The practice of ecological restoration, firmly grounded in the science of restoration ecology, provides governments, organizations, and landowners a means to halt degradation and restore function and resilience to ecosystems stressed by climate change and other pressures on the natural world. Foundational theory is a critical component of the underlying science, providing valuable insights into restoring ecological systems effectively and understanding why some efforts to restore systems can fail. In turn, on-the-ground restoration projects can help to guide and refine theory, advancing the field and providing new ideas and innovations for practical application.
This new edition of Foundations of Restoration Ecology provides the latest emerging theories and ideas in the science of restoration ecology. Fully one-third longer than the first edition and comprehensive in scope, it has been dramatically updated to reflect new research. Included are new sections devoted to concepts critical to all restoration projects as well as restoration of specific ecosystem processes, including hydrology, nutrient dynamics, and carbon. Also new to this edition are case studies that describe real-life restoration scenarios in North and South America, Europe, and Australia. They highlight supporting theory for restoration application and other details important for assessing the degree of success of restoration projects in a variety of contexts. Lists at the end of each chapter summarize new theory introduced in that chapter and its practical application.
Written by acclaimed researchers in the field, this book provides practitioners as well as graduate and undergraduate students with a solid grounding in the newest advances in ecological science and theory.
|Series:||Science and Practice of Ecological Restoration Series|
|Edition description:||Second Edition|
|Product dimensions:||6.90(w) x 9.90(h) x 1.30(d)|
About the Author
Margaret A. Palmer is a Distinguished University Professor at the University of Maryland, College Park, and Director of the National Socio-Environmental Synthesis Center.
Joy B. Zedler is the Aldo Leopold Professor of Restoration Ecology and Professor of Botany at the University of Wisconsin-Madison.
Donald A. Falk is Associate Professor at the University of Arizona School of Natural Resources and the Environment, with joint appointments at the Laboratory of Tree-Ring Research and the Institute of the Environment.
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Foundations of Restoration Ecology
By Margaret A. Palmer, Joy B. Zedler, Donald A. Falk
ISLAND PRESSCopyright © 2016 Island Press
All rights reserved.
Ecological Theory and Restoration Ecology
Margaret A. Palmer, Joy B. Zedler, and Donald A. Falk
Rather than explaining ecosystem structure and function under a single "unified theory," ecologists deploy a strong and diverse body of theory to address a wide range of ecological problems (Weiner 1995; Pickett et al. 2007; Hastings and Gross 2012). Theories come in many forms — predictive statements, explanatory concepts, and mathematical and computational models (Scheiner and Willig 2011); yet all share a focus on causal explanation. In restoration, theories help to explain historical events, understand current observations, and predict future states. This last application is particularly important because ecosystems, and the task of restoring them, take place in an increasingly altered world (Steffen et al. 2015). Grounded in theory and empiricism from the ecological sciences, restoration ecology provides the science essential to the practice of ecological restoration, which in turn can be used to test those theories in real world contexts (Palmer and Ruhl 2015; Suding et al. 2015).
What Is Restoration Ecology?
Population, community, and ecosystem ecology are well-established branches of ecological science that focus on specific levels of organization, while restoration ecology is much younger and more comprehensive. As "the study of the relationships among organisms and their environment in a restoration context," restoration ecology draws on all branches of ecological science and spans genes to entire landscapes (Falk et al. 2006). The homology with the general definition of ecology is not coincidental; restoration ecology can be thought of as a special domain of ecological research, defined by context. Typically, this context includes a natural system of some kind that has been altered in composition, structure, or function. The central aim of restoration ecology is thus to describe and quantify those departures from a characteristic ecosystem state (including the full range of spatial and temporal variation), understand what drives and regulates them, and then project how the system can be moved back toward a less disturbed state (Hobbs and Suding 2009). Restoration ecology also integrates a number of related disciplines, including hydrology, geomorphology, oceanography, and others, particularly various social science disciplines.
Ecological theories can inform the design, implementation, and assessment of restoration projects that range in area from small sites to watersheds. Conceptual theories tend to be the broadest, such as the theory of evolution by natural selection, or models of macroecology (chaps. 3,15, and 16). Other theories may be specific to a particular type of ecosystem or group of organisms, such as biogeo-chemical cycling, community assembly, or disturbance ecology (Young et al. 2001;chaps. 2, 9, 12, 13). Theories that employ mathematical or statistical models may take the form of simple equations derived from first principles or complex sets of equations drawn from extensive empirical observations. For example, a recent set of theoretical models links a wide range of organism and community traits on the basis of energetics (Schramski et al. 2015). Predictions from models can be very general: for example, that restoring large or well-connected parcels of land will enhance restoration of biodiversity (Tambosi et al. 2014; chap. 4). They can also be specific to a particular time period or ecological system; for example, restoring seagrass in Middle Tampa Bay (FL) to levels observed in the 1950s requires reducing chlorophyll below some threshold (Sherwood et al. 2016), and restoring grasslands benefits from relating plant functional diversity to nutrient cycling and soil carbon (Bach et al. 2012).
Theories provide us with templates and logic paths for predictions. Theories are used to guide the framing of research questions, the design of experiments, collection of data, and ways to organize information to understand the natural world. Theories can be used to explore the impacts of assumptions we might make about ecosystems, and deviation from theories can help inform future research. For all of these reasons theory is fundamental, not only to restoration ecology but to the practice and advancement of ecological restoration.
What is Ecological Restoration?
The Society for Ecological Restoration (SER 2004) defines ecological restoration as, "the process of assisting the recovery of an ecosystem that has been degraded, damaged, or destroyed." Restorationists attempt to move the composition, structure, and dynamics of a damaged system to an ecological state that is within some acceptable limit relative to a less altered and (probably) more sustainable system (Falk 1990; Allen et al. 2002). Informed by the work of Clewell and Aronson (2013), we simplify the SER (2004) framework and attributes of restored systems to define science-based ecological restoration as in Palmer and Ruhl (2015) (table 1–1).
In this simplified framework, features refer to the structural components of an ecosystem. For example, floodplains are a key component of river ecosystems; their connection to the water and land is an aspect of pattern. Similarly, the structure of a forest includes tree size classes and canopy properties; one aspect of its pattern is the spatial distribution of trees on the landscape. Processes (also called functions) include a wide range of dynamic attributes, such as primary production, stream discharge, fire regimes, dispersal and migration, population dynamics, and biogeochemical cycling. Processes vary over time and space, and ideally lead to recovery of a self-sustaining dynamic system that requires less human intervention than during the process of restoration (Beechie et al. 2010).
The framework for defining ecological restoration specifies that it "aims to" recover the properties of an intact system such as species assemblages, food webs, and functional attributes similar to reference systems (chaps. 7, 8, 9, and 11). However, restoration can take decades, and even when a design is science based, unexpected alternative states or incomplete recovery may result (chap. 2). An unexpected outcome is different from knowingly targeting an end state other than full ecosystem recovery and fidelity to an appropriate reference system (Clewell 2000; Egan and Howell 2005). Attempts to reverse environmental degradation that are not ecological restoration include the use of hardscapes or nonnative species to reduce excessive soil erosion and run-off, and other types of engineered systems that cannot be self-sustaining given their design or placement in a highly modified landscape context, such as strip mines, chemically polluted brownfields, or severely eroded sites (Palmer and Ruhl 2015). Other examples of projects with limited objectives (Suding et al. 2015) include maximizing a single ecosystem service, such as stabilizing a steep slope using a monoculture of nonnative, deep-rooted trees (Mao et al. 2012), or postmining reclamation of a formerly forested region to a nonnative grassland (Yeiser et al. 2016). So long as objectives are not too narrowly focused (e.g., on a single social goal), recovering a broad range of ecosystem services is possible and the chances of this may be increased if efforts are invested in maximizing functional biodiversity and associated ecological processes (chap. 3).
A "fully restored" ecosystem is inferred to be self-sustaining and resilient; that is, it has the capacity for recovery from expected change and stress (SER 2004). In cases where landscape-scale processes no longer occur naturally, restoration can compensate for some constraints on self-sustainability by reintroducing the missing process (chaps. 4 and 16). Examples include controlled burning to restore grasslands or forests, and flood pulsing to restore riparian habitat and stream channels. Moreover, invasion by an aggressive nonnative species or an uncharacteristic disturbance may trigger the need for ongoing maintenance (Shaish et al. 2010; Dickson et al. 2014). In such cases, "restoration" sensu stricto may never be finished. It is uncertain whether fully restored ecosystems will be resilient to all future stressors, especially with changing climate and other stressors that occur at a greater rate or magnitude than the system has experienced over recent evolutionary time (chaps. 5, 6, 15, and 17).
The Restoration-Theory Linkage
The acid test of our understanding is not whether we can take ecosystems to bits on paper, however scientifically, but whether we can put them together in practice and make them work. — A. D. Bradshaw (1983)
Restoration ecology and ecological restoration are reciprocal concepts. Ecological theory informs the practice of restoration but the converse is also true: restoration science and practice can contribute to basic ecological theory (Bradshaw 1983; Jordan et al. 1987; Perring et al. 2015). Ecological restoration is especially useful for testing theories associated with understanding the processes that govern ecosystem trajectories (assembly rules, postdisturbance succession, alternative stable states; chaps. 2, 8, and 9). For example, work in Poland showed that restoration of drained fens may result in communities with different levels of plant functional diversity due to the differential effects of competition and habitat filters (Hedberg et al. 2014). This work demonstrated that knowing which filters act in a particular setting is essential to predicting which species or functional groups are likely to dominate (chaps. 3, 6, and 9). Efforts to restore natural fire regimes in forested communities have informed general understanding of fire ecology where disturbance dynamics have been disrupted (Falk et al. 2011; Young et al. 2015). Restoration studies have informed our understanding of the link between biodiversity and habitat heterogeneity or complexity (Bell et al. 1997; Zedler 2000; Palmer et al. 2010; chap. 10). Because restoration scientists work, by definition, in systems that have been disrupted, their observations and experiments have especially informed — and been informed by — theories of the ecology of disturbance (Temperton et al. 2004; Lake 2013; chap. 9).
As Bradshaw's (1983, 1987) famous remark anticipates, the use of restoration research to test theory and challenge dogma has grown dramatically (Young et al. 2005; Zedler et al. 2007). For example, recent work by Ford et al. (2015) showed that the expected trophic cascade effect of restoring a top predator (Kenyan wild dogs that significantly reduced a dominant ungulate herbivore) did not increase tree abundances, even though the herbivores were known to suppress tree abundance and despite a positive correlation between trees and dog abundance. The authors suggest alternative hypotheses including significant time delays in indirect effects and the possibility of a reticulate food web such that, once the dominant herbivore declines, herbivory by other species increases. In a very different type of ecosystem, work by Hamilton et al. (2014) supported ecological theory linking dietary niche breadth to the size structure of a predator population. Fishing pressures selectively removed large sheepshead fish in a California kelp bed, but when the size structure of the fished population was restored, the predator's dietary niche expanded, with implications for urchins, algae, and kelp.
Conducting large-scale experiments that test basic ecological theory while restoring a site simultaneously can advance both the practice and the science of restoration (Zedler and Callaway 2003). For example, a nitrogen-addition experiment coupled with restoration of an endangered tidal marsh plant demonstrated that nutrient levels affected the annual plant's abundance, suggesting that in some instances strategic modification of biogeochemical properties can reinforce species-level responses (Parsons and Zedler 1997). Efforts to reintroduce wildland fire as a keystone ecosystem process have enabled forest scientists to study fire effects on vegetation dynamics, biogeochemical cycling, and carbon sequestration in more detail than would be possible in uncontrolled wildfires (Schoennagel and Nelson 2010). Working on strip-mined areas in Brazil, Silva et al. (2015) showed that nutrient limitation, plant community composition, and microbially mediated biogeochemical reactions interacted to determine soil development, carbon sequestration, and restoration trajectories. Their tests included trait-based, functional ecology theory, which Laughlin (2014) recommended for experimentation in restoration sites to advance both theory and practice.
Ecological theory and contemporary modeling approaches can also be coupled to explore ways to enhance restoration projects. As an example, a recent study by Crandall and Knight (2015) used spatially explicit modeling to explore factors that may weaken the positive feedbacks that often allow exotic species to replace natives. Theory suggests that dominance by exotics is due either to major fitness advantages, or because they create positive feedbacks that benefit conspecifics more than individuals from other species. As the population size of the exotic species increases, self-reinforcing feedbacks may become stronger, making it difficult to eradicate nonnatives (Stevens and Falk 2009; Larkin et al. 2012; Yelenick and D'Antonio 2013). Crandall and Knight's (2015) work suggests that once exotics have become established and dominate a system, it is less likely that the system can be moved back to a native state unless disturbance strongly reduces the fitness of the exotic relative to the native. This theoretical work implies that intervention before an exotic becomes dominant is essential, but in later stages of invasion, experimenting with different disturbance regimes, perhaps implementing them even more frequently than was the case historically, can be productive (e.g., "manipulating disturbance"; chap. 8).
These examples illustrate our fundamental premise: ecological restoration benefits from a strong grounding in theory, while at the same time ecological theory benefits from the unique opportunities to test theory in restoration contexts. Specific examples of this reciprocity are provided throughout this book, covering major areas of ecological theory spanning multiple levels of ecological organization from genetics to whole ecosystems (table 1–2).
Foundations of Restoration Practice
Some view ecological restoration as an art or a skill honed by practice, experience, and tutelage. As we have suggested, ecological theory is a foundation for restoration practice; however, restorationists can also learn from empirical "vernacular" experimentation and traditional ecological knowledge (TEK) (Martinez 2014). Both modes of learning develop over time, based on varying trials (intentionally or otherwise) and selecting approaches that best achieve desired outcomes, informing others of advances and adapting practices to new knowledge. Both approaches also identify "what works" over multiple trials, which can sometimes extend over many years. Together, science-based, experiential, and TEK approaches can guide restoration goals, treatments options, and experimental designs (Rieger et al. 2014). Implementation of the project should be accomplished in an adaptive management framework in which scientific monitoring informs each step of the process, including the need for additional actions to move the restoration project forward (fig. 1–1).
As a general principle, the first step in restoring an ecosystem is to remove or at least reduce causes of degradation so the system can begin to recover on its own via natural processes (Batchelor et al. 2015). Following this, the preferred or lowest-cost approach to the restoration of degraded ecosystems is often to allow them to recover on their own. This approach, sometimes referred to as passive restoration, is based on the premise that natural systems have their own recovery pathways, mechanisms, and timetables, which may not be mirrored in human-driven designs or implementation. In a sense, this approach is a null test of the potential for spontaneous recovery without human intervention. For instance, many forests recover essential attributes following low-severity wildfire, because biota are pre-adapted to such events (Keeley et al. 2011). Healthy stream systems adjust their channel morphology in response to flooding and seasonal variation in streamflow as it interacts with sediment inputs and redistribution; river forms remain dynamically stable if this process is not interfered with by human actions such as building of dams or levees to constrain channels (Wohl et al. 2015). Perhaps the classic example of passive restoration is fisheries management, when populations can recover spontaneously (Hilborn and Ovando 2014) once overfishing or harmful harvest practices are eliminated. Similarly, eradication of nonnative mammalian predators on islands (>800 projects to date) allowed passive recovery of seabird colonies with stable metapopulations on New Zealand islands near source populations (Buxton et al. 2014). Likewise, removal of livestock grazing led to passive recovery of native riparian vegetation in rangelands of the US Central Basin (Hough-Snee et al. 2013), and fencing areas to limit human access resulted in the recovery of Mediterranean coastal dunes (Acosta et al. 2013).
Excerpted from Foundations of Restoration Ecology by Margaret A. Palmer, Joy B. Zedler, Donald A. Falk. Copyright © 2016 Island Press. Excerpted by permission of ISLAND PRESS.
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Table of Contents
ContentsFOREWORD Karen D. Holl,
PART I. Introduction to Restoration and Foundational Concepts,
Chapter 1. Ecological Theory and Restoration Ecology Margaret A. Palmer, Joy B. Zedler, and Donald A. Falk,
Chapter 2. Ecological Dynamics and Ecological Restoration Katharine Suding, Erica Spotswood, Dylan Chapple, Erin Beller, and Katherine Gross,
Chapter 3. Biodiversity as a Goal and Driver of Restoration Shahid Naeem,
Chapter 4. Landscape Ecology and Restoration Processes Jean Paul Metzger and Pedro H. S. Brancalion,
PART II. Ecological Theory and the Restoration of Populations and Communities,
Chapter 5. Population and Ecological Genetics in Restoration Ecology Christopher M. Richards, Donald A. Falk, and Arlee M. Montalvo,
Chapter 6. Ecophysiological Considerations for Restoration Sarah Kimball, Jennifer L. Funk, Darren R. Sandquist, and James R. Ehleringer,
Chapter 7. Implications of Population and Metapopulation Theory for Restoration Science and Practice Joyce Maschinski and Pedro F. Quintana-Ascencio,
Chapter 8. Invasive Species and Restoration Challenges Carla M. D'Antonio, Elizabeth August-Schmidt, and Barbara Fernandez-Going,
Chapter 9. Assembly Theory for Restoring Ecosystem Structure and Functioning: Timing is Everything? Vicky M. Temperton, Annett Baasch, Philipp von Gillhaussen, and Anita Kirmer,
Chapter 10. Heterogeneity Theory and Ecological Restoration Daniel J. Larkin, Gregory L. Bruland, and Joy B. Zedler,
Chapter 11. Food Web Theory and Ecological Restoration M. Jake Vander Zanden, Julian D. Olden, Claudio Gratton, and Tyler D. Tunney,
PART III. Ecosystem Processes and Restoration Ecology,
Chapter 12. Nutrient Dynamics as Determinants and Outcomes of Restoration Sara G. Baer,
Chapter 13. Recovery of Ecosystem Processes: Carbon and Energy Flows in Restored Wetlands, Grasslands, and Forests Erika Marín-Spiotta and Rebecca Ostertag,
Chapter 14. Watershed Processes as Drivers for Aquatic Ecosystem Restoration David Moreno-Mateos and Margaret A. Palmer,
PART IV. The Spatial and Temporal Dimensions of Restoration,
Chapter 15. Evolutionary Restoration Ecology Craig A. Stockwell, Michael T. Kinnison, Andrew P. Hendry, and Jill A. Hamilton,
Chapter 16. Macroecology and the Theory of Island Biogeography: Abundant Utility for Applications in Restoration Ecology Andrew J. Dennhardt, Margaret E. K. Evans, Andrea Dechner, Lindsay E. F. Hunt, and Brian A. Maurer,
Chapter 17. The Influence of Climate Variability and Change on the Science and Practice of Restoration Ecology Donald A. Falk and Constance I. Millar,
PART V. Synthesis and Challenges,
Chapter 18. Persistent and Emerging Themes in the Linkage of Theory to Restoration Practice Margaret A. Palmer,
ABOUT THE EDITORS,
ABOUT THE CONTRIBUTORS,