Ecological Restoration

Transcription

1 Ecological Restoration Introduction So far in this course we ve focused on conservation in the sense of preventing extinction of individual species or preventing degradation of habitats or ecosystems. We haven t considered how we might go about restoring systems that have been degraded, or at least we haven t talked about it except in the context of re-introducing individuals of endangered species to the wild. Well, that s not entirely true. When we talked about Pleistocene rewilding as an example of how to set a target for managing an ecosystem, we were implicitly considering the possibility of restoring large predators to ecosystems from which they had long been absent. Here we ll focus a little more specifically on the issues surrounding ecological restoration. Assisted migration Before we get started with ecological restoration per se, I want to mention a related topic assisted migration. 1 Assisted migration is the purposeful movement of species to facilitate or mimic natural range expansion, as a direct management response to climate change [7]. Those who argue that assisted migration is necessary point out that the pace of climate change is much faster than many plant and animal species may be able to adapt to and that many species will be unable to migrate rapidly enough to new areas that match their climate tolerances. They argue that if we want to prevent extinction of those species, we have no choice but to move them to places where future conditions will allow them to persist. It shouldn t come as a surprise that the suggestion is controversial. Ricciardi and Simberloff [3], for example, argue that assisted migration is likely to have many unpredictable consequences. They argue that conservation biologists have not yet developed a sufficient understanding of the impacts of introduced species to make informed decisions regarding species translocations. 1 Also known as managed relocation. c Kent E. Holsinger

2 The issues are ones we ve encountered repeatedly by now. The logic of the argument on each side is similar to those in favor of biological control and those opposed. There are risks associated with every conservation decision we make, and we can t avoid risk by not making a decision, because even deciding to not to decide is a decision. Vitt et al. [7] argue that the risks associated with loss of species identified for assisted migration efforts are greater than the risks associated with introduction of those species into to new areas. 2 Ricciardi and Simberloff weight the risks differently. Ricciardi and Simberloff are right that accurate risk assessment is very difficult, but isn t that as true of the risks associated with extinction of the species being considered for translocation as it is with their introduction elsewhere? You know what my conclusion is going to be. There isn t a scientific resolution to this controversy. The resolution depends on how much you value persistence of species that might be lost without intervention versus qualities of the system into which they might be introduced that could be threatened. In neither case do we have good data on the costs and benefits. The choice will be made based on intuition, and different people will have different intuitions. If you see a different way to resolve the controversy, I d be delighted to hear it, but I think assisted migration is merely a more extreme case of the challenge conservation biologists always face: making a recommendation for action on the basis of incomplete and uncertain data. Sandler [5] reaches more or less the same conclusion, but he s a philosopher. He not only recognizes that the ethical underpinnings of the case for assisted colonization are claims about the value of species, he evaluates those value claims. We ll return to the types of value he considers at the end of the course. 3 For now, it s enough to note his conclusion: that The vast majority of species, including several that have been proposed as candidates for assisted colonization, have much less value than is often presumed. He concludes that assisted colonization should have a very minor role in ecosystem restoration projects. Fair enough? But what about projects designed to prevent extinction of particular species of concern? Would the values he identifies still lead to the same conclusion? The approach that Richardson et al. [4] describe suggests that there might be instances where assisted migration makes sense in the context of a single-species conservation program even if it rarely makes sense as part of an ecosystem restoration project. The Managed Relocation Working Group recently recommended that government agencies and nongovernmental conservation organizations develop detailed policies on managed relocations [6]. They recommend that such policies address four sets of questions: 4 2 In the interest of full disclosure I should point out that Pati Vitt got her Ph.D. with me in He considers ecological, instrumental (including option), existence, and intrinsic values. 4 Notice that the questions explicitly include ethical, legal, and policy questions as well as ecological questions. The list of ethical, legal, and policy issues doesn t include the full list from the paper, only a couple. The full list of ecological and integrated questions is included. 2

3 1. Ethical questions: What are the goals of conservation, and why do we value those goals? Which conservation goals take ethical precedence over others and why? 2. Legal and policy questions: Do existing laws and policies enable appropriate managed relocation actions? Do existing laws and policies inhibit inappropriate managed relocation actions? 3. Ecological questions: To what extent do local adaptation, altered biotic interactions, no-analog climate space, and the persistence of suitable microhabitats within largely unsuitable landscapes mitigate the extinction risk (and managed relocation need) of species listed as vulnerable? What evidence suggests that species are absent from climatically suitable locations because of dispersal limitations that could be addressed by managed relocation? What are the limits of less dramatic alternatives to managed relocation, such as increasing habitat connectivity? How well can we predict when management must address interacting suites of species rather than single species? How well can we predict when relocated species will negatively affect host system species or ecosystem functioning (e.g., nutrient flux through food webs, or movement of individuals)? How well can we predict the likelihood of a species successful long-term establishment in light of a changing climate? 4. Integrated questions: What are the priority taxa, ecosystem functions, and human benefits for which we would consider invoking managed relocation? What evidence of threat (extinction risk, loss of function, loss of benefit to people) triggers the decision process? What is adequate evidence that alternatives to managed relocation are unavailable and that the probability that managed relocation will succeed is adequate? What constitutes an acceptable risk of harm and what are adequate assurances for the protection of recipient ecosystems? Who is empowered to conduct managed relocation, and what is their responsibility in the event that the consequences are not those predicted? 3

4 Implementing a restoration project Even before I start, I m sure you can anticipate a couple of the points I m going to make. A restoration effort may be directed at introducing or re-introducing an endangered species or some other species of conservation interest, at restoring the species composition of a community to some desired state, at restoring ecosystem services that have been degraded (e.g., soil retention, water filtration), or at restoring structural characeristics of a particular habitat or ecoystem. Implicit in the idea of restoration is the idea that a system has been degraded in some sense. That means that we must have some idea of what we want the system to look like, some goal we are trying to accomplish. So first we return to the problem we just finished discussing identifying a baseline against which we will measure the success or failure of our efforts. Groom et al. [1] provide a nice conceptual outline of the steps involved in a restoration effort (Figure 1). Notice that their first step Restore what? addresses precisely these two questions. Conceptually the process they outline makes a lot of sense: (1) Determine what you re going to restore, (2) Identify constraints that you ll have to work with, (3) Decide which of those constraints are most important, (4) Address the most important constraints, (5) Measure the system after restoration to make sure it s what you want, and (6) Maintain the system. The linear presentation, however, obscures the ways in which the different pieces feed off one another. Think about how setting goals and identifying constraints interact with one another, for example. Since we spent quite awhile talking about southern Florida as an example of ecosystem management, let s return to it now as an example of ecological restoration. Remember that the goals for the project included Restoring dynamic water storage to capture water releases from Lake Okechobee. Restoring normal water depths and sheetflow patterns. Reducing seepage losses to the east. Restoring and protecting the original core area of the Everglades. Notice that the goals don t include Returning the hydrology of south Florida to what it was in the mid-19th century. Clearly, the goals that were set reflect the constraints within 4

5 Figure 1: A flowchart illustrating a conceptual outline of the steps involved in a restoration project. 5

6 Figure 2: A conceptual diagram illustrating the relationship between the degree to which a system has been modified and the amount of effort required to return that system to a previous state. which the project is being implemented. Some of those constraints are social, political, and economic, but some of them are ecological. As Jackson and Hobbs [2] point out, the land use history of a system may play a large role in determining the restoration goals we select (Figure 2). In south Florida, the system has been substantially modified by more than half a century of agriculture, irrigation, drainage, and road system development. Even if it were socially and politically desirable to return the hydrology of south Florida to a mid-19th century condition, it probably isn t possible. Restoration and adaptive management There s another feature implicit in the outline Groom et al. [1] present that I d like to point out. Notice that two of the three questions posed in step 5, Characterize changed system, point back to step 1, Determine restoration goal. A restoration project is implicitly a test of our ecological understanding. Every restoration project should be regarded as an experiment, even if we can t design it in a such a way that it s a fully replicated and controlled experiment. 5 5 Of course, if we can design the project in such a way that it includes replicated and controlled experiments, we ll learn a lot more about the system and we ll have a better chance of identifying management 6

7 We choose particular management actions because we hypothesize that they will lead to desirable results. We implement those actions and monitor the results. If the results match what we want, we pat ourselves on the back and continue doing what we ve been doing. If the results don t match what we want, we ve learned something. Either we didn t actually implement the actions we said we were going to implement, or our hypothesis was wrong, i.e., the system doesn t work the way we thought it did. And if the system doesn t work the way we thought it did what do we do? We revise our understanding based on these results, develop a new hypothesis for how the system works, design new management strategies based on that hypothesis, implement them, monitor the results, and evaluate them. And keep doing it until we get it right. Sound familiar? That s just another way of describing adaptive management, which we discussed earlier in the context of ecosystem management. There s one more thing to mention. In implementing any restoration plan, or any conservation plan for that matter, it is important to document as much of the process as possible, both so you can remember what you did later and so that others can learn from your successes (and your mistakes). The Collaboration for Environmental Evidence ( has a library of systematic reviews examining the effectiveness of different conservation strategies. Many of those reviews include data from the gray literature and from unpublished work documented by conservation organizations. By documenting the work you do and by making it available, you can contribute to this effort. References [1] M Groom, G K Meffe, and C R Carroll. Principles of Conservation Biology. Sinauer Associates, Sunderland, MA, 3rd edition, [2] Stephen T Jackson and Richard J Hobbs. Ecological Restoration in the Light of Ecological History. Science, 325(5940): , approaches that will help us reach our goal. 7

8 [3] Anthony Ricciardi and Daniel Simberloff. Assisted colonization is not a viable conservation strategy. Trends in Ecology & Evolution, 24(5): , [4] David M Richardson, Jessica J Hellmann, Jason S McLachlan, Dov F Sax, Mark W Schwartz, Patrick Gonzalez, E Jean Brennan, Alejandro Camacho, Terry L Root, Osvaldo E Sala, Stephen H Schneider, Daniel M Ashe, Jamie Rappaport Clark, Regan Early, Julie R Etterson, E Dwight Fielder, Jacquelyn L Gill, Ben A Minteer, Stephen Polasky, Hugh D Safford, Andrew R Thompson, and Mark Vellend. Multidimensional evaluation of managed relocation. Proceedings of the National Academy of Sciences, 106(24): , [5] RONALD SANDLER. The Value of Species and the Ethical Foundations of Assisted Colonization. Conservation Biology, 24(2): , [6] Mark W Schwartz, Jessica J Hellmann, Jason M McLachlan, Dov F Sax, Justin O Borevitz, Jean Brennan, Alejandro E Camacho, Gerardo Ceballos, Jamie R Clark, Holly Doremus, Regan Early, Julie R Etterson, Dwight Fielder, Jacquelyn L Gill, Patrick Gonzalez, Nancy Green, Lee Hannah, Dale W Jamieson, Debra Javeline, Ben A Minteer, Jay Odenbaugh, Stephen Polasky, David M Richardson, Terry L Root, Hugh D Safford, Osvaldo Sala, Stephen H Schneider, Andrew R Thompson, John W Williams, Mark Vellend, Pati Vitt, and Sandra Zellmer. Managed Relocation: Integrating the Scientific, Regulatory, and Ethical Challenges. BioScience, 62(8): , [7] Pati Vitt, Kayri Havens, Andrea T Kramer, David Sollenberger, and Emily Yates. Assisted migration of plants: Changes in latitudes, changes in attitudes. Biological Conservation, 143:18 27, Creative Commons License These notes are licensed under the Creative Commons Attribution-NonCommercial-ShareAlike License. To view a copy of this license, visit or send a letter to Creative Commons, 559 Nathan Abbott Way, Stanford, California 94305, USA. 8