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The Ecological Basis of Conservation Heterogeneity, Ecosystems, and Biodiversity Edited by S.T.A. Pickett1 R.S. Ostfeld1 M. Shachak1-2 G.E. Likens1 Institute of Ecosystem Studies Mary Flagler Gary Arboretum Millbrook, New York 2 Mitrani Center for Desert Ecology The Jacob Blaustein Institute for Desert Research Ben-Gurion University of the Negev, Sede Boker, Israel E3 CHAPMAN & HALL X \1) I International Thomson Publishing New York • Albany • Bonn • Boston • Cincinnati • Detroit • London • Madrid • Melbourne Mexico City • Pacific Grove • Paris • San Francisco • Singapore • Tokyo • Toronto. • Washington Contents Foreword: Bruce Babbitt Preface x. Contributors XV Participants xix I. Introduction: The Needs for a Comprehensive Conservation Theory 1 1. Defining the Scientific Issues R. S. Ostfeld, S. T. A. Picket!, M. Shachak, and G. E. Likens 2. Part 1. Gretchen Long Glickman—Science, Conservation, Policy, and the Public Part 2. H. Ronald Pulliam—Providing the Scientific Information that Conservation Practitioners Need Part 3. Michael J. Bean—A Policy Perspective on Biodiversity Protection and Ecosystem Management 3 11 16 23 3. Conservation and Human Population Growth: What are the Linkages? Joel E. Cohen 29 4. Developing an Analytical Context for Multispecies Conservation Planning Barry Noon, Kevin McKelvey, and Dennis Murphy 43 5. Operatibnalizing Ecology under a New Paradigm: An African Perspective Kevin H. Rogers 60 vi / The Ecological Basis for Conservation n. Foundations for a Comprehensive Conservation Theory Themes—S. T. A. Pickett, R. S. Ostfeld, M. Shachak, & G. E. Likens 6. The Paradigm Shift hi Ecology and Its Implications for Conservation Peggy L Fiedler, Peter S. White, and Robert A. Leidy 7. The Emerging Role of Patchiness in Conservation Biology John A. Wiens 8. Linking Ecological Understanding and Application: Patchiness in a Dryland System Moshe Shachak and S. T. A. Pickett HI. Biodiversity and Its Ecological Linkages themes—R. S. Ostfeld, S. T. A. Pickett, M. Shachak, & G. E. Likens 9. The Evaluation of Biodiversity as a Target for Conservation M. Philip Nott and Stuart L Pimm 10. Conserving Ecosystem Function Jui3y MMeyer 11. The Relationship between Patchiness and Biodiversity in Terrestrial Systems Lennart Hansson 12. Reevaluating the Use of Models to Predict the Consequences of Habitat Loss and Fragmentation Peter Kareiva, David Skelly, and Mary Ruckelshaus 13. Managing for Heterogeneity and Complexity on Dynamic Landscapes Norman L. Christensen, Jr. 14. Toward a Resolution of Conflicting Paradigms S. L. Tartowski, E. B. Allen, N. E. Barrett, A. R. Berkowitz, R. K. Colwell, P. M. Groffman, J. Harte, H. P. Possingham, C. M. Pringle, D. L Strayer, and C. R. Tracy 15. The Land Ethic of Aldo Leopold A. Carl Leopold TV Toward a New Conservation Theory Slmes-R S. Ostfeld, S. T. A. Pickett, M. Shachak, and 81 83 93 108 123 125 136 146 156 167 187 193 201 G. E. Likens .. 16. The Future of Conservation Biology: What's a Genemst to Do? 202 Kent E. Holsinger and Pati Vttt 10 Conserving Ecosystem Function Judy L. Meyer Summary' Successful conservation efforts require a consideration of ecosystem function. In this chapter, I present seven principles from ecosystem science to serve as a foundation for ecosystem conservation: 1. Ecosystems are open, which should lead to an emphasis on conserving the fluxes across ecosystem boundaries and linkages with surrounding ecosystems. 2. Ecosystems are temporally variable and continuously changing; the present bears the legacies of past disturbances. 3. Ecosystems are spatially heterogeneous on a range of scales, and essential processes depend on that heterogeneity. 4. Indirect effects are the rule rather than the exception in most ecosystems. 5. Ecosystem function depends on its biological structure. 6. Although several species perform the same function in ecosystems, they respond differently to variations in their biotic and abiotic environment, thereby reducing variation hi ecosystem function in a changing environment. 7. Humans are a part of all ecosystems. A river restoration project provides an example of the use of ecosystem principles to design effective conservation strategies; yet we have little experience with the use of measures of ecosystem structure or function to measure the efficacy of conservation efforts. Research is needed to find appropriate metrics and to determine their range in regional reference systems. A critical first step in using such 136 Conserving Ecosystem Function / 137 an approach is to identify and preserve a wide range of ecosystems that could be used for regional references. Unanswered questions remain that limit our ability to use measures of ecosystem structure and function to guide conservation practices. Finding answers to these questions is critical because the public values the goods and services that are a consequence of ecosystem function. Introduction Conservation must consider the ecosystem if it is to be successful. Species networks exist in geologic, hydrologic, climatic, and chemical contexts. The total biological diversity on Earth is in part a consequence of heterogeneity in abiotic features of the planet. For example, the heterogeneity inherent in a stream is a consequence of its geomorphology, hydrology, and chemistry: different plant and animal communities occupy bedrock outcrop versus depositional areas (Huryn and Wallace, 1987); hydrologic regime influences the outcome of food web interactions (Power, 1992); and patterns of nutrient upwelling from the sediments alter the distribution and abundance of algae (Pringle et al., 1988). Without the understanding gained from analysis of the physical and chemical setting as well as the biological and societal context, conservation efforts are doomed. Attempting to conserve a wetland bird species without understanding the wetland's hydrologic regime would be courting failure. To say it as provocatively as possible: conservation will fail if it is the exclusive territory of biologists. Conservation ecology requires expertise from hydrology, geology, geochemistry, meteorology, history, sociology, and other disciplines as well as from the traditional biological sciences. Many other arguments have been offered for why we must manage at the ecosystem scale (Grumbine, 1990). For example, Franklin (1993b) offers two: there are too many species to deal with them individually and the ecosystem approach offers an effective way to conserve poorly known species and habitats (e.g., belowground). Despite the declared need for an ecosystem perspective, ecosystem principles are rarely presented in papers and books dealing with conservation; for example, May's (1994b) discussion of ecological principles relevant to the management of protected areas stopped at the level of communities. Hence I begin by outlining a set of basic ecosystem principles that could serve as a beginning foundation for ecosystem conservation. I explore by example how these principles have been and could be used as a basis for effective conservation efforts and then consider possible measures of ecosystem function that could guide future conservation efforts. My focus hi this chapter is on ecosystem function, what environmental ethicists term the "instrumental value" of nature (producing goods and services of value to humans) (Callicott, 1989). Nature's "intrinsic values" are equally worthy of preservation. 138 / Judy L Meyer Basic Principles From Ecosystem Science What are some principles of ecosystem science on which to base a theory of conservation? • Ecosystems are open to flows of energy, elements, and biota. Application of this principle requires consideration of the fluxes across ecosystem boundaries and identifying linkages with surrounding ecosystems. There are examples of successful management based on this principle. One is the Clean Water Act, which, among other things, regulates the inputs of nutrients into our nation's waters. Although it is far from perfect, in part because it does not adequately cover diffuse fluxes across ecosystem boundaries (i.e., nonpoint sources), this act has had a positive impact on the preservation and improvement of aquatic ecosystems in the United States. There are also situations in which our current conservation policy does not adequately consider fluxes. For example, U.S. Department of Agriculture (USDA) quarantine officials are charged with inspecting material crossing our borders to intercept pests that pose a threat to species of economic importance; as explained to me by a frustrated quarantine officer, there is no mention of ecological or evolutionary importance, only economic. Although we outlaw trade in endangered species, U.S. quarantine officers do not have the authority to block the importation of species that pose a threat to our native flora and fauna. The Wild and Scenic Rivers Act is another example of a conservation action that did not adequately take into account fluxes across boundaries. The act protects reaches of rivers, but does not protect the river above or below the reach of concern or the watershed as a whole. The reach is vulnerable to poor agricultural practices in the headwaters that add nutrients and sediments or to toxic emissions or dams downstream that restrict the migration of anadromous species. This became apparent to conservation groups who had fought hard for protection of rivers under this act, and then found themselves unable to truly protect the river. Hence many adopted an ecosystem perspective to seek solutions that will protect more than just the reach (e.g., Doppelt et al., 1993). • Ecosystems are continuously changing; yet the present bears the legacies of the past. Failure to adequately consider this principle has lead to misguided conservation strategies (e.g., fire exclusion), which have been thoroughly discussed elsewhere (Botkin, 1990; Pickett et al., 1992; Meyer, 1994). Although disturbance is now recognized to be a part of natural ecosystems, human disturbance can not simply be substituted for natural disturbance (Ewel, this volume); logging an old growth forest is not the same disturbance as a lightning-ignited fire. The legacies of past disturbances (e.g., beaver removal; Naiman et al., 1988) Conserving Ecosystem Function / 139 is whatMagnuson (1990) has called the "invisible present." Finding that "invisible present" requires us to look in the past, to do some historical reconstruction, and design our conservation strategy accordingly. I provide an example of that process at work in a river basin later. • Ecosystems are spatially heterogeneous on a range of scales, and ecosystem structure and function depend on that heterogeneity. To a stream ecologist, spatial heterogeneity is an obvious fact of life (e.g., Pringle et al., 1988). The communities of benthic invertebrates and the relative rates of key ecosystem processes like primary production and respiration vary at scales ranging from the landscape to an individual rock on the stream bed. This variability is a function of the geographical setting of the river basin (e.g., Minshall et al., 1983), where you are in the river network (e.g., Naiman et al., 1987, Meyer and Edwards, 1990), the nature of the stream reach (e.g., constrained or unconstrained), and the nature of the substrate (e.g., bedrock versus a pool). This hierarchy of spatial heterogeneity has been well classified, categorized, and used to guide stream research and conservation (Frissell et al., 1986; Hawkins et al., 1993; Rogers, this volume). Critical ecosystem processes depend on it. For example, the nitrogen cycle depends on spatial heterogeneity hi oxygen content: nitrification proceeds in oxygenated environments whereas denitrification occurs where there is little or no oxygen. Elimination of this spatial heterogeneity (e.g., by channelization) alters both structure and function of the riverine ecosystem (Allan, 1995). • Indirect effects are the rule rather than the exception in most ecosystems. The conservation message hi this principle is that disruption of one part of an ecosystem will have broader repercussions. Ecosystems are not assembled at random. They are the product of a long history of interaction (e.g., Thompson, this volume). It is the province of ecologists to assess the strength of those interactions among both biotic and abiotic components of the ecosystem. This principle has been well documented in experimental manipulations of lakes, where alteration of vertebrate predator abundance impacts not only abundance of their zooplanktivorous prey but also abundance of zooplankton and algae as well as lake temperature regime (Mazumber et al., 1990) and sedimentation rates (Pace et al., 1995). Ecologists are most familiar with the importance of indirect effects in species interactions (e.g., Wootton, 1992); yet there can also be indirect effects in elemental cycles. For example, alterations in sulfur deposition can impact phosphorus burial in lake sediments (Caraco et al., 1991), and the presence of deep-burrowing fauna alters the ratio of pyrite to carbon in marine sediments (Giblin et al., 1995). 140 / Judy L. Meyer • The function of an ecosystem depends on its biological structure; species do not have equal effects on ecosystem function; and an organism's size is not a good indicator of its influence on ecosystem function. A recent study in a stream experimentally altered by pesticides offers a striking example of the relationship of function to structure (Wallace et al., in press). Values of an index of macroinvertebrate community structure increased and decreased coincidentally with a measure of ecosystem function (seston concentration, which reflects rate of organic matter processing). The second part of this principle is a restatement of keystone species concept, which has been thoroughly explored elsewhere (e.g., Bond, 1992). The third part is a recognition of our dependence on the microbes of the world for essential functions like nutrient regeneration. The application of this principle by conservationists broadens their focus well beyond the charismatic megafauna. • Although several species perform the same function in ecosystems, they respond differently to variations hi their biotic and abiotic environment, thereby reducing variation in ecosystem function in a changing environment. When lakes were experimentally acidified, primary productivity changed relatively little, despite striking changes in algal species composition (Schindler, 1990). A similar phenomenon has also been observed hi a stream being recolonized after experimental alteration of invertebrate assemblages with pesticides: the same rates of leaf decay were observed despite shifts in the species of invertebrates consuming the leaves (Wallace et al., 1986). In this case, recovery of ecosystem function (rate of leaf decay) occurred more rapidly than did taxonomic recovery. In experimental plots in Costa Rica, the first several species added to the plots greatly altered ecosystem function; but after the first few species, there was little change (Ewel et al., 1991; Vitousek and Hooper, 1992). In all of these examples, one is tempted to view the array of species performing the same function as functionally redundant, but they are not. This becomes apparent when ecosystem function is considered in a longer time frame and in the context of environmental change. For example, zooplankton species that appeared after acidification of a lake were those that had been rare earlier (Frost et al., 1995). They may have appeared to be a small and functionally redundant part of the assemblage of grazers before acidification, but were a dominant member of the assemblage when environmental conditions changed. The conservation message is clear: one goal for conservation is maximization of functional redundancy because that offers the best insurance for maintenance of ecosystem function in a changing environment. The diversity represented by today's rare species relates to future ecosystem function in an environment altered by natural or anthropogenic processes. Conserving Ecosystem Function / 141 • Humans are a part of all ecosystems. Not only have we altered Earth's ecosystems, we are also dependent on them. This is a principle we ecologists have finally assimilated into our research agendas (Lubchenco et al., 1991; Naiman et al., 1995), which acknowledge the impact of human activity on the biosphere and the need to understand its effect Ecologists recognize that we can no longer study pristine environments, for there are none (Vitousek, 1994). This principle is recognized to be of critical importance in conservation ecology (e.g., Meffe and Carroll, 1994). Conservation is essentially management of human activity hi the landscape, so to ignore the societal context for conservation efforts, is to invite failure. The success of conservation efforts often rests on their ability to incorporate indigenous peoples, whether they are tribes in the Amazon or ranchers on the borders of Yellowstone National Park. I offer these as a beginning set of ecosystem principles that can be combined with already elaborated principles from genetics (e.g., Holsinger and Vitt, this volume), population biology (e.g., Nott and Pimm, this volume), and community ecology (e.g., Simberloff, this volume) to broaden the scientific basis for conservation. Applying These Principles To Conservation How might an understanding of ecosystem function be used to design better conservation strategies? I offer an example from a river restoration effort on Knowles Creek in Oregon. This is a project conceived and carried out by Charley Dewberry of the Pacific Rivers Council working with staff from the Siuslaw National Forest and Champion International, a timber products company (Dewberry, 1995, 1996). This project is unique in that their efforts have been directed at understanding and recreating long-term ecosystem processes while recognizing that emergency stopgap measures are necessary hi the short term. Knowles Creek is a tributary of the Siuslaw River, draining the western slopes of the Cascade Mountains. It has populations of coho salmon, chinook salmon, and steelhead and cutthroat trout. The project began with a historical reconstruction: What were the key functional processes hi the basin prior to European invasion? The basin can be divided into valley and upland. Sediments from the uplands collected in hollows, which pulsed the accumulated sediment load into the valley hi debris torrents at about 6,000-year intervals. The debris torrent stopped hi the tributary junction with the mainstem or when it contacted the huge cedars characteristic of the riparian zones of the valley floor. Hence certain sites in the basin were the "geomorphic control points" with extensive flats behind them that provided essential backwater habitat and areas of high aquatic productivity. These areas also helped control stream temperatures by storing large amounts of water 142 / Judy L Meyer in the sediments. But the flats were not permanent features; eventually the debris dams that formed them would be breached, the flat cut down to bedrock, and the material it had held was pulsed downstream to the next flat. When the first European settlers arrived in the 1870s, the basin was recovering from extensive fires of the previous decade, fires that naturally recur every century or two. Because of increased erodability after fires, it is likely that the uplands were supplying considerable sediment to the valley floor at this time. Flooding of the valley floor occurred frequently: a flood triggered by typical June rainstorm in the 1880s would require a 75-year storm today. Logging in the valley floor altered its sediment storage capacity, and the channel downcut rapidly. Logging and roadbuilding in the uplands was intense from 1950 to 1985, delivering two centuries worth of sediments to the channel in a period of 35 years. With reduction in storage capacity of the valley floor, those sediments were lost from the basin and with them was lost essential habitat for salmonids. In this stream, where around 100,000 coho smolts would be expected to migrate to the ocean, only 1,660 did in 1982. So in the 1990s we are left with an upland that has recently lost much of its erodable sediment and a valley floor that has little capacity to store sediment, resulting in loss of productive habitat, accentuated low flows and elevated water temperatures. What conservation/restoration decisions have been made based on this understanding of ecosystem processes? 1. Protect the intact areas to serve as refuges while the basin recovers. 2. Begin the recovery process in the valley floors by replanting cedars, beginning a process that wDl take a century before its full impact will be felt. 3. Manage uplands to reduce likelihood of major debris torrents in the next century. 4. Simulate debris torrent deposits at sites at the geomorphic control points where they would have naturally occurred. This involved a. identifying areas where flats were likely to be formed and would remain at least 50 years, b. spacing the flats so that a couple tributaries could contribute sands and gravel to each, c. choosing sites that would give greatest immediate storage for the least investment in material, and d. choosing sites that posed the least threat to existing roads and bridges. Ten sites were identified. Crews cabled in a few key pieces of downed timber at each site to mimic the huge immovable trees that would previously have provided the structural stability for the deposit, but the rest of the debns was allowed to move and set up again at the next flat downstream. All major flats AA Conserving Ecosystem Function / 143 have been mapped, and all large pieces of wood tagged so their movements can be followed. The number of coho salmon smolt is being monitored, because that was chosen as the biological response variable. The debris dams have functioned as predicted, trapping sediments during a major storm in January 1995 that approached the storm of record hi its magnitude. This project has elements of many of the principles I discussed: it recognizes the openness of ecosystems and linkages between different ecosystems, the temporal variability of important habitat features (the flats), the importance of an historical perspective, the spatial heterogeneity of systems, the importance of productivity of the smallest members of the food web, and incorporation of the human element Using Measures of Ecosystem Function As A Target For Conservation The previous example demonstrates how we can use an understanding of ecosystem function to guide conservation practices. Yet the tough question remains: Can we use measures of ecosystem structure or function as a target for and a way of assessing the efficacy of conservation efforts? The goal is to find measures of ecosystem structure and function with sensitivity, diagnostic capacity, and ability to offer early warning of problems (Nip and de Haes, 1995). Yet there are examples of extremely useful indicators that do not meet all these criteria; for example, atmospheric CO2. Its utility as an indicator has been demonstrated; yet it has little diagnostic capacity. We are still arguing about which human activity causes elevated atmospheric CO2. Finding indicators that meet all these criteria is a challenge that those interested in detecting effects of toxins on ecosystems have been facing for decades. What have they learned? 1. Seek not a single metric. What is needed is a suite of measures that indicate the function of a facet of the ecosystem of concern (Kelly and Harwell, 1990). We are not going to find a single index that will measure the "pulse" of an ecosystem. In our search for measures, it is important to recognize the diversity of ecosystems on the planet and devise measures of local interest so that our management can be particularistic; that is, guided by the peculiarities of the site (Norton, 1992) 2. Consider the structure of the food web as a whole or those portions leading to species of interest, which could be native or endemic species. For example, evidence from a thermally altered river shows the number of links in the food web as the variable showing the greatest change under an altered thermal regime (Ulanowicz, 1992). 3. Look to key geochemical processes. Biological oxygen demand (BOD) has been a useful indicator of threats to stream ecosystems from organic pollution for decades; significant improvement in lakes has been achieved by controlling the supply of phosphorus to the biota. We need additional indicators of system geochemistry because they can tell a manager about the availability of essential 144 / Judy L Meyer elements to species of concern. In the forests of the eastern United States, the nitrogen cycle seems to be a sensitive indicator of change. Nitrate losses have been seen in response to the human disturbance of logging, as well as to the invasion of defoliators such as the gypsy moth or the fall cankerworm (Swank and Crossley, 1988). Nitrogen mineralization is a key process that supplies biologically available nitrogen to the ecosystem. Hence indicators that consider the forms, stocks, or recycling of essential elements such as nitrogen or phosphorus offer promise. 4. Indicators of productivity and physiological or reproductive function in key species provide an early warning of problems. This has been clearly demonstrated in lake acidification research (Schindler, 1990), where, for example, periphyton productivity was a sensitive and early indicator of acidification. The greatest alterations in ecosystems resulted when species without functional analogs in the system were eliminated (Schindler, 1990); these are the species whose productivity and physiology offer the most promise as indicators. 5. Look to the resource base: has there been a shift hi the relative importance of allochthonous versus autochthonous energy resources? In the thermally altered Crystal River, there was a shift from detritivory to herbivory (Ulanowicz, 1992). New techniques of stable isotope analysis offer promise for indicators to detect these kinds of changes: hi streams, delta13C signatures of samples of benthic invertebrates could be used to detect shifts in the relative importance of allochthonous and autochthonous carbon sources (Bunn, 1995). 6. Look to key processes. In streams draining forested catchments, leaf litter decay is a key process. Decades ago, Egglishaw demonstrated the connection between nutrient concentration, fungal degradation of a standard C source, and trout growth (Kelly and Harwell, 1990). Decreases in fungal diversity or activity in a system like this indicates a serious threat to the food web. 7. Look to abiotic regulators of key processes. Temperature is of course the most basic, but hi lakes and streams, measures of water residence time are critical. For example, transient storage zones hi streams (e.g., pools forming behind debris dams, deep gravel beds that exchange water with the surface) alter the length of time water is hi contact with stream sediments, thereby affecting the ability of sediment biota to take up nutrients (D'Angelo et al., 1993). An alteration in volume of transient storage zones caused by changes hi channel structure will eventually be manifested in reduced capability for nutrient uptake and storage. 8. Look to biotic regulators of key processes. Indicators of the condition of some of the "engineer" species (such as beavers, woodpeckers, earthworms and other burrowers; e.g., Lawton and Jones, 1995) offer insight into the future condition of the ecosystem. 9. Look for integrators. Atmospheric CO2 is an example of an indicator that integrates human activity over a broad scale. Similarly, aquatic systems can serve as integrators of management of terrestrial landscapes (Naiman et al., 1995). Conserving Ecosystem Function / 145 Indices of the integrity of the aquatic biota offer tools to assess the cumulative impact of watershed management practices (e.g., Rosenberg and Resh, 1993). 10. Expect the unexpected. Disturbances are a feature of the natural world that cause changes in ecosystems, only some of which we are able to predict. Yet they also offer valuable insight into the mechanisms driving observed patterns. This list is not a primer of measures of ecosystem function that offers useful targets for conservation. We are not yet ready to write that primer. Still needed are further development, testing, and application of measures of ecosystem function that could serve as targets for ecosystem conservation hi a wide range of environments. These will add to the effectiveness of our conservation toolbox. Assuming we add these measures to our toolbox, what numeric values of the measures should management seek to achieve? Here there is a deceptively simple answer: the range of values observed in regional reference systems. A critical first step in taking such an approach is to identify and preserve a wide range of ecosystems that could be used for regional references (Christensen, this volume; Barrett and Barrett, this volume; Thompson, this volume). These ecosystems provide us with the baselines we need for evaluating our compliance with environmental laws and for assessing the efficacy of conservation and restoration efforts. Ecosystems with minimal human impact offer us the moving target we need to design and evaluate restoration and conservation efforts. By referencing our activities to an ever-changing natural system, we are incorporating into our management scheme one of the basic principles presented earlier, the temporal variability of ecosystems. By considering ecosystem function in addition to evolutionary heritage, conservation will also broaden its list of places worthy of protection. Conservation of systems that provide essential ecosystem services will receive increased attention. We may also want to consider conservation of ecosystems with unique functional attributes, because these are places where we are likely to find species with unusual characteristics that could be beneficial to humankind. Extreme environments, such as hot springs, offer a unique environment selecting for unusual functional adaptations; this is an environment that has already yielded products of economic benefit to humans. It would be fruitful to seek out and conserve environments that are likely to select for organisms with unique functional attributes. Unanswered questions remain that limit our ability to use measures of ecosystem structure and function to guide conservation practices. Finding answers to these questions is both intellectually challenging and critical to the success of conservation efforts because the ecosystem goods and services valued by the public are a consequence of ecosystem function. Conservation will enjoy wider public support if we are able to relate conservation efforts to services the public cares about, such as providing clean water, clean air, and productive soils (Harte, this volume). These are the products of conserving ecosystem function.