Ecosystem services

chapter Fourteen

Ecosystem Services Arnas Palaima

CONTENTS

ation), and supporting (e.g., primary production, soil formation). For instance, we benefit from provisioning services when we catch and eat animals that live and breed in estuaries. Estuaries provide regulating services because they absorb the force of storms in coastal areas and regulate changes in air and water temperature; air temperatures in coastal areas are less variable than inland temperatures. Currently, there are two paradigms for generating ecosystem service assessments that are meant to influence policy decisions. Under the first paradigm, researchers use broadscale assessments of multiple services to extrapolate a few estimates of values, based on habitat types, to entire regions or the entire planet (e.g., Costanza et al. 1997; Troy and Wilson 2006; Turner et al. 2007). Although simple, this “benefits transfer” approach incorrectly assumes that every hectare of a given habitat type is of equal value—regardless of its quality, rarity, spatial configuration, size, proximity to population centers, or the prevailing social practices and values. Furthermore, this approach does not allow for analyses of service provision and changes in value under new conditions. For example, if a wetland is converted to agricultural land, how will this affect the provision of clean drinking water, downstream flooding, climate regulation, and soil fertility? Without information on the impacts of land-use management practices on ecosystem services production, it is impossible to design policies or payment programs that will provide the desired ecosystem services.

Ecosystem-Based Management (EBM) Approach Challenges of Applying EBM to Specific Ecosystems Modeling Suite InVEST Ecosystem Services of Tidal Marshes Ecosystem Services of Tidal Marshes of the San Francisco Bay Estuary Synthesis and Future Directions

E

cosystems generate a range of goods and services important for human well-being, collectively called ecosystem services. Ecosystem services provide economic benefits to society, although humans are not always aware of these benefits. Over the past decade, progress has been made in understanding how ecosystems provide services and how service provision translates into economic value (Millennium Ecosystem Assessment 2005; National Research Council 2005; Daily et al. 2009; Tallis et al. 2009). The Millennium Ecosystem Assessment (MEA), generally regarded as standard guidance on this issue, is a comprehensive report on the status of ecosystems worldwide that was commissioned by United Nations Secretary-General Kofi Annan in 2000. The MEA outlined four categories of ecosystem services: provisioning (e.g., food, freshwater), regulating (e.g., regulation of climate and erosion), cultural (e.g., spiritual values, recre-

 

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In contrast, under the second paradigm for generating policy-relevant ecosystem service assessments, researchers carefully model the production of a single service in a small area with an “ecological production function”—how provision of that service depends on local ecological variables (e.g., Kaiser and Roumasset 2002; Ricketts et al. 2004). Some of these production function approaches also use market prices and nonmarket valuation methods to estimate the economic value of the service and how that value changes under different ecological conditions. Although these methods are superior to the habitat assessment benefits transfer approach, these studies lack both the scope (number of services) and scale (geographic and temporal) to be relevant for most policy questions. What is needed are approaches that combine the rigor of the small-scale studies with the breadth of broadscale assessments (see Boody et al. 2005; Jackson et al. 2005; Antle and Stoorvogel 2006; Chan et al. 2006; Naidoo and Ricketts 2006; Jansson and Colding 2007; Egoh et al. 2008; and Nelson et al. 2008 for some initial attempts).

importance of interactions between many target species or key services and other nontarget species and services; •

acknowledges interconnectedness among systems, such as among air, land, and sea;

•

integrates ecological, social, economic, and institutional perspectives, recognizing their strong interdependences (McLeod et al. 2005).

 

Ecosystem-Based Management (EBM) Approach Growing recognition that single-sector management leads to socially and ecologically harmful “unintended consequences” has motivated the development of ecosystem-based management (EBM), an approach capable of incorporating effects of management on multiple ecosystem services in an integrated systems approach (Christensen et al. 1996; National Research Council 1999; Food and Agriculture Organization 2003; Pikitch et al. 2004; Guerry 2005). The EBM paradigm recognizes that human and ecological well-being are tightly coupled so that sustainability only occurs when it is pursued in both arenas simultaneously (Food and Agriculture Organization 2003). More specifically, EBM •

emphasizes the protection of ecosystem structure, functioning, and key processes;

•

is place-based in focusing on a specific ecosystem and the range of activities affecting it;

•

explicitly accounts for the interconnectedness within systems, recognizing the

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The EBM approach is meant to provide a framework to enable managers to broaden their perspectives and consider the multiple linked consequences of their decisions. What makes for a good EBM approach, in theory, is now well understood (Christensen et al. 1996). Further, the MEA contributed substantially to our understanding of an EBM framework applied at a global scale (Millennium Ecosystem Assessment 2005). Within a year of its completion, findings from the MEA were incorporated into the Convention on Biological Diversity, the Ramsar Convention on Wetlands, and the Convention to Combat Desertification. There are also a few examples of successful application of EBM in specific terrestrial, aquatic, estuarine, and marine settings (Imperial 1999). These successes are evidence that the EBM integrated approach can be practical and operational. Despite the overall success of the MEA at the global scale, we are still left with the grand challenge of bringing useful models and information to bear at local, regional, and national scales, where most decisions are made.

Challenges of Applying EBM to Specific Ecosystems Although there are several cases where people have attempted EBM at subglobal scales (see Imperial 1999 for a review, and MEA subglobal assessments), there have been very few attempts made in a general, consistent way across many sites at the spatial scales and time frames relevant to subglobal decisions. One of the most challenging aspects of such an approach is the application of sound ecological models that define how the structure and function of ecosystems ultimately lead to resulting levels of ecosystem services provided. This challenge is particularly acute with ecosystem functions and ecosystem services that act across ecosystem boundaries (such as nutri-

Conservation and Restoration

ent transport from land to sea) and across scales (Engel et al. 2008). A second major challenge of applying EBM to specific ecosystems centers on generating estimates of the value of ecosystem services, a task that requires linking ecological models with social and economic models to reveal the values people hold for different ecological services (National Research Council 2005). This task is easier for many provisioning services that are traded in markets with observable prices. The same task is especially hard for the many ecosystem services that generate public goods, such as climate regulation or existence value of species, for which there is no market price or other readily available signals of value. Over the past 40 years or so, economists have developed a number of methods and tools for nonmarket valuation that can be applied to estimate the value of ecosystem services (Freeman 2003; National Research Council 2005). Whether for market or nonmarket values, appropriately linking social and economic valuation with ecological production functions is necessary to ensure that values reflect underlying ecological conditions.

Modeling Suite InVEST In general, it has proven difficult to move from general pronouncements about the tremendous benefits nature provides to people to credible, quantitative estimates of ecosystem service values. Spatially explicit values of services across landscapes that might inform land-use and management decisions are still lacking (Balmford et al. 2002; Millennium Ecosystem Assessment 2005). Over the last few years, the Natural Capital Project (which represents efforts of scientists from Stanford University, The Nature Conservancy, and World Wildlife Fund) has developed a new modeling tool (InVEST, for Integrated Valuation of Environmental Services and Trade offs) designed to address the principles of EBM, bringing together credible, useful models based on ecological production functions and economic valuation methods, with the intention of bringing biophysical and economic information about ecosystem services to bear on conservation and natural resource decisions at an appropriate scale (Tallis et al. 2010; for discussion about other modeling tools, see Nelson and Daily 2010). InVEST is a set of computer-based models that (1) clearly reveals relationships among multiple services,

(2) focuses on ecosystem services rather than biophysical processes, (3) is spatially explicit, (4) provides output in both biophysical and economic terms, (5) is scenario driven, and (6) has a tiered approach to deal with data availability and the state of system knowledge. Both EBM (as a paradigm) and InVEST (as a methodology) represent the latest attempt to combine the rigor of small-scale studies with the breadth of broadscale assessments. InVEST is a freely available, open-source product that is designed to inform decisions about natural resource management. Decision makers, from governments to nonprofits to corporations, often manage land for multiple uses and inevitably must evaluate trade-offs among these uses; InVEST’s multiservice, modular design provides an effective tool for evaluating these trade-offs. For example, government agencies could use InVEST to help determine how to manage lands to provide an optimal mix of benefits to people or to help design permitting and mitigation programs that sustain nature’s benefits to society. Conservation organizations could use InVEST to better align their missions to protect biodiversity with activities that improve human livelihoods. Corporations, such as bottling plants, timber companies, and water utilities, could also use InVEST to decide how and where to invest in natural capital to ensure that their supply chains are preserved. The current available InVEST 2.1 package for lands and waters offers models in carbon sequestration, hydropower, water purification, reservoir sedimentation, managed timber production, and crop pollination. For oceans and coasts the package offers models in wave energy, coastal vulnerability, marine fish aquaculture, aesthetic quality, overlap analysis: fisheries-recreation, and habitat risk assessment. It also includes a biodiversity model so that trade-offs between biodiversity and ecosystem services can be assessed (http://www.natural capitalproject.org). Currently, InVEST models run as script tools in the ArcGIS Arc ToolBox environment and require ESRI's ArcGIS software. InVEST is most effectively used within a decision-making process that starts with a series of stakeholder consultations. Through discussion, questions of interest to policy makers, communities, and conservation groups are identified. These questions may concern service delivery on a landscape today and how these services may be affected by new programs, policies, and

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conditions in the future. For questions regarding the future, stakeholders develop “scenarios” to explore the consequences of expected changes on natural resources. These scenarios typically include a map of future land use and land cover, which is a critical input in all InVEST models. Following stakeholder consultations and scenario development, InVEST can estimate the amount and value of ecosystem services that are provided on the current landscape or under future scenarios. InVEST models are spatially explicit, using maps as information sources and producing maps as outputs. InVEST returns results in either biophysical terms (e.g., tons of carbon sequestered) or economic terms (e.g., net present value of that sequestered carbon). The spatial resolution of analyses is also flexible, allowing users to address questions at the local, regional, or global scale. InVEST results can be shared with the stakeholders and decision makers who created the scenarios, to inform upcoming decisions. Using InVEST in an iterative process, these stakeholders may choose to create new scenarios based on the information revealed by the models until suitable solutions for management action are identified. To date, InVEST has been applied in decisionmaking processes at several sites around the world, including the Willamette Basin (Oregon, USA), Oahu (Hawaii, USA), the state of California (USA), Puget Sound (Washington State, USA), the Eastern Arc Mountains (Tanzania), the Upper Yangtze Basin (China), and the Amazon Basin and Northern Andes (South America), as well as at a national level in Ecuador and Colombia (Tallis and Polasky 2009). In addition to application to other ecosystems, InVEST can be effectivelly applied to tidal marshes, contributing to its conservation and restoration efforts.

Ecosystem Services of Tidal Marshes Tidal marshes consist of salt marshes, brackishwater marshes, and tidal freshwater marshes. They are arrayed along a gradient of salinity and vary in terms of the ecosystem services they provide. Ecosystem services of tidal marshes may include (1) habitat and food web support (e.g., high production at the base of the food chain; vascular plants; microphytobenthos; microbial decomposers; benthic and phytal invertebrates; refuge and foraging grounds for small fishes 210

during high water; habitat for wildlife such as birds, mammals, reptiles), (2) buffering against storm wave damage, (3) shoreline stabilization, (4) hydrologic processing (e.g., flood water storage), (5) water quality (e.g., sediment trapping, nutrient cycling, chemical and metal retention, pathogen removal), (6) biodiversity preservation, (7) carbon storage, and (8) socioeconomic services to humans (e.g., aesthetics, natural heritage, ecotourism, education, physiological health) (Peterson et al. 2008; also see Chapter 1, this volume). It has been estimated that tidal marshes provide nearly US$10,000/ha/y of ecosystem services to society (Costanza et al. 1997). Salt marshes, dominated by smooth cordgrass (Spartina alterniflora Loisel), are known for their high levels of primary and secondary production (Daiber 1982; Wiegert and Freeman 1990) and for their role as nursery and feeding grounds for estuarine organisms (Kneib 1997). They are also known for their ability to trap sediment, nutrients, and pollutants (Nixon 1980; DeLaune et al. 1981; Khan and Brush 1994); sequester carbon (Conner et al. 2001); and export organic carbon to estuarine food webs (Peterson et al. 1985; Childers 1994). Less is known regarding ecosystem services of brackish and tidal freshwater marshes. In a review article, Odum (1988) speculated about ecosystem services of salt marshes versus tidal freshwater marshes. He hypothesized that net primary production (NPP) is lower in salt marshes because of stress associated with salinity and sulfides, both of which will increase in response to rising sea level. This hypothesis was supported by measurements of NPP in tidal freshwater marshes that were comparable to or greater than those in saline tidal wetlands (Whigham et al. 1978; Doumlele 1981; Perry and Atkinson 1997). Reduced levels of stressors also result in greater plant diversity in tidal freshwater marshes (Simpson et al. 1983; Odum 1988). Diversity of consumers, invertebrates and fish, is thought to be lower in tidal freshwater marshes than in salt and brackish marshes (Odum 1988), but it is not known how secondary production varies among tidal marshes. Odum hypothesized that organic matter accumulation is higher in tidal freshwater versus salt marshes as a result of greater NPP and reduced decomposition, which is supported by published studies (Bowden 1984; Craft et al. 1988). Finally, he hypothesized that sediment deposition is greater in tidal freshwater marshes


than in salt marshes because of the proximity to riverine sediment inputs and flocculation of suspended sediment by saltwater intrusion during periods of low flow. Paludan and Morris (1999), however, observed that sediment deposition was highest in brackish marshes near the turbidity maximum in the estuary. A range of studies support some of Odum’s hypotheses regarding ecosystem services of salt versus tidal freshwater marshes. For example, some studies show greater organic matter and nitrogen accumulation in tidal freshwater and brackish marshes than in salt marshes (Hatton et al. 1981; Craft et al. 1993; Merrill and Cornwell 2000). Denitrification, another ecosystem service related to waste treatment, is greater in freshwater than saline environments (Seitzinger 1988) and also greater in intertidal than in subtidal sediment (Merrill and Cornwell 2000). Denitrification is strongly coupled to nitrification of ammonium (Jenkins and Kemp 1984), and in saline environments, sulfide inhibits nitrification (Joye and Hollibaugh 1995). When nitrate is not limiting, denitrification is regulated by availability of labile organic carbon (Groffman 1994), which has been shown to vary among salt, brackish, and tidal freshwater marshes. Methanogenesis also is greater in freshwater than saline wetlands (Bartlett et al. 1988; Capone and Kiene 1988; Oremland 1988). Findings of greater biodiversity and carbon sequestration in tidal freshwater marshes of the Altamaha River and other estuaries agree with predictions made by Odum regarding ecosystem services of salt versus tidal freshwater marshes. However, some findings from the Altamaha River estuary suggest that Odum’s predictions regarding ecosystem functions of tidal freshwater and salt marshes may not be correct. For example, there was no difference in aboveground NPP among salt marshes (Spartina alterniflora, 2,840 g/m2/y), brackish marshes (Spartina cynosuroides, 3,080 g/m2/y), and tidal freshwater marshes (giant cutgrass, Zizaniopsis miliacea, 2,490 g/m 2/y) (Schubauer and Hopkinson 1984; Hopkinson 1992), contradicting the hypothesis of greater NPP in tidal freshwater versus salt marshes. Almost no comparisons of ecosystem services of salt, brackish, and tidal freshwater marshes have been made in single estuarine systems using standard methods. Thus, although some of Odum’s hypotheses can be examined using literature data, this typi

cally requires comparing studies done at different times in different estuaries by different investigators using different methods.

Ecosystem Services of Tidal Marshes of the San Francisco Bay Estuary San Francisco Bay Estuary tidal marshes perform a number of functions that can be considered important ecosystem services for humans (Peterson et al. 2008). In terms of habitat (food production and feeding habitat), the tidal marshes maintain high primary productivity due to the Bay’s mediterranean climate (year-round growing season) and high proportion of algal productivity, which leads to efficient energy transfer in the algae-invertebrate-fish food web. It also maintains high fish and shellfish production. In terms of acting as a buffer (wave dissipation and water absorption), the tidal marshes are locally important. The total length of marsh-urban buffer is short, but real estate value is exceptionally high. The San Francisco Bay has most of California’s salt marsh that helps protect homes, industry, highways, and three major airports. The Bay’s tidal marshes are also important for shoreline stabilization and sedimentation to accommodate sea level rise. In terms of hydrological services (floodwater storage), San Francisco Bay tidal marshes and the adjacent estuary are large enough, in comparison with other North America Pacific Southwest tidal marshes, to have a major water storage function. In terms of water quality improvement (sediment, nutrient, and pathogen removal in estuary and ocean waters), the tidal marshes mainly act as sediment traps, accreting much faster than the sea level is rising. In terms of its biodiversity support (including for threatened and endangered species and its resilience to perturbations), the tidal marshes play an extremely important role due to historical loss of more than 90% of original wetlands. Mudflats provide an additional habitat for biodiversity support. The tidal marshes’ carbon storage function is low because of warm year-round climate and semidiurnal mixed tides that favor decomposition. In terms of socioeconomic services (aesthetics, heritage, ecotourism, education, and human health), the tidal marshes have high value due to the highly populated coast. The San Francisco Bay contains hundreds of outdoor coastal recreation sites within the estuarine drainage areas

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that have high value for ecotourism, education, and open space.

Synthesis and Future Directions San Francisco Bay tidal marshes play an important role in the Estuary’s ecosystem services for human society and local economy. The next steps in application of the ecosystem services concept to marsh conservation and restoration would be movement from general pronouncements about the tremendous benefits tidal marshes provide for society toward credible quantitative estimates of ecosystem service values, which can be relatively easy to obtain and interpret, and incorporation of such information into decision-making / business-conducting / consumer-behavior realities. Preferably such estimates of ecosystem service values should be presented in an ecosystembased (EBM) integrated approach that explicitly accounts for the interconnectedness within and among systems, recognizing the importance of interactions among many target species or key services and other nontarget species and services. One such quantitative approach is the recently developed modeling suite InVEST, which is designed to address the principles of EBM, bringing together credible, useful models based on ecological production functions and economic valuation methods, with the intention of bringing biophysical and economic information about ecosystem services to bear on conservation and natural-resource decisions at an appropriate scale. Literature Cited

 

 

 

 

 

 

 

 

 

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