About the Author
Vicky M. Temperton is plant ecologist at the Max Planck Institute for Biogeochemistry in Jena, Germany.
Richard J. Hobbsis professor of environmental science at Murdoch University in Western Australia.
Tim Nuttleis research fellow at the Institute of Ecology, University of Jena.
Stefan Halleis head of the Institute of Ecology, University of Jena.
Read an Excerpt
Assembly Rules and Restoration Ecology
Bridging the Gap between Theory and Practice
By Vicky M. Temperton, Richard J. Hobbs, Tim Nuttle, Stefan Halle
ISLAND PRESSCopyright © 2004 Island Press
All rights reserved.
Introduction: Why Assembly Rules Are Important to the Field of Restoration Ecology
VICKY M. TEMPERTON, RICHARD J. HOBBS, TIM NUTTLE, MARZIO FATTORINI, AND STEFAN HALLE
How are ecosystems assembled? How do the species that make up a particular biological community arrive in an area, survive, and interact with other species? Why do only some species succeed in particular places? Why are similar assemblages of species seen in different parts of the landscape? These questions are fundamental elements of the science of ecology, and ecologists have been asking questions like these for centuries. This set of questions has been formulated into a search for what have been termed assembly rules: if only certain species can establish and survive in any given area, and if species tend to occur in recognizable and repeatable combinations or temporal sequences, then maybe we can identify a set of rules governing the assembly of ecosystems and communities.
Another group of people have been asking a different set of questions. How do we repair the damage caused to natural and managed ecosystems by overexploitation, misuse, pollution, mining, and so forth? How can we return a biological assemblage to mine-spoil heaps? How can we return a degraded area to a functioning ecosystem that can serve as habitat or perform useful ecosystem services? These are the questions asked by restoration ecologists, who aim to tackle the problems arising from the increasing human use—and misuse—of the planet's ecosystems.
In this book, we work from the premise that these two sets of questions are not really very different; indeed, there is considerable overlap between them. In fact, ecological restoration involves putting lost parts back into a system, and obviously any assembly rules that may exist must be considered to ensure success. Nevertheless, there have been few attempts so far to explore and develop that overlap.
Recent ideas about assembly rules have come primarily from community ecology (for example, Belyea and Lancaster 1999, Weiher and Keddy 1999), but this work has not yet been translated into practical outcomes. This fact is not really surprising, however. If one looks at the history of ecologists' work on constraints to community development, one finds intense debates running from the beginning of the twentieth century up to the present (see Chapter 3), none of which are adequately resolved as yet (Booth and Larson 1999). Two central questions have been at the root of this whole century of debate: How do communities of organisms come to be the way they are, and what are the constraints on membership in a community? Today's ecologists, who are having another shot at these two biggest questions in ecology, can be considered either the perseverant, ever-curious descendants of Darwin, Clements, Gleason, MacArthur, and Wilson, or quixotic adventurers trying to tame a windmill, as the complexity of nature has notoriously evaded simple description. Whatever your opinion, the questions are still there, and we need the answers. These answers are becoming more and more important in a world dominated and transformed by humanity, in which the understanding and repair of damaged ecosystems will be essential to our future survival (Hobbs and Harris 2001). Given that ecological restoration, as defined by the Society for Ecological Restoration International (SERI), is an intentional activity that initiates or accelerates the recovery of an ecosystem, it seems almost essential to consider possible rules or principles that can guide how components should be added to an ecosystem.
The concepts of succession and assembly rules are related, and yet there are important distinctions between the two (Young et al. 2001). One of the main distinctions is focus. Succession follows the dynamics of changes in a community's development, often with particular reference to an endpoint or deviations from this endpoint (climax). Assembly theory and the search for assembly rules focuses more on interactions among organisms within a community and the actual pathways a community can take in response to such interactions. Ecologists seek the mechanisms behind organism assemblages in different situations. This approach is directly relevant to ecological restoration, in which one seeks to guide an ecosystem toward a specific stable state after a disturbance. Lockwood (1997) and Young (2000) suggested that assembly and succession are the core concepts in restoration ecology. Yet very little overt attention has been paid to this suggestion, either in the scientific literature or in practical restoration. In this book, we aim to fill this gap and to provide an introduction, overview, and synthesis of the potential role of assembly rules in restoration ecology.
Themes to be Explored
Ecologists have worked on ecological assembly and assembly rules in a number of different ways, and a comparison of the current approaches is provided in Chapter 3. Certain aspects of the ecological debate about assembly rules have recently attracted increasing attention. One of these issues involves abiotic and biotic filters through which species or organisms trying to enter a community must pass in order to arrive, establish themselves, and survive there (Keddy 1992). How do these filters act and interact, and how do they change over time, especially as a system regenerates? Are they inextricably linked, or do the abiotic environmental conditions of an ecosystem act separately from the biotic interactions? This is one of the central issues addressed in this book (see Part II: "Ecological Filters as a Form of Assembly Rule"). A critique of the filter concept is provided in Chapter 7.
Another main theme of this book is a question of level of abstraction: Are assembly rules constraints imposed by interactions among organisms alone, or does the sum of the interactions between organisms and their environment limit membership to certain species only? In other words, do assembly rules include abiotic effects and biotic effects, or do the abiotic conditions form a backdrop against which biotic interactions form the "real" rules of assembly? (See Chapter 7.) There are two schools of thought among ecologists on this issue (see Chapter 3), and we have deliberately included proponents from both sides of the debate in this book.
Another important issue is that of disturbance. Disturbance produces change, such as alterations in the availability of resources, and provides opportunities to organisms. It is increasingly being seen as a positive (as well as a negative) force that is necessary to many species in ecosystems (Pickett and White 1985, White and Jentsch 2001). Disturbance, of course, is also an integral part of restoration ecology. It has not generally been considered much in the assembly rules debate, just as the dynamics of assembly rules over time have generally been neglected until now (see Chapter 3). Disturbance and assembly are strongly related, of course, since the disturbance regime of an ecosystem exists over a period of time and affects assembly of the community differently at different times. Thus, the role disturbance plays in assembly needs to be an integral part of the search for generality in the assembly of communities and ecosystems. This issue is addressed primarily in Part V, "Disturbance and Assembly."
The idea of thresholds (Hobbs and Norton 1996) between alternative stable states of a system is the final theme woven into the book. If a threshold divides different stable equilibria, then ecosystem restoration aims to allow a system to overcome this threshold when it cannot be overcome without intervention. It is important to know what intensity, frequency, and quality of disturbance might be necessary to achieve the desired goal, and to what extent the ecosystem requires a helping hand in returning to or reaching a desired stable state. Knowing more about how disturbance relates to such system thresholds can help us move forward and improve our restoration of ecosystems.
This book is unique in that it attempts to develop ideas arising from theoretical and empirical community ecology and places them in a practical restoration context. All too often, restoration and conservation management practice lags well behind current developments in theoretical ecology and related fields; hence, this book attempts to bring current ideas to the forefront and interpret them from a restoration perspective. In this regard, this book is a combination of theoretical and empirical research on ecological assembly with an attempt to use the concepts and findings arising from the research reviewed herein to guide future restoration efforts. Thus, rather than being a restorationists' handbook, this book is a summary of the current status of an emerging field and will be of immediate use to practitioners. We hope that it will be used widely to develop the ideas further and apply them in a wider array of ecosystems and situations.
We wrote this book for academic restoration ecologists and restoration practitioners, particularly those employed by government agencies, nongovernmental organizations (NGOs), and others who have supervisory roles in restoration projects. We assume that the reader will already have some understanding of the concepts and practice of restoration ecology, although these will be summarized or referenced as necessary. The book may be attractive as a text for university courses in restoration ecology and professional training courses. It also may be useful as a supplemental text in more basic ecology courses.
How This Book Is Organized
What follows is an overview of the book's structure. After this introductory chapter, which outlines why the subject of ecological assembly is inherently related to the subject of restoration ecology, the book is divided into five parts.
In Part I, "Assembly Rules and the Search for a Conceptual Framework for Restoration Ecology," we examine the theoretical background for ecological assembly rules and how this background might be relevant to ecological restoration. The discipline of restoration ecology aims to provide a scientifically sound basis for the recovery of degraded ecosystems and to produce self-sustaining systems. However, despite some recent attempts to consolidate the scientific theory (Hobbs and Norton 1996, Urbanska et al. 1997; also see Chapter 3), we are still far from achieving a conceptual framework in restoration ecology. Part I includes one provocative contribution on restoration ecology (Chapter 2) and two reviews of the current status of assembly rules research and its relevance to restoration ecology (Chapters 3 and 4). The search for assembly rules in ecosystems has taken on many different forms and has involved a number of quite different approaches. One of these approaches looks at the constraints on species membership in a community in terms of a filtering out of those species unable to establish themselves (under the conditions reigning in that community).
Part II, "Ecological Filters as a Form of Assembly Rule," explores different facets of this approach to assembly and its relevance to restoration ecology. The composition of a biotic community in any particular place arises because of the action of a number of biotic and abiotic filters on the arrival and survival of species. How can an understanding of such filters help in restoration? For instance, can filters be modified to speed up restoration? Part II explores the idea in three chapters that bring together important aspects of filters in relation to ecology and restoration science. Chapter 5 deals with ecological filters as gradients in resistance to restoration. Chapter 6 proposes a dynamic filter model that could be implemented at the beginning of restoration projects to assess the current status of an ecosystem. Chapter 7 is a critique of the ecological filters approach and a plea to consider systems approaches to assembly and restoration as well.
An important aspect of ecological communities is how they are structured and how we as humans perceive this structure. Part III, "Assembly Rules and Community Structure," looks at various methods and approaches in elucidating community structure and their potential relevance to restoration ecology projects. At what level of abstraction should one look for assembly rules in a community? Are species, functional groups, or other levels of organization most fruitful in, for example, plankton communities (Chapter 8)? Do consumer guilds in a regenerating grassland follow specific rules that might provide a potential guide in restoration efforts (Chapter 9)? Chapter 10 explores a group of organisms—arbuscular mycorrhizae-that fails to be simply categorized into species units and yet forms an indispensable contribution to the recovery of ecosystems. Chapter 11 provides a model of how plant community structure responds to disturbance. Chapter 12 examines how stable isotopes may be useful to investigate food web development in regenerating ecosystems.
When restoration practitioners are faced with restoring a severely disturbed or degraded ecosystem, any knowledge of rules or guidelines applicable to ecosystem assembly will be welcomed. A critical question, however, is whether such severe environments are governed by the same rules as govern natural or seminatural environments. Do such environments require specific, concerted actions when guiding reassembly of ecological communities?
Part IV, "Assembly Rules in Severely Disturbed Environments," presents a series of examples from a variety of ecosystems that are in the process of regenerating after considerable human disturbance, such as mining or severe air pollution. What can we learn from these systems that will be relevant when we come to assemble ecosystems in a restoration context? The focus here is on the dynamics of the systems over time and on how different organism groups play essential roles at various steps in the regeneration process. Systems that have been reduced to a handful of species through severe disturbance form an excellent opportunity to investigate invasion and the reassembly of a system.
Restoration efforts are often directed at areas that have been severely disturbed or impacted by mining activity, pollution, or other highly disruptive activities. The physical and chemical properties of these sites often impose severe limitations on the ability of biota to recolonize. This section examines the recolonization process on such sites (Chapters 13 and 15) and how it is affected by manipulations of various sorts (Chapter 14), from which we can gain important insights into both intrinsic colonization processes and restoration methods. Chapter 16 reviews the importance of nutrients and ecosystem function in the assembly and restoration of ecosystems.
Finally, in Part V, "Disturbance and Assembly," disturbance as a driver of change in ecological communities is explored in relation to its role in assembly as well as in ecological restoration. Disturbances such as fires and storms are natural parts of many ecosystems, and ecosystem reassembly following such events is an important process. Increasingly, humans are altering disturbance regimes with respect to frequency, intensity, and type of disturbance. Chapter 17 explores the relationship among disturbance, succession, and community assembly. Chapters 18 and 19 take a look at disturbance in different zones of rivers and how it relates to community assembly and restoration of rivers. Most ecosystems in need of restoration have been disturbed beyond the point where they can reassemble unaided. However, targeted disturbances at definite phases of natural succession may be just the tool needed in restoration management. In the case of rivers, this may involve restoration of disturbance regimes via restoration of natural flooding regimes. Hence, this section examines what we can learn from examining ecosystem response to disturbances, which can be of benefit when we aim to assist the assembly process.
Excerpted from Assembly Rules and Restoration Ecology by Vicky M. Temperton, Richard J. Hobbs, Tim Nuttle, Stefan Halle. Copyright © 2004 Island Press. Excerpted by permission of ISLAND PRESS.
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Table of Contents
ContentsABOUT ISLAND PRESS,
ABOUT THE SOCIETY FOR ECOLOGICAL RESTORATION INTERNATIONAL,
Chapter 1 - Introduction: Why Assembly Rules Are Important to the Field of Restoration Ecology,
PART ONE - Assembly Rules and the Search for a Conceptual Framework for Restoration Ecology,
Chapter 2 - Advances in Restoration Ecology: Insights from Aquatic and Terrestrial Ecosystems,
Chapter 3 - The Search for Ecological Assembly Rules and Its Relevance to Restoration Ecology,
Chapter 4 - Assembly Models and the Practice of Restoration,
PART TWO - Ecological Filters as a Form of Assembly Rule,
Chapter 5 - Ecological Filters, Thresholds, and Gradients in Resistance to Ecosystem Reassembly,
Chapter 6 - The Dynamic Environmental Filter Model: How Do Filtering Effects Change in Assembling Communities after Disturbance?,
Chapter 7 - Beyond Ecological Filters: Feedback Networks in the Assembly and Restoration of Community Structure,
PART THREE - Assembly Rules and Community Structure,
Chapter 8 - Self-Organization of Plankton Communities: A Test of Freshwater Restoration,
Chapter 9 - Functional Group Interaction Patterns Across Trophic Levels in a Regenerating and a Seminatural Grassland,
Chapter 10 - Structure, Dynamics, and Restoration of Plant Communities: Do Arbuscular Mycorrhizae Matter?,
Chapter 11 - Modeling of Plant Community Assembly in Relation to Deterministic and Stochastic Processes,
Chapter 12 - Application of Stable Nitrogen Isotopes to Investigate Food-Web Development in Regenerating Ecosystems,
PART FOUR - Assembly Rules in Severely Degraded Environments,
Chapter 13 - The Roles of Seed Dispersal Ability and Seedling Salt Tolerance in Community Assembly of a Severely Degraded Site,
Chapter 14 - Order of Arrival and Availability of Safe Sites: An Example of Their Importance for Plant Community Assembly in Stressed Ecosystems,
Chapter 15 - Are Assembly Rules Apparent in the Regeneration of a Former Uranium Mining Site?,
Chapter 16 - The Role of Nutrients and the Importance of Function in the Assembly of Ecosystems,
PART FIVE - Disturbance and Assembly,
Chapter 17 - Disturbance, Succession, and Community Assembly in Terrestrial Plant Communities,
Chapter 18 - Disturbance, Assembly Rules, and Benthic Communities in Running Waters: A Review and Some Implications for Restoration Projects,
Chapter 19 - How Structure Controls Assembly in the Hyporheic Zone of Rivers and Streams: Colmation as a Disturbance,
Chapter 20 - Assembly Rules and Ecosystem Restoration: Where to from Here?,
ABOUT THE CONTRIBUTORS,
Island Press Board of Directors,