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Broader perspective on ecosystemsustainability: Consequences fordecision makingRoy C. Sidlea,1, William H. Bensonb, John F. Carrigerb, and Toshitaka KamaicaEcosystems Research Division, National Exposure Research Laboratory, US Environmental Protection Agency-ORD, Athens, GA 30605;bGulf Ecology Division, National Health and Environmental Effects Laboratory, US Environmental Protection Agency-ORD, Gulf Breeze, FL32561; and cResearch Center on Landslides, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan

Edited by Stephen R. Carpenter, University of Wisconsin, Madison, WI, and approved April 2, 2013 (received for review February 4, 2013)

Although the concept of ecosystem sustainability has a long-term focus, it is often viewed from a static system perspective. Because mostecosystems are dynamic, we explore sustainability assessments from three additional perspectives: resilient systems; systems where tippingpoints occur; and systems subject to episodic resetting. Whereas foundations of ecosystem resilience originated in ecology, recent discussionshave focused on geophysical attributes, and it is recognized that dynamic system components may not return to their former state followingperturbations. Tipping points emerge when chronic changes (typically anthropogenic, but sometimes natural) push ecosystems to thresholdsthat cause collapse of process and function and may become permanent. Ecosystem resetting occurs when episodic natural disasters breachthresholds with little or no warning, resulting in long-term changes to environmental attributes or ecosystem function. An example ofsustainability assessment of ecosystem goods and services along the Gulf Coast (USA) demonstrates the need to include both the resilient anddynamic nature of biogeomorphic components. Mountain road development in northwest Yunnan, China, makes rivers and related habitatvulnerable to tipping points. Ecosystems reset by natural disasters are also presented, emphasizing the need to understand the magnitudefrequency and interrelationships among major disturbances, as shown by (i) the 2011 Great East Japan Earthquake and resulting tsunami,including how unsustainable urban development exacerbates geodisaster propagation, and (ii) repeated major earthquakes and associatedgeomorphic and vegetation disturbances in Papua New Guinea. Although all of these ecosystem perturbations and shifts are individuallyrecognized, they are not embraced in contemporary sustainable decision making.

ecosystem stressors | complex system behavior | sustainability analysis | cascading effects | coastal zone management

The concept of sustainability increasinglypermeates government, academic, andprivate-sector organizational mantras. Sus-tainability is defined in many ways, but acommon thread lies in its goal of harmo-nizing environmental, economic, and so-cial opportunities for the benefit of presentand future generations (1–4). In ecosystemresearch and management, the underlyingfoundations of environmental sustainabilityare system attributes—biosphere, hydro-sphere, geosphere, and atmosphere, andthe linkages among them. Superimposedon these natural ecosystem attributes is thehuman component, consisting of humansthemselves, their economies, institutions,infrastructures, cultures, and related landuse (5–7).Belief in the balance of nature gave rise

to early ecological concepts such as carry-ing capacity and maximum sustained yield,which view ecosystems as permanent inform and structure that strive to recover toan “equilibrium” state following distur-bances (8–10); thus, much thought andresearch have been invested in incorporat-ing the concept of resilience into sustainabil-ity assessments (11–13). Resilience addressesthe ability of ecosystems to absorb changeand disturbance and adapt to small-scaleperturbations, both in the length of time

it takes to recover from external stressand in the magnitude of stress from whicha system can recover without rapidly movingto a new stable condition (7, 14). Whilemany resilience concepts evolved fromecology (15), resilience has relevance toother ecosystem characteristics, such asthe sustainability of surface water (16–18)and groundwater (19). Although perturbedecosystems and components do not alwaysreturn to the exact state before a distur-bance, there is a recognized bound on thebreadth of resilience (20): if a system isviewed as resilient, it is generally perceivedas remaining within specified “bounds.”While this notion of an essentially finitesystem is accepted even by critics of sus-tainable development (21), the concepts ofpermanent ecosystem change are typicallyabsent from sustainability discussions.Tipping points are encountered one step

beyond ecosystem resilience and representthresholds that, when crossed, result incatastrophic collapse of processes or func-tions that are extremely difficult to restore.These tipping points are closely associatedwith complex system behavior where smalland cumulative anthropogenic and/or nat-ural stressors push ecosystems toward criticaltransitions, causing an abrupt shift from onestate to another (16, 22, 23). Negative tipping

points are applied to projected collapses inecosystems related to climate change (24),climate anomalies (25), and land-use change(26). In most scenarios, protracted dis-turbance or stress causes the system tolose resilience, followed by an abrupt al-teration in state once the tipping point isexceeded (27). Positive tipping points mayoccur when interventions in degraded eco-systems allow processes and populations torecover with the help of human innova-tion (28).A different kind of threshold is crossed

when episodic natural disasters affect eco-systems. These are reached suddenly withlittle or no warning, and the resulting im-pacts on ecosystems can be dramatic andfar-reaching (16). Examples include thedevastating 2011 earthquake-tsunami di-saster in eastern Japan (29); lahars ema-nating from the 1985 volcanic activity atNevado del Ruiz, Colombia (30); climate

Author contributions: R.C.S. conceived the perspective; and R.C.S.,

W.H.B., J.F.C., and T.K. wrote the paper.

The authors declare no conflict of interest.

This article is a PNAS Direct Submission.

1To whom correspondence should be addressed. E-mail: sidle.roy@epa.gov.

This article contains supporting information online at www.pnas.org/

lookup/suppl/doi:10.1073/pnas.1302328110/-/DCSupplemental.

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change-induced glacial dam collapse andjökulhlaups in the Karakoram Himalaya(31); isostatic rebound in the Copper RiverDelta, Alaska, following the Great AlaskaEarthquake of 1964 that caused a seawardshift in the salt marsh (32); and massivelandslides in central China during a majorearthquake in 1920 (33). These were all ex-treme events, but more frequent disasters ofsmaller magnitude can also inflict long-term ecosystem resetting, albeit at smallerscales. Although it is difficult to predict thetiming and areal extent of sudden, episodicdisasters, probabilistic hazard maps, assess-ments, and predictive models can help guidesustainability analysis and thus reduce risk invulnerable regions (34–36). Furthermore,knowledge gained from episodic disasterscan help break down barriers based on pastexperiences and ideas and reframe futuredecisions by noticing and bracketing new ev-idence, working cognitively to elucidate in-terconnected processes, and retaining thisknowledge (37).Because ecosystems are intrinsically linked

to dynamic earth system properties, con-fusion persists about what sustainableecosystems and management practices are.Vulnerability analysis links sustainabilityand the stressors and perturbations that in-teract within resilient ecosystems and theirsocioeconomic counterparts (6, 38), butchallenges to connecting sustainability withepisodic threshold changes remain (10, 16).Given that an inherent tenet of sustainabil-ity is long-term viability of ecosystem func-tion, better focus needs to be placed on thenatural resources that form the backboneof these systems—their spatial and temporalattributes and resilience—and how anthro-pogenic and natural stressors compromisesystem resilience, breach tipping points,and cause episodic change.

Implementing a Broader SustainabilityPerspectiveIncluding sustainability in ecosystem re-search and assessment requires fundamen-tal knowledge of earth system dynamics atappropriate scales to assess future trajecto-ries of rural and community development,food security, disaster mitigation, reclamation,infrastructure, site productivity, hazardouswaste disposal, water use, and contaminanttransport. Once spatial and temporal scalesof sustainability are defined, ecosystemattributes must be carefully articulated. Be-cause sustainability has a long-term focus,ecosystem resilience should be incorporatedinto these attributes (6, 14, 18, 20, 27, 38)(Fig. 1). Chronic agents of ecosystem change,such as soil development, disease, and eco-logical succession, are accommodated byresiliency, as are minor episodic events (e.g.,small earthquakes, floods, wildfires).

In cases where long-term anthropogenicpressures such as forest conversion, wetlanddestruction, overhunting/overfishing, poor

irrigation practices, and overgrazing haveimpacted ecosystems, tipping points in sys-tems may be reached. Chronic disturbancesor changes may exhaust ecosystem resil-ience, leading to a rapid change of state(7, 27, 39). Anthropogenic perturbations canalso lower the initiation threshold for certainnatural disasters (40–42), complicating ex-ceedance thresholds for ecosystem change.Furthermore, when major episodic processesexceed thresholds of resilience, they mayreset ecosystem attributes (16) (Fig. 1). Forexample, sustainable development in citiessuch as San Francisco and Tokyo mustconsider how major earthquakes may altertopography, coastal conditions, and vegeta-tion, and how ecosystem resilience accom-modates chronic changes such as sea-levelrise and vegetation change induced by globalclimate change. This decision making can beimproved by adapting and learning frompast experiences such as natural disasters ormore subtle signs of resilience loss (14, 37).

Dynamic ecosystem attributes also affecthow we assess sustainable management ofrural lands. Widespread conversion of trop-ical forests to cultivated agriculture, planta-tions, pasture, residential developments, andrecreational use has led to increased erosion,water stress, nutrient depletion, and loss ofbiodiversity (43–45). Although chronic eco-system shifts are often the focus of sustain-ability assessments, we need to understandhow land uses exacerbate episodic processessuch as landslides, floods, wildfires, anddroughts that can reshape systems. Severalexamples are presented in the next sectionillustrating how management decisionscould benefit from broader sustainabilityassessments.

Understanding the potential for naturalchange in ecosystems is essential not only tothe environmental “pillar” of sustainabilitybut also to economic and social compo-nents. The natural system, along with eco-nomic and social counterparts, shapes andinfluences the well-being of individuals, so-cieties, and ecosystems, both now and inthe future (2, 10, 14, 46). For individuals,meeting basic needs such as food, shelter,and health maintenance is a prerequisite toeconomic and social well-being. These aremet through adequate access to health care,employment, and education. Well-beingfor ecological systems can be defined usingconcepts similar to those for humans. Thequality and quantity of habitat, includingall facets required for survival, mainte-nance, and proliferation of populations andecological functions, are analogous to hu-man “wealth.” Although nonhuman speciesand their ecological systems are unlikely tobe as aware of their own well-being ashumans, drawing the parallel between well-being of humans and nonhumans recog-nizes interconnections among the natural,economic, and social components of sus-tainability (46). If, for example, a majorpower plant or toxic waste repository is sitedin an area that has potential for episodicsystem change (e.g., major earthquake,flooding), there are strong implications forboth economics and society. More gradualchanges that fall within the resilience ca-pacity of ecosystems may test the limits ofsocietal adaptability and may incur signifi-cant economic costs to cope. A prominentexample of gradual environmental changeis the effect of sea-level rise on coastal eco-systems and communities (47). A socio-economic dilemma is that huge investments

Ecosystem Attributes

• Biosphere• Hydrosphere• Geosphere•Atmosphere

EcosystemResilience

Thresholds

FloodsEarthquakesVolcanos DroughtLandslidesStorm surgesTsunamiIce dam collapse

Natural Re-setting of Ecosystems

Static system sustainability analysis

Broader focus of resilient ecosystem sustainability analysis

Chronic ecosystem change• soil development• climate anomalies and change• weathering processes• succession

Anthropogenic change

Traditional Sustainable Decision-Making

Challenges to Decision-Making

Fig. 1. Ecosystem attributes of sustainability. How assessments and decision making may change with chronicperturbations and episodic resetting.

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continue to be made in increasingly vul-nerable coastal areas when a philosophy ofadaptation should be encouraged instead(48). In such cases, although the ecosystemsthemselves may be resilient, socioeconomicissues are driving the sustainability agenda.

Examples of Improving SustainabilityAnalysis in Different EcosystemsAs noted, most ecosystem sustainabilityassessments are conducted within static or,at best, resilient settings. Few assessmentsconsider the potential for tipping points,such as induced by climate change orland degradation. Even greater challenges tosustainability arise when system thresholdsare exceeded because of natural disasters orepisodic environmental change (16). Exam-ples exist where sustainability assessmentsfor land, coastal, energy, and industrial de-velopment are satisfactory for static orresilient ecosystems but become highlyproblematic when subtle anthropogenic ornatural pressures push systems to tippingpoints or when thresholds are exceededdue to episodic change. Here we presentfour cases where resilience, tipping points, orecosystem resetting should be considered insustainability assessments. Key environmen-tal issues and attributes of each system, alongwith natural and anthropogenic stressors, aredetailed in Table S1 with suggested correctivemeasures that support sustainability.

Cases That Would Benefit from Consid-ering Ecosystem Resilience and TippingPoints. Coastal zone management, Gulf ofMexico. Gulf of Mexico ecosystems are es-sential to regional socioeconomics, and pro-vide a foundation for rare, unique, and valuedfish and wildlife species. Gulf Coast estuariesand wetlands are feeding, spawning, andnursery habitats for a rich assemblage of fishand wildlife, including shorebirds, colonialnesting birds, and migratory waterfowl. How-ever, increasing population pressures in theGulf of Mexico create increased use of anddemands on Gulf resources (Table S1).

Given the variety of ecosystem servicesprovided on the Gulf Coast, including com-mercial and sport fisheries, biodiversity, andrecreation, we must understand how theyinteract with dynamic coastal features. Forexample, barrier islands, wetlands, sloughs,and the coastline itself collectively form anatural defense against landfall hurricanesas well as buffer the coast from floodwatersemanating from rivers (49). These featuresalso provide diverse habitats for an array offish and other marine resources. An impor-tant aspect of this complex system that isoften overlooked in development, manage-ment, and restoration efforts is the transientnature of the biogeomorphic attributes. Al-though delta building is a progressive process(50), once these sites are developed, we tendto view the systems as static and attempt toforce them to prior conditions following

extreme natural events. Similarly, barrier is-lands, beaches, reefs, and mainland shorelinesare naturally dynamic, responding to majorstorms and sea-level rise (51, 52). Anthro-pogenic activities exacerbate coastal systemdynamics, including coastal development;dredging sediments from rivers; enhancedriverine flood flows from development; in-creased nutrient fluxes and oxygen depletion;sea-level rise due to subsidence and climatechange; coastal erosion control structures;and alteration of vegetation (50, 53–56).

Turning a blind eye toward biogeo-morphic processes within coastal systemsposes difficulties in separating anthropo-genic effects from natural phenomena, andcan misguide restoration efforts. As such,there are strong implications for the lu-crative commercial and recreational fishingindustry along the Gulf Coast. A recentreport from a federal advisory group (57)emphasizes balancing ecosystem sustain-ability and resilience with other priorities(e.g., navigation and structural flood con-trol) in restoration efforts. Nevertheless, theseproposed tradeoffs would benefit in the longterm by recognizing natural dynamics ofbarrier islands and coastal features in thiscomplex ecosystem, as well as how suchchanges and resilience can affect fisheriesand other ecological services.

Significant restoration efforts along theGulf Coast have focused on coastal regions ofthe Mississippi Deltaic and Chenier Plains,where wetlands are being lost to the sea. InLouisiana, 4,877 km2 have been lost since the1930s, comprising 80% of US coastal wetlandlosses (58, 59). Land loss in Louisiana hasbeen called a “national emergency,” withup to 4,533 km2 threatened under statusquo management (59). Louisiana wetlandsare significant to the welfare of the UnitedStates—∼80% of Louisiana fisheries speciesuse wetlands for nurseries and 75% offisheries landings in the Gulf of Mexico areadjacent to Louisiana (60). Moreover, in-land flooding from storm surges, exacer-bated by loss of wetlands, swamps, andbarrier islands, threatens property, people,infrastructure, and unique cultural heritages(59). On average, Gulf Coast communitieslose $14 billion annually from storms, whichcould be compounded to $350 billion by in-creased development and land loss (61).

Both natural and human factors have ledto wetland loss in Louisiana (62). Processesidentified in wetland losses range from eu-static sea-level rise and delta construction ordestruction to modifications such as failedreclamation projects, canal construction, andimpoundments (63). Subsidence from natu-ral compaction and restricted sediment inputcaused by levees frequently leads to wetlandloss (62), but debates about the strength ofthe effects of natural and anthropogenicfactors on land-loss rates are ongoing. Loca-tions and time periods with exceedances ofnatural geological subsidence rates might

identify where some anthropogenic stressorshave accelerated wetlands loss (64). A recentstudy found that decadal changes in sub-sidence rates trended with hydrocarbon ex-traction, indicating a historical influence ofthe latter on accelerated loss of wetlands insome areas (65).

Wetland restoration and risk reductionmeasures are being implemented to preventfuture, as well as redress past, losses to humanand wildlife habitat. Management optionsbeing developed and applied in wetlands re-newal and land building initiatives includelarge-scale river diversions, marsh terracing,sediment-slurry additions, plantings, dammodifications, shoreline protection, sedimentfences, and placement of dredged materials(59, 66–68). Major river diversions are criticalto supplying sediment and nutrients, pre-cipitating sulfides, and preventing saltwaterintrusion in coastal wetlands, but requireunderstanding of diverse considerations dur-ing implementation (59, 66). For example,positive and negative ancillary impacts ona range of attributes including eutrophica-tion, hazardous algal blooms, and salinitychanges in estuaries could occur from di-version discharges (60, 66, 68). Restorationdecisions require understanding dynamicsurficial and subsidence processes (63). Saltmarsh areas can reach such a low verticalelevation threshold that management mustfocus on complete rebuilding (69). The ef-fectiveness and uncertainties of land buildingand sustaining projects for keeping pace withsea-level rise, subsidence, and other factorsare being both investigated and questioned.For example, predictive modeling has shownthat sea-level rise and subsidence couldoutpace many of the benefits from sedimentdelivery, especially if river sediment loadsare not restored to levels before damming(70). However, immediate initiation of proj-ects to optimally decrease land loss and/ormove communities away from danger isneeded because of the increased future costs ofdelaying these efforts due to uncertainties (70).

The importance of improving decisionmaking and learning capabilities in theGulf region has spurred recent activitiesby private, federal, state, tribal, local, andnongovernmental entities. The Gulf CoastRestoration Task Force, established byexecutive order to address long-term Gulf-wide restoration beyond the 2010 oil spill,has identified tipping points as one criticallearning need (58). Efforts of a ScienceCoordination Team expanded ideas in thisreport (58) to include additional actionsfor increasing resiliency in habitat typesand coastal communities (71). Focusedwork on coastal sustainability and safetyissues has culminated in the most recentLouisiana Coastal Master Plan (59), whichassesses scientific and value-based needs forland-loss prevention decisions, includingresiliency-related issues (Fig. 2). For deci-sions addressing land losses, considerations

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include ecosystems services (e.g., fisheriesand nature-based tourism), socioeconomicissues (e.g., protecting strategic assets andsignificant cultural sites), and threats to re-siliency (e.g., sea-level rise and invasive spe-cies) (59). Defining variables and criteria thatimpact stakeholders and ecological viability,along with other important factors such ascausal relations and uncertainties, will supportmanagement efforts to achieve desired andavoid undesired outcomes.

Due to the magnitude of the land-losscrisis, improved governance capabilities forderiving, using, and exchanging processknowledge across scales of decision makingis being implemented. The Coastal Protec-tion and Restoration Authority (CPRA) wasestablished to coordinate planning, imple-mentation, and enforcement for restoringand protecting coastal Louisiana (59). De-velopment of CPRA management plans in-volves community stakeholders, industry

representatives, government officials, andexperts. The CPRA organizes teams to im-plement selected projects, including evalu-ating and addressing design considerations,implementation barriers, and regional con-sequences, and develops an adaptive man-agement framework to foster participatorybenefits from collaboration, coordination,and communication (59).

Ensuring resilience in complex environ-ments with multiple stressors requires man-agement that is flexible and responsive tonew information. Elements of structureddecision making can be adapted for highlydynamic environments including frequentlyreexamining objectives, adapting manage-ment actions to changes, and incorporatingmodel uncertainty into predictions (72).Although private and public decision makerswork to prevent shifts from desirable to un-desirable ecosystem states, consideration ofthe dynamic and varied nature of Gulf

Coast ecosystems could improve man-agement in all phases of decisions. Im-proving the decision-making process alsorequires a critical appraisal of the collection,interpretation, use, and communication ofknowledge on ecological and social dy-namics at all scales of governance. In addi-tion to understanding the dynamic nature ofGulf ecosystems, addressing concerns ofcommunity members is essential to makeinformed tradeoffs in large-scale restorationprojects.Episodic erosion related to expansion ofroads, Yunnan, China. Significant increasesin both surface and landslide erosion causedby road construction in the mountains ofnorthwest Yunnan, China, affect not only siteproductivity but also exacerbate sedimentdelivery to rivers (73). Unimproved roads areproliferating in this developing region dueprimarily to economic and tourism pressures(74, 75). This region is home of the ThreeParallel Rivers of Yunnan Protected Areas,designated by the United Nations Educa-tional, Scientific, and Cultural Organization(UNESCO) as a World Heritage site. In thisunique geologic and ecological area, the Jin-sha, Salween, and Mekong Rivers run ap-proximately parallel in deep gorges withinless than a 100-km wide corridor. Sedimentsrouted into the Salween and Mekong Riversand their tributaries eventually flow throughpoorer nations (Myanmar, Thailand, Laos,and Cambodia) that depend on these watersfor fishing, aquaculture, irrigation, and otherlivelihoods. In addition to degrading siteproductivity and water quality, sedimentsimpact aquatic habitat, damage hydropowerfacilities, and transfer pollutants. Excessivesediment deposition in steeper headwatersmay also increase the potential for floodingand catastrophic debris flows (76). The larg-est sediment inputs from mountain roads torivers do not emanate from surface erosionbut from landslides (Fig. 3A). Landslide ero-sion along recently constructed roads in thesemountains varies from about 3,000–48,000Mg·ha−1·y−1 (74), values that dwarf aver-age landslide erosion rates along forestroads in unstable terrain in the northwestUSA (60 Mg·ha−1·y−1), which were suffi-cient to suspend forest-logging operationson federal lands due to concerns overaquatic habitat (40). Surface erosion fromand along these roads, although significant,is typically <10% of the landslide erosion.Oftentimes, >80% of the landslide and sur-face-eroded sediments directly reach streamand river systems (Fig. 3B) (76).

Thus, a more sustainable approach to ruralroad development in Yunnan would be toconsider potential landslides as the primarysediment source and to evaluate alternativesfor road location, construction, and structuraland nonstructural protection against end usesand socioeconomic benefits. Many newlyconstructed roads in northeastern Yunnanare inoperable during wet seasons or require

Socioeconomic Drivers:• Energy supplies•Water supplies• Food security• Housing• Equity• Community bonds & heritage• Income & employment

Environmental Issues:• Hydrodynamics• Land building & preservation• Geological subsidence• Habitat availability• Carbon sequestration• Nitrogen uptake• Fish & wildlife viability

Criteria to avoid tipping points:• Sea level rise/Subsidence/Vertical accretion• Rainfall /Storm patterns/Storm surge depth•Wave & wind erosion• Inundation timing & depth• Sediment/Nutrients delivery & assimilation• Risks from pollutants, invasive species, saltwater intrusion, salinity levels•Marsh collapse threshold• Vegetation structure & function• Barrier shoreline morphology•Wetland morphology

Flood risk assessment

Land building & preservation assessment

Impacts on:• Ecosystem services• Public & private property• Commerce & employment• Human health & safety• Cultural heritage

Socioeconomic tradeoffs:• Operation & maintenance costs• Distribution of risks• Oil & gas infrastructure support• Navigation support• Loss of cultural heritage

Sustainable Management Plan

+ -

Implementation/Adaptive managementOutreach and engagement

Expert knowledge

(science-based, traditional, etc.)

Fig. 2. Sustainability assessment example for land-loss issues in coastal Louisiana (59).

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extensive maintenance to remove landslidesediment, which eventually makes its wayinto rivers. In the worst cases, mountain roadconstruction is abandoned, leaving no accessand a legacy of sedimentation problems.Examples of landslide-related deaths alongthese lightly traveled mountain routes havealready been reported (76). Current de-velopment is paying little attention to roadlocation or construction methods to controlthe mass wasting of rock and soil (40). Thesesecondary roads are typically constructedwith hydraulic shovels, back hoes, or in-discriminate blasting, and the excavatedmaterial is simply disposed of onto slopesbelow the road. Much of the terrain is verysteep (>30°) with few breaks in gradient,and thus once a landslide initiates along aroad there is little chance of sediment en-trapment on the slope. Until urgent attentionis directed toward this problem, local resi-dents and downstream communities will bearthe burden of such unsustainable practices,not to mention damage to fragile terrestrialand aquatic habitats.

This example shows how ecosystems couldbe pushed to tipping points because of poormanagement decisions. Consequences thathave appeared or could develop include (i)extensive road-related landslides and surfaceerosion that progressively strip soil to thepoint where vegetation is altered and habi-tation downslope is unsafe; (ii) degradedwater quality exerting long-term downstreamimpacts; (iii) catastrophic debris flows insediment-laden headwaters; and (iv) impactson livelihoods or economies of downstreamwater users. An effective sustainability as-sessment before extensive road constructionand other land development activities in thismountainous region should include land-slide hazard assessments and analysis ofpotential trigger mechanisms with proba-bility thresholds for different road locationsand construction methods (Fig. 4). Ac-ceptable levels of landslide and surfaceerosion need to be articulated, as well asthresholds that equate to tipping points,

that is, where site productivity, human wel-fare, ecological attributes, or river conditionsare severely impacted in the long term.Management activities (e.g., road build-ing) could be constrained to options thatwould not approach tipping points.

Cases That Would Have Benefited fromConsidering Ecosystem Resetting. Cas-cading effects of linked episodic disastersand urban development, Tohoku, Japan. Thecomplex cascade of damage in the Pacificcoastal region of Tohoku, Japan, was initiallytriggered by the March 11, 2011, Great EastJapan Earthquake. This was the largest earth-quake ever measured in Japan in terms ofgroundmotion,magnitude (M= 9.0), shakingduration, and magnitude and number ofaftershocks. Much of the coastal damage oc-curred when a huge tsunami, with run-upheights exceeding 39 m in some areas, struckwithin 30–40 min of the earthquake (29) (Fig.5A). Even with the most advanced tsunamiwarning system in the world, a large per-centage of the 20,000+ lives lost in this disasterwas directly attributed to tsunami impacts.The tsunami inundated dikes and breakwatersalong the coast, bringing into question theprotective value of such countermeasures fortruly episodic events. On one hand, it can beargued that these countermeasures (althoughbreached) ameliorated the extent of tsunamidamage; on the other, a case can be made that

Fig. 3. Landslides along a road constructed in 2002 in the upper Mekong River basin near Weixi, China, northwestYunnan Province. (A) A large landslide originating in the cutslope of the road killed six people traveling in a minivan. (B)Most of the sediment from the cutslope failure and shallow fillslope landslides directly entered the stream channel,posing a future threat for episodic evacuation. Reproduced with kind permission from Springer Science+BusinessMedia: from ref. 76, figure 2a, Springer Science+Business Media B.V. 2010.

Socioeconomic Drivers:• economic ties to remote villages• hydropower development• tourism• national defense• evacuation routes

Environmental Issues:• landslide susceptibility

• rainfall thresholds• earthquakes

• surface erosion potential• site productivity• water quality/downstream effects

Criteria to avoid tipping points:• levels of landslide & surface erosion• loss of site productivity• water quality/habitat degradation• probability of massive debris flows• risk of human welfare problems

Surface erosion assessment

Landslide assessment• rainfall• earthquakes

Impacts on:•Water quality• Site Productivity• Human welfare• Debris flows•Aquatic habitat

Socioeconomic tradeoffs:• Necessity of the road• Road location/alternate routes• Construction alternatives/costs• Long-term maintenance needs

Sustainable Management Plan

+ -

Fig. 4. Sustainability assessment example in ecosystems of northwestern Yunnan, China, where extensive roadnetworks are being proposed in steep terrain with protected river basins.

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such measures may lead to a false sense ofsecurity for residents and that emphasizingdisaster prevention education is more effec-tive, particularly in a nation where residentsare aware of such hazards (29).

Along with the lives that were lost duringthis composite disaster, extensive infrastruc-ture damage occurred including roads, rail-ways, artificial fills, lifelines, and earthendam collapse, and some 76,000 homes weredestroyed (Fig. 5). Although reinforced con-crete structures mitigated some of the dam-age (77), the combination of earthquake andsubsequent tsunami waves liquefied foun-dation materials and actually toppled manyreinforced structures (Fig. 5C). Associated“natural” disasters affected by the earth-quake/tsunami included fires, landslides, anddebris flows. The largest long-term conse-quence of the disaster is the accident at theFukushima Nuclear Power Plant No. 1. Afterthe earthquake, the two most-affected nu-clear reactors were shut down successfully;however, earthquake damage to the electricalfeeder lines required that backup generatorssupply power to emergency cooling systemsfor the reactors. Within less than 1 h,the backup generators were inundated bythe tsunami surge, causing power loss to thecooling systems. Subsequent actions taken todeal with the system failures resulted in arelease of radioactive material into the en-vironment. The regional deposition of radi-oisotopes may have long-term implicationsfor agricultural production and land usethroughout coastal Fukushima Prefectureand neighboring regions (78). Furthermore,

evidence exists that cesium has penetratedthe bark of Japanese cedar (the most im-portant regional commercial tree species)to the extent that it may have contaminatedwood to be used in housing and furnitureconstruction. The Fukushima governmentis attempting to mitigate economic impactsof the disaster by supporting the localforest industry, thus exacerbating this con-tamination problem.

This catastrophic set of disasters underlinesthe necessity for concurrent hazard analysis insustainability assessments and decision mak-ing. The cumulative cascade of disasters—earthquakes, tsunami, landslides/debris flows,fires, radioactive releases from damagedpower plants—emphasizes the need to baseenvironmental safeguards on joint probabili-ties of the occurrence of multiple, interrelatedhazards in dynamic settings. Siting criteriaand contingency plans for facilities such asnuclear power plants that pose severe envi-ronmental risks if compromised must care-fully consider the range and interaction ofgeohazards. Whereas the vulnerable sub-duction zone off Japan’s east coast is knownfor its earthquake potential, the combinationof episodic effects that occurred on March 11,2011, together with power outages, were notanticipated in the siting and emergencyplanning of the Fukushima power plants.The radioactive releases that followed nowbring into question the need for contin-gency planning that could anticipate suchhuman and environmental exposures (intime and space) and how to proceed withmanaging contaminated areas (79, 80). By

reinterpreting planning and response strat-egies based on experiences gained duringthis multifaceted disaster, decision makerscan learn ways of promoting more sustain-able approaches of mitigating risk (37). Al-though human health must be of paramountconcern, related issues include soil andwater contamination and equitable com-pensation to owners of contaminated areas,as well as science-based decisions on futureland-use trajectories in affected regions. Inhindsight, sustainability assessments in tec-tonically active coastal settings should con-sider such low-frequency, high-magnitudeevents and weigh the risks of siting vul-nerable facilities there. Additionally, assess-ments must evaluate long-term ecosystemchanges that follow uplift, subsidence, coast-line alterations, and sedimentation (81, 82).

In the shadow of the damage caused bytsunami waves, more than 200 residential lotsin Sendai City were impacted (Fig. 5B).Among these, at least 50 residential lots weredamaged by landslides in the urban region,and several hundred houses were destroyedby landslides, all of which were associatedwith artificial landforms, especially valley fills(embankments), created during residentialdevelopment on slopes (83) (Fig. 5B). In-frequent, very large magnitude earthquakes(M ≥ 8) have occurred off the eastern coastof Japan, but smaller major earthquakes(M ≥ 7) have struck much closer to themainland with greater frequency and causedmore severe damage in this urban region. Inparticular, the 1978 Miyagi Prefecture OffShore Earthquake (M = 7.4) disaster was thefirst case of a modern urban complex affectedby a major earthquake (84). Before thisearthquake, Japan had experienced severaldecades of postwar growth (1954–1973) thataffected socioeconomic conditions and in-creased the demand for labor and housing inlarge cities, such as Sendai City. Concur-rently, energy sources evolved from charcoalto fossil fuels, eliminating harvesting of for-ests around the urban area. Even after the1978 earthquake, Sendai City continued toexpand in response to population growth,especially during the bubble economy fromthe mid-1980s through the early 1990s, withlarge numbers of residential lots being con-structed on surrounding hillsides. Crests ofhills were removed and valleys were filled bysoils from cuts and industrial waste. The poorquality of fills and degraded subsurfacewater drainage were major contributors tothe widespread valley fill landslides thatoccurred in the urban region during the2011 earthquake (83). In contrast, smallercities in Japan experienced less populationgrowth, thus precluding the need for ex-tensive fill construction for residential lotson hillsides. As such, the population dy-namics and urban development in theTohoku region during the past half-centurywere reflected in the distribution of urbanlandslides induced by the 2011 earthquake

Fig. 5. Ecosystem impacts and urban/residential damage caused by the March 11, 2011, earthquake (M = 9.0) andtsunami off the east coast of Japan. (A) Tsunami damage and potential ecosystem changes along the coastline northof Sendai (US Navy photo; D. McCord). (B) Homes and roads built on valley fills in Sendai destroyed by slope collapse(valley fill-type landslide). (C ) Overturned reinforced concrete building with a pile foundation in Tohoku Prefecture, anexample of a complex disaster where earthquake shaking liquefied the foundation ground and subsequent tsunamiwaves overcame resistance to pull-out forces.

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(83). Current government relocation ofcoastal communities to inland hillsides isdesigned to provide safe residential/businesssites as well as bolster the devastated localeconomy. However, cuts and fills used toimplement this massive relocation exemplifyhow power relations and mismatches ofinformational flows create a scenario wheregovernment decision makers ignore lessonsfrom past experiences instead of retainingthis knowledge and acting accordingly (37).The disproportional number of landslidesthat occurred in artificial valley fills duringthe 1995 Kobe earthquake further highlightsthe need to avoid residential fills and opt formore sustainable alternatives such as building“contour line cities,” with houses distributedalong topographic contours to reduce thecascading linkage between development andlandslides in hilly urban regions (85).Repeated natural disturbances affecting eco-system structure, Papua New Guinea. Con-tinual natural disturbances (e.g., earthquakes,volcanism, tectonic uplift, landslides) in themountains of Papua New Guinea have cre-ated an ecosystem in a kind of “dynamicequilibrium.” An estimated 8–16% of NewGuinea’s tropical forests are disturbed everycentury by earthquakes and related landslides(86). Earlier studies in a portion of this ter-rain revealed that large single earthquakes in1935 (M = 7.9) and 1970 (M = 7.0) denuded8% and 25% of affected forested areas (130and 60 km2), respectively (87, 88). An addi-tional 3% of the New Guinea landscape isdisturbed by landslides not associated withearthquakes—mostly initiated by the highrainfall (2,500–6,000 mm·y−1) that exhibitsstrong but spatially variable seasonal cycles.Natural episodic disturbances maintain largeareas of successional forest that, in the ab-sence of these disturbances, would even-tually be replaced by other tree species (86).Extraction of natural resources further exacer-bates terrain instability and resultant forestcomposition. Timber harvesting, mining, en-ergy development, and associated infrastruc-ture all affect the stability of steep slopes (40).

Because earthquake-initiated landslides aremore common on steep hillsides and ridge-lines (40), these sites are where vegetation dis-turbance is most prominent. Rainfall-initiatedlandslides typicallyoccuronsteepslopes, aswellas in concave depressions (hollows) whereshallow groundwater concentrates (40), but notalong ridgelines. The ecosystem resetting asso-ciated with these different mechanisms andtopographic features, therefore, should be in-cluded in sustainability assessments.

The juxtaposing forces and influences ofrapid tectonic uplift and denudation by masserosion and other surficial processes areevident in the development of drainagenetworks in this geologically youthful ter-rain. The early phase of rapid tectonic upliftcreates a pre–steady-state evolution of to-pography in Papua New Guinea that can becharacterized by the following sequences in

the Finisterre Mountains: (i) watershed ini-tiation in isolated gorges in terrain withsubdued relief where drainages are createdby dissolution processes and tectonic up-lift dominates erosion; (ii) watershed ex-pansion where mass wasting (landslidescontrolled by groundwater seepage) rap-idly supplies sediment to streams, whichaccelerates channel erosion, lowers valleys,and steepens topography; (iii) tributary ex-pansion by slope-clearing landslides alongvalley sides; and (iv) stream entrenchmentdue to runoff concentration and associatedfluvial incision of landslide scars and de-posits (89). Each unique setting must berecognized in sustainability assessments ofland use in this dynamic terrain, especiallyin how management decisions affect streamchannel morphology, erosion, and sedimenttransport. Treating responses to manage-ment decisions similarly for these dif-ferent geomorphic settings is fraught withproblems.

SummaryEcosystems are impacted by natural andanthropogenic stressors. Resilience in thesesystems accommodates certain levels ofboth stressor types and should be consid-ered to properly frame ecosystem assess-ments. A more difficult issue occurs whenstressors push systems to tipping points,causing a regime shift. Whereas chronicanthropogenic activities such as progressivesoil degradation, land-cover change, and airpollution are often linked to tipping points(25, 39), natural changes can also pushsystems to their limits (16, 24). Recognizingtipping points and implementing strategiesto avoid (in terms of anthropogenic stres-sors) or cope (in the case of natural stres-sors) is a challenge that requires thoroughunderstanding of ecosystem processes andresponses to stressors. Cumulative-effectsanalysis can help separate effects of an-thropogenic activities from those of naturalprocesses and is useful in sustainabilityassessments (90).

The most difficult ecosystems to assess forsustainability are those predisposed to epi-sodic natural disasters—major earthquakes,tsunami, large landslides, widespread wildfire,and volcanic activity—that can reset entiresystems for long periods. Oftentimes, majorevents initiate a cascade of linked disasters, asin the case of the 2011 Great East JapanEarthquake, where tsunami, fires, landslides,fillslope collapses, radioactive releases, andassociated health effects occurred. Such dis-asters are often devastating because lack ofwarning inhibits response, and the infrequentnature of these events precludes the in-corporation of past episodes into contempo-rary decision making (14, 37). Capturing theprobability of ecosystem resetting in sustain-ability assessments is necessary, as evidencedby recent disasters throughout Asia andNorth America.

A paradigm shift is required for us toembrace concepts of sustainability and ex-plore the consequences of decision makingthat affects human and ecosystem integrity.Harmonizing environmental, economic, andsocial opportunities for the benefit of presentand future generations creates an opportu-nity to understand the influence of inherentchemical, geophysical, and social attrib-utes and stressors on human health andecological integrity. It is further recog-nized that whereas underestimating theimpact of certain stressors and relatedexposures may result in contamination oradverse health effects, overestimating thepotential hazards could create an eco-nomic burden on communities. Land-management and regulatory agencies of-ten rely on indicators of sustainability inecosystems (3, 91, 92), but it is importantto understand how anthropogenic andnatural ecosystem processes force changesin system behavior as well as the goodsand services they provide (16, 24, 90).

ACKNOWLEDGMENTS. This document has been re-viewed in accordance with US Environmental Protec-tion Agency policy and is approved for publication.

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