycott by texts. These evidence bases may not cover the multi- farmers and several lawsuits. Finally, the Buffer Zone functionality and potential goal conflicts of vegetated Act was withdrawn in 2016 as part of the main goals of strips that can be identified through a regional or global the new Danish government. An evidence synthesis on assessment of evidence, such as the one presented here. the topic would have greatly assisted in this instance, The systematic mapping approach outlined herein since the production of evidence on ecosystem services along with associated systematic review methods (col- from across an international evidence base would likely lectively referred to as evidence synthesis methods) have been influential in the debate. are a reliable, transparent and comprehensive means of identifying and characterising knowledge gaps and Knowledge gaps and clusters clusters relating to a particular topic. In this case we Knowledge gaps have utilized international evidence from all relevant The following topics represent knowledge gaps where climate zones to assemble an extensive, comprehensive no studies exist or a relatively small number of studies evidence base that investigates a plethora of contextual have been conducted. The review team feel that these Haddaway et al. Environ Evid (2018) 7:14 Page 37 of 43 Fig. 26 Measured outcomes affected by vegetated strips in relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 38 of 43 Table 11 Ecosystem services represented across  relevant 9. What are the characteristics that improve multiple reviews along with the ratio of primary studies to reviews outcomes in multi-use vegetated strips (i.e. those designed to have many different social-ecological Service type Ecosystem service Number Primary of reviews studies benefits)? per review 10. To what extent does the implementation of multi- ple interventions targeting different outcomes lead Provisioning services Food 25 1.76 to synergies or conflicts? Fresh water 15 3.07 Fiber and fuel 24 1.08 Knowledge clusters Biochemical products 1 0.00 The following topics represent knowledge clusters Genetic materials 3 1.33 that the review team believes are important topics for Regulating services Climate regulation 15 3.20 researchers and decision-makers for further synthesis Hydrological regimes 30 6.50 (approximately ordered by volume of evidence). We have Pollution control 70 4.47 used an arbitrary cut-off of a minimum of 40 studies to Erosion protection 47 2.51 be mentioned below, acknowledging that heterogeneity Natural hazards 2 7.50 amongst studies is likely to preclude meaningful synthe- Pest regulation 15 8.87 sis for small numbers of studies. Since we have not con- Nutrient cycling 10 29.70 ducted critical appraisal, we are unable to prioritise the Cultural services Spiritual and inspira‑ 0 – suitability of these clusters for synthesis. tional Recreational 6 1.67 1. How do vegetated strips affect terrestrial biodiver - Aesthetic 8 1.38 sity (n = 596)? Educational 0 2. What are the impacts of different vegetated strips Supporting services Biodiversity 51 12.98 on nutrient (nitrogen and phosphorus) retention Pollination 6 5.17 (n = 242)? OR How effective are vegetated strips at Soil formation 7 20.57 reducing nitrogen losses to water and air (n = 212)? 3. What are the impacts of vegetated strips on hydro- topics are important social or ecological issues that logical regimes (n = 195)? warrant further investment in terms of research fund- 4. What are the impacts of buffer size or width ing and primary research efforts. (n = 154) on biodiversity (n = 88), nitrogen nutri- ents (n = 25), phosphorus nutrients (n = 27), soil 1. What role can vegetated strips play in climate regu- loss/retention (n = 25), soil chemistry (n = 14), and lation? water loss/retention (n = 35)? 2. What are the impacts of vegetated strips on aquatic 5. What are the impacts of vegetated strips on sedi- and semi-aquatic biodiversity? ment-associated chemicals, including priority sub- 3. What are the impacts of harvesting strip vegetation stances under the EU Water Framework Directive on all outcomes? (n = 123)? 4. What are the possible cultural ecosystem services 6. What are the impacts of vegetated strips on erosion (spiritual, recreational, aesthetic, educational) of protection (n = 118)? vegetated strips? 7. What are the impacts of vegetated strips on pests 5. What are the long-term impacts (> 2 years) of veg- in arable fields (n = 104)? etated strips, and how do impacts vary over time or 8. What role can vegetated strips play in terms of car- measurement season. bon sequestration (n = 87)? 6. What is the relationship between the presence of 9. How do soil physical/chemical characteristics pests or predators of pests and the impacts of veg- of vegetated strips affect terrestrial biodiversity? etated strips on crop yield and weed seed bank in Specifically, the what is the link between: terres - soil of nearby agricultural fields? trial biodiversity and nutrients (n = 29); terrestrial 7. What is the role of vegetated strips in terms of fibre biodiversity and physical characteristics of the soil and fuel production in a circular bioeconomy? (n = 10)? 8. What are the impacts of vegetated strips on all 10. How do different types of strip affect biodi - outcomes from the following un- and under-rep- versity (n = 42)?: for field edge versus riparian resented countries and regions, including: eastern strips (n = 23); for in-field versus field edge strips Europe; Russia; Asia; South America (specifically, (n = 19)? Argentina, Brazil, Chile and Uruguay)? Haddaway et al. Environ Evid (2018) 7:14 Page 39 of 43 Fig. 27 The publication rate for primary studies (green) and review articles (blue) in the evidence base In conclusion, this systematic map highlights a knowledge clusters. Further research effort, both in large and heterogeneous evidence base relating to the terms of primary studies and syntheses, is necessary impacts of vegetated strips in boreo-temperate agri- to understand these diverse impacts of the various culture, containing a suite of knowledge gaps and types of vegetated strips, particular in understanding: Haddaway et al. Environ Evid (2018) 7:14 Page 40 of 43 Fig. 28 The number of primary studies per review article reporting each outcome, displaying the mean study:review ratio of 5.4 as a dashed grey line. Outcomes that are struck through represent those for which no reviews were identified Haddaway et al. Environ Evid (2018) 7:14 Page 41 of 43 Funding (1) the role of landscape context in the effectiveness of This review report is financed by the Mistra Council for Evidence ‑Based Envi‑ vegetated strips; (2) potentially conflicting outcomes ronmental Management (EviEM). between different management options; and (3) con - flicts between high production targets and environ - Publisher’s Note mental objectives. Springer Nature remains neutral with regard to jurisdictional claims in pub‑ lished maps and institutional affiliations. Additional files Received: 12 February 2018 Accepted: 24 April 2018 Additional file 1. Search string development. Additional file 2. Web ‑based searching record. Additional file 3. Unobtainable articles. References Additional file 4. List of articles excluded at full text along with reasons. 1. Stoate C, Boatman N, Borralho R, Carvalho CR, De Snoo G, Eden P. Ecological impacts of arable intensification in Europe. J Environ Manage. Additional file 5. Coding and meta‑ data extraction schema. 2001;63(4):337–65. Additional file 6. Primary research studies systematic map database. 2. Stoate C, Báldi A, Beja P, Boatman N, Herzon I, Van Doorn A, De Snoo G, Rakosy L, Ramwell C. Ecological impacts of early 21st century agricultural Additional file 7. Review articles database. change in Europe—a review. J Environ Manage. 2009;91(1):22–46. Additional file 8. Articles excluded at full text due to language. 3. Lal R. Soils and sustainable agriculture. A review. Agron Sustain Dev. 2008;28(1):57–64. Additional file 9. Term use in primary studies by study location. 4. Sutton MA, Howard CM, Erisman JW, Billen G, Bleeker A, Grennfelt P, van Grinsven H, Grizzetti B. The European nitrogen assessment: sources, effects and policy perspectives. Cambridge: Cambridge University Press; Abbreviation 2011. p. 664. N O: nitrous oxide. 5. Gill RJ, Ramos‑Rodriguez O, Raine NE. 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The multifunctional roles of vegetated strips around and within agricultural fields

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Copyright © 2018 by The Author(s)
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Environment; Environmental Management; Ecosystems; Environmental Law/Policy/Ecojustice; Environmental Policy; Forestry Management
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Abstract

Background: Agriculture can have substantial negative impacts on the environment. The establishment and man‑ agement of vegetated strips adjacent to farmed fields (including various field margins, buffer strips and hedgerows) are commonly advocated mitigation measures for these negative environmental impacts. However, it may be difficult to obtain reliable evidence on the effects of implementation and management of vegetated strips, even though a substantial body of evidence exists. We describe a systematic map of research relating to vegetated strips in boreo‑ temperate farming systems to answer the question: What evidence exists regarding the effects of field margins on nutrients, pollutants, socioeconomics, biodiversity, and soil retention in boreo‑ temperate systems? Methods: We searched 13 bibliographic databases, 1 search engine and 37 websites of stakeholder organisations using a predefined and tested search string focusing on a comprehensive list of English language vegetated strip synonyms. Searches in Danish, Finnish, Spanish, and Swedish were also conducted using web searches. We screened search results at title, abstract and full text levels, recording the number of studies deemed non‑ relevant (with reasons at full text). A systematic map database of meta‑ data (i.e. descriptive summary information about the settings and methods) for relevant studies was produced following full text assessment. The systematic map database is provided as an evidence atlas: interactive, web‑ based geographical information system. Results: Over 31,000 search results were identified, resulting in a total of 1072 relevant primary research studies and 130 evidence reviews. Articles used a variety of terminology to describe vegetated strips, with ‘field margin’, ‘hedge ‑ row’, ‘shelterbelt’ and ‘riparian buffer’ most common. The volume of primary research is increasing linearly year ‑ by‑ year, whilst the increase in reviews has tailed off in the last 10 years. The USA and UK were most frequently studied and reviewed. Arable systems were investigated in c. 70% of primary research but 50% of reviews. Some 50% of primary research vegetated strips were field edge and 25% riparian, whilst riparian and field edge strips were roughly equally the focus of around a half of all described strips in reviews. Terrestrial biodiversity, nutrients (nitrogen and phospho‑ rus) and soil/water loss or retention were the most commonly measured outcomes in primary studies and reviews, although some other outcomes were more common in reviews than research articles (e.g. pesticides). Conclusions: We identified substantial bodies of evidence on particular sets of related outcomes and ecosystem services, which constitute important knowledge clusters/synthesis gaps relating to: strip width, terrestrial biodiversity, nutrient retention, hydrological regimes, toxic substances, erosion protection, pests, carbon sequestration, and soil and biodiversity combined. We also identified key knowledge gaps relating to: climate regulation, freshwater biodi‑ versity, strip harvesting, cultural ecosystem services, long‑ term impacts, the relationship between pest populations and crop yield, fuel and fibre production, specific regions and countries (e.g. Russia and South America), and multi ‑ use *Correspondence: neal.haddaway@sei.org; neal_haddaway@hotmail.com Mistra Council for Evidence‑Based Environmental Management (EviEM), Stockholm Environment Institute, Box 24218, 10451 Stockholm, Sweden Full list of author information is available at the end of the article © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Haddaway et al. Environ Evid (2018) 7:14 Page 2 of 43 vegetated strips. This systematic map is an important step in identifying what research has been done to date, and what primary and secondary research is needed as the next step for this topic. Keywords: Vegetative strip, Hedgerow, Beetlebank, Riparian buffer, Buffer strip, Filter strip, Buffer, Agri‑ environment, Agricultural policy, Mitigation, Agricultural pollution, Agricultural management Background fixtures in agricultural landscapes, and the interventions The ecological impacts of agricultural intensification must therefore be in place for longer than 12 months (see and change in Europe since the Second World War are inclusion criteria for further details). well documented and affect both agricultural areas and Vegetated strips may have a multi-functionality that their surrounding systems [1]. Biodiversity, air and water covers a range of processes, including protection of quality and soil structure of ecological systems have all water quality in surface waters and soil conservation of been affected [2]. Well-documented impacts of agricul - slopes, habitat improvement, biodiversity, shading, car- tural development include: widespread negative effects bon sequestration, flow capture, biomass production, of the application of nutrients in fertilisers (mineral and landscape diversity, and societal services [10]. These pro - organic) and agro-chemicals on soil, and surface and cesses occur through a set of pathways that impact socio- ground water quality [3]; emission of N O as a potent economic and environmental outcomes (Fig. 2). greenhouse gas [4]; negative effects of pesticides on non- target invertebrate species [5], birds [6] and biological Vegetated strips, water flow and sediment control potential [7]; and loss of ecological heterogeneity Many of the ecosystem services provided by some veg- at multiple spatial and temporal scales [8]. The establish - etated strips exist because of a reduction in water flow ment and management of vegetated strips (including field that occurs due to soil properties induced by the strip margins, buffer strips and hedgerows) are key mitigation and the presence of roots and above-ground vegetation. measures for these negative environmental impacts [9]. As surface runoff passes across field margins, the veloc - ity of shallow uniform flow tends to decrease in response Definition of vegetated strips to the type and density of strip vegetation as well as any Here, we define vegetated strips as any vegetated area set- decrease in slope. This reduction in flow velocity allows aside from the main cropping regime within or around a suspended sediment to be deposited, which decreases field, and installed for the purposes of benefiting native the transport of sediment and sorbed nutrients and biota, water and air quality, socio-economics, and yield. other contaminants beyond the strip. Strips with per- Examples of such interventions include: hedgerows, ennial vegetation, such as grasses, trees and/or shrubs, field margins, buffer strips, beetlebanks and shelterbelts can counter soil erosion via filtration of larger sediment (Fig. 1). For the purposes of this review, we focus on those particles [11, 12], and by increasing soil stability through interventions that are permanent or semi-permanent increased root density [13]. The reduction in flow veloc - ity also provides potential for infiltration of water into the strip, decreasing the total volume of runoff water and the associated load of dissolved contaminants; this process is controlled by the infiltration capacity of the soil and vegetated strips are known to modify this soil parameter relative to adjacent agricultural land [14]. The effective - ness of vegetated strips in reducing sediment transport off-site is known to vary with the ratio of runoff area to the area of the strip [15] as well as with other factors including soil type, topography, soil–water management (such as drainage pipes), land use, rainfall intensity and antecedent moisture conditions [16]. For instance, heavy rainfall may cause fast preferential flow where nutrients and pollutants readily flow from the soil surface through macropores, cracks and root channels into drainage Fig. 1 Illustration of the variety of vegetated strips used within pipes, particularly in dry clay soils [17]. In addition to soil and around fields. Interventions include: in‑field strips such as beetlebanks, hedgerows, forested shelterbelts, shrubs, grassy strips, cracking, high water repellence of old vegetated strips and wildflower margins. Illustration: Gunilla Hagström/Form Nation with a mossy soil surface may enhance preferential flow Haddaway et al. Environ Evid (2018) 7:14 Page 3 of 43 Fig. 2 Conceptual model of pathways to impact for vegetated strips within or around fields. Illustration: Neal Haddaway or surface runoff thus increasing the potential for erosion margin are one of the most commonly applied manage- on steep slopes under dry soil conditions [18]. In these ment measures, and are mainly designed and imple- kinds of situations, vegetated strips are not effective in mented to control sediment, phosphorus, nitrogen and retaining soluble or particle bound nutrients. Any condi- pesticide losses to off-site surface waters [23, 24]. They tion that promotes the formation of channel flow (rather have been shown to be highly efficient for reducing nutri - than sheet runoff) will reduce the flow reduction and ent runoff from farmed fields in a wide range of climatic sediment capture [e.g. 19]. This can be associated with regions across the world [19, 25]. Vegetated strips in steepness of slope, local topography and/or intensity of riparian zones can also remove nitrogen in proximity to rainfall. Gully formation caused by concentrated flows in watercourses, particularly subsurface nitrogen, although agricultural fields can be hindered by grassed waterways. their effectiveness appears to be less than for sediment The grassed waterway outlet is kept wide and shallow to or sediment bound contaminants [26]. The efficiency slow the velocity of water and spread the flows evenly of vegetated strips in reducing dissolved phosphorus before entering a vegetated strip [20]. Similarly, the bene- is dependent on the dynamic equilibrium between soil ficial flow reduction properties of vegetated strips can be and dissolved phosphorus. Phosphorus is adsorbed by negated where the strip occurs on steep ditch banks. In soil when the phosphorus concentration in soil water such cases, the design of ditch banks or implementation is higher than the equilibrium level and vice versa [27]. of two-stage ditches may improve planting of banks and Generally, the effectiveness of vegetated strips in con - flow reduction properties. trolling transport of soluble contaminants is less than for strongly-sorbed chemicals because the reduction Vegetated strip effects on nutrients and other in water transfer across the buffer is generally smaller contaminants than the reduction in sediment transfer [28]. There is Nutrients and pesticides are amongst the most important also potential for dissolved contaminants infiltrating pressures on aquatic ecosystems, where excess inputs into the margin to reach surface water subsequently via may deteriorate ecosystem integrity and/or threaten subsurface drains and/or shallow groundwater. In some drinking water resources [21, 22]. Even strongly-sorbed circumstances, vegetated strips may change from a nutri- compounds, including faecal pathogens from livestock ent trap into a nutrient source. For example, phosphorus or slurry fertiliser applications, can harm surface water may be desorbed from the deposited soil particles and quality through runoff. Vegetated strips at the field soil surface or liberated from the frost-broken plant cells Haddaway et al. Environ Evid (2018) 7:14 Page 4 of 43 in vegetated strips during heavy rainfall events or spring semi-natural landscapes [48]. Finally, vegetated strips runoff [19, 29]. To cycle the nutrients assimilated by the around and within fields may also impact on crop pro - plants, vegetation in vegetated strips should be harvested duction. Field margins can support beneficial inverte - and plant waste removed from strips [29]. brates such as natural enemies of pest invertebrates, but Where contaminants may be emitted to the air, as for also may harbour weeds, pests and diseases (e.g. viruses), pesticide spraying, vegetated strips have a dual function- which could potentially create a conflict between crop ality in increasing the distance between the emission production and biodiversity conservation [9, 49, 50]. source and vulnerable habitats such as surface waters Increased habitat heterogeneity may also have negative or non-crop habitats, but also through the potential impacts on some migratory (grass-eating) species (e.g. for interception of spray drift. Finally, it is known that geese) or farmland species such as skylarks that rely on pharmaceuticals used in animal husbandry may also be the cropped area of large fields, for breeding and foraging important contaminants of terrestrial environments adja- [51, 52]. For these species, homogeneous environments, cent to agricultural fields [e.g. 30]. In such cases, veg - commonly considered to be the result of agricultural etated strips can again increase distance from source for development and intensification, may represent preferred operations such as spreading of manure and biosolids, as habitat equivalent to permanent grassland ecosystems in well as having potential for interception of airborne par- central and eastern Europe [53]. ticulates at time of spreading. Other effects Vegetated strip effects on biodiversity Depending on the nature of their management, vegetated The widespread loss of spatial landscape heterogene - strips can provide various other services. Some resources ity, associated with the cultivation of a few high yielding from vegetated strips can be harvested periodically, such crop types across large uniform fields [8], is often viewed as wood and fodder [23]. Strips are also used to provide as a key driver of biodiversity loss on arable land [31– nesting and foraging habitat for game bird populations 34]. Hence, the creation and management of vegetated [e.g. 54], although elevated mortality and nest predation strips such as field margins have the potential to restore can occur in these habitats [55, 56]. A less well-studied habitat diversity for the benefit of associated farmland aspect of vegetated strips is their potential to enhance biodiversity [35]. Hedgerows and other field margin veg - aesthetic values and perceived “naturalness” of agricul- etation types have been shown to affect the richness and tural landscapes, especially when vegetated with trees abundance of flora, invertebrates and birds [36–38]. For and/or shrubs and employed in areas where such features instance, grassy field margins have been shown to pro - are absent [23]. Similarly, other values may include amen- vide important refuge and food for invertebrates, mam- ity use of agricultural land, for example by horse riders. mals and birds [39, 40]. Yet, these effects may depend on landscape structure and regional levels of agricultural intensification [41]. As a result measures are sometimes Multipurpose vegetated strips and conflicting objectives implemented in landscapes where their effects are small One key question relating to vegetated strips as an or even negative for some species [42]. environmental intervention on farmland is how to eval- As vegetated strips comprise a variety of different veg - uate multifunctional effects; that is, impacts of single etation types that are managed for different purposes, strips on multiple outcomes. True evaluation for areas their effects on biodiversity and associated ecosys - larger than the plot-scale is difficult to undertake due to tem services may vary. For instance, pollinator habitat difficulties in having representative controls. One pos - enhancement in the form of hedgerows and flower-rich sibility to overcome large-scale evaluation problems is strips may contribute to yield on adjacent fields [43], but therefore upscaling of plot results and/or modelling, also overall biodiversity and biological control poten- and in both cases collection of data from experimental tial in the surrounding landscape [44]. Vegetated strips studies conducted around the world will be invaluable established using densely planted perennial grasses may as a baseline. In their review of the multifunctional role primarily benefit invertebrates for pest suppression [45], of vegetated strips on arable farms, Hackett and Law- but also increase the availability of suitable nesting sites rence [57] concluded that although different strip types for ground-foraging farmland birds on adjacent crop can produce multiple benefits, none can wholly provide fields [46]. At the regional scale these benefits may be for all environmental outcomes. One way to optimise particularly valuable in resource-poor landscapes [47]. multiple benefits from field margins at the field and In addition, both at local and regional scales, vegetated landscapes scale could therefore be to adjust manage- strips provide valuable linear habitats that may promote ment practices locally according to purpose. Cresswell connectivity between areas of non-agricultural land or et  al. [58] used systematic mapping to identify which Haddaway et al. Environ Evid (2018) 7:14 Page 5 of 43 Identification of the Topic and Stakeholder Engagement plant traits deliver different ecosystem services to help The topic was suggested at a general stakeholder meet - inform future plant community design of vegetative ing arranged by MISTRA EviEM on September 24th, strips. 2012. Suggestions for the topic were made by the Swed- In reality, many vegetated strips vary in their purpose, ish Board of Agriculture, the Swedish Environmental method of establishment and ongoing management. Protection Agency, the Swedish Ministry of the Envi- Common forms include those that are naturally regen- ronment, Svensk Sigill, Hushållningssällskapet, WWF, erated from unused farmland, those sown with grass and researchers from the Centre for Biodiversity and or wildflower mixes, those sown specifically for target the Department of Ecology at the Swedish University of organisms such as pollinators (nectar and pollen mixes) Agricultural Sciences. The focus and scope of the review or for wild birds (seed mixes), those that are annu- was narrowed and better defined during a specific stake - ally cultivated and those that are unmanaged [57]. The holder event on September 1st, 2015. Details of this specific design and management of a vegetated strip meeting and the modifications in scope are available may depend on the main reason for the intervention, on request. Stakeholders who attended this event were and the resultant efficacy for the different outcomes invited to comment on the draft protocol prior to sub- described above may vary accordingly. Wildflower mission for publication, although none did. Stakeholders strips, for example, are designed to benefit pollinators were not engaged during the conduct of the review. such as bees [39], whereas densely vegetated strips typi- cally established by sowing a mixture of perennial grass species adjacent to water courses, are primarily used to mitigate soil erosion [59] and reduce runoff of nutrients Objective of the review and agro-chemicals [60]. The access to foraging oppor - The aims of this review were to identify, collate, and tunities for insectivorous birds in strips designed for describe relevant published research relating to the effec - water protection may be substantially lower compared tiveness of vegetated strips in and around farmland for to strips planted with wildflower mixes [61] or naturally a wide variety of purposes, including but not limited to: regenerating strips on poor soils with a diverse seed the enhancement of biodiversity; the reduction of pesti- bank [40]. Accordingly, managing vegetated strips for cide and nutrient drift/runoff/leaching; the mitigation biodiversity or for diffuse pollution purposes may entail of soil loss; the reduction of pathogens and toxins; and, very different management practices, since retained socioeconomic values, such as provision of game habi- dissolved or particulate matter eventually accumulates tat and reduction of crop pests. The map is restricted in within the strip, which in turn may reduce the poten- geographical scope to boreal and temperate systems (see tial for biodiversity benefits. However, removal of plant inclusion criteria below), and this report is accompanied material from vegetated strips could help maintain by a searchable database describing the identified rel - long-term retaining capacity, avoiding their transfor- evant studies, and an evidence atlas, an interactive, web- mation into nutrient sources, and with simultaneous based geographical information system (GIS) displaying benefits of lower nutrient levels and/or sparser veg - the contents of the database. etation for wild flora and visual foragers such as birds [62]. An additional consideration in this context relates Primary Question: What evidence exists regard- to pollution swapping [63], where mitigation measures ing the effects of field margins for one pollutant cause an increase in another pollut- on nutrients, pollutants, socio- ant. In this way, vegetated strips for controlling nitro- economics, biodiversity, and soil gen leaching could lead to simultaneous transformation retention? of sediment-bound phosphorus into soluble reactive Secondary Question: To what extent has this research phosphorus. focused on multi-use vegetated Whilst a large volume of evidence is known to exist strips? on these varied impacts of vegetated strips around and Population: Boreo-temperate regions as within agricultural fields, and whilst various literature defined by the following Köp- reviews have sought to examine their impacts for specific pen–Geiger climate classification outcomes [e.g. 26, 64–66], no review has systematically zones [67]: Cfa, Cfb, Cfc, Csb, collated evidence on their impacts, certainly not across Csc, Dfa, Dfb, Dfc (see Fig. 3). multiple diverse outcomes. Here, we report on the results Intervention: Vegetated strip interventions of a comprehensive systematic mapping of all avail- around and within fields used for able evidence relating to the impacts of vegetated strips crop production (arable), grazing within and around fields in boreo-temperate regions. Haddaway et al. Environ Evid (2018) 7:14 Page 6 of 43 Main climates Precipitation Temperature World Map of Köppen−Geiger Climate Classification A: equatorial W: desert h: hot arid F: polar frost updated with CRU TS 2.1 temperature and VASClimO v1.1 precipitation data 1951 to 2000 B: arid S: steppe k: cold arid T: polar tundra C: warm temperate f: fully humid a: hot summer Af Am As Aw BWk BWh BSk BSh Cfa Cfb Cfc Csa Csb Csc Cwa D: snow s: summer dry b: warm summer E: polar w: winter dry c: cool summer m: monsoonal d: extremely continental Cwb Cwc Dfa Dfb Dfc Dfd Dsa Dsb Dsc Dsd Dwa Dwb Dwc Dwd EF ET 90 −160 −140 −120 −100−80 −60−40 −20 020406080100 120140 160 180 Resolution: 0.5 deg lat/lon Version of April 2006 80 80 ET EF 70 70 Dfd ET Dwd Dfc Dsc Dfc 60 60 Dfc Dwc Dfb 50 50 Dwb Dfb Dfa Cfb BSk Dwa Csb Dfa Csb BWk 40 40 Cfb Cfa Csa BSk Csa Cwa ET 30 30 Cfa BWh BSh Cwb BWh Cwa BWh BWh Csa BSh Aw 20 20 Aw Am Aw Am Aw Am BSh 10 10 Aw Cwb Af Am Aw Am 0 Af Af 0 Af As Am Af BWh Aw BSh −10 −10 Aw Aw Cwa Af Af BSh Aw −20 BSh −20 BWk Cwa Cfa BWh Cfa Cwb BWh BWk −30 −30 Cfb Cfa Csa Csb BSk Csb Csb Cfb Cfb −40 −40 Cfb BSk −50 −50 Cfc ET −60 −60 Kottek, M., J. Grieser, C. Beck, −70 −70 B. Rudolf, and F. Rubel, EF 2006: World Map of Köppen- http://gpcc.dwd.de Geiger Climate Classification −80 −80 http://koeppen-geiger.vu-wien.ac.at updated. Meteorol. Z., 15, 259-263. −90 −160 −140 −120 −100−80 −60−40 −20 020406080100 120140 160 180 Fig. 3 Map of Koppen Geiger climate zones (http://koepp en‑geige r.vu‑wien.ac.at/prese nt.htm) websites to our search strategy, including a database of and horticulture, orchards and review articles as an additional output, and our inability vineyards, where presence of a to screen and code a small number of articles in German vegetated strip or management and Swedish due to a change in availability of the Ger- of the strip is investigated. man and Swedish speaking review team member. Comparator: Before vegetated strip establish- ment, before a change in veg- Searches etated strip management (tem- Bibliographic databases poral comparisons); no vegetated The following bibliographic databases were searched for strip, different vegetated strip studies using English search terms (non-English arti- management, including strip cles, where present, are typically catalogued with English width (spatial comparisons); out- titles, abstracts and/or keywords): side a vegetated strip. Outcome: All and any outcomes were 1. Academic Search Premier (http://www.ebsco host. included iteratively as they com/acade mic/acade mic-searc h-premi er). are identified within the rel- 2. Agricola (http://agric ola.nal.usda.gov/). evant literature and were coded 3. AGRIS: agricultural database (FAO) (http://agris accordingly. .fao.org/agris -searc h/index .do). 4. Biosis Citations Index (http://wok.mimas .ac.uk/). 5. Directory of Open Access Journals (http://doaj. Methods org/). The methods described herein reflect those outlined in 6. PubMed/MEDLINE (http://www.ncbi.nlm.nih. the published protocol [68]. Our methods deviate from gov/pubme d). the protocol only in adding a number of organisational Haddaway et al. Environ Evid (2018) 7:14 Page 7 of 43 7. Scopus (http://www.scopu s.com/). OR “forest boundar*” OR “forested boundar*” OR “non- 8. Web of Science Core Collections (http://wok. cropped boundar*” OR “non-cropped boundar*” OR mimas .ac.uk/). “plant boundar*” OR “planted boundar*” OR “*flower 9. Zoological Record (http://thoms onreu ters.com/ boundar*” OR “wood boundar*” OR “wooded boundar*” pr o du ct s_s er v i c e s/s c ien c e/s c ien c e_pr o du ct s/a-z/ OR “woody boundar*” OR “herbacious boundar*” OR zoolo gical _recor d). “cultivated boundar*” OR “uncultivated boundar*” 10. JSTOR (http://www.jstor .org/). OR “bird cover boundar*” OR “grazed boundar*” OR 11. DART-Europe E thesis (http://www.dart-europ “weedy boundar*” OR “weeded boundar*” OR “peren- e.eu/basic -searc h.php). nial boundar*” OR “*grass buffer*” OR “grassed buffer*” 12. EThOS (British Library) (http://ethos .bl.uk/Home. OR “grassy buffer*” OR “managed buffer*” OR “ripar - do). ian buffer*” OR “sown buffer*” OR “uncropped buffer*” 13. Index to Theses Online (http://www.these s.com/). OR “un-cropped buffer*” OR “unmanaged buffer*” OR “unploughed buffer*” OR “un-ploughed buffer*” OR “veg - Search string etated buffer*” OR “vegetation buffer*” OR “vegetative The following search string was used as a basis for buffer*” OR “forest buffer*” OR “forested buffer*” OR “non - searches within each of the above databases and was cropped buffer*” OR “non-cropped buffer*” OR “plant adapted using database-specific syntax as appropriate buffer*” OR “planted buffer*” OR “*flower buffer*” OR (see Additional file  1). Searches in bibliographic data- “wood buffer*” OR “wooded buffer*” OR “woody buffer*” bases were performed on 13/11/15 and have not been OR “herbacious buffer*” OR “cultivated buffer*” OR updated during the conduct of the review. “uncultivated buffer*” OR “bird cover buffer*” OR “grazed (“*grass barrier*” OR “grassed barrier*” OR “grassy bar- buffer*” OR “weedy buffer*” OR “weeded buffer*” OR “per - rier*” OR “managed barrier*” OR “riparian barrier*” OR ennial buffer*” OR “*grass filter*” OR “grassed filter*” OR “sown barrier*” OR “uncropped barrier*” OR “un-cropped “grassy lter*” fi OR “managed lter*” fi OR “riparian filter*” barrier*” OR “unmanaged barrier*” OR “unploughed bar- OR “sown filter*” OR “uncropped filter*” OR “un-cropped rier*” OR “un-ploughed barrier*” OR “vegetated barrier*” lter*” OR “ fi unmanaged filter*” OR “unploughed filter*” OR “vegetation barrier*” OR “vegetative barrier*” OR OR “un-ploughed filter*” OR “vegetated filter*” OR “veg - “forest barrier*” OR “forested barrier*” OR “noncropped etation filter*” OR “vegetative filter*” OR “forest filter*” barrier*” OR “non-cropped barrier*” OR “plant barrier*” OR “forested filter*” OR “noncropped filter*” OR “non- OR “planted barrier*” OR “*flower barrier*” OR “wood cropped filter*” OR “plant filter*” OR “planted filter*” OR barrier*” OR “wooded barrier*” OR “woody barrier*” OR “*flower filter*” OR “wood filter*” OR “wooded filter*” OR “herbacious barrier*” OR “cultivated barrier*” OR “uncul- “woody filter*” OR “herbacious filter*” OR “cultivated fil - tivated barrier*” OR “bird cover barrier*” OR “grazed ter*” OR “uncultivated filter*” OR “bird cover filter*” OR barrier*” OR “weedy barrier*” OR “weeded barrier*” OR “grazed filter*” OR “weedy filter*” OR “weeded filter*” OR “perennial barrier*” OR “*grass border*” OR “grassed “perennial filter*” OR “*grass margin*” OR “grassed mar - border*” OR “grassy border*” OR “managed border*” OR gin*” OR “grassy margin*” OR “managed margin*” OR “riparian border*” OR “sown border*” OR “uncropped “riparian margin*” OR “sown margin*” OR “uncropped border*” OR “un-cropped border*” OR “unmanaged bor- margin*” OR “un-cropped margin*” OR “unmanaged der*” OR “unploughed border*” OR “un-ploughed border*” margin*” OR “unploughed margin*” OR “un-ploughed OR “vegetated border*” OR “vegetation border*” OR “veg- margin*” OR “vegetated margin*” OR “vegetation mar- etative border*” OR “forest border*” OR “forested border*” gin*” OR “vegetative margin*” OR “forest margin*” OR OR “noncropped border*” OR “non-cropped border*” OR “forested margin*” OR “noncropped margin*” OR “non- “plant border*” OR “planted border*” OR “*flower bor - cropped margin*” OR “plant margin*” OR “planted der*” OR “wood border*” OR “wooded border*” OR “woody margin*” OR “*flower margin*” OR “wood margin*” OR border*” OR “herbacious border*” OR “cultivated border*” “wooded margin*” OR “woody margin*” OR “herbacious OR “uncultivated border*” OR “bird cover border*” OR margin*” OR “cultivated margin*” OR “uncultivated “grazed border*” OR “weedy border*” OR “weeded bor- margin*” OR “bird cover margin*” OR “grazed margin*” der*” OR “perennial border*” OR “*grass boundar*” OR OR “weedy margin*” OR “weeded margin*” OR “peren- “grassed boundar*” OR “grassy boundar*” OR “managed nial margin*” OR “*grass strip*” OR “grassed strip*” OR boundar*” OR “riparian boundar*” OR “sown boundar*” “grassy strip*” OR “managed strip*” OR “riparian strip*” OR “uncropped boundar*” OR “un-cropped boundar*” OR “sown strip*” OR “uncropped strip*” OR “un-cropped OR “unmanaged boundar*” OR “unploughed boundar*” strip*” OR “unmanaged strip*” OR “unploughed strip*” OR “un-ploughed boundar*” OR “vegetated boundar*” OR “un-ploughed strip*” OR “vegetated strip*” OR “veg- OR “vegetation boundar*” OR “vegetative boundar*” etation strip*” OR “vegetative strip*” OR “forest strip*” OR Haddaway et al. Environ Evid (2018) 7:14 Page 8 of 43 “forested strip*” OR “noncropped strip*” OR “non-cropped agroecosystem* OR agricult* OR agronom* OR arable* OR strip*” OR “plant strip*” OR “planted strip*” OR “*flower crop* OR cultivat* OR farm* OR field* OR grassland* OR strip*” OR “wood strip*” OR “wooded strip*” OR “woody “grass land*” OR horticult* OR meadow* OR orchard* OR strip*” OR “herbacious strip*” OR “cultivated strip*” OR plantation* OR ranch* OR vineyard* OR pasture* OR cat- “uncultivated strip*” OR “bird cover strip*” OR “grazed tle* OR graz*). strip*” OR “weedy strip*” OR “weeded strip*” OR “per- Search terms were identified through a scoping pro - ennial strip*” OR “*grass zone*” OR “grassed zone*” OR cess. Firstly, we generated a list of 120 articles known by “grassy zone*” OR “managed zone*” OR “riparian zone*” the review authors to be relevant to the topic. The titles, OR “sown zone*” OR “uncropped zone*” OR “un-cropped keywords and abstracts were then subjected to textual zone*” OR “unmanaged zone*” OR “unploughed zone*” analysis to identify the most frequently occurring words. OR “un-ploughed zone*” OR “vegetated zone*” OR “veg- Key terms were then selected from this list and added to etation zone*” OR “vegetative zone*” OR “forest zone*” OR a pre-existing list generated by the review authors. Key “forested zone*” OR “noncropped zone*” OR “non-cropped terms were then used to probe the titles and keywords of zone*” OR “plant zone*” OR “planted zone*” OR “*flower articles in the above list to identify common co-locators zone*” OR “wood zone*” OR “wooded zone*” OR “woody (i.e. words located next to key terms in the text). Com- zone*” OR “herbacious zone*” OR “cultivated zone*” OR mon pairs (i.e. any pair of words that frequently occur “uncultivated zone*” OR “bird cover zone*” OR “grazed together in the corpus) were also identified. All key terms zone*” OR “weedy zone*” OR “weeded zone*” OR “peren- were then assembled and tested both individually and in nial zone*” OR “barrier strip*” OR “border strip*” OR combination. Terms that resulted in very large numbers “boundary buffer*” OR “boundary margin*” OR “bound - of results but that were also subjectively assessed as hav- ary strip*” OR “boundary management*” OR “field bor - ing low relevance (i.e. the terms ‘vfs’, ‘bz’, ‘bzs’, ‘fbz’) were der*” OR “field buffer*” OR “field margin*” OR “buffer excluded from the final search string. strip*” OR “buffer zone*” OR “filter strip*” OR “filter zone*” OR “managed edge*” OR “buffer management*” OR buff - Specialist searches erstrip* OR bufferzone* OR “cropland buffer*” OR “farm - Searches for grey literature were performed in two key land buffer*” OR “farmland margin*” OR “ditch bank*” ways (in addition to the searches as part of the biblio- OR “farm buffer*” OR “farm edge*” OR “farm interface*” graphic database searches above; i.e. thesis databases and OR “field bank*” OR “field boundary*” OR “field edge*” Scopus). OR “field interface*” OR “filter margin*” OR “filter strip*” Firstly, searches were conducted using an extensive OR filterstrip* OR “filter zone*” OR filterzone* OR “mar - (i.e. downloading and assessing the first 1000 results) gin strip*” OR beetlebank* OR “beetle bank*” OR “hedge title-only search of Google Scholar (https ://schol ar.googl row*” OR hedgerow* OR shelterbelt* OR “shelter belt*” OR e.ca/intl/en/schol ar/about .html), which has been proven “grassed waterway*” OR “grassed water way*” OR “grass to return a high percentage of grey literature (c. 37%; waterway*” OR “grass water way*” OR “grassy waterway*” [69]). Searches were conducted for a range of key inter- OR “grassy water way*” OR “vegetated waterway*” OR vention search terms that individually returned more “vegetated water way*” OR “vegetative waterway*” OR than 100 search results in Web of Science during scop- “vegetative water way*” OR “wind buffer*” OR “agrofor - ing. Details of these searches are provided in Additional estry buffer*” OR “conservation buffer*” OR “conservation file  1. Searches were performed in English, French, Span- headland*” OR “conservation head land*” OR “stream ish, Swedish, German, Finnish and Danish. Only the first border*” OR “stream barrier*” OR “stream buffer*” OR 1000 results are viewable within Google Scholar due to “stream margin*” OR “river border*” OR “river barrier*” restrictions in the search engine, but these records were OR “river buffer*” OR “river margin*” OR “waterway downloaded into a database for later screening using the border*” OR “waterway buffer*” OR “waterway mar - method outlined in Haddaway et al. [70]. gin*” OR “water way border*” OR “water way buffer*” Secondly, searches of 43 websites of key organisations OR “water way maring*” OR “countour strip*” OR “nec- were undertaken (see Table  1). For each of the websites, tar strip*” OR “widlife strip*” OR “wildlife corridor*” OR web scraping was employed where possible to search for “set-aside margin*” OR “set-aside border*” OR “set-aside key terms using the built-in search facility using the soft- buffer*” OR “setaside margin*” OR “setaside border*” OR ware Import.io (http://www.impor t.io). See Haddaway “setaside buffer*” OR “permanent strip*” OR “perma - et  al. [70] for a detailed description of the web-scraping nent margin*” OR “permanent border*” OR “permanent methods used. Where automatic web-scraping could not buffer*” OR “sterile strip*”) AND (“agro-ecosystem*” OR be used due to incompatibility with the website, searches Haddaway et al. Environ Evid (2018) 7:14 Page 9 of 43 Eligibility criteria were performed, and results recorded by hand using the built-in search facilities on each site. Additional file  2 outlines the terms used for each website. The results Eligible subjects: Boreo-temperate regions from all searches across all databases were combined into as defined by the follow - one database for each language and screened by a review ing Köppen-Geiger climate team member with relevant language expertise. classification zones [67]: Cfa [warm temperate]; Cfb and Cfc [maritime temper- Supplementary searches ate or oceanic]; Csb [dry The comprehensiveness of results of the above searches summer or Mediterranean]; was tested by comparing a predefined test list of 114 Csc [dry summer mari- studies against the combined results to ensure all of these time subalpine]; Dfa [hot relevant studies are found. This checking was performed summer continental]; Dfb iteratively at the start of the searching process. In addi- [warm summer continental tion, bibliographic checking was performed by screening or hemiboreal]; and, Dfc the reference lists of 96 relevant reviews that were iden- [continental subarctic or tified during screening of search results to retrieve any boreal (taiga)]. potentially relevant studies missed by the search strategy described above. Eligible interventions: Vegetated strip interven- Following feedback on our original search string, we tions in or around fields performed an additional search to include records men- used for arable, grazing tioning the term ‘riparian buffer’ in all bibliographic and horticulture, orchards databases. This supplementary search was conducted on and vineyards, where pres- 21/12/15. ence of a vegetated strip or management of the strip is Screening investigated. All articles identified through searching were screened Eligible comparators: Before vegetated strip for eligibility at title, abstract and then full text levels establishment, before a using predefined inclusion criteria (detailed below). Con - change in vegetated strip sistency in the application of the inclusion criteria was management (temporal tested by comparing agreement between two review- comparisons); no vegetated ers at title, abstract and full text level screening, using a strip, different vegetated subset of records. All disagreements were discussed. The strip management, includ- level of agreement was tested formally using a kappa test ing strip width (spatial [71], and where agreement score fell below 0.6, indicat- comparisons); outside a ing moderate agreement, a third reviewer was consulted vegetated strip. and a further set of records screened following discus- Eligible outcomes: Outcomes were included sion of disagreements. Consistency checking results were iteratively as they were as follows: title level, n = 149 kappa = 0.66; abstract level identified within the rel- first test, n = 200 kappa = 0.46; abstract level second test, evant literature and were n = 205 kappa = 0.82; full text level, n = 50 kappa = 0.62. coded accordingly. All Following abstract screening, potentially relevant stud- social and ecological out- ies were retrieved in full text. Unobtainable articles are comes were included, such listed in Additional file  3. All screened full texts that were as: terrestrial and aquatic excluded from the review are listed along with exclusion biodiversity (including con- reasons in Additional file 4. nectivity); nutrient runoff During screening, relevant reviews were placed into a or leaching; pesticide run- separate database for coding (see below). This coding of off, leaching or drift; soil reviews was restricted to English language reviews only, due to resource constraints. retention; socioeconomics. Haddaway et al. Environ Evid (2018) 7:14 Page 10 of 43 Table 1 List of organisational websites searched for evidence Organisation Website searched Aalto Universityhttp://www.otali b.fi/tkk/index ‑eng.html Aarhus University, Department of Agroecology http://agro.au.dk/en/ Adas http://www.adas.uk/ Alterra, Wageningen Universityhttp://www.wagen ingen ur.nl/en/Exper tise‑Servi ces/Resea rch‑Insti tutes /alter ra.htm ARTOhttps ://arto.linne anet.fi/vwebv /searc hBasi c?sk=fi_FI Arvalishttp://www.arval isins titut duveg etal.fr/index .html Columbia Basin Agricultural Research Centerhttp://cbarc .aes.orego nstat e.edu/long_term_pubs European Crop Protection Association http://www.ecpa.eu/ European Environment Agencyhttp://www.eea.europ a.eu/ European Soil Portalhttp://eusoi ls.jrc.ec.europ a.eu GRACEnet, USDA Agricultural Research Servicehttp://www.ars.usda.gov/resea rch/progr ams/progr ams.htm?np_code=212&docid =21223 Greppa Näringenhttp://www.grepp a.nu Hankehaavihttp://www.hanke haavi .fi/ Hydrotekniska Sällskapethttp://www.hydro tekni skasa llska pet.se/ INIAhttp://www.inia.es/IniaP ortal /verPr esent acion .actio n INRA http://www.inra.fr/ IRSTEAhttp://www.irste a.fr/accue il LUKEhttp://jukur i.luke.fi/ NABUhttps ://www.nabu.de/ National Farmers Unionhttp://www.nfuon line.com/home/ OPERAhttp://opera resea rch.eu/ Rothamsted Researchhttp://www.rotha msted .ac.uk/ RSPB http://www.rspb.org.uk/ SERA‑17http://sera1 7.org/ Soilservice http://www4.lu.se/o.o.i.s/26761 Swedish Board of Agriculturehttp://www.jordb ruksv erket .se Swedish Environmental Protection Agencyhttp://www.natur vards verke t.se Swedish University of Agricultural Sciences http://www.slu.se SYKEhttp://www.syke.fi/fi‑FI/Julka isut Theseushttps ://www.these us.fi/ UC Davis, Agricultural Sustainability Institutehttp://ltras .ucdav is.edu/ University of Copenhagenhttp://www.ku.dk/engli sh University of Illinois, Department of Crop Scienceshttp://crops ci.illin ois.edu/resea rch/morro w USDA Agricultural Research Servicehttp://www.ars.usda.gov/resea rch/progr ams/progr ams.htm?np_code=211&docid =22480 VIIKKIhttp://eviik ki.hulib .helsi nki.fi/ Wageningen Universityhttp://www.wagen ingen ur.nl/en/wagen ingen ‑unive rsity .htm World bankhttp://www.world bank.org/refer ence/ BioRxivhttp://biorx iv.org/ ArXivhttp://arxiv .org/ Nature Precedingshttp://prece dings .natur e.com/ Peer J Preprintshttps ://peerj .com/prepr ints/ Science paper onlinehttp://www.paper .edu.cn/en Research gatehttps ://www.resea rchga te.net/home Haddaway et al. Environ Evid (2018) 7:14 Page 11 of 43 Eligible types Primary research stud- appropriate, flagging up clearly unreliable research that of study design: ies involving field-based should be excluded from further synthesis, and serious deficiencies that should be pointed out in those studies experimental manipula- that remain in the map. tions and observations. Interventions must have been in place for 12 months Data coding strategy or more. Management Meta-data (i.e. descriptive data regarding the methods and interventions within fields setting of each study, provided as free text) were extracted that are applied to existing from included, relevant studies and entered into a search- crops (such as cover crops, able database: one database was produced for primary intercropping, etc.) were research studies and another for relevant reviews. The not considered. Further- database was populated with a number of variables, each more, only direct evidence given a category according to a predetermined strategy of the impacts of vegetated (also known as coding). This database forms one of the main outputs of the review and is supplied herein as a strips were included in the Additional files 1 , 2, 3, 4, 5, 6, 7, 8 and 9. During meta-data map: i.e. not indirect evi- extraction, each study will be assigned codes correspond- dence, such as the ability ing to the ecosystem services explicitly mentioned. The list of a border species grown of ecosystem services was adapted from Cork et  al. [72], elsewhere to alter an out- adding a code for ‘pest regulation’ as a regulating service. come. Modelling studies Consistency of data extraction across team mem- were included where they bers was assessed by double checking a subset of stud- provided primary data. ies between two reviewers (NRH and JE). Where Laboratory studies were meta-data were missing from articles this was stated as not included. Relevant “not reported”/“not stated”, since making efforts to obtain reviews and meta-analyses these data was not possible within the resources allocated were recorded in a separate to this project. database. Coding and meta-data was extracted for relevant Eligible languages: All languages were included reviews identified during screening using the schema where possible. Studies in provided in Additional File 5. This database is provided languages not able to be as an interactive, searchable database in a Additional files translated were included in 1, 2, 3, 4, 5, 6, 7, 8 and 9 (see "Results"). a separate supplementary database. Study mapping and presentation (narrative synthesis) Key variables were described in the form of tables and figures. Multiple variables were cross-tabulated in heat Efforts were made to ensure that authors of research maps that display the volume of evidence across two cat- studies included in this review were not involved in any egorical meta-data variables. In addition, we have sum- decisions regarding their own work. For Finnish studies, marised the relevant evidence identified in the form of an however, this was not possible, and JUK was involved in evidence atlas, an interactive geographical information screening a small number of studies for which she was system (GIS), that maps studies by their location across an author. Studies were further checked for relevance by a cartographical map. This evidence atlas is published on NRH following screening, however, and no articles were the EviEM website (http://www.eviem .se/en/proje cts/ included that did not meet the review’s inclusion criteria. Buffe r-strip s/). Knowledge gap and cluster identification Critical appraisal Knowledge gaps (subtopics that are un- or under-rep- Critical appraisal was not undertaken within this map, resented in the evidence base) and knowledge clusters since the measurement methods and study designs (subtopics with sufficient numbers of studies to allow varied substantially across different outcomes. A very meaningful synthesis) were identified by the review team basic quality assessment was conducted in the form of by cross-tabulating key meta-data variables in heat maps. a ‘free text’ meta-data variable where a brief description Specific, arbitrary cut-offs (described in the Results text of the study quality was made for some studies where Haddaway et al. Environ Evid (2018) 7:14 Page 12 of 43 and legends of each heat map in tables, below) were used Results to identify poorly studied topics. The team discussed all The mapping process knowledge gaps and clusters, including those that they Figure  4 displays the flow of articles and studies through felt were of key relevance to decision-makers and read- the systematic mapping process. From over 31,000 ers. No prioritisation was performed, and gaps and clus- search results there were 19,457 unique records that ters are displayed in order of the volume of evidence. were then screened on title, with 8094 abstracts screened Fig. 4 Flow diagram showing the flow of articles and studies through the systematic mapping process Haddaway et al. Environ Evid (2018) 7:14 Page 13 of 43 Fig. 5 Screenshot of the evidence atlas for the systematic review database of primary research studies in the next stage. Some 3000 articles remained for full Primary research studies text screening, although 1123 of these (37%) could not Vegetated strip terminology be found or accessed (see Additional file  3). A total of A wide variety of different terminology was used to 417 potentially relevant articles were added in for full describe vegetated strips across studies in the system- text screening from bibliographic checking, and from atic map (Fig.  6). The most commonly used terms were searches of Google Scholar and organisational websites. ‘field margin’ (n = 152), ‘hedgerow’ (n = 146), ‘shelter- Following full text screening, 1089 articles were excluded belt’ (n = 80), ‘riparian buffer’ (n = 73), and ‘buffer strip’ (see Additional file  4 for exclusion reasons). This left a (n = 55). Table 2 lists the terms that were used only once. final set of 1072 studies reporting primary data relevant In total, across the 1072 studies in the systematic map to the review in the systematic map database (see Addi- database there were 205 different terms relating to vege - tional file  6), and a further 130 review articles within the tated strips that were used a total of 1220 times (multiple review article database (see Additional file  7). Due to terms within some articles). In comparison, there were resource constraints, we were unable to screen German 360 search terms in our search string. However, of these, or Swedish articles at full text, which left 26 potentially only 84 search terms were represented in articles within relevant articles unscreened (see Additional file 8). the systematic map database. Thus, sources of articles other than the formalised database searches (i.e. biblio- Evidence atlas graphic searching) were a vital methodological addition We have produced an evidence atlas (see Fig.  5 for a to ensure we captured any article using some of the other screenshot and visit http://www.eviem .se/en/proje cts/ 121 terms and none of the 84 search term synonyms. Buffe r-strip s/) that displays the studies in the primary Additional file  9 includes a table of the primary vegetated research systematic map database visually on a carto- strip terms (first, main mention) used across different graphic map. This map is interactive and allows the user field study locations, indicating, for example, that ‘ripar - to search for specific evidence both using a visual interface ian buffer’ is most common for US studies (n = 52), whilst and a text search facility. A small number of studies (n = 8) ‘field margin’ is most common in the UK (n = 66). could not be displayed on the map because they lacked information about sample location (including country). Publications per year Figure 7 displays the number of relevant research studies published per year from within the systematic map data- base. Currently the publication rate is approximately 70 Haddaway et al. Environ Evid (2018) 7:14 Page 14 of 43 Fig. 6 Tree map of terminology used to describe vegetated strips in studies within the systematic map. Only showing terms used in 10 studies or more. Polygon area corresponds to the number of studies using the term Haddaway et al. Environ Evid (2018) 7:14 Page 15 of 43 Table 2 Vegetated strip terms used only once in primary studies within the systematic map database Agricultural buffer Forest margin Meadow strip Uncropped edge Agroforestry buffer strip Forest shelter belt Perennial filter strip Uncropped margin Agroforestry vegetated filter strip Forested buffer zone Perennial grass buffer Uncropped wildlife strip Arable margin Forested riparian buffer Perennial grass strip Uncultivated strip Barrier strip Forested riparian corridor Permanent vegetation strip Unploughed strip Biocorridor Forested strip Plant strip Upland habitat buffer Border crop Gamagrass strip Pond buffer Vegetated buffer system Border strip Game‑ cover strip Prairie edge Vegetated field border Border zone Grass bank Prairie filter strip Vegetated field margin Boundary strip Grass buffer zone Prairie strip Vegetated margin Conservation buffer strip Grass hedgerow Restored/natural riparian zone Vegetated riparian buffer Conservation strip Grass margin strip Retired pasture strip Vegetated strip Contour strip Grass vegetated filter strip Riparian conservation buffer Vegetated waterway Conventional hedgebank Grass waterway Riparian filter strip Vegetational corridor Cover strip Grass‑ wetland buffer Riparian forest buffer strip Vegetative barrier Crop margin Grassed channel Riparian margin Water margin Ditch slope Grassed strip Riparian vegetated buffer strip Watercourse margin Earth bank Grassy field boundary Riparian wood Weed border Fencerow Green fence Riparian woods Weedy field margin Field adjacent woodlot Headland Rose bush strip Wild bird mix Field bank Hedge and ditch Ruderal vegetation strip Within‑field refuge Field corner plantation Hedge bank Set‑aside Within‑field ridge Field strip Herbaceous border Shelter tree Wooded riparian strip Field windbreak Herbaceous buffer Sown patch Woodlot edge Field‑adjacent grassland strip Herbaceous field edge Sown weed strip Woody border Filter Herbaceous strip Streamside management zone Floral field margin Herbaceous vegetated strip Successional strip Flowering plant strip Improved field margin Successional weed strip Forest belt Insect border Switchgrass barrier Forest border Isolated hedge Switchgrass hedge Forest buffer Live fence Tree belt Forest edge Marginal grassland Tree row studies per year. Whilst many other systematic reviews the third highest number of studies was France, with 64 and maps have identified exponential growth in research studies. publications over recent decades [73–75], publication rates within the topic of this review appear to be more Study design linear, increasing from a minimum of approximately 5/ More studies were observational (i.e. quasi-experimental) year in 1990 at the rate of c. 2.7 studies per year from (n = 660) than manipulative (i.e. experimental) (n = 406), that point onwards. This suggests a more stable growth in with only six studies combining observation and manipu- research on the topic. lative designs. It is worth noting that reviewers identified a spectrum of study designs between purely observa- Study location tional studies and purely manipulative ones: these stud- Out of 1072 studies within the systematic map, the ies may have used observational methods to investigate majority of studies come from North America (n = 393, a prior manipulation. This was common in long-term 37%) (Fig.  8), with most of these coming from the USA experiments. (n = 341). Of these US studies, many were undertaken in Figure  9 shows the duration of studies included in the Iowa (n = 70), North Carolina (n = 40), Missouri (n = 33) systematic map database. Around two-thirds (n = 710) and Mississippi (n = 27) (Table 3). After the USA, the UK of studies were only 1 or 2 years in length, with very few was most commonly studied (n = 213). The country with Haddaway et al. Environ Evid (2018) 7:14 Page 16 of 43 Fig. 7 The number of research studies published per year in the systematic map database (Fig.  11). Some 344 studies investigated the impact of studies lasting longer than 10 years (n = 23). A large num- the presence of a strip or strip management relative to a ber of studies did not report their study length (n = 70). control site lacking a strip, or to the same system before Study spatial scale is shown in Fig.  10, showing that the change was put in place. A similar number of studies studies were fairly evenly distributed across plot-, field- (n = 329) investigated differences in outcomes resulting and regional-scales. Farm- and catchment-scale studies from strips of different vegetation. Only 5 studies failed were less common, with only a minor proportion not to describe the intervention in detail. describing the scale. However, the distinction between A large proportion of the evidence base did not catchment and regional is questionable. Following report the duration of the intervention (i.e. the time screening, reviewers noted that spatial scale was not easy period that the vegetated strip or management prac- to code and often overlapped. This may result in confu - tice was in place) (n = 592). Of those reporting dura- sion when (1) different levels of organisation are char - tion, a third of the studies were 10  years or less since acterised by a variety of processes that have their own establishment of the vegetated strip or strip manage- scales of space and time, (2) replication is low and plot ment (n = 366). The most common duration over size is large and (3) comparisons are made among sam- which strips or strip management were in place was ples that are not independent (i.e. pseudoreplication). 2 years (Fig. 12). The distinction between catchment and regional is there - fore unlikely to be a useful one. It was most common for measurements within studies Vegetated strip type, location and management to be conducted across two quarters (n = 392), followed by Field edge vegetated strips were most common only one quarter (n = 225). Considering the timings specif- (n = 651), followed by riparian strips (n = 304), and ically, measurements were most commonly taken over the very few within-field strips (n = 86) (Fig .  13). A total of spring and summer (Q2 [April–June] and Q3 [July–Sep- 96 studies did not report strip location: this was com- tember], n = 272), with studies spanning the whole year mon for studies examining strips as pollutant filters in a the next most common time period (n = 171) (Table 4). manipulative design, where the experimental filter trips were placed fully within a field. Grasses were the most common type of vegetation Interventions in strips (n = 530), followed by trees (n = 354) (Fig . 14). Most studies investigated the change in an outcome from Many other strips had a combination of vegetation or within a field into or across a vegetated strip (n = 472) Haddaway et al. Environ Evid (2018) 7:14 Page 17 of 43 Fig. 8 Number of studies per country in the systematic map database (grouped by continent) Haddaway et al. Environ Evid (2018) 7:14 Page 18 of 43 Table 3 Number of  studies per  US State in  the  systematic (n = 214), a lack of management (n = 110), and other map database less common practices (see Fig. 16). State Number of studies Measured outcomes and ecosystem services The most commonly measured outcome across the Iowa 70 evidence base was terrestrial biodiversity (in all cases North Carolina 40 some surrogate measure of biodiversity was used) Missouri 33 (n = 596), which was almost three times more com- Mississippi 27 mon than the second most common outcome, nitrogen Nebraska 19 nutrients (n = 201). Following this, over 100 studies Maryland 13 quantified the following outcomes: water loss/reten - Minnesota 12 tion (n = 183); phosphorus nutrients (n = 140); soil Oregon 11 chemical (n = 123) and physical (n = 107) characteris- Georgia 10 tics; and pest control (n = 104). Social impacts of veg- Michigan 10 etated strips were not commonly investigated: social, Wisconsin 9 n = 19; farming economics, n = 15; and, recreation, Illinois 8 n = 9 (Fig .  17). Table  5 displays the number of studies Virginia 8 in which multiple outcomes were reported together. California 6 Commonly co-occurring outcomes (i.e. n > 50 studies) Arkansas 5 were: biodiversity (terrestrial) and pest control (n = 61) New York 5 (although many pest control outcomes were also meas- Ohio 5 ures of diversity); nutrients N and nutrients P (n = 99); Washington 5 nutrients N and soil soil/sediment (chemical not N/P) Florida 4 (n = 75); nutrients N and water loss/retention (n = 86); Indiana 4 nutrients P and water loss/retention (n = 56); soil loss/ Kansas 4 retention and water loss/retention (n = 56); and, soil/ Kentucky 4 sediment (chemical, not N/P) and soil/sediment (physi- Texas 3 cal) (n = 53). Oklahoma 2 The most common groups of ecosystem services were Pennsylvania 2 regulating services (n = 1119), followed by supporting Colorado 1 services (n = 836) (Fig. 18). The most frequently reported Connecticut 1 single ecosystem service was biodiversity (n = 662), fol- Louisiana 1 lowed by pollution control (n = 313) and nutrient cycling Massachusetts 1 (n = 297). Under-reported ecosystem services were: all Nevada 1 provisioning services (food, fresh water, fibre and fuel, North Dakota 1 biochemical products, genetic materials); climate regula- South Dakota 1 tion; natural hazards; all cultural services (spiritual and Utah 1 inspirational, recreational, aesthetic, educational); and Vermont 1 pollination. It is worth noting, however, that some studies Multiple 8 may have focused on pollinators without describing them Not stated 5 as such, and this may result in under-representation of research on this topic. Figure 19 displays how studies of the various ecosystem other groups of plants (n = 295), perhaps indicating the services have increased in frequency over time. There are need for more specific coding. no clear trends, with all services increasing in representa- The majority of studies were performed in arable sys - tion over time in a similar way. tems (n = 738), followed by livestock (n = 351) (Fig . 15). Ecosystem services reported in studies differed Many studies did not describe the farming production depending on the location of the vegetated strip (Fig. 20), system (n = 168). with riparian strips more commonly associated with Management of strips was generally not described fresh water, fibre and fuel, hydrological regimes, pollu - across the evidence base (n = 513), but where descrip- tion control, erosion protection, nutrient cycling, and soil tions existed they related to sowing or planting of veg- formation services than average. Conversely, field margin etation in strips (n = 394), cutting of strip vegetation strips were more commonly associated with food, genetic Haddaway et al. Environ Evid (2018) 7:14 Page 19 of 43 Fig. 9 Study length for primary research included in the systematic map Fig. 10 Spatial scale of studies included in the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 20 of 43 Table 4 Study measurement quarter (a) Nothern Hemisphere (b) Southern Hemisphere Q1 Q2 Q3 Q4 # studies Q1 Q2 Q3 Q4 # studies 0 1 10 261 1 1 1 110 1 1 1 1 155 10 0 18 00 10 96 0 1 10 6 0 10 087 1 10 04 0 1 1 1730 00 14 00 1 1350 0 10 3 1 10 028 10 00 3 1 1 10 25 0 1 1 12 10 0 1240 0 1 11 00 0 116 1 1 10 1 0 10 1150 10 11 10 00 13 1 10 11 1 10 18 10 1 11 10 1 14 10 10 1 10 10 10 10 00 Totals 258 652 650 330 29 25 25 28 Not described 154 Not described17 The total number of studies performed across combinations of quarters (rows) and the total number of studies employing measurements within the quarter (columns) Q1, January–March; Q2, April–June; Q3, July–September; Q4, October–December. Data are separated for northern (a) and southern (b) hemispheres Fig. 11 Type of intervention investigated within studies in the systematic map database materials, pest regulation, spiritual and inspirational, rec- further synthesis in a meta-analysis or similar). There reational, aesthetic, biodiversity and pollination services may exist more, important knowledge gaps in the evi- than average. dence base for each country, but these other gaps would When comparing ecosystem services studies within reflect larger gaps in research across each country in each country (Table  6), some pairs of countries and ser- general. vices can be highlighted as knowledge gaps (underrep- Table  7 shows that different vegetated strip locations resented by primary studies) and some as synthesis gaps were the focus of different ecosystem service measure - or knowledge clusters (many studies, possibly permitting ments. Particularly noticeable is the high level of research Haddaway et al. Environ Evid (2018) 7:14 Page 21 of 43 Fig. 12 Intervention duration for studies in the systematic map database Fig. 13 Vegetated strip location in studies from within the systematic map database into biodiversity measurements in field edge vegetated expected focus on pollution control and nutrient cycling strips (and within field strips to a lesser extent), whilst in riparian strips. Research on pollination services and pest regulation in riparian strips is perhaps lacking. this is less common in riparian strips. There is also an Haddaway et al. Environ Evid (2018) 7:14 Page 22 of 43 Fig. 14 Vegetation described in strips from studies within the systematic map database Fig. 15 Farming production systems studied within the systematic map database The reviews Vegetated strip terminology A total of 130 reviews were identified through screen - Across the reviews, 153 different main terms (i.e. the ing. These are outlined in a reviews database that can be predominant term used in each review) were used found in Additional file 7. to describe vegetated strips (see Table  8). The most Haddaway et al. Environ Evid (2018) 7:14 Page 23 of 43 Fig. 16 Strip management in studies within the systematic map database Farming system frequently used term was shelterbelt (n = 19), followed Approximately half of the reviews referred to arable by field margin (n = 15), riparian buffer (n = 14), wind- farming systems (n = 63), with livestock farming being break (n = 14), and hedgerow (n = 13). the second most commonly studied system (n = 22); 55 reviews did not specify the system considered (Fig.  22). Publications per year Horticulture (n = 1), viticulture (n = 1), orchard fruit sys- The number of reviews has increased roughly linearly tems (n = 3) and grasslands (n = 3) were also represented. since the 1980s (Fig.  21), with around a third of these reviews published in the last 10  years (n = 43). The use Studied vegetated strips of individual terms varies over time (Table  9), with sev- Most reviews did not specify the vegetation type within eral terms clearly more historically used than others (i.e. the described strips (n = 74), but trees were most com- hedgerow, shelterbelt and windbreak) perhaps with some monly described (n = 38) (Fig.  23). The majority of of these also becoming less commonly used (i.e. shelter- reviews did not report management of strips (n = 105), belt and windbreak). with sowing and harvesting reported in 15 and 8 reviews, respectively (Fig.  24). The vegetated strips described in reviews were mostly riparian (n = 53) or at the field edge Review focus and type (n = 45), with a smaller number of in-field strips (n = 18) Of the 130 relevant reviews that we identified, the major - and 50 strips with no specified location. The interven - ity had a primary focus on vegetated strips (n = 84), tions most commonly described were the presence of whilst 46 reviews mentioned vegetated strips as a sec- vegetated strips (n = 114), with many studies examining ondary topic. Most reviews were not specific to a geo - the change in an outcome across the strip from within the graphical region (n = 99), with only 30 reviews focusing field to outside the strip (n = 82) (Fig.  25). Strip dimen- on specific locations or regions: the most frequently ref - sion (i.e. width) and vegetation type were also moderately erenced were the USA (n = 9) and UK (n = 4) (Table 10). common (n = 28 and 23, respectively). The vast majority of reviews were narrative (n = 107), with a small number of theses (n = 7), quantitative reviews (i.e. meta-analyses or similar) (n = 11), and Measured outcomes reviews that were to some extent systematic (i.e. a doc- Figure 26 displays the outcomes that were reported to be umented search and/or screening phase) (n = 7). One affected by vegetated strips. The most commonly meas - review was a quantitative systematic review and one was ured outcomes were nutrients (N), terrestrial biodiver- a quantitative narrative review. sity and nutrients (P) (n = 53, 52 and 52, respectively). Of Haddaway et al. Environ Evid (2018) 7:14 Page 24 of 43 Fig. 17 Measured outcomes in studies within the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 25 of 43 Table 5 Co-occurrence matrix, showing the number of studies in which outcomes were measured together Darker cells indicate a greater proportion of each row and column Comparing primary literature findings to review findings these, 19 reviews considered terrestrial biodiversity and Terminology both nutrients (N) and (P). Nutrients (N) and (P) were Across primary studies and reviews, the most common reported together in 44 reviews. Least commonly meas- terms were similar; the four terms ‘field margin’, ‘hedge - ured were impacts on soil physical characteristics (n = 2) row’, ‘shelterbelt’, and ‘riparian buffer’ were all in the five and recreation (n = 2), with social impacts, pathogens, most frequently cited terms for both databases. non-crop yield, physical habitat, water chemistry, light, greenhouse gasses, game species and genetically modi- Volume of evidence fied pollen being measured in fewer than 10 reviews each. The publication rate of primary studies and review arti - The most common ecosystem service described in cles is similar (Fig. 27), although there is a relative reduc- reviews was pollution control (n = 70), followed by tion in the number of reviews over the past 10  years, biodiversity (n = 51) and erosion protection (n = 47) whilst the number of primary research articles continues (Table  11). Cultural ecosystem services were poorly rep- to increase linearly. resented (n = 14 in total). Haddaway et al. Environ Evid (2018) 7:14 Page 26 of 43 Fig. 18 Ecosystem services reported within studies in the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 27 of 43 Fig. 19 Measured ecosystem services over time in studies within the systematic map database Haddaway et al. Environ Evid (2018) 7:14 Page 28 of 43 Fig. 20 Ecosystem services reported for different strip locations in studies within the systematic map database Locations Strip type The most frequently investigated countries in primary Reviews did not often mention vegetation type, probably research were the USA and UK, and this pattern was because they included relevant studies with any vegeta- reflected in the subset of reviews that focused on a spe - tion type, whilst grasses were most commonly reported cific location. in primary studies. Strip management was infrequently described in both reviews and primary studies. Around Farming system half of vegetated strips in primary studies were field edge Approximately half of the reviews focused on arable and a quarter were riparian, whilst riparian and field farming, whilst this system was investigated in almost edge strips were roughly equally the focus of around a 70% of primary studies. half of all described strips in reviews. Strip presence and Haddaway et al. Environ Evid (2018) 7:14 Page 29 of 43 Table 6 Heat map showing the number of studies across all ecosystem services in each studied country County Grandtotal Argenna 2 010010010000000400 9 Australia 0100004630670000 11 03 41 Austria 000000010011000020 0 5 Belgium 0020002310130000 13 01 26 Brazil 0200000310030000102 12 Canada 3110138 20 60 1 18 2110 30 17 104 Chile 0000001100010000000 3 China 100001535013000020 4 25 Colombia 0000000000000000100 1 CzechRepublic 0000031010000000102 8 Denmark 010000153023000030 0 18 Equador 100000010001000000 1 4 Estonia 0010011500050000400 17 Finland 004001 16 24 41 1 21 3030 20 25 105 France 2200028 11 23 8121020 42 16 102 Germany 210000685 01050000 28 12 68 Hungary 000000101100000050 0 8 Ireland 0000000000100000 11 00 12 Italy 1510005 15 20 2120000 20 07 70 Japan 000000000010000010 0 2 Kenya0 00000121002000000 1 7 NewZealand 1210035710560000 13 05 49 Norway 000000022011000040 0 10 Poland 1100023300270100 24 25 51 Romania 010000111001000000 1 6 Russia 000000010004000020 4 11 Serbia 000000000000000010 0 1 Slovakia 000000110001000010 1 5 SouthAfrica0 00000010000000000 0 1 South Korea 000000000000000010 0 1 Spain 111001431004000090 0 25 SriLanka 1010000000000000000 2 Sweden 000001000010000094 0 15 Switzerland 200000010 1 19 0001 0 44 10 69 Taiwan 000010010001000000 0 3 TheNetherlands 1020005610670000 17 11 47 Turkey 000000000000000010 0 1 UK 32201 3 16 25 61 31 24 1610 191 11 4 328 USA 22 26 80 1 25 97 149 68 8 29 141 1230 135 5 79 799 Notstated 000000222020000040 1 13 Mulple 001001120023000071 2 20 GrandTotal 44 46 26 04 48 195313 11815133 2978 10 11 0662 30 1442104 Knowledge gaps (cells within with < 3 studies where (i) country (row) totals are > 50, AND (ii) where ecosystem service (column) totals are > 20) are indicated with a red border. Synthesis gaps/knowledge clusters (cells with > 14 studies) are indicated with pink highlighting and red text comparisons between strips and field environments were Measured outcomes the most common types of comparison in both primary Primary studies and reviews generally prioritised similar studies and reviews, whilst vegetation type was the focus sets of outcomes (i.e. terrestrial biodiversity, nitrogen and of around a quarter of primary studies, but only 17% of phosphorus nutrients, soil and water loss or retention). reviews. Some 22% of reviews focused on the impact of However, several outcomes, including wind, pesticides, vegetated strip width, whilst only 14% of primary studies and crop yield, were the focus of a substantial number of investigated this factor. reviews despite being relatively poorly represented in the primary literature. Overall there were 5.4 primary studies Food Freshwater Fiberand fuel Biochemicalproducts Genec materials Climate regulaon Hydrological regimes Polluon control Erosionprotecon Naturalhazards Pest regulaon Nutrient cycling Spiritualand inspiraonal Recreaonal Aesthec Educaonal Biodiversity Pollinaon Soil formaon Haddaway et al. Environ Evid (2018) 7:14 Page 30 of 43 Table 7 The number of studies for all ecosystem services across different types of vegetated strip Vegetated sp locaon Within field 93 54 11 21 24 61617224 11 5 Field edge 55 27 5158 85 83 1102 35 86 61 20 3111729 Riparian 72 1115 22 2169 54 47 179871915196 Notdescribed 15 2261 11 41 64 28 45 36 62 94 per review article identified and catalogued within this Most studies last only a few years and vegetated strips project. Figure 28 displays the primary study: review arti- or strip management were in place for a similar length of cle ratios for all reported outcomes. Studies with ratios time before being studied. Studies most commonly com- greater than the average indicate that further synthesis pared vegetated strips to conditions within a field, fol - may be a priority. Outcomes with lower ratios are not lowed by conditions in fields without strips or different necessarily well-synthesised, however, since the total strip vegetation. Field edge strips were most frequently number of primary studies measuring these outcomes studied, followed by riparian strips. Strip vegetation was may be low. most commonly grasses, then trees. The most common farming system studied was arable fields. The manage - Ecosystem services ment of strips was generally not described, but beyond The mean number of primary studies per review across planting or sowing to establish the strip, cutting was all ecosystem services was 6.6, with higher values the most common management practice that was men- (lower numbers of reviews relative to primary stud- tioned. Terrestrial biodiversity was the most frequently ies) for several regulating services (natural hazards, measured outcome, followed by nitrogen, water loss pest regulation, and nutrient cycling) and supporting and phosphorus, but a suite of other outcomes was also services (biodiversity and soil formation) (Table  11). reported in the evidence base. Across all outcomes, the Despite having more than the average number of most commonly identified ecosystem services related to primary studies per ecosystem service (x  ̄=  17.6), biodiversity, pollution control and nutrient cycling. hydrological regimes, pollution control, and erosion protection were relatively under-represented in terms Notable patterns across the evidence base of syntheses, representing a possible synthesis gap. It is notable that more than half of the studies in the pri- mary studies systematic map database originate from Discussion either the USA or the UK (38 and 16% of total studies, General observations regarding the evidence base respectively; Fig. 8). For comparison, Canada, France and We have found a substantial body of evidence investigat- Finland each contribute c. 5% of the total number of stud- ing and reviewing the various impacts of vegetated strips. ies, and no other countries contribute more than 3% of It seems that the publication rate of primary research the total. Research from the USA is itself strongly skewed, continues to increase, beyond that of synthetic research with 20% of studies undertaken in Iowa and a further that reviews this work. It is unsurprising that research on 30% in North Carolina, Missouri and Mississippi com- the topic continues to increase in popularity. Countries bined. The reasons and implications for these geographi - such as the UK, Denmark, The Netherlands, the USA, cal biases in the dataset are worthy of consideration in Sweden, and New Zealand, amongst others, are moving synthesising the data to inform policy. There is also geo - towards targeted regulation of nutrient losses from agri- graphical bias in the study of particular ecosystem ser- cultural fields. As a result, there is a strong incentive to vices (Table  6). Biodiversity is the most studied service understand how vegetated strips can be used to remove (31% of total studies) and there are marked variations N and P through both simple and more advanced tech- across the evidence base, with biodiversity investigated nologies, including saturated buffers, intelligent buffer in 17% of US studies, but in 58 and 64% of studies in the zones, etc. [31, 76]. UK and Switzerland, respectively. These differences most Soil formaon Pollinaon Biodiversity Educaonal Aesthec Recreaonal Spiritualand inspiraonal Nutrientcycling Pest regulaon Naturalhazards Erosion protecon Polluon control Hydrologicalregimes Climateregulaon Genec materials Biochemicalproducts Fibre andfuel Fresh water Food Haddaway et al. Environ Evid (2018) 7:14 Page 31 of 43 Table 8 Frequency of  main terms used to  describe protection is a particular focus for studies in China (20% vegetated strips in the reviews identified in our systematic of total studies compared to 6% for studies from all coun- map tries combined). Pest regulation is a particular focus in Switzerland (28% of total studies), and with a wide range Term Frequency of authors, this appears to be a specific concern in this Shelterbelt 19 country rather than disproportionate impact from a sin- Field margin 15 gle research group. Windbreak 14 Figure  16 shows that studies investigating certain Hedgerow 13 ecosystem services are often strongly associated with Riparian buffer 12 a specific type of vegetated strip. For example, studies Buffer zone 9 into effects on biodiversity, pest regulation and polli - Buffer strip 9 nation focus predominantly on strips at the field edge Vegetative filter strip 6 rather than either in-field or riparian strips. In contrast, Filter strip 4 studies into pollution control and nutrient cycling tend Riparian buffer strip 4 to consider riparian strips. There are very few studies Vegetated buffer strip 4 that consider more than one strip location (field mar - Pollen barrier 3 gin vs. in-field vs. riparian), so there is a strong possi - Shelter belt 3 bility that this association between ecosystem service Vegetative buffer 3 studied and strip type is influenced by existing practice Buffer 2 and concepts rather than clear evidence that a particu- Conservation buffer 2 lar strip location is optimal for a specific ecosystem Field boundary 2 service. In-field strips have been shown to be highly Grass buffer strip 2 effective in control of erosion and associated transport Riparian area 2 of pollution through inhibiting the formation of con- Riparian buffer zone 2 centrated flow pathways [80]; nevertheless, strips that Riparian zone 2 are studied for this purpose are overwhelmingly either Agricultural buffer 1 riparian or at the field edge (Fig.  16). Overall, there are Agroforestry buffer 1 very few studies that consider in-field vegetated strips, Flower strip 1 presumably because this is the most difficult strip type Grass buffer 1 for farmers to implement. Grassed buffer strip 1 Grassed waterway 1 Multifunctionality of vegetated strips Grassy field margin 1 The review has identified 30 different measured out - Herbaceous wind barrier 1 comes across 19 ecosystem services. Although vegetated Non‑ crop habitat 1 strips may be implemented for a specific function, their Non‑ crop strip 1 design and management may influence their ability to Refuge strip 1 support other ecosystem services [81]. Riparian forest buffer 1 In most cases, where authors studied multiple out- Riparian vegetative buffer strip 1 comes (Table  5), they were closely related; the most Stream buffer 1 common of these were the nutrients N and P (where 99 Vegetated buffer 1 studies reported on both), followed by N and water loss/ Vegetation border 1 retention (85 studies). Many pest control and pollina- Vegetation filter 1 tion outcomes (61 and 31 respectively) were reported Wildflower strip 1 together with biodiversity, but this is largely because Woody border 1 these outcomes, such as species abundance, are also a Grand total 151 feature of wider biodiversity. Studies that looked at more contrasting ecosystem services were less common, but biodiversity and nutrients were notably studied together likely relate to differences in national frameworks for the in a number of studies; nitrogen (24 studies) and phos- protection of biodiversity [77–79]. Studies of nutrient phorus (20 studies). Similarly, biodiversity was co-meas- cycling, hydrological regime, and pollution control were ured with a variety of soil outcomes. These studies often relatively evenly spread geographically, whereas erosion considered the soil or plant communities associated with Haddaway et al. Environ Evid (2018) 7:14 Page 32 of 43 Fig. 21 The number of reviews published by 5‑ year period soil or nutrient outcomes, but a few did consider wider representing a very sensitive approach. We also under- biodiversity, such as Stockan et al. [82], who studied car- took extensive bibliographic searching, screening the abid species together with outcomes related to soil and reference lists of almost 100 relevant literature reviews. water nutrients. This supplementary searching was vital to identify arti - The intensification and expansion of agriculture means cles that might have used other synonyms for buffer that both quantity and quality of off-crop habitats, such strips that were identified in the evidence base. However, as vegetated strips, are likely to be increasingly important there is a risk that some studies using less common syno- in supporting a wide variety of ecosystem services [83], nyms may have been missed from the database and bibli- and further primary studies into the value and enhance- ography searches. Future updates or amendments to this ment of multifunctional services offered by vegetative topic should integrate the synonyms that we identified strips would be useful. into new searches to minimise this risk. Additionally, our organisational website searches for grey literature were focused more on European contexts, Limitations of the systematic map given the experience of the review team. We did attempt We searched for evidence using a suite of synonyms to include non-European organisations, but future work for vegetated strips that included 360 search terms, of could direct effort particularly towards organisations in which only 84 were represented in the evidence base, Haddaway et al. Environ Evid (2018) 7:14 Page 33 of 43 Table 9 Trends in the use of vegetated strip terminology over time: (a) only years with publications reported, (b) 5-year periods (a) Year 1944 11 1954 1 1 1983 1 1 1984 1 1 2 1986 1 1 2 1988 1 5 1 8 15 1990 1 1 1991 1 1 1992 1 1 1993 1 1 1 3 1994 3 1 1 5 1995 1 1 2 1996 3 1 1 5 1997 1 1 1 1 4 1998 1 12 1999 1 1 1 1 1 1 1 1 8 2000 1 1 1 1 1 1 1 1 1 9 2001 1 1 1 3 2002 1 2 1 4 2003 1 1 1 3 2004 2 1 1 1 1 1 1 8 2005 1 1 3 1 1 1 1 1 1 11 2006 1 1 1 1 1 5 2007 1 1 2 2 2 1 9 2008 12 1 1 5 2009 1 1 1 2 1 1 7 2010 11 11 11 6 2011 1 1 1 1 1 5 2012 1 1 1 1 2 1 7 2013 1 1 2 1 2 7 2014 1 1 1 1 1 5 2015 1 1 1 3 Grand Total2 29 92 215413 11 1131 11 31 2124 21 12 319114 11 36 1141 151 (b) Period 1940-1944 11 1945-1949 1 1 1950-1954 0 1955-1959 0 1960-1964 0 1965-1969 0 1970-1974 0 1975-1979 0 1980-1984 1 2 3 1985-1989 1 6 2 8 17 1990-1994 3 1 2 1 1 1 1 1 11 1995-1999 1 4 2 2 1 1 1 1 1 2 1 3 1 21 2000-2004 1 1 2 2 4 1 2 1 1 2 1 1 2 1 1 1 1 1 1 27 2005-2009 21 22 61 11 12 15 11 31 12 21 37 2010-2014 12 21 21 41 24 11 13 21 130 2015-2019 1 1 1 3 Grand Total2 29 92 215413 11 1131 11 31 2124 21 12 319114 11 36 1141 151 Agricultural buffer Agricultural buffer Buffer Buffer Buffer strip Bufferstrip Buffer zone Bufferzone Conservaonbuffer Conserva on buffer Field boundary Fieldboundary Fieldmargin Fieldmargin Filter strip Filter strip Flower strip Flower strip Grass buffer strip Grass buffer strip Grassed buffer strip Grassed buffer strip Grassedwaterway Grassed waterway Grassy field margin Grassy field margin Hedgerow Hedgerow Herbaceous windbarrier Herbaceouswindbarrier Non-crop habitat Non-crop habitat Non-crop strip Non-crop strip Pollen barrier Pollen barrier Refuge strip Refugestrip Riparian area Riparian area Riparian buffer Riparian buffer Riparian bufferstrip Riparian buffer strip Riparian bufferzone Riparian buffer zone Riparian forest buffer Riparian forest buffer Riparian vegetave buffer strip Riparian vegeta vebuffer strip Riparian zone Riparian zone Shelterbelt Shelterbelt Shelterbelt Shelterbelt Stream buffer Stream buffer Vegetated buffer Vegetated buffer Vegetated buffer strip Vegetated buffer strip Vegetaon border Vegetaonborder Vegetaon filter Vegetaonfilter Vegetave buffer Vegetave buffer Vegetavefilter strip Vegetave filter strip Wildflower strip Wildflower strip Windbreak Windbreak Woodyborder Woodyborder GrandTotal Grand Total Haddaway et al. Environ Evid (2018) 7:14 Page 34 of 43 Table 10 Number of reviews focusing on specific regions several institutions, including Stockholm University and SLU, which are together relatively comprehensive, but Specific region Frequency evidently not completely so. Future work could attempt USA 6 to source these difficult to access articles. Piedmont‑ Coastal Plain, USA 1 Europe and USA 1 Limitations of the evidence base Virginia, USA 1 Missing meta-data was a consistent issue with a small UK 4 number of studies, even with basic information, such New Zealand 3 as the study country (n = 8). Occasionally high levels of Australia 3 missing meta-data at times reflect the study topics: for North America 2 example, 592 studies did not report the intervention Northern Europe 2 duration, but this is perhaps to be expected with field Poland 2 margins and hedgerows that may have been in place for Central and Northern Europe 1 extensive periods, and this information may be unavail- Europe and Mediterranean 1 able. Other meta-data is surprising in its absence: for Brittany, France 1 example, 99 studies did not report the type of strip veg- European Union 1 etation and 168 studies did not report the type of farming Sweden 1 system investigated. We echo previous calls for improved No region specified 99 reporting to facilitate synthesis and repeatability [e.g. 84, 85]. The publication rate of primary research studies on this the USA, where a great deal of evidence was identified by topic can perhaps be considered to deviate from common our work. patterns in other systematic reviews [e.g. 86] in that there Finally, we were unable to source 276 papers due to is an abrupt change in rate from the late 1980s and a a lack of subscription. We used subscriptions across steady, linear increase in papers thereafter. Other reviews Fig. 22 Farming systems described within relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 35 of 43 Fig. 23 Vegetated strip vegetation type within relevant reviews Fig. 24 Strip management described within relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 36 of 43 Fig. 25 Strip interventions described within relevant reviews suggest a more exponential growth rate. This difference features. This evidence base is vital for making the possibly reflects the fact that this topic is broader than best use of available evidence in national (and other) many other systematic reviews (and some maps) to date, policy-making. or that there was some shift in research funding during The expertise of the author team is European focused, the late 80 s that has remained in constant growth since. and as such we are unable to discuss in detail North American policy, and focus instead on EU policy, with Conclusions which we are most familiar. The experience from Den - Implications for policy, practice and research mark with the Buffer Zone Act adopted in 2011 that To date, the evidence bases used in national level pol- implemented 50,000 ha of 10 m wide mandatory buffer icy settings have often been drawn from national level strips along all watercourses and lakes is an illustrative research evidence, which can be restricted in nature, example of the need for reliably synthesised evidence showing only one or a limited number of outcomes or [87]. The Buffer Zone Act was revised after 3  years, ecosystem services and including a narrow set of con- halving the area of buffer strips following boycott by texts. These evidence bases may not cover the multi- farmers and several lawsuits. Finally, the Buffer Zone functionality and potential goal conflicts of vegetated Act was withdrawn in 2016 as part of the main goals of strips that can be identified through a regional or global the new Danish government. An evidence synthesis on assessment of evidence, such as the one presented here. the topic would have greatly assisted in this instance, The systematic mapping approach outlined herein since the production of evidence on ecosystem services along with associated systematic review methods (col- from across an international evidence base would likely lectively referred to as evidence synthesis methods) have been influential in the debate. are a reliable, transparent and comprehensive means of identifying and characterising knowledge gaps and Knowledge gaps and clusters clusters relating to a particular topic. In this case we Knowledge gaps have utilized international evidence from all relevant The following topics represent knowledge gaps where climate zones to assemble an extensive, comprehensive no studies exist or a relatively small number of studies evidence base that investigates a plethora of contextual have been conducted. The review team feel that these Haddaway et al. Environ Evid (2018) 7:14 Page 37 of 43 Fig. 26 Measured outcomes affected by vegetated strips in relevant reviews Haddaway et al. Environ Evid (2018) 7:14 Page 38 of 43 Table 11 Ecosystem services represented across  relevant 9. What are the characteristics that improve multiple reviews along with the ratio of primary studies to reviews outcomes in multi-use vegetated strips (i.e. those designed to have many different social-ecological Service type Ecosystem service Number Primary of reviews studies benefits)? per review 10. To what extent does the implementation of multi- ple interventions targeting different outcomes lead Provisioning services Food 25 1.76 to synergies or conflicts? Fresh water 15 3.07 Fiber and fuel 24 1.08 Knowledge clusters Biochemical products 1 0.00 The following topics represent knowledge clusters Genetic materials 3 1.33 that the review team believes are important topics for Regulating services Climate regulation 15 3.20 researchers and decision-makers for further synthesis Hydrological regimes 30 6.50 (approximately ordered by volume of evidence). We have Pollution control 70 4.47 used an arbitrary cut-off of a minimum of 40 studies to Erosion protection 47 2.51 be mentioned below, acknowledging that heterogeneity Natural hazards 2 7.50 amongst studies is likely to preclude meaningful synthe- Pest regulation 15 8.87 sis for small numbers of studies. Since we have not con- Nutrient cycling 10 29.70 ducted critical appraisal, we are unable to prioritise the Cultural services Spiritual and inspira‑ 0 – suitability of these clusters for synthesis. tional Recreational 6 1.67 1. How do vegetated strips affect terrestrial biodiver - Aesthetic 8 1.38 sity (n = 596)? Educational 0 2. What are the impacts of different vegetated strips Supporting services Biodiversity 51 12.98 on nutrient (nitrogen and phosphorus) retention Pollination 6 5.17 (n = 242)? OR How effective are vegetated strips at Soil formation 7 20.57 reducing nitrogen losses to water and air (n = 212)? 3. What are the impacts of vegetated strips on hydro- topics are important social or ecological issues that logical regimes (n = 195)? warrant further investment in terms of research fund- 4. What are the impacts of buffer size or width ing and primary research efforts. (n = 154) on biodiversity (n = 88), nitrogen nutri- ents (n = 25), phosphorus nutrients (n = 27), soil 1. What role can vegetated strips play in climate regu- loss/retention (n = 25), soil chemistry (n = 14), and lation? water loss/retention (n = 35)? 2. What are the impacts of vegetated strips on aquatic 5. What are the impacts of vegetated strips on sedi- and semi-aquatic biodiversity? ment-associated chemicals, including priority sub- 3. What are the impacts of harvesting strip vegetation stances under the EU Water Framework Directive on all outcomes? (n = 123)? 4. What are the possible cultural ecosystem services 6. What are the impacts of vegetated strips on erosion (spiritual, recreational, aesthetic, educational) of protection (n = 118)? vegetated strips? 7. What are the impacts of vegetated strips on pests 5. What are the long-term impacts (> 2 years) of veg- in arable fields (n = 104)? etated strips, and how do impacts vary over time or 8. What role can vegetated strips play in terms of car- measurement season. bon sequestration (n = 87)? 6. What is the relationship between the presence of 9. How do soil physical/chemical characteristics pests or predators of pests and the impacts of veg- of vegetated strips affect terrestrial biodiversity? etated strips on crop yield and weed seed bank in Specifically, the what is the link between: terres - soil of nearby agricultural fields? trial biodiversity and nutrients (n = 29); terrestrial 7. What is the role of vegetated strips in terms of fibre biodiversity and physical characteristics of the soil and fuel production in a circular bioeconomy? (n = 10)? 8. What are the impacts of vegetated strips on all 10. How do different types of strip affect biodi - outcomes from the following un- and under-rep- versity (n = 42)?: for field edge versus riparian resented countries and regions, including: eastern strips (n = 23); for in-field versus field edge strips Europe; Russia; Asia; South America (specifically, (n = 19)? Argentina, Brazil, Chile and Uruguay)? Haddaway et al. Environ Evid (2018) 7:14 Page 39 of 43 Fig. 27 The publication rate for primary studies (green) and review articles (blue) in the evidence base In conclusion, this systematic map highlights a knowledge clusters. Further research effort, both in large and heterogeneous evidence base relating to the terms of primary studies and syntheses, is necessary impacts of vegetated strips in boreo-temperate agri- to understand these diverse impacts of the various culture, containing a suite of knowledge gaps and types of vegetated strips, particular in understanding: Haddaway et al. Environ Evid (2018) 7:14 Page 40 of 43 Fig. 28 The number of primary studies per review article reporting each outcome, displaying the mean study:review ratio of 5.4 as a dashed grey line. Outcomes that are struck through represent those for which no reviews were identified Haddaway et al. Environ Evid (2018) 7:14 Page 41 of 43 Funding (1) the role of landscape context in the effectiveness of This review report is financed by the Mistra Council for Evidence ‑Based Envi‑ vegetated strips; (2) potentially conflicting outcomes ronmental Management (EviEM). between different management options; and (3) con - flicts between high production targets and environ - Publisher’s Note mental objectives. Springer Nature remains neutral with regard to jurisdictional claims in pub‑ lished maps and institutional affiliations. Additional files Received: 12 February 2018 Accepted: 24 April 2018 Additional file 1. Search string development. Additional file 2. Web ‑based searching record. Additional file 3. Unobtainable articles. References Additional file 4. List of articles excluded at full text along with reasons. 1. Stoate C, Boatman N, Borralho R, Carvalho CR, De Snoo G, Eden P. Ecological impacts of arable intensification in Europe. J Environ Manage. Additional file 5. Coding and meta‑ data extraction schema. 2001;63(4):337–65. Additional file 6. Primary research studies systematic map database. 2. Stoate C, Báldi A, Beja P, Boatman N, Herzon I, Van Doorn A, De Snoo G, Rakosy L, Ramwell C. Ecological impacts of early 21st century agricultural Additional file 7. Review articles database. change in Europe—a review. J Environ Manage. 2009;91(1):22–46. Additional file 8. Articles excluded at full text due to language. 3. Lal R. Soils and sustainable agriculture. A review. Agron Sustain Dev. 2008;28(1):57–64. Additional file 9. Term use in primary studies by study location. 4. Sutton MA, Howard CM, Erisman JW, Billen G, Bleeker A, Grennfelt P, van Grinsven H, Grizzetti B. The European nitrogen assessment: sources, effects and policy perspectives. Cambridge: Cambridge University Press; Abbreviation 2011. p. 664. N O: nitrous oxide. 5. Gill RJ, Ramos‑Rodriguez O, Raine NE. 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Environmental EvidenceSpringer Journals

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