The state and use of municipal tree inventories in Swedish municipalities – results from a national survey

The state and use of municipal tree inventories in Swedish municipalities – results from a... Urban trees are an essential component of urban ecosystems, and management of this resource constitutes an essential element of urban open space management. However, municipal tree inventories in Sweden and elsewhere have received limited attention. It is unknown how common municipal tree inventories are in Sweden, factors governing whether a municipality has an inventory and what the inventories are used for. This study therefore sought to: Create an overview of the state of Swedish municipal tree inventories and determine how municipality size, green space budget and management organisation affect the presence and scope of municipal tree inventories. The research questions examined were: What is the current state of Swedish municipal tree inventories? and what affects the status of these municipal tree inventories? A survey with questions related to strategic and operational perspectives of municipal tree inventories, e.g. how they are conducted and used, together with questions relating to budget and potential use of consultants, was sent to all 290 Swedish municipalities. The response rate was 55.5%. The main findings were that municipality size affects whether a municipality has an urban tree inventory and that the municipal organi- sation form affects how inventories are used. The existence of an inventory also increased the probability of the municipality having a tree management plan. Based on these results we recommend further research related to strategic management per- spectives of tree inventories. . . . . . . Keywords Survey Municipality Street trees Park trees Management Ecosystem services Ecosystem disservices Introduction perceived as negative for human well-being^ (Lyytimäki 2014, p. 311), and how management can affect the extent of ecosystem Research has clearly shown the importance of urban trees for disservices caused by urban trees (Östberg et al. 2012; sustainable urban development through their capacity for de- Delshammar et al. 2015; Dobbs et al. 2017; Lyytimäki 2017). livering numerous important ecosystem services, which in- Management of urban trees is key to sustaining and increas- clude: Provisioning services (e.g. fuel and food), regulating ing important ecosystem services (Dobbs et al. 2017)and re- services (e.g. stormwater management, urban heat island mit- ducing the amount of ecosystem disservices (Lyytimäki 2017), igation, air pollution regulation), cultural services (e.g. recre- and municipal tree inventories are the foundation on which ation, physical and mental health benefits) and supporting management of urban trees is based (Kielbaso 2008;Miller services (e.g. wildlife habitats) (Grahn and Stigsdotter 2003; et al. 2015; Morgenroth et al. 2016). In recent decades there Tyrväinen et al. 2005; Gilletal. 2007; Jones 2008; has therefore been increasing interest in municipal tree inven- Morgenroth et al. 2016; Dobbs et al. 2017). tories, resulting from e.g. growing problems with pest and Another concept gaining attention is ecosystem disservices, disease attack on the urban tree stock (Raupp et al. 2006)and defined as Bfunctions or properties of ecosystems that are growing awareness among decision-makers of the multiple ecosystem services trees provide in the cityscape (Roy et al. 2011; Hubacek and Kronenberg 2013; Nielsen et al. 2014). * Johan Östberg Municipalities, especially in North America and Europe, have johan.ostberg@slu.se therefore increasingly started to perform municipal tree inven- tories (e.g. Nowak et al. 2001; Keller and Konijnendijk 2012; Department of Landscape Architecture, Planning and Management, Sjöman et al. 2012). Municipal tree inventories in North Swedish University of Agricultural Sciences, P.O. Box 66, SE-230 America have largely involved the use of i-Tree to perform 53 Alnarp, Sweden 468 Urban Ecosyst (2018) 21:467–477 economic valuations of urban trees (Kielbaso 2008; i-Tree & Budget/Financing included questions relating to the 2017; Morgenroth and Östberg 2017; Rogers et al. 2017), municipality’s economic situation and specifically whereas Northern Europe has focused more on management which economic resources are available for manage- issues, e.g. tree health and management related to monitoring ment of green spaces and trees. Questions relating to the dynamics of the tree stands (Keller and Konijnendijk 2012; historical developments and how municipal man- Morgenroth and Östberg 2017). agers viewed future resource allocations were also Municipal tree inventories in Sweden have only recently included. received attention among researchers. One of the first studies & Maintenance of green spaces and trees included questions to compare municipal tree inventories presented data for 10 relating to the daily maintenance, e.g. personnel, type of Nordic cities (Sjöman et al. 2012). Since then, a related prac- contractors being used (public/private), total amount of tical national standard focusing on what to include and how to green spaces/trees, and how these have developed over perform an urban tree inventory in Swedish municipalities has time and how they are expected to be developed in the been published (Östberg et al. 2013). However, there is no future. overview of the current state of municipal tree inventories & Policy, plans and strategies included questions about the and thus there is a lack of understanding of how municipality strategic documents used in order to steer and develop size, green space budget and management organisation affect green spaces/trees. the presence and state of municipal tree inventories. The rela- & Quality included questions relating to municipal man- tionship between tree inventory and green space budget may agers’ perceptions on the quality of their green spaces be a prerequisite for good tree management, while and urban trees. organisational aspects might also be important since there is & Tree inventories included questions specifically re- an obvious need for an inventory if tree maintenance is lating to urban trees, e.g. about management sys- outsourced (Lindholst 2009; Randrup and Persson 2009). tems such as tree inventories and use of digital data Hauer and Peterson (2016) suggest that the execution of mu- systems. nicipal tree inventories can be connected to factors such as size of the municipality, green space budget, or perceived need This paper primarily deals with the questions specifically for the municipality to maintain a high number of urban trees relating to trees and tree inventories. The survey was first and related records of tree removal and planting. tested in a pilot study involving 15 municipalities representing Therefore, the objective of the present study was to gain different sizes and locations around Sweden. Based on the further insights into Swedish practice concerning tree inven- comments collected from the pilot study, the survey questions tories, driven by the following research questions: What is were revised. the current state of Swedish municipal tree inventories? and All 290 Swedish municipal websites were visited in What affects the status of the municipal tree inventories?In December 2015 in order to obtain correct contact names order to analyse these research questions, five sub-questions and addresses and personal contact was made with some were formulated: municipal arborists known to the authors. Municipal personnel with the greatest responsibility for green a. What is the extent of municipal tree inventories in spaces and trees were selected as contact persons. If Sweden? more than one person was identified, all were included b. What areas are included in the inventories? as recipients of the survey. The actual distribution of the c. Who conducted the inventories? survey and issue of reminders were performed via e- d. What kind of data has been collected? mail, with reminders being sent to all non-respondents e. What are the inventories used for? at 2, 3, 4 and 8 weeks after the initial distribution. Written responses received via ordinary mail (n =17) were entered manually into Netigate (Netigate AB, Sweden) and then all responses was downloaded to Materials and methods Microsoft Excel 2010 (Microsoft Corporation, USA). All responses were evaluated manually for obvious er- The survey rors, and in this process eight duplicate answers were deleted. In cases where a municipality had submitted Based on recent surveys in the United States of America, two responses, the most recent and most comprehensive Canada and the United Kingdom (Neal et al. 2014; Hauer was kept. Responses that were less than 10% complete and Peterson 2016; Bardekjian et al. 2016), a survey was were also deleted. In total, 161 surveys (55.5% response developed for the Swedish context. The survey was divided rate for all Swedish municipalities) were included in the into five parts, each consisting of 5–11 questions: dataset and formed the basis for further analysis. Urban Ecosyst (2018) 21:467–477 469 Statistical analysis same generalized linear modelling approach as above was used. The response was derived from the subset of the data All statistical tests were performed at a significance level of having an inventory and then split into having the inventory 0.05. To test the representativeness of the survey concerning digitalised or not. The same approach was used to analyse the spatial distribution and municipal types, a Chi-square test was reasons for updating the inventory or not. performed on the observed distribution of responses between To test the relationship between population size and num- municipal groups as defined by the Swedish Association of ber of municipal trees, Spearman correlation and associated Local Authorities and Regions (SKL 2011)compared withthe test was calculated between population size and number actual distribution for Sweden. This test was non-significant of municipal trees as well as municipal trees per capita (χ = 8.086, df = 9, n = 161, p = 0.525). To test whether the (R Core Team 2016). responding municipalities differed in population size and area To gain an insight into factors that might influence changes from Swedish municipalities in general, one-sample Z-tests in the number of trees in the urban municipal tree population, based on national statistics were performed. Neither of these we calculated the net gain of trees by subtracting the number tests gave a significant result (Z = 0.97; p = 0.331 and Z = of trees removed from the number of reported planted trees. −1.30; p = 0.194, respectively). Accounting for eventual This value was then modelled as the response in a general skewed distribution by using one-sample sign test did not linear model using proc. mixed (SAS 9.4) and population, produce any significant results. As such, the responses to the budget per capita, contractors and presence of a management survey can be seen as a fair representation of Sweden as a plan as explanatory variables. whole. The statistical tests performed for the research questions Analysis of multiple choice questions and the five sub-questions are described below. For the multiple choice questions ‘Who conducted the inven- What is the extent of municipal tree inventories in Sweden? tory?’, ‘What kind of data have been collected?’, ‘What are the inventories used for?’ and ‘What areas are included in the In order to study the factors affecting the presence of an urban inventories?’ we used the approach presented below for each tree inventory, we modelled this in several steps. First, due to individual question, using the binary matrix of variables for the strong evidence in the literature (Miller 1997) that having a the specific question as analytical unit. To give an overview of tree management plan is dependent on having a tree inventory, the relations and eventual grouping between the variables we explored this relationship with 2 × 2 cross tables and concerning each question, we used clustering with additional Fisher’s exact test (R Core Team 2016) and found that it was graphical tools. This was performed by average agglomerative significant (p < 0.0001). Based on this, in a second step we clustering using the unweighted pair group method with arith- only used inventory as response variable and excluded man- metic mean (UPGMA) (Maechler et al. 2014) with binary agement plan due to their collinearity. To explore the reasons distances from the dist function in R (R Core Team 2016). for having a tree inventory, we employed generalised linear We verified that UPGMA had the highest cophenetic correla- modelling in SAS 9.4, using the genmod procedure with a tion coefficient compared with single-linkage agglomerative binomial distribution and logit link function (i.e. binary logis- clustering, complete-average agglomerative clustering and tic regression). The p-scale option was used to avoid problems Ward’s minimum variance clustering. We used Mantel statics of over-dispersion in the models. Having a tree inventory was to decide on number of clusters to display in the dendrogram. modelled as the binomial response. As explanatory variables, We then applied the vegemite and heatmap function in R the following variables were included: population (Koeser package vegan (Oksanen et al. 2013) to produce a graphical et al. 2016), greenspace budget per capita (Randrup and overview of the data matrix in relation to the clustering. To get Persson 2009), percentage of contractors used in tree manage- an approximation of the differences between the different ment (Hauer and Peterson 2016), number of trees planted per response rates for each area, multiple Chi-square tests capita (Bardekjian et al. 2016) and record of trees being re- with Holm’s correction for multiple testing were per- moved or planted (Kuhns et al. 2005). formed (Holm 1979;R Core Team 2016). These approxi- Using the Bayesian information criteria (BIC) and Type 3 mations were added to the graphs using the convention where- significance test of the variables, the most theoretically sound by variables sharing the same letter do not differ significantly and parsimonious model was selected based on adding the from each other. variables to the models individually in the order above that To explore the relationship with population size, budget per reflected our hypothesis on their importance, with significance capita and percentage of contractors, we used these as explan- level for inclusion in the model set to p <0.05. atory variables in a multivariate regression tree (Therneau To test the hypothesis that ‘number of municipalities with a et al. 2013; Ouellette and Legendre 2013) of the response digitalised tree inventory increases with population size’,the matrix with a chord transformation (to linearise the data). 470 Urban Ecosyst (2018) 21:467–477 Discriminate variables for the different branches of the regres- confirmed by statistical analysis, which showed that popula- sion tree and significant coding for them were added. The tion size of the municipality was the only variable significant- results of the regression tree were verified by comparing the ly related to the presence of an inventory (F = 23.51, 1,148 results with a global non-metric multidimensional scaling with p < 0.0001) when comparing the factors: Population, a Gower distance and post-hoc testing of the explanatory var- greenspace budget per capita, percentage of contractors used iables with the Envfit function (Oksanen et al. 2013). in tree management, number of trees planted per capita and record of trees being removed or planted. There was also a significant positive correlation (r = 0.6721256, n =83, Spearman Results and discussion p < 0.0001) between population size and number of municipal trees. The results suggested that, if a municipality has a tree in- The results are structured around the research questions and sub-questions and are addressed in the following order: ventory (54.5% of all), it is also likely to have a tree manage- ment plan (55.2% of those with an inventory). Only 2% of all 1. What is the extent of municipal tree inventories in municipalities had a tree management plan without the pres- Sweden? ence of a tree inventory. This difference was supported by the 2. What areas are included in the inventories? Fisher exact test, which gave a significant result (p <0.0001), 3. Who conducted the inventories? implying that for almost all municipalities a tree inventory 4. What kind of data has been collected? forms the basis for their tree management plan. These results 5. What are the inventories used for? confirm findings in a number of studies and recommendations that stress the need to first conduct an tree inventory and then create a management plan (e.g. Kielbaso 2008;Milleretal. 2015; Morgenroth et al. 2016;Zürcher 2017). What is the extent of municipal tree inventories in Sweden? The reason why population size influences the presence of municipal tree inventories is unknown. Since most national Of the 161 municipalities that responded to the survey, 85 and international surveys have focused on existing inventories (52.8%) had a municipal tree inventory. The number of mu- (e.g. Sjöman et al. 2012; McPherson et al. 2016), have con- nicipalities that had an inventory increased with municipal ducted their own inventories (Britt and Johnston 2008)or population, from 34.4% for cities with populations ranging have been limited to specific regions (Kuhns et al. 2005; from 2500 to 9999 to 92.3% for the largest municipalities Schroeder et al. 2003), it is difficult to compare the Swedish (100,000 to 500,000 inhabitants). A similar trend was seen situation with that internationally. However, the effect of pop- for the number of inventories digitalised, which ranged from ulation size might be due to several different factors. (1) 27.3% to 83.3%. However, a large number of inventories were Municipalities with larger population size will, in most cases, have relatively larger tree populations and therefore it is more either ‘under development’ (54.1%) or ‘outdated’ (27.1%) (Table 1). There were no significant relationships between difficult to get an overview of the whole tree population with- any of the parameters tested and whether the inventory was out a municipal tree inventory. This is supported by the trend updated or not. that larger municipalities had more trees per capita (r = Spearman The probability of the inventory being digitalised increased 0.3323806, n =83, p < 0.0021), and is in line with previous significantly with population size of the municipality (F = findings by Kuhns et al. (2005). Larger municipalities might 1,80 6.68, p = 0.0116). This influence of population was also thereby not only have more trees, but also more trees per capita, Table 1 Number of responding municipalities that had an urban tree inventory and the status of those inventories Population size nHavean Digitalised inventories Updated inventories Inventories that are under Inventories that are of the municipality inventory of all inventories of all inventories development of all outdated of all (n and %) (n and %) (n and %) inventories (n and %) inventories (n and %) 2500 to 9999 32 11 (34.4%) 3 (27.3%) 2 (18.2%) 6 (54.5%) 4 (36.4%) 10,000 to 24,999 61 24 (39.3%) 10 (41.7%) 6 (25.0%) 11 (45.8%) 6 (25.0%) 25,000 to 49,999 33 21 (63.6%) 15 (71.4%) 4 (19.0%) 13 (61.9%) 4 (19.0%) 50,000 to 99,999 22 17 (77.3%) 14 (82.4%) 2 (11.8%) 10 (58.8%) 5 (29.4%) 100,000 to 500,000 13 12 (92.3%) 10 (83.3%) 2 (16.7%) 6 (50.0%) 4 (33.3%) Total 161 85 (52.8%) 52 (61.2%) 16 (18.8%) 46 (54.1%) 23 (27.1%) The municipalities were asked if the inventory was digitalised or not, and if the inventory was updated, in-development or outdated Urban Ecosyst (2018) 21:467–477 471 which creates an even higher need for an urban tree inventory In the multivariate regression tree (MRT), there was a ten- and a management plan. In comparison with North American dency for municipalities with large budgets (≥72.5 SEK/ cities (Hauer and Peterson 2016; Bardekjian et al. 2016), person (7.5 Euros/person)) to inventory woodlands and other Swedish municipalities have fewer municipal tree inventories. properties to a greater extent than other municipalities, where- (2) There could be an organisationalaspectthatdifferentiates as municipalities with lower budgets had a tendency to focus large and small municipalities, where larger municipalities have on street trees (Appendix). Sjöman et al. (2012) found that a higher number of decision steps between the tree work and the many inventories begin with street trees and then later add highest level of administration. This is supported by findings by other trees, which is in line with international recommenda- Hauer and Peterson (2016) that large communities have 6.7 tions that street trees should be prioritised due to risk (Long description steps, while smaller communities have 2.6 steps. et al. 2008; Sreetheran et al. 2011), contribution to ecosystem This difference might thereby create a need not only to collect services (McPherson et al. 2016) and higher costs than other data, but also to present it to politicians in a comprehensive way trees (McPherson et al. 2016). This is supported by the (Miller et al. 2015). This theory is supported by the fact that findings of the present study, where 65% of responding larger municipalities to a higher degree than smaller have cre- municipalities included risk as a parameter. However, ated a management plan. we also found that smaller municipalities included in- ventories of greenbelts and woodlands. The reason for this may lie in the fact that many Swedish municipali- What areas are included in the inventories? ties with smaller populations are primarily rural, and thus almost integrated in highly forested areas where Most municipalities reported that they conduct inventories on street trees (93%) and park trees (79%), but inventories are urban woodlands are a natural part of the urban fabric (Rydberg and Falck 2000). A traditional forestry operat- also conducted on other municipal areas, although to a lesser ing approach (Mikkonen 2004; Andersson et al. 2013) extent: Municipal urban woodlands, i.e. woodlots (26%), green corridors managed by the municipality, i.e. greenbelts is likely in these municipalities, thus including also green spaces, green corridors and urban woodlands in (20%), other municipal buildings such as urban real estate/ kindergarten/school/home for the elderly (15%), and private operations. Due to weak legal protection, urban woodlands are fre- trees (2%). There was no statistically significant difference between street and park trees and all other areas except for quently exploited as part of urban densification (Tallhagen 1999; Nielsen et al. 2017) and as such often fall within the private trees, which differed significantly from all other groups (Fig. 1). remit of the municipal planning department instead of the management department. This discrepancy between sin- gle tree approaches and stand approaches to the urban forest as a whole might be one important aspect that hinders effective adoption of a total green infrastructure approach (Matthews et al. 2015). Private trees emerged as the area that received least atten- tion in all Swedish municipalities, although private trees have started to attract more attention from the scientific community (McPherson 1998; Jones 2008; Jones and Davis 2017). Private trees also constitute a large part of the total urban forest in the USA, with studies showing that they account for rough- ly 75% of all trees in cities (McPherson 1998). While most planting decisions are made by private landowners and devel- opers (Berland and Elliot 2014), only two municipalities in our survey have conducted municipal tree inventories on pri- vate land. This is probably related to the many problems as- sociated with conducting inventories on private land, e.g. ac- cess to the trees (McPherson 1998), but also to the fact that municipalities prioritise their focus to what is directly admin- Fig. 1 Heatmap of the unweighted pair group method with arithmetic istrated by the city administration. Swedish municipal tree mean (UPGMA) clustering for BWhat areas have been inventoried?^. inventories are primarily conducted for management purposes Grouping and dendrogram at the top and variable names to the right. and therefore the areas that are used most, i.e. streets and Approximation of significant difference in frequencies based on parks, are prioritised. In Denmark, many inventories are con- pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other ducted due to risk (Keller and Konijnendijk 2012) and the 472 Urban Ecosyst (2018) 21:467–477 same seems to apply in Sweden which also explains why None of the municipal tree inventories in Sweden had used private trees are not prioritised. If the focus instead were to volunteers, which is in line with the results of Keller and create strategic plans for e.g. ecosystem services, private trees Konijnendijk (2012, p. 28) who concluded that BNo volun- might be a higher priority, but Swedish tree inventories are teers were used in Scandinavia when carrying out the inven- primarily used for maintenance and not for planning (see sec- tory, and no further community-engaging projects were tion: What kind of data have been collected?). started as a result of the inventory^. The results of the present study and that by Keller and Konijnendijk (2012) can be com- Who conducts the municipal tree inventories? pared to the situation reported by Hauer and Peterson (2016), where 14% of the inventories were conducted by volunteers, Overall 64% of all municipalities used Consultants for or Roman et al. (2013) where 42% used volunteers. According collecting tree inventory data, and 58% used in-house staff. to Keller and Konijnendijk (2012), the use of volunteers raises Seasonal employee/temporary employee was used by only concerns over the validity of the inventory itself. However, 12%, and no-one used volunteers (Fig. 2). However, as seen Roman et al. (2016) found very little difference in the quality in Fig. 2 and confirmed by the multiple branching of the MRT of data collection between volunteers and professionals. In (Appendix), the use of contractors is not an ‘either/or’ re- Sweden, there might also be a cultural reason for the lack of sponse, as many municipalities use both municipal staff and volunteers used in urban tree inventorying. Swedes in general consultants, and sometimes even interns. do not volunteer for issues that they regard as a government/ The use of both in-house staff and consultants is probably municipal responsibility, whereas they spend rather much time due to available resources, where municipalities sometimes volunteering for e.g. sport organisations (Grassman and lack sufficient in-house staff to conduct the inventory. This Svedberg 1996). However, there may be some changes occur- assumption is supported by a study in Norway, which also ring concerning the willingness of Swedes to actively partic- describes a situation where specific green space management ipate in the management of urban trees. A study conducted by tasks might be performed by consultants (Leiren et al. 2016). Östberg and Kleinschmit (2016) showed how private citizens This could also be the case for municipal tree inventories, in Stockholm were highly involved in demonstrating against where e.g. risk assessments are performed by consultants felling of a large oak. Similar situations have arisen all around (Terho and Hallaksela 2005). Sweden, ranging from avenue trees in Gothenburg (GP 2013) to a large apple tree in Gävle (SR 2014). What kind of data have been collected? In tree inventories, Swedish municipalities primarily focus on tree species (89%) and information on vitality (74%), follow- ed by risk (65%), the need for removal (64%) and diameter at breast height (DBH) (57%), whereas locations for planting trees, economic value and woody debris are not often included (Fig. 3). In the MRT, smaller municipalities (population lower than 7128, corresponding to the 15th percentile) focused more on risk and removal (operational aspects), than more analyti- cal variables such as DBH, vitality, insects/pest and species (Appendix). Otherwise, as seen in Fig. 3, no major differences in data collection could be seen. The urban tree inventory parameters measured have a di- rect impact on the potential use of the inventory (Miller 1997; Östberg et al. 2013; Miller et al. 2015) and it is therefore crucial to select appropriate tree inventory parameters (Östberg et al. 2013). Many of the Swedish municipalities are following the international trend of prioritising species, DBH and vitality (Roman et al. 2013; Östberg et al. 2013). Fig. 2 Heatmap of the unweighted pair group method with arithmetic However, Scandinavian municipalities seem to collect infor- mean (UPGMA) clustering for BWho conducts the urban tree mation on risk to a higher degree than other urban tree man- inventory?^. Grouping and dendrogram at the top and variable names to agers, as also observed by Keller and Konijnendijk (2012) the right. Approximation of significant difference in frequencies based for Danish municipalities. The origins of this risk focus on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other are difficult to discern, but personal communications Urban Ecosyst (2018) 21:467–477 473 Fig. 3 Heatmap of the unweighted pair group method with arithmetic mean (UPGMA) clustering for BWhat kind of data have been collected?^. Grouping and dendrogram at the top and variable names to the right. Approximation of significant difference in frequencies based on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other with Swedish municipalities suggest that risk is some- What are municipal tree inventories used for? times used as an excuse to conduct municipal tree in- ventories since politicians are more willing to pay for Tree inventories in Swedish municipalities are focused on the inventories that have a risk focus than e.g. an inventory of tree day-to-day maintenance of urban trees, where tree removal canopy cover. This reflects the claim by Matthews et al. accounts for 71% of all use, pruning 55%, tree care planning (2015) that green infrastructure questions are often seen as 52%, dealing with complaints 45% and height pruning 31%. either capital-based or risk-based. There is also a focus on planning, which includes policy The risk focus can also be associated with the cost of (42%), tree selection (41%) and place for planting (40%). managing the damage that urban trees can cause, so-called Only a few municipalities use their inventory for anything ecosystem disservices (Lyytimäki 2014;Delshammar etal. other than strategic purposes, e.g. canopy cover (5%) and 2015; Cariñanos et al. 2017), including risk-based removal ecosystem services (5%) (Fig. 4). of urban trees (Cariñanos et al. 2017), which suggests that The MRT showed a clear difference between those munic- Swedish municipalities have a lower tolerance to both risk ipalities with higher amounts of contractors (>35%), which and ecosystem disservices and the costs associated with focused more on policy development than those municipali- these. This might in turn be due to the fact that economic ties primarily using in-house staff for the collection of data valuation of ecosystem services is a very new field, and (Appendix). The latter municipalities use their inventory more thereby Swedish municipalities have only seen the costs of for operational management aspects and especially overall urban trees, the ecosystem disservices (Lyytimäki 2014), and tree management planning. not the economic savings in the form of ecosystem services There was no significant relationship between changes in by which urban trees contribute to the overall municipal urban tree population development (sum of trees planted mi- economy (Rogers et al. 2017). nus trees removed) and any of the variables tested, including The survey results indicated that smaller municipalities fo- the presence of a management plan. cus more on risk, contradicting findings in previous studies of The limited use of tree inventories for strategic pur- no significant difference in frequency of tree risk assessments poses is rather surprising, since Swedish municipalities depending on municipality size (Koeser et al. 2016). It might have a government mandate to work with ecosystem be due to the fact that smaller municipalities focus more on services (Regeringen 2014). However, there might be a operational tasks and may not collect information to create discrepancy between the long-term goals which ecosys- management plans (see section What is the extent of munici- tem services often represent (Jones 2008;Dobbsetal. pal tree inventories in Sweden?). 2017) and the fact that most green space managers are 474 Urban Ecosyst (2018) 21:467–477 Fig. 4 Heatmap of the unweighted pair group method with arithmetic mean (UPGMA) clustering for BWhat are the inventories used for?^. Grouping and dendrogram at the top and variable names to the right. Approximation of significant difference in frequencies based on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other operating on a day-to-day basis (Randrup and Persson municipalities being more likely to perform municipal tree 2009). In relation to this, the fact that municipalities inventories. This can be seen as an indication that the larger which used contractors to a greater extent also more the municipal budget, the more likely the municipality often used their tree inventory for policy development is to conduct a tree inventory. These results are in line is worth noting. It reflects the fact that in previous with international findings. We found large differences studies, use for strategic purposes is a strong driver between Swedish municipalities in all aspects of urban for the collection of data (Miller 1997; Östberg et al. 2013; tree inventorying, ranging from Which municipalities Miller et al. 2015). conduct inventories?to What data are collected?and Use of the inventory was linked with the use of contractors, What are the data used for?. which might be due to the fact the closer the organisation is to The inventories are conducted by both consultants the practical management level, the more focus needs to be and in-house staff and the parameters they collect data aimed at operational questions, whereas municipalities that on are primarily species, vitality, risk and DBH.The work with consultants probably need to focus more on policy inventory data are primarily used for operational tasks, documents in order to steer the organisation and its which might indicate the difficulty in moving from op- consultants. This is supported by findings of Randrup and erational to the much wider and strategic ecosystem Persson (2009) that the distribution of the budget between services approach. At present there are no guidelines municipal authorities responsible for green space planning, describing how municipalities should work with this including trees, other public organisations, and private com- topic, and therefore, we foresee a future potential, but panies is 53%, 21% and 26% respectively, in Sweden. The also a challenge municipal tree inventories for Swedish similar figures for Denmark are 29%, 63% and 8%, indicating municipalities when, by law, they are expected to go from an that a focused green space authority (as in Sweden), also has a operational to a more strategic management level. We there- larger use of private contractors. fore recommend further research on how municipalities can move towards a more strategic perspective and how municipal tree inventories can be used as a resource in describing the Conclusions services – and dis-services of urban trees, based on compre- hensive municipal tree inventories. Most Swedish municipalities have conducted an urban tree inventory, but the size of the municipality strongly affects Acknowledgements The authors want to thank the municipalities that the presence of an inventory, with primarily larger answered the survey. Urban Ecosyst (2018) 21:467–477 475 Appendix Bardekjian A, Kenney A, Rosen M (2016) Trends in Canada’surban Open Access This article is distributed under the terms of the Creative forests. 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The state and use of municipal tree inventories in Swedish municipalities – results from a national survey

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Life Sciences; Urban Ecology; Environmental Management; Ecology; Nature Conservation
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Abstract

Urban trees are an essential component of urban ecosystems, and management of this resource constitutes an essential element of urban open space management. However, municipal tree inventories in Sweden and elsewhere have received limited attention. It is unknown how common municipal tree inventories are in Sweden, factors governing whether a municipality has an inventory and what the inventories are used for. This study therefore sought to: Create an overview of the state of Swedish municipal tree inventories and determine how municipality size, green space budget and management organisation affect the presence and scope of municipal tree inventories. The research questions examined were: What is the current state of Swedish municipal tree inventories? and what affects the status of these municipal tree inventories? A survey with questions related to strategic and operational perspectives of municipal tree inventories, e.g. how they are conducted and used, together with questions relating to budget and potential use of consultants, was sent to all 290 Swedish municipalities. The response rate was 55.5%. The main findings were that municipality size affects whether a municipality has an urban tree inventory and that the municipal organi- sation form affects how inventories are used. The existence of an inventory also increased the probability of the municipality having a tree management plan. Based on these results we recommend further research related to strategic management per- spectives of tree inventories. . . . . . . Keywords Survey Municipality Street trees Park trees Management Ecosystem services Ecosystem disservices Introduction perceived as negative for human well-being^ (Lyytimäki 2014, p. 311), and how management can affect the extent of ecosystem Research has clearly shown the importance of urban trees for disservices caused by urban trees (Östberg et al. 2012; sustainable urban development through their capacity for de- Delshammar et al. 2015; Dobbs et al. 2017; Lyytimäki 2017). livering numerous important ecosystem services, which in- Management of urban trees is key to sustaining and increas- clude: Provisioning services (e.g. fuel and food), regulating ing important ecosystem services (Dobbs et al. 2017)and re- services (e.g. stormwater management, urban heat island mit- ducing the amount of ecosystem disservices (Lyytimäki 2017), igation, air pollution regulation), cultural services (e.g. recre- and municipal tree inventories are the foundation on which ation, physical and mental health benefits) and supporting management of urban trees is based (Kielbaso 2008;Miller services (e.g. wildlife habitats) (Grahn and Stigsdotter 2003; et al. 2015; Morgenroth et al. 2016). In recent decades there Tyrväinen et al. 2005; Gilletal. 2007; Jones 2008; has therefore been increasing interest in municipal tree inven- Morgenroth et al. 2016; Dobbs et al. 2017). tories, resulting from e.g. growing problems with pest and Another concept gaining attention is ecosystem disservices, disease attack on the urban tree stock (Raupp et al. 2006)and defined as Bfunctions or properties of ecosystems that are growing awareness among decision-makers of the multiple ecosystem services trees provide in the cityscape (Roy et al. 2011; Hubacek and Kronenberg 2013; Nielsen et al. 2014). * Johan Östberg Municipalities, especially in North America and Europe, have johan.ostberg@slu.se therefore increasingly started to perform municipal tree inven- tories (e.g. Nowak et al. 2001; Keller and Konijnendijk 2012; Department of Landscape Architecture, Planning and Management, Sjöman et al. 2012). Municipal tree inventories in North Swedish University of Agricultural Sciences, P.O. Box 66, SE-230 America have largely involved the use of i-Tree to perform 53 Alnarp, Sweden 468 Urban Ecosyst (2018) 21:467–477 economic valuations of urban trees (Kielbaso 2008; i-Tree & Budget/Financing included questions relating to the 2017; Morgenroth and Östberg 2017; Rogers et al. 2017), municipality’s economic situation and specifically whereas Northern Europe has focused more on management which economic resources are available for manage- issues, e.g. tree health and management related to monitoring ment of green spaces and trees. Questions relating to the dynamics of the tree stands (Keller and Konijnendijk 2012; historical developments and how municipal man- Morgenroth and Östberg 2017). agers viewed future resource allocations were also Municipal tree inventories in Sweden have only recently included. received attention among researchers. One of the first studies & Maintenance of green spaces and trees included questions to compare municipal tree inventories presented data for 10 relating to the daily maintenance, e.g. personnel, type of Nordic cities (Sjöman et al. 2012). Since then, a related prac- contractors being used (public/private), total amount of tical national standard focusing on what to include and how to green spaces/trees, and how these have developed over perform an urban tree inventory in Swedish municipalities has time and how they are expected to be developed in the been published (Östberg et al. 2013). However, there is no future. overview of the current state of municipal tree inventories & Policy, plans and strategies included questions about the and thus there is a lack of understanding of how municipality strategic documents used in order to steer and develop size, green space budget and management organisation affect green spaces/trees. the presence and state of municipal tree inventories. The rela- & Quality included questions relating to municipal man- tionship between tree inventory and green space budget may agers’ perceptions on the quality of their green spaces be a prerequisite for good tree management, while and urban trees. organisational aspects might also be important since there is & Tree inventories included questions specifically re- an obvious need for an inventory if tree maintenance is lating to urban trees, e.g. about management sys- outsourced (Lindholst 2009; Randrup and Persson 2009). tems such as tree inventories and use of digital data Hauer and Peterson (2016) suggest that the execution of mu- systems. nicipal tree inventories can be connected to factors such as size of the municipality, green space budget, or perceived need This paper primarily deals with the questions specifically for the municipality to maintain a high number of urban trees relating to trees and tree inventories. The survey was first and related records of tree removal and planting. tested in a pilot study involving 15 municipalities representing Therefore, the objective of the present study was to gain different sizes and locations around Sweden. Based on the further insights into Swedish practice concerning tree inven- comments collected from the pilot study, the survey questions tories, driven by the following research questions: What is were revised. the current state of Swedish municipal tree inventories? and All 290 Swedish municipal websites were visited in What affects the status of the municipal tree inventories?In December 2015 in order to obtain correct contact names order to analyse these research questions, five sub-questions and addresses and personal contact was made with some were formulated: municipal arborists known to the authors. Municipal personnel with the greatest responsibility for green a. What is the extent of municipal tree inventories in spaces and trees were selected as contact persons. If Sweden? more than one person was identified, all were included b. What areas are included in the inventories? as recipients of the survey. The actual distribution of the c. Who conducted the inventories? survey and issue of reminders were performed via e- d. What kind of data has been collected? mail, with reminders being sent to all non-respondents e. What are the inventories used for? at 2, 3, 4 and 8 weeks after the initial distribution. Written responses received via ordinary mail (n =17) were entered manually into Netigate (Netigate AB, Sweden) and then all responses was downloaded to Materials and methods Microsoft Excel 2010 (Microsoft Corporation, USA). All responses were evaluated manually for obvious er- The survey rors, and in this process eight duplicate answers were deleted. In cases where a municipality had submitted Based on recent surveys in the United States of America, two responses, the most recent and most comprehensive Canada and the United Kingdom (Neal et al. 2014; Hauer was kept. Responses that were less than 10% complete and Peterson 2016; Bardekjian et al. 2016), a survey was were also deleted. In total, 161 surveys (55.5% response developed for the Swedish context. The survey was divided rate for all Swedish municipalities) were included in the into five parts, each consisting of 5–11 questions: dataset and formed the basis for further analysis. Urban Ecosyst (2018) 21:467–477 469 Statistical analysis same generalized linear modelling approach as above was used. The response was derived from the subset of the data All statistical tests were performed at a significance level of having an inventory and then split into having the inventory 0.05. To test the representativeness of the survey concerning digitalised or not. The same approach was used to analyse the spatial distribution and municipal types, a Chi-square test was reasons for updating the inventory or not. performed on the observed distribution of responses between To test the relationship between population size and num- municipal groups as defined by the Swedish Association of ber of municipal trees, Spearman correlation and associated Local Authorities and Regions (SKL 2011)compared withthe test was calculated between population size and number actual distribution for Sweden. This test was non-significant of municipal trees as well as municipal trees per capita (χ = 8.086, df = 9, n = 161, p = 0.525). To test whether the (R Core Team 2016). responding municipalities differed in population size and area To gain an insight into factors that might influence changes from Swedish municipalities in general, one-sample Z-tests in the number of trees in the urban municipal tree population, based on national statistics were performed. Neither of these we calculated the net gain of trees by subtracting the number tests gave a significant result (Z = 0.97; p = 0.331 and Z = of trees removed from the number of reported planted trees. −1.30; p = 0.194, respectively). Accounting for eventual This value was then modelled as the response in a general skewed distribution by using one-sample sign test did not linear model using proc. mixed (SAS 9.4) and population, produce any significant results. As such, the responses to the budget per capita, contractors and presence of a management survey can be seen as a fair representation of Sweden as a plan as explanatory variables. whole. The statistical tests performed for the research questions Analysis of multiple choice questions and the five sub-questions are described below. For the multiple choice questions ‘Who conducted the inven- What is the extent of municipal tree inventories in Sweden? tory?’, ‘What kind of data have been collected?’, ‘What are the inventories used for?’ and ‘What areas are included in the In order to study the factors affecting the presence of an urban inventories?’ we used the approach presented below for each tree inventory, we modelled this in several steps. First, due to individual question, using the binary matrix of variables for the strong evidence in the literature (Miller 1997) that having a the specific question as analytical unit. To give an overview of tree management plan is dependent on having a tree inventory, the relations and eventual grouping between the variables we explored this relationship with 2 × 2 cross tables and concerning each question, we used clustering with additional Fisher’s exact test (R Core Team 2016) and found that it was graphical tools. This was performed by average agglomerative significant (p < 0.0001). Based on this, in a second step we clustering using the unweighted pair group method with arith- only used inventory as response variable and excluded man- metic mean (UPGMA) (Maechler et al. 2014) with binary agement plan due to their collinearity. To explore the reasons distances from the dist function in R (R Core Team 2016). for having a tree inventory, we employed generalised linear We verified that UPGMA had the highest cophenetic correla- modelling in SAS 9.4, using the genmod procedure with a tion coefficient compared with single-linkage agglomerative binomial distribution and logit link function (i.e. binary logis- clustering, complete-average agglomerative clustering and tic regression). The p-scale option was used to avoid problems Ward’s minimum variance clustering. We used Mantel statics of over-dispersion in the models. Having a tree inventory was to decide on number of clusters to display in the dendrogram. modelled as the binomial response. As explanatory variables, We then applied the vegemite and heatmap function in R the following variables were included: population (Koeser package vegan (Oksanen et al. 2013) to produce a graphical et al. 2016), greenspace budget per capita (Randrup and overview of the data matrix in relation to the clustering. To get Persson 2009), percentage of contractors used in tree manage- an approximation of the differences between the different ment (Hauer and Peterson 2016), number of trees planted per response rates for each area, multiple Chi-square tests capita (Bardekjian et al. 2016) and record of trees being re- with Holm’s correction for multiple testing were per- moved or planted (Kuhns et al. 2005). formed (Holm 1979;R Core Team 2016). These approxi- Using the Bayesian information criteria (BIC) and Type 3 mations were added to the graphs using the convention where- significance test of the variables, the most theoretically sound by variables sharing the same letter do not differ significantly and parsimonious model was selected based on adding the from each other. variables to the models individually in the order above that To explore the relationship with population size, budget per reflected our hypothesis on their importance, with significance capita and percentage of contractors, we used these as explan- level for inclusion in the model set to p <0.05. atory variables in a multivariate regression tree (Therneau To test the hypothesis that ‘number of municipalities with a et al. 2013; Ouellette and Legendre 2013) of the response digitalised tree inventory increases with population size’,the matrix with a chord transformation (to linearise the data). 470 Urban Ecosyst (2018) 21:467–477 Discriminate variables for the different branches of the regres- confirmed by statistical analysis, which showed that popula- sion tree and significant coding for them were added. The tion size of the municipality was the only variable significant- results of the regression tree were verified by comparing the ly related to the presence of an inventory (F = 23.51, 1,148 results with a global non-metric multidimensional scaling with p < 0.0001) when comparing the factors: Population, a Gower distance and post-hoc testing of the explanatory var- greenspace budget per capita, percentage of contractors used iables with the Envfit function (Oksanen et al. 2013). in tree management, number of trees planted per capita and record of trees being removed or planted. There was also a significant positive correlation (r = 0.6721256, n =83, Spearman Results and discussion p < 0.0001) between population size and number of municipal trees. The results suggested that, if a municipality has a tree in- The results are structured around the research questions and sub-questions and are addressed in the following order: ventory (54.5% of all), it is also likely to have a tree manage- ment plan (55.2% of those with an inventory). Only 2% of all 1. What is the extent of municipal tree inventories in municipalities had a tree management plan without the pres- Sweden? ence of a tree inventory. This difference was supported by the 2. What areas are included in the inventories? Fisher exact test, which gave a significant result (p <0.0001), 3. Who conducted the inventories? implying that for almost all municipalities a tree inventory 4. What kind of data has been collected? forms the basis for their tree management plan. These results 5. What are the inventories used for? confirm findings in a number of studies and recommendations that stress the need to first conduct an tree inventory and then create a management plan (e.g. Kielbaso 2008;Milleretal. 2015; Morgenroth et al. 2016;Zürcher 2017). What is the extent of municipal tree inventories in Sweden? The reason why population size influences the presence of municipal tree inventories is unknown. Since most national Of the 161 municipalities that responded to the survey, 85 and international surveys have focused on existing inventories (52.8%) had a municipal tree inventory. The number of mu- (e.g. Sjöman et al. 2012; McPherson et al. 2016), have con- nicipalities that had an inventory increased with municipal ducted their own inventories (Britt and Johnston 2008)or population, from 34.4% for cities with populations ranging have been limited to specific regions (Kuhns et al. 2005; from 2500 to 9999 to 92.3% for the largest municipalities Schroeder et al. 2003), it is difficult to compare the Swedish (100,000 to 500,000 inhabitants). A similar trend was seen situation with that internationally. However, the effect of pop- for the number of inventories digitalised, which ranged from ulation size might be due to several different factors. (1) 27.3% to 83.3%. However, a large number of inventories were Municipalities with larger population size will, in most cases, have relatively larger tree populations and therefore it is more either ‘under development’ (54.1%) or ‘outdated’ (27.1%) (Table 1). There were no significant relationships between difficult to get an overview of the whole tree population with- any of the parameters tested and whether the inventory was out a municipal tree inventory. This is supported by the trend updated or not. that larger municipalities had more trees per capita (r = Spearman The probability of the inventory being digitalised increased 0.3323806, n =83, p < 0.0021), and is in line with previous significantly with population size of the municipality (F = findings by Kuhns et al. (2005). Larger municipalities might 1,80 6.68, p = 0.0116). This influence of population was also thereby not only have more trees, but also more trees per capita, Table 1 Number of responding municipalities that had an urban tree inventory and the status of those inventories Population size nHavean Digitalised inventories Updated inventories Inventories that are under Inventories that are of the municipality inventory of all inventories of all inventories development of all outdated of all (n and %) (n and %) (n and %) inventories (n and %) inventories (n and %) 2500 to 9999 32 11 (34.4%) 3 (27.3%) 2 (18.2%) 6 (54.5%) 4 (36.4%) 10,000 to 24,999 61 24 (39.3%) 10 (41.7%) 6 (25.0%) 11 (45.8%) 6 (25.0%) 25,000 to 49,999 33 21 (63.6%) 15 (71.4%) 4 (19.0%) 13 (61.9%) 4 (19.0%) 50,000 to 99,999 22 17 (77.3%) 14 (82.4%) 2 (11.8%) 10 (58.8%) 5 (29.4%) 100,000 to 500,000 13 12 (92.3%) 10 (83.3%) 2 (16.7%) 6 (50.0%) 4 (33.3%) Total 161 85 (52.8%) 52 (61.2%) 16 (18.8%) 46 (54.1%) 23 (27.1%) The municipalities were asked if the inventory was digitalised or not, and if the inventory was updated, in-development or outdated Urban Ecosyst (2018) 21:467–477 471 which creates an even higher need for an urban tree inventory In the multivariate regression tree (MRT), there was a ten- and a management plan. In comparison with North American dency for municipalities with large budgets (≥72.5 SEK/ cities (Hauer and Peterson 2016; Bardekjian et al. 2016), person (7.5 Euros/person)) to inventory woodlands and other Swedish municipalities have fewer municipal tree inventories. properties to a greater extent than other municipalities, where- (2) There could be an organisationalaspectthatdifferentiates as municipalities with lower budgets had a tendency to focus large and small municipalities, where larger municipalities have on street trees (Appendix). Sjöman et al. (2012) found that a higher number of decision steps between the tree work and the many inventories begin with street trees and then later add highest level of administration. This is supported by findings by other trees, which is in line with international recommenda- Hauer and Peterson (2016) that large communities have 6.7 tions that street trees should be prioritised due to risk (Long description steps, while smaller communities have 2.6 steps. et al. 2008; Sreetheran et al. 2011), contribution to ecosystem This difference might thereby create a need not only to collect services (McPherson et al. 2016) and higher costs than other data, but also to present it to politicians in a comprehensive way trees (McPherson et al. 2016). This is supported by the (Miller et al. 2015). This theory is supported by the fact that findings of the present study, where 65% of responding larger municipalities to a higher degree than smaller have cre- municipalities included risk as a parameter. However, ated a management plan. we also found that smaller municipalities included in- ventories of greenbelts and woodlands. The reason for this may lie in the fact that many Swedish municipali- What areas are included in the inventories? ties with smaller populations are primarily rural, and thus almost integrated in highly forested areas where Most municipalities reported that they conduct inventories on street trees (93%) and park trees (79%), but inventories are urban woodlands are a natural part of the urban fabric (Rydberg and Falck 2000). A traditional forestry operat- also conducted on other municipal areas, although to a lesser ing approach (Mikkonen 2004; Andersson et al. 2013) extent: Municipal urban woodlands, i.e. woodlots (26%), green corridors managed by the municipality, i.e. greenbelts is likely in these municipalities, thus including also green spaces, green corridors and urban woodlands in (20%), other municipal buildings such as urban real estate/ kindergarten/school/home for the elderly (15%), and private operations. Due to weak legal protection, urban woodlands are fre- trees (2%). There was no statistically significant difference between street and park trees and all other areas except for quently exploited as part of urban densification (Tallhagen 1999; Nielsen et al. 2017) and as such often fall within the private trees, which differed significantly from all other groups (Fig. 1). remit of the municipal planning department instead of the management department. This discrepancy between sin- gle tree approaches and stand approaches to the urban forest as a whole might be one important aspect that hinders effective adoption of a total green infrastructure approach (Matthews et al. 2015). Private trees emerged as the area that received least atten- tion in all Swedish municipalities, although private trees have started to attract more attention from the scientific community (McPherson 1998; Jones 2008; Jones and Davis 2017). Private trees also constitute a large part of the total urban forest in the USA, with studies showing that they account for rough- ly 75% of all trees in cities (McPherson 1998). While most planting decisions are made by private landowners and devel- opers (Berland and Elliot 2014), only two municipalities in our survey have conducted municipal tree inventories on pri- vate land. This is probably related to the many problems as- sociated with conducting inventories on private land, e.g. ac- cess to the trees (McPherson 1998), but also to the fact that municipalities prioritise their focus to what is directly admin- Fig. 1 Heatmap of the unweighted pair group method with arithmetic istrated by the city administration. Swedish municipal tree mean (UPGMA) clustering for BWhat areas have been inventoried?^. inventories are primarily conducted for management purposes Grouping and dendrogram at the top and variable names to the right. and therefore the areas that are used most, i.e. streets and Approximation of significant difference in frequencies based on parks, are prioritised. In Denmark, many inventories are con- pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other ducted due to risk (Keller and Konijnendijk 2012) and the 472 Urban Ecosyst (2018) 21:467–477 same seems to apply in Sweden which also explains why None of the municipal tree inventories in Sweden had used private trees are not prioritised. If the focus instead were to volunteers, which is in line with the results of Keller and create strategic plans for e.g. ecosystem services, private trees Konijnendijk (2012, p. 28) who concluded that BNo volun- might be a higher priority, but Swedish tree inventories are teers were used in Scandinavia when carrying out the inven- primarily used for maintenance and not for planning (see sec- tory, and no further community-engaging projects were tion: What kind of data have been collected?). started as a result of the inventory^. The results of the present study and that by Keller and Konijnendijk (2012) can be com- Who conducts the municipal tree inventories? pared to the situation reported by Hauer and Peterson (2016), where 14% of the inventories were conducted by volunteers, Overall 64% of all municipalities used Consultants for or Roman et al. (2013) where 42% used volunteers. According collecting tree inventory data, and 58% used in-house staff. to Keller and Konijnendijk (2012), the use of volunteers raises Seasonal employee/temporary employee was used by only concerns over the validity of the inventory itself. However, 12%, and no-one used volunteers (Fig. 2). However, as seen Roman et al. (2016) found very little difference in the quality in Fig. 2 and confirmed by the multiple branching of the MRT of data collection between volunteers and professionals. In (Appendix), the use of contractors is not an ‘either/or’ re- Sweden, there might also be a cultural reason for the lack of sponse, as many municipalities use both municipal staff and volunteers used in urban tree inventorying. Swedes in general consultants, and sometimes even interns. do not volunteer for issues that they regard as a government/ The use of both in-house staff and consultants is probably municipal responsibility, whereas they spend rather much time due to available resources, where municipalities sometimes volunteering for e.g. sport organisations (Grassman and lack sufficient in-house staff to conduct the inventory. This Svedberg 1996). However, there may be some changes occur- assumption is supported by a study in Norway, which also ring concerning the willingness of Swedes to actively partic- describes a situation where specific green space management ipate in the management of urban trees. A study conducted by tasks might be performed by consultants (Leiren et al. 2016). Östberg and Kleinschmit (2016) showed how private citizens This could also be the case for municipal tree inventories, in Stockholm were highly involved in demonstrating against where e.g. risk assessments are performed by consultants felling of a large oak. Similar situations have arisen all around (Terho and Hallaksela 2005). Sweden, ranging from avenue trees in Gothenburg (GP 2013) to a large apple tree in Gävle (SR 2014). What kind of data have been collected? In tree inventories, Swedish municipalities primarily focus on tree species (89%) and information on vitality (74%), follow- ed by risk (65%), the need for removal (64%) and diameter at breast height (DBH) (57%), whereas locations for planting trees, economic value and woody debris are not often included (Fig. 3). In the MRT, smaller municipalities (population lower than 7128, corresponding to the 15th percentile) focused more on risk and removal (operational aspects), than more analyti- cal variables such as DBH, vitality, insects/pest and species (Appendix). Otherwise, as seen in Fig. 3, no major differences in data collection could be seen. The urban tree inventory parameters measured have a di- rect impact on the potential use of the inventory (Miller 1997; Östberg et al. 2013; Miller et al. 2015) and it is therefore crucial to select appropriate tree inventory parameters (Östberg et al. 2013). Many of the Swedish municipalities are following the international trend of prioritising species, DBH and vitality (Roman et al. 2013; Östberg et al. 2013). Fig. 2 Heatmap of the unweighted pair group method with arithmetic However, Scandinavian municipalities seem to collect infor- mean (UPGMA) clustering for BWho conducts the urban tree mation on risk to a higher degree than other urban tree man- inventory?^. Grouping and dendrogram at the top and variable names to agers, as also observed by Keller and Konijnendijk (2012) the right. Approximation of significant difference in frequencies based for Danish municipalities. The origins of this risk focus on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other are difficult to discern, but personal communications Urban Ecosyst (2018) 21:467–477 473 Fig. 3 Heatmap of the unweighted pair group method with arithmetic mean (UPGMA) clustering for BWhat kind of data have been collected?^. Grouping and dendrogram at the top and variable names to the right. Approximation of significant difference in frequencies based on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other with Swedish municipalities suggest that risk is some- What are municipal tree inventories used for? times used as an excuse to conduct municipal tree in- ventories since politicians are more willing to pay for Tree inventories in Swedish municipalities are focused on the inventories that have a risk focus than e.g. an inventory of tree day-to-day maintenance of urban trees, where tree removal canopy cover. This reflects the claim by Matthews et al. accounts for 71% of all use, pruning 55%, tree care planning (2015) that green infrastructure questions are often seen as 52%, dealing with complaints 45% and height pruning 31%. either capital-based or risk-based. There is also a focus on planning, which includes policy The risk focus can also be associated with the cost of (42%), tree selection (41%) and place for planting (40%). managing the damage that urban trees can cause, so-called Only a few municipalities use their inventory for anything ecosystem disservices (Lyytimäki 2014;Delshammar etal. other than strategic purposes, e.g. canopy cover (5%) and 2015; Cariñanos et al. 2017), including risk-based removal ecosystem services (5%) (Fig. 4). of urban trees (Cariñanos et al. 2017), which suggests that The MRT showed a clear difference between those munic- Swedish municipalities have a lower tolerance to both risk ipalities with higher amounts of contractors (>35%), which and ecosystem disservices and the costs associated with focused more on policy development than those municipali- these. This might in turn be due to the fact that economic ties primarily using in-house staff for the collection of data valuation of ecosystem services is a very new field, and (Appendix). The latter municipalities use their inventory more thereby Swedish municipalities have only seen the costs of for operational management aspects and especially overall urban trees, the ecosystem disservices (Lyytimäki 2014), and tree management planning. not the economic savings in the form of ecosystem services There was no significant relationship between changes in by which urban trees contribute to the overall municipal urban tree population development (sum of trees planted mi- economy (Rogers et al. 2017). nus trees removed) and any of the variables tested, including The survey results indicated that smaller municipalities fo- the presence of a management plan. cus more on risk, contradicting findings in previous studies of The limited use of tree inventories for strategic pur- no significant difference in frequency of tree risk assessments poses is rather surprising, since Swedish municipalities depending on municipality size (Koeser et al. 2016). It might have a government mandate to work with ecosystem be due to the fact that smaller municipalities focus more on services (Regeringen 2014). However, there might be a operational tasks and may not collect information to create discrepancy between the long-term goals which ecosys- management plans (see section What is the extent of munici- tem services often represent (Jones 2008;Dobbsetal. pal tree inventories in Sweden?). 2017) and the fact that most green space managers are 474 Urban Ecosyst (2018) 21:467–477 Fig. 4 Heatmap of the unweighted pair group method with arithmetic mean (UPGMA) clustering for BWhat are the inventories used for?^. Grouping and dendrogram at the top and variable names to the right. Approximation of significant difference in frequencies based on pairwise Chi-square tests with Holm correction to the left. Variables sharing the same letter do not differ significantly from each other operating on a day-to-day basis (Randrup and Persson municipalities being more likely to perform municipal tree 2009). In relation to this, the fact that municipalities inventories. This can be seen as an indication that the larger which used contractors to a greater extent also more the municipal budget, the more likely the municipality often used their tree inventory for policy development is to conduct a tree inventory. These results are in line is worth noting. It reflects the fact that in previous with international findings. We found large differences studies, use for strategic purposes is a strong driver between Swedish municipalities in all aspects of urban for the collection of data (Miller 1997; Östberg et al. 2013; tree inventorying, ranging from Which municipalities Miller et al. 2015). conduct inventories?to What data are collected?and Use of the inventory was linked with the use of contractors, What are the data used for?. which might be due to the fact the closer the organisation is to The inventories are conducted by both consultants the practical management level, the more focus needs to be and in-house staff and the parameters they collect data aimed at operational questions, whereas municipalities that on are primarily species, vitality, risk and DBH.The work with consultants probably need to focus more on policy inventory data are primarily used for operational tasks, documents in order to steer the organisation and its which might indicate the difficulty in moving from op- consultants. This is supported by findings of Randrup and erational to the much wider and strategic ecosystem Persson (2009) that the distribution of the budget between services approach. At present there are no guidelines municipal authorities responsible for green space planning, describing how municipalities should work with this including trees, other public organisations, and private com- topic, and therefore, we foresee a future potential, but panies is 53%, 21% and 26% respectively, in Sweden. The also a challenge municipal tree inventories for Swedish similar figures for Denmark are 29%, 63% and 8%, indicating municipalities when, by law, they are expected to go from an that a focused green space authority (as in Sweden), also has a operational to a more strategic management level. We there- larger use of private contractors. fore recommend further research on how municipalities can move towards a more strategic perspective and how municipal tree inventories can be used as a resource in describing the Conclusions services – and dis-services of urban trees, based on compre- hensive municipal tree inventories. Most Swedish municipalities have conducted an urban tree inventory, but the size of the municipality strongly affects Acknowledgements The authors want to thank the municipalities that the presence of an inventory, with primarily larger answered the survey. Urban Ecosyst (2018) 21:467–477 475 Appendix Bardekjian A, Kenney A, Rosen M (2016) Trends in Canada’surban Open Access This article is distributed under the terms of the Creative forests. 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Urban EcosystemsSpringer Journals

Published: Feb 8, 2018

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