Biogeochemistry https://doi.org/10.1007/s10533-018-0453-y Characterization of ten extreme disturbance events in the context of social and ecological systems Ariel E. Lugo Received: 27 June 2017 / Accepted: 17 May 2018 The Author(s) 2018 Abstract An extreme disturbance event is one in response of social systems is different from the which any of its component disturbance forces and response of the ecological systems. Also, social their interactions with affected systems have dimen- systems recovered quicker to a category 3 hurricane sions and responses that exceed the known range of than did ecological systems. Both social and ecolog- variation expected of those parameters. If the exposed ical systems have the capacity to evolve, adapt, system does not respond or exhibits a low level innovate, and develop novelty in response to the response to an event, the event was not extreme to the selective pressure of extreme events. exposed system, regardless of the dimensions of its disturbance forces. Extreme disturbance events are Keywords Disturbances Extreme events complex and require disaggregation to improve Hurricanes Landslides Drought Economic collapse understanding of their effects. The areas affected by extreme events and the duration of the events are related but involve many orders of magnitude in terms of area affected and duration. One way to compare Introduction events is through a common and objective unit of measure such as energy. A comparison of ten extreme Extreme disturbance events (from now on extreme events in terms of their power and total energy events) are at center stage among social-ecological delivered per unit area revealed a broad range of scientists dealing with issues of sustainability, climate values among them. The power of events ranged 8 change, and resiliency. These are the main issues orders of magnitude and the total load per unit area being addressed in the context of the Anthropocene ranged 14 orders of magnitude. Each event had Epoch. At the onset of ecosystem-level ecology in the different points of interaction with exposed ecosys- 1970s (Golley 1993) ecologists paid little attention to tems. When exposed to the same extreme event, the extreme events because ecological attention was focused on the understanding of complex mature ecosystems at steady state. In Puerto Rico, for example, the study of ecological systems progressed Responsible Editor: Sujay Kaushal. through a period of about 60 years uninterrupted by A. E. Lugo (&) extreme events (Lugo 1996). This gave ecologists an International Institute of Tropical Forestry, USDA Forest opportunity to improve understanding of the function- Service, Calle Ceiba 1201, Rıo Piedras 00926-1115, ing of rain, wet, moist, and dry tropical forests in the Puerto Rico absence of disturbances. Ironically, while this research e-mail: email@example.com 123 Biogeochemistry on complex mature ecosystems was underway, insular resilience of forests and the adaptability of their biota forests were recovering from one of the most signif- through their selective pressure on populations of icant extreme events in the island, one that went plants, animals, and microbes. Adaptation is one of the unattended by ecologists until very recently. I am keys for dealing with disturbance events, which in the referring to massive deforestation. In the 1960s the long-term beneﬁts the biota because adapted popula- island hit bottom in forest cover (Fig. 1). This event tions survive extreme events. We also learned that the marked the beginning of an ecological transformation intensity of an extreme event is not uniform over the of island forests that took everyone by surprise (Grau landscape (see Fig. 4a in Peters et al. 2011). There are et al. 2003; Brandeis and Turner 2013). always locations where the intensity of the event is not The passage of hurricane Hugo over Puerto Rico in as severe as in others, a reality that provides refuge to 1989 was a wake-up call to ecologists regarding the organisms experiencing the event. The severity or effects of extreme events on the functioning of island harshness of a disturbance event on a system depends forests. This 4-h event and its ecological consequences on the type of disturbance, its strength, and the led to a new synthesis of how tropical forests respond component of the exposed system that it affects (Lugo to disturbances (Brokaw et al. 2012). Some of the 1978; Peters et al. 2011). lessons learned regarding the relationship between I will add several observations about extreme extreme events and forest ecosystems (Lugo 2008) are events to the list above using a comparative social- relevant to this analysis and I use them as givens. For ecological approach. I aim to apply the Peters et al. example, disturbances have visible and ‘‘invisible’’ (2011) framework for comparing and interpreting the effects and usually only visible effects get attention. social-ecological effects of ten extreme events. The An ‘‘invisible’’ effect has to be measured for it to Peter et al. framework is their Fig. 2, in which they become visible to science. Also, the ecological effects disaggregate the drivers of a disturbance event that of disturbances are not as negative as they appear in affect ecosystems, and trace their independent inter- the moments after the end of the event. It was clear that action with sectors of the ecosystem. Thus, a hurricane in spite of the physical effects of hurricanes on forest is not a single force affecting a forest, but it is structure and the loss of the old-growth aspect of the composed of wind energy and rainfall, each with a forest, hurricanes make forests young and productive different effect on a sector of a forest (wind affects and set them in succession to recover the old growth mostly the canopy and rainfall the soil, where it can characteristics. Moreover, disturbances sharpen the trigger other disturbances such as landslides). The questions that I address include: What makes a disturbance event an extreme event? What do different types of extreme events have in common and how do they differ? How do extreme events affect social- ecological systems and how do affected systems respond? The selected extreme events The following ten extreme events, arranged in chrono- logical order, have taken place or culminated over the last 100 years in Puerto Rico and I have had the opportunity to experience them. The list is biased by my experience and is not intended to be comprehen- sive. For example, I do not include all drought, hurricane, or ﬂood events through this time period. Fig. 1 Forest area of Puerto Rico between 1800 and 2009. Each Figure 2 shows the geography over which the ten point represents an estimate obtained from a variety of sources selected extreme events occurred. including Wadsworth (1950) for older estimates and Brandeis and Turner (2013) for the most recent estimates 123 Biogeochemistry Fig. 2 Geographic location of extreme events within Puerto within the city of San Juan, and the Luquillo Experimental Rico and the Caribbean. The tracks of hurricanes depict their Forest (LEF) is where the radiation experiment occurred at El strength from tropical depressions (TD), tropical storms (TS) Verde, where the 300,000-m landslide is located, and hurricane and hurricanes (H) of different intensities in the Safﬁr-Simpson response research is conducted scale (1–5). Within Puerto Rico, the Rı´o Piedras watershed is Deforestation of the Island. The forest cover of different from that of native forests before deforesta- Puerto Rico decreased continuously between 1800 and tion (Lugo and Helmer 2004). the 1960s (Fig. 1). The island was believed to have Island-wide sea level rise. Since 1956, monitoring been 100% forest covered at the time of its discovery of sea levels in the Atlantic and Caribbean coasts of by Europeans (Wadsworth 1950). Forest cover Puerto Rico has shown steady increases in sea levels declined to a historic low of about 5–10% as the (Fig. 3). While the slope of the increase suggests a rate Island was colonized and its economy transformed of 3.2 mm/year (near the global average), recent into an agrarian economy based on sugar cane, coffee, values have jumped to double ﬁgures (about 10 mm/ and tobacco (Pico´ 1969). Post agricultural economic year). Loss of beach sand and destruction of coastal transformation coupled to land abandonment, exten- property and infrastructure are some of the visible sive human migration, and urbanization allowed for effects of sea level rise in Puerto Rico. the recovery of forest cover to the present 60% (Grau Exposure to ionizing radiation with 10,000 curies of et al. 2003; Brandeis and Turner 2013). However, the Cs. This was an experiment that lasted about 3 months species composition of regenerated forests was during 1965 at El Verde sector of the Luquillo Experimental Forest (Odum and Drewry 1970; 123 Biogeochemistry 0.1 0.08 0.06 0.04 0.02 -0.02 -0.04 -0.06 -0.08 -0.1 1950 1960 1970 1980 1990 2000 2010 2020 Year Fig. 3 Smoothed monthly sea level rise around Puerto Rico. in the Atlantic Ocean. Aurelio Mercado Irizarry of the The longer record (black line) is for Magueyes Island in the University of Puerto Rico at Mayagu¨ez provides these data Caribbean Sea, and the shorter record in blue is for San Juan Bay Fig. 4). Radiation levels reached a million roentgens water depth of about 5 m, and lasts 5 h. Based on within a meter from the radiation source. Extensive historical ﬂoods in the 1970s, the US Army Corps of dosimetry established the radiation loads around and Engineers estimates a cost to the economy of millions above the radiation source (McCormick 1970), which of dollars in lost infrastructure and economic activity exposed a mature tabonuco (Dacryodes excelsa) wet as a result of this event. forest. Category 3-4 hurricanes. The Caribbean is in the A 300,000-m landslide. Landslides are triggered hurricane belt of the Atlantic Ocean and is subject to when excessive rainfall that saturates soil on steep frequent passages of storms and hurricanes of various terrain overcomes a threshold of intensity and duration categories in the Safﬁr-Simpson scale. I focus on the (Larsen and Torres Sanchez 1998). During the 1970s effects of category 3 and 4 hurricanes (sustained wind the passage of several low-pressure systems over the speeds between 196 and 251 km/h), speciﬁcally slopes of the Luquillo Mountains saturated the terrain hurricanes Hugo, Georges, and Allen. In this compar- and triggered one of the largest landslides in Puerto ison I address wind and waves over forests and coral Rico. Within minutes, about 300,000 m of soil, the reefs, respectively. High winds and tall waves have forests growing on that substrate, and a major highway signiﬁcant effects on terrestrial infrastructure, both (PR 191) rushed down the mountain slope, exposing coastal and inland. the saprolite beneath, and leaving no trace of what was Economic collapse of Island ﬁnances. In 2006, the originally primary forest cover and soil (Fig. 4b in economy of Puerto Rico began a contraction trend that Peters et al. 2011). This event permanently interrupted continued uninterrupted over the next ten years, highway trafﬁc as the road was closed. declining to 1994 economic level of activity (Fig. 6). A 100-year urban ﬂood. The 100-year ﬂood event The Island accumulated a debt of about 72 billion for the city of San Juan was simulated by the US Army dollars, leading to a current state of bankruptcy and Corps of Engineers as part of their analyses for the large levels of population emigration to the United channelization of the Rı´o Piedras river (Fig. 5). Such a States of America. ﬂood covers approximately 240 hectares, reaches a Sea Level above MSL (m) Biogeochemistry Island-wide 1 year ? drought. Atmospheric con- ditions in the Caribbean and around Puerto Rico resulted in a drought that began in January 2014 and ended in November 2016. At its peak level in August 2015, the drought affected almost all of Puerto Rico (Fig. 7), including the wettest sectors of the Luquillo Mountains. Water was rationed for millions of people. Affected aquifers, rivers, and streams reached the lowest levels measured in available records (Depart- ment of Natural Resources and the Environment 2016). Methods For each selected extreme event, I searched for records that indicated the area affected and the duration of the event. I then estimated the intensity or power of seven of the ten extreme events using the same energy units of power (j/m s), so that they could be compared on an equal basis. Odum (1996) contains many of the Fig. 4 Picture of the radiation source installed in a wet forest at formula and procedures for the energy calculations. El Verde, Luquillo Experimental Forest. The two-Mg lead The level of ionizing radiation produced by the container at the center of the concrete base contains the radiation source in roentgens (r) was converted to radioactive Cs source, which would be magnetically hoisted to Grays in j/kg (1 r = 0.00,877 Grays). This energy was below the oval metal structure when in operation (from Odum and Drewry 1970) converted to power units (j/m s) by multiplying by the air density in a cone 10 m in radius and 20 m Heat island over San Juan. Me´ndez La´zaro et al. canopy height around the radiation source. The (2016) deﬁned urban heat episodes as those with an air radiation ﬁeld emitted by the radiation source and surface temperature greater than the 90th percentile of the duration of the emission (2228 h) was obtained measured temperatures. Records for San Juan contain from Odum and Drewry (1970). McCormick (1970) heat episodes of up to 40 days in 2012 with sustained reported the pattern of radiation exposure around the air surface temperatures above 30 C and up to 38 C radiation source. The radiation measured within the (Me´ndez La´zaro et al. 2016). A surface temperature volume around the source (283 m ) ranged from one map for the city showed locations with temperatures as million to 50,000 r. ´ ´ high as 63 C (Mendez Lazaro et al. 2017). Increased To estimate the kinetic energy of a landslide and a mortality among the oldest and youngest age classes 100-year ﬂood, I used E = 0.5 (m/v ), where E is the and increased electric energy consumption for air kinetic energy in joules, m is the mass in kilograms, conditioners are associated with these events (Me´ndez and v is the velocity in m/s. To estimate the mass of Lazaro et al. 2016). soil that slid, I multiplied the volume of the landslide Low-pressure system over San Juan, Puerto Rico. (300,000 m ) estimated by the USGS by a bulk Low-pressure atmospheric systems trigger heavy density of 1.28 g/cm (Larsen and Torres Sa´nchez urban rains and ﬂoods, which interrupt the normal 1998), and used a velocity of 3 m/s reported by Walker functioning of the city and cause economic losses. I and Shields (2013). The area of the slide was estimated use the July 18, 2013 low-pressure event that passed at 10 ha and its duration was 5 min. For the ﬂood, the over San Juan. The US Weather Service measured the mass of water was obtained from its area (240 ha), highest 24-h rainfall precipitation on record for the depth (1 m), and the density of water. To complete the city (234 mm) and estimated a 50 years recurrence kinetic energy calculation I used a water velocity of interval for this event. 123 Biogeochemistry Flood Hazard Areas (FEMA 2008) 100 year floodzone 500 year floodzone Waterbody 2km Stream network Fig. 5 Map of the 100- and 500-ﬂood zones (red) in the municipality of San Juan. This map is by the Federal Emergency Management Agency (FEMA) produced for Flood Insurance purposes. Flood zones are deﬁned in https://www.fema.gov/ﬂood-zones 1 m/s and ﬂood duration of 5 h reported by the US Lugo et al. (2004). Calculations require information Army Corps of Engineers (in Lugo et al. 2013). on wave height in m, wave periodicity in seconds, The power of hurricane winds and waves was wavelength in m, water depth in m, water density (g/ obtained from Lugo et al. (2000, 2004). The estimate cm ), and acceleration by gravity. of the most powerful waves was based on the surge To estimate the energy equivalency of the eco- caused by hurricane Allen over Jamaica on August 6, nomic collapse of Puerto Rico, I estimated the loss in 1980. That storm surge reached 12 m. Calculations for economic activity during the decade of 2006–2016 the power of waves are based on equations in Dean and (Fig. 6). This loss was equivalent to 14.1 billion Dalrymple (1991) with examples in Odum (1996) and dollars. Using data compiled for a dissertation 123 Biogeochemistry Fig. 6 Monthly Index of Economic Activity for Puerto Rico between February 1980 and February 2016. The Government Developmental Bank for Puerto Rico provides this record. In this record, the activity level in January 1980 is equivalent to and index of 100 Fig. 7 Drought intensity in Puerto Rico during August, 2015. This map and others for different months are produced by the Drought Monitor and are available at http://droughtmonitor.unl.edu/ research in progress by Braulio Quintero, State use by the Puerto Rico economy between 1982 and University of New York at Syracuse, I averaged the 2014. The resulting energy equivalency of one dollar annual ratio of economic activity to fossil fuel energy in the puertorrican economy was 5.66 Tjoules. The 123 Biogeochemistry energy equivalency of the economic collapse was disruption relative to a system property in time and expressed per island (8800 km ) and per urban space. (1760 km ) area over a decade. The Peters et al. (2011) modiﬁcations to the The energy radiated by a heat wave was estimated deﬁnition of disturbance are implemented by disag- with the relationship E = a T , where E is the energy gregating disturbance events into their component 2 -8 in watts/m , a = 5.67 9 10 , and T is the tempera- forces and identifying the sectors of the affected ture of the event in K. This assumes an emissivity of ecosystem that interact with each of the forces of 1, when in reality the emissivity of asphalt, concrete, disruption. Peters et al. (2011) provide many examples glass, paint, and water (common urban surfaces) of this approach, which I discuss further later. ranges from 0.88 to 0.96. Applying such corrections One can identify ﬁve points of interaction or according to their proportion on the city would not ‘‘sectors’’ within an ecosystem where external distur- alter the order of magnitude of E. The duration of the bance forces interact with the biota and other compo- heat wave (30 days) and temperature (38 C) were nents of the ecosystem (Fig. 8). These interactions can ´ ´ obtained from Mendez Lazaro et al. (2016, 2017). The be categorized in order of severity because the effects duration in seconds was used to convert watts/m to at the point of interaction within the ecosystem affect joules/m . other sectors of the system and thus it’s functioning To estimate the chemical potential energy of (Lugo 1978). One can expect that as energy cascades rainfall during the extended low pressure event over through the ecosystem from producers to consumers, San Juan, I multiplied the Gibbs free energy value of to eventual dissipation as heat, those disturbances that pure water in relation to seawater of 4.94 j/g (Odum affect ﬂuxes upstream in the cascade will have greater 1996), by the 24-h rainfall of 0.234 m, the density of effects than the ones that interrupt downstream in the 3 7 2 water in g/m , and the area of the city (12.7 9 10 m ). cascade. While the model in Fig. 8 does not contain The result is the energy equivalency of the leaching social elements, the functioning of social systems (cleaning) capacity of rainwater as it ﬂows over city relative to energy transformations will not differ, as surfaces. I also estimated the kinetic energy of falling the laws of mass and energy transformation are water (its erosion potential) over city surfaces, using universal. Anthropogenic systems are thus subject to the relationship Energy in joules = mass of water (kg) metabolic analyses as are non-anthropogenic ones multiplied by the height of the clouds (assumed to be (Lugo 1988; Baccini and Brunner 2012). As I proceed 2500 m) and by the gravitational constant of 9.8 m/s . with my analysis I will provide examples from both Results were converted to an area basis using the area the social and ecological systems. of San Juan. The ranking of disturbance forces in Fig. 8 in terms of severity and starting with the most severe (left to right on Fig. 8), would be: (1) Those disturbances that What is an extreme event? change or transform the main energy source of an ecosystem and in so doing change the nature of the An extreme event is a subcategory of disturbance ecosystem. These are state-changing disturbances events. To properly deﬁne an extreme event requires such as transforming a ﬂowing system into a ponded an understanding of what constitutes a disturbance. one, or changing the REDOX (reduction–oxidation) Disturbances are deﬁned as any relatively discrete potential of a soil from aerobic to anaerobic, drying a wetland and converting it into a dry land system, or event in time that disrupts ecosystem, community or population structure and changes resource, substrate cutting off the input of fossil fuels to a city. (2) availability, or the physical environment (White and Disturbances involving a reduction in the main system Pickett 1985). Peters et al. (2011) sharpened this driver. For example, draining freshwater from an deﬁnition by pointing out two reﬁnements. First, that estuary, diverting water from an agricultural ﬁeld, or the discrete event needs to be deﬁned either based on skimming large quantities of money from an urban the onset, duration, or release of a driver (force) or on economy. (3) Disturbances that affect the energy the time over which a mechanism operates relative to transformers of the system (plants in non-anthro- the lifespan of organisms dominating system behavior. pogenic systems and electric energy producers in Second, is the need to deﬁne the nature of the anthropogenic systems) such as timber harvesting, 123 Biogeochemistry Fig. 8 Model of a wetland ecosystem illustrating ﬁve points of inside the circles on the bottom of the diagram. The severity of interaction between disturbances and ecosystem structure and the disturbance increases numerically from one to ﬁve, and functioning. A number inside the interaction symbol indicates examples of the disturbances are given (from Lugo et al. 1990) the severity of each stressor and the identity of the stressor is defoliation, or excessive herbivory for plants, and with some being extreme while others are not. power failures for electric generation. (4) Distur- Disaggregation implies that for each component of a bances that affect the state variables of the ecosystem. disturbance we need to know its intensity, duration, Examples include the depletion of nutrients by soil area affected, frequency or return interval, type of erosion, harvesting of wildlife, or money or fuel disturbance, and point of interaction with the affected supply in cities. (5) Disturbances with physiological system. We also need information about the affected effects such as droughts, toxic substances, heat, or system. For example, the sector(s) affected, level of ionizing radiation. Table 1 categorizes the main point visible effects, level of delayed effects, ‘‘invisible’’ of interaction of the ten selected extreme events. All effects (if measured), rate of response (positive, ﬁve points of interaction are illustrated. negative or neutral), and any change in the state of The disaggregation of a disturbance event into its the system. Moreover, any one of those parameters component disturbance forces and their coupling to that deﬁne a disturbance and its effects on ecosystems those sectors of ecosystems that interact with each can be the reason for judging the event as extreme; it individual disturbance force improves understanding all depends on their magnitude relative to past events of the effects of the disturbance but complicates the and ecosystem response. deﬁnition of an extreme event. The reason is that what In conclusion, both its characteristics and its effects appears to be an extreme event (say a hurricane) may on exposed ecosystems deﬁne an extreme event. in fact be many interacting events (wind, rain, ﬂoods) Therefore, an extreme event is one in which any of 123 Biogeochemistry Table 1 Criteria used to designate disturbance events as extreme events and the point of interaction of the event with the idealized ecosystem model component of Fig. 8 Event Why it is extreme? Point of interaction Deforestation of the Island* Area affected 3, reduction of state variables (above and belowground) Island-wide sea level rise* Area affected 1, 3, and 5, change in state through salinization, reduction of state variables, and physiological effects of salinity Exposure to ionizing radiation One million times background 5, physiological stress radiation A 300,000-m landslide* Its size 1, change in state (from forest to saprolite) 100-year urban ﬂood Recurrence interval and area ﬂooded 4 and 5, reduction of state variables and physiological stress of anoxic and polluted waters A category 3–4 hurricane Recurrence interval and wind speed 3, reduction of state variables Economic collapse of island Duration and level of economic loss 2, reduction of revenue to the economy ﬁnances* Heat island over San Juan* 90th percentile intensity and 5, physiological stress duration Low-pressure system over San 50-year recurrence and amount of 3 and 4, reduction of state variables and changes in ﬂux Juan rainfall rates Island-wide 1-year ? drought* Duration and area affected 2 and 5, reduction of water input and physiological stress Those events marked with an asterisk (*) behave as ‘‘invisible’’ events until a threshold of detection or effects passes and the event is ‘‘discovered’’ its component forces and their interaction with measurements of the magnitude of its component affected systems has dimensions that exceed the disturbance forces and their effects on ecosystems. known range of variation expected of those parame- ters. A problem with this deﬁnition is that there are insufﬁcient data to deﬁne the known range of variation Disaggregating extreme events of most events as well as insufﬁcient knowledge to identify critical thresholds of response of affected An extreme event, regardless of type (meteorological, systems. We are left with imperfect information to hydrological, geological, social, or experimental), is a make determinations. In Table 1, I list the criteria that complex event with multiple forces and effects. That led me to classify as extreme each of the ten events that complexity has an inﬂuence on how organisms are I analyze in this essay. Two points are notable. First, affected by the event and is revealed when the event is there are no consistent criteria for determining what disaggregated, as suggested by Peters et al. (2011). extreme is, as each event is extreme for a reason When hurricane Hugo passed near the Luquillo particular to the event. Moreover, an extreme event Experimental Forest as a category-3 hurricane its can affect any sector of the ecosystems based on passage had a return probability of 60 year while its Fig. 8. hurricane winds had a return probability of 50 years Second, extreme events can be ‘‘invisible’’ for (Scatena and Larsen 1991). In contrast, the accompa- considerable periods of time, i.e., an extreme event nying rainfall and stream discharge events had return may be in progress without it being detected. Some times of 10 and 31 years, respectively (Scatena and would argue they are ‘‘invisible’’ until they pass an Larsen 1991). Landslides associated with hurricane effects threshold. Such is the case of a drought, a Hugo in turn responded to rainfall intensity and landslide, a heat wave, economic collapse, sea level duration (Larsen and Torres Sa´nchez 1998). There- rise, and deforestation. In all these cases the extreme fore, the ecosystems and their component biota facing nature of the event is revealed after it is in progress by this once in 60-year hurricane event in some cases its effects and responses. Once the effects of an event were facing moderate stream discharges, in other cases are discovered, the determination of whether the event extreme wind conditions, and a relatively frequent it is or not an extreme event will depend on rainfall intensity. These differences in severity 123 Biogeochemistry translate to different effects on organisms and other them. The duration of the selected extreme events ecosystem components. ranges from minutes to centuries, affect areas that For example, the intensity and affected area of the range from hundredths of hectares to almost tens of 400 plus landslides were mostly shallow landslides thousands of hectares (Fig. 9). I grouped those events affecting a limited forest area depending mostly on lasting a year or less as acute events, and those lasting slope, aspect, and proximity to the hurricane track greater than 1 decade as chronic events. All chronic (Larsen and Torres Sanchez 1998). For comparison, events affect large areas. Excluding the radiation the largest landslide associated with hurricane Hugo experiment, there is a signiﬁcant (p \ .05) power 3 2 had a volume of 30,000 m , while the landslide that relation between affected area in km and duration in 0.49 2 resulted from a low-pressure system that I analyzed days (y = 41.2 x ; R = 0.53). was ten times larger and was not associated with a hurricane. Regarding the effects on the biota, studies Energy level revealed that shrimp, walking sticks, frugivore birds, tabonuco trees, and insectivorous predators, in spite of Extreme events also varied in power or dissipated being located in close proximity experienced different energy. The range in power level among extreme levels of disruption by the hurricane (Brokaw et al. events ranged eight orders of magnitude (Fig. 10). The 2012). Levels of disruption varied from slight highest power was associated with hurricane waves (tabonuco trees and shrimp) to severe (walking sticks, and the least with ﬂooding. Notably, hurricane winds frugivore birds), to positive (insectivorous predators). are not as comparatively powerful as one would have A chronic event such as a drought cascades through expected, and the economic collapse, when expressed the landscape as different systems exceed their over the urban area has the same power as 1 m waves. tolerance thresholds and exhibit effects at different This does not mean that they have the same effects times. As it evolves, what appears as one disturbance because they represent different kinds of energy and (drought) becomes many disturbances in relation to interact with different types of systems. The duration affected ecosystems. For example a meteorological of events determined the total energy dissipated over drought, followed by a hydrologic drought, followed affected systems and this estimate changed the order by an agricultural drought, an urban drought, and a of events compared to their power delivery (Fig. 10). forest drought. The reversal of the drought also occurs The range of the absolute energy load of extreme in a cascade of response. As it interacts with different events was 14 orders of magnitude. Chronic events systems, different tolerance thresholds are exceeded such as the economic collapse gained importance and different ecosystem components and processes are relative to the physical events associated with hurri- affected. canes. Low power events with a longer duration Excessive borrowing by the Commonwealth gov- Economic Collapse ernment subsidized the economy and hid the 10-year Drought Deforestation economic downturn that led to bankruptcy. In this case Hurricane Hugo Heat Event Sea Level Rise the disaggregation of an extreme economic event Low Pressure System involves all the actions of government designed to counter the economic decline. Borrowing, annual government budgets, laws and regulation, and gov- 100-yr Flood ernment efﬁciency and ethics are all part of the 0.1 Radiation Experiment complexity associated with economic collapse. Landslide 0.01 Comparison of extreme events Duration of Extreme Event Fig. 9 Relation between the area affected and duration of ten Duration and area affected extreme events that affected Puerto Rico over the last 100 years. Solid circles represent chronic events, open circles are acute In terms of the duration and area affected by the ten events, and the open square represents an acute ionizing events of this study, there is no commonality among radiation experiment Affected Area (km ) Biogeochemistry Fig. 10 Power (blue bars) 1.00E+13 1.00E+12 and absolute load (red bars) 1.00E+11 of extreme events or their 1.00E+10 component disturbance 1.00E+09 forces. These estimates are 1.00E+08 1.00E+07 based on real values 1.00E+06 observed in Puerto Rico 1.00E+05 over the last 100 years 1.00E+04 1.00E+03 1.00E+02 1.00E+01 1.00E+00 1.00E-01 1.00E-02 increased their rank order relative to higher power differential mortality of some species of plants and events with shorter duration (e.g., compare the leach- animals were not severe and were quickly reversed ing power and kinetic energy of 50-year rainfall event with the onset of rains. Thus, such an extreme drought with the landslide). to social and hydrological systems would not qualify as an extreme event for forests. Similarly, an extreme Effects ﬂood event on a neighborhood adapted to ﬂoods would not be considered extreme unless it overwhelms its Being affected or not by an extreme event is haphaz- adaptations to ﬂooding. ard. But when exposed to an extreme event, the effects can be different for social and ecological systems Adaptability (Table 2). In fact, in the case of ﬂoods the ecological system might beneﬁt while the social systems can The level of adaptability to ﬂooding in social systems experience losses in life and property. Economic and to drought in ecological systems determines the collapse beneﬁted some sectors of a social system level required for an event to become an extreme event (banks, ﬁnancial and legal ﬁrms) while most citizens, in terms of effects. This is so because the affected insurance companies, and institutions experience systems have memories (genetic memory in ecolog- losses, and the ecological system experiences no ical systems and cultural memory in social ones) from effects or a positive response to lower intensity of the past that have resulted in adaptation for particular human activity. The effects on exposed systems also levels of intensity and frequency of events that when deﬁne if an event is extreme or not. For example, an they occur might appear extreme for systems without extreme drought for agricultural, social, and hydro- adaptation, but are within the range of functioning for logical systems may not have signiﬁcant effects on those with the adaptations. An ecological example is forests, even though the drought had a low frequency the response of Palicourea riparia, a tree, to high of occurrence. This was evident during the 2015 levels of ionizing radiation. This tree grew faster, drought in Puerto Rico. While there were measurable sprouted, reproduced, established populations, and losses in agriculture and commerce, and proﬁts in the gained dominance closer to the radiation source than service sector of the economy, ecologists had a any other tree species in the tabonuco forest (Jordan difﬁcult time documenting severe effects on forests. 1970; Mercado 1970; Watson 1970). Its genetic make Drought effects such as increased leaf fall and up was pre-adapted to ionizing radiation (Koo and De Power (j/m .s) Absolute Load (j/m ) Biogeochemistry Table 2 Social and ecological effects of ten extreme events that occurred in Puerto Rico over the past 100 years Event Effects Social Ecological Deforestation of the Island A necessity for survival; part of the economic Dramatic changes in species abundances and strategy of the government distribution, emergence of novel forests Island-wide sea level rise Millions lost in property and economic Beach ecosystem affected, changes in coastal opportunity; disruption of vital infrastructure vegetation and animal distribution Exposure of a forest to ionizing No effect Vegetation changed from forest to herbaceous; radiation biomass recovery was slowed; the growth and radiation resistance of Palicourea riparia was a surprise A 300,000-m landslide No effect. However, a similar landslide in an Succession ﬂipped from primary forest to urban setting caused hundreds of lives lost primary succession; a loss of over 500 years of succession 100-year urban ﬂood Loss of property and infrastructure, reduced Increased productivity and nutrient enrichment productivity A category 3–4 hurricane No lives lost, millions of dollars in property Visible and ‘‘invisible’’ effects; positive long- loss term ecological effects Economic collapse of island Potential social chaos and collapse; massive No immediate effect, long-term reduction of ﬁnances human population emigration; disruption of anthropogenic stressors government services; individual and institutional economic loss Heat island over San Juan Lives lost (young and old people); increased Increased respiration energy consumption Low-pressure system over San Life and property loss Increased productivity Juan Island-wide 1-year ? drought Millions of dollars lost in economic activity; Minor effects on vegetation and on some animal enormous inconvenience to people, and species; dramatic change in soil oxygen and alteration of social activities microbial activity of rain forest soils Irizarry 1970; Venator and Koo 1970) and thus gave long-term ecological processes in progress after the species an advantage in post-radiation succession deforestation and land degradation. In this example, (Odum 1970). Examples of memory and adaptability the hurricane can affect the structure of existing in social ecological systems are discussed in Gunder- systems, but the successional development of affected son and Holling (2002). systems continues its slower and long-term response to past deforestation and land degradation (Thompson Recovery et al. 2002). Site degradation (deforestation, landslides) and The recovery from the hurricane required more time in physiological stress (ionizing radiation, extreme ecological than in social systems (Table 3). Social drought) can delay recovery in ecological and agri- systems can concentrate fossil fuel energy and effort to cultural systems. For example, the inﬂux of ionizing repair structures and functions, while ecological radiation had a retarding effect in the post radiation systems must do so with solar energy, which is a biomass accumulation of the tabonuco forest (Lugo diluted energy source, and through time-consuming and Heartsill Scalley 2014). Moreover, some extreme ecological processes such as succession and self- events erase previous ecological systems and pro- organization. The inﬂux of borrowed money during cesses causing a change in ecosystem state or long the developing economic collapse of Puerto Rico recovery time (landslides, volcanic eruption). represented an energy subsidy to help repair or overcome the effects of a reduced economic output. Other extreme events such as hurricanes, do not affect 123 Biogeochemistry Table 3 Time required for recovery after ten extreme events that occurred in Puerto Rico over the past 100 years Event Recovery time Social system Ecological system Deforestation of the Island No visible effect because the economy 100 years; shift to novel systems appears shifted energy sources permanent Island-wide sea level rise 100 years Shift in ecological zones Exposure of a forest to ionizing No effect Probably 100 years, since forest biomass radiation has not recovered after 50 years A 300,000-m landslide No effect 100 years to forest cover and functioning; longer to original structure and composition 100-year urban ﬂood Six months for cleanup and repair; some No visible effects, functions continue communities experience signiﬁcant uninterrupted losses and longer recovery A category 3–4 hurricane Several years 60 years on average Economic collapse of island Decades No visible effect ﬁnances Heat island over San Juan Recovery is rapid, except for those with No visible effects, high respiration rates chronic ailments probably return to normal when the temperature decreases Low-pressure system over San Six months for cleanup and repair; some No visible effects, functions continue Juan communities experience signiﬁcant uninterrupted losses and longer recovery Island-wide 1-year ? drought Over a year to recover lost revenues and No visible effects. Increased leaf drop agricultural production returns to normal within weeks Implications to the study of social and ecological the processes that result in adaptability and innovation systems (see Gunderson and Holling 2002 for underpinning theory). The Anthropocene Epoch represents a challenge to the One of the consequences of the passage of extreme functioning of social and ecological systems because events is the generation of novelty in response to the changing environmental conditions test resilience and extreme conditions that they generate. This was the adaptability of the biotic and non-biotic components case with the emergence of novel forests after massive of those systems. The shifting of environmental deforestation in Puerto Rico (Lugo and Helmer 2004). regimes will also involve shifting disturbance regimes, Soils had been so eroded after deforestation and with some disturbances becoming more extreme in agricultural use that most native tree species could not both their nature and effects. These tendencies require reassemble the original forests. Instead, non-native precise disaggregation of disturbance forces and their tree species colonized degraded sites and over decades effects, with the understanding that these events have contributed to the assembly of forests with novel positive as well as negative effects on social and species combinations that included both native and ecological systems. In fact, extreme events are agents non-native species. An analogous response in social of evolutionary change and innovation by exerting systems is the ﬂood prooﬁng of buildings and infras- strong selective pressure on organisms and on social tructure after extreme ﬂoods, or the passing of laws learning (Fig. 11). Both social and ecological systems and regulations after economic collapse to avoid gain adaptation to changing conditions when natural repeating past ﬁnancial mistakes. Novelty and adapt- selection forces select the most successful alternative ability are linked responses to extreme events that lead solutions for coping with the environment (Fig. 11). to resiliency and survival in social and ecological Extreme environments expose systems to stronger systems. gradients of environmental change and thus accelerate 123 Biogeochemistry Fig. 11 Heuristic schematic of the evolution of solutions to generated. These alternative solutions involve novelty and ﬂooding in a social ecological system (from Mun˜oz-Erickson constitute available choices. The right side of the diagram et al. 2014). The basic social ecological conﬁguration is illustrates the role of adaptability, choice, learning, and selection subjected to extreme ﬂooding events (left side of the diagram). in the development of future adaptable solutions As a result, a variety of alternatives solutions to ﬂooding are Foundation Grant 1444755 to the Urban Resilience to Extreme Conclusions Weather-Related Events Sustainability Research Network. The comparison of different extreme events and how Open Access This article is distributed under the terms of the they interact with social and ecological systems leads Creative Commons Attribution 4.0 International License (http:// creativecommons.org/licenses/by/4.0/), which permits unre- me to three conclusions. First, extreme events are stricted use, distribution, and reproduction in any medium, inherently complex and need to be characterized by provided you give appropriate credit to the original the intensity, frequency, and extent of its component author(s) and the source, provide a link to the Creative Com- driving forces as well as by their distinct effects on mons license, and indicate if changes were made. components of social and ecological systems. Second, the response of social and ecological systems to References extreme events is different and depends on what sectors of those systems are affected by the forces of Baccini P, Brunner PH (2012) Metabolism of the anthropocene, the event and the energy available to overcome the 2nd edn. The MIT Press, Cambridge effects. In some cases, extreme events that affect Brandeis TJ, Turner JA (2013) Puerto Rico’s forests, 2009. 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Biogeochemistry – Springer Journals
Published: Jun 1, 2018
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