As I see it, there are five steps to be taken in producing a preserve design.
1. What are the elements3 of concern?
2. Where are the elements of concern found?
3. How large must the reserve be to serve its purpose?
4. What features of the reserve must be protected/managed to allow the elements to persist in the area, e.g., patch dynamics, landscape context?
5. How large a buffer zone is required to prevent/reverse degradation of the primary habitat?
Once these decisions have been made, many other decisions must be made about exactly how the land is to be protected - whether by purchase, conservation easement, partnership agreement, etc. Moreover, there's a sixth step that should be added to those I just mentioned:
- 6. How does this reserve fit into a system of conservation reserves? Is it a stand-alone reserve? If not, how ought the size, number, and spatial configuration of reserve components to be selected?
The design of reserve systems involves a ``representation problem,'' i.e., finding a configuration of reserves that ensures all elements of concern are ``represented.''4 Formal approaches to solving these problems are often described in terms of minimizing either the number of areas to be protected or the total area of areas to be protected. Pressey et al. [9], for example, identify four problems for which solutions might be required:
1. Identify the minimum number of sites needed to represent at least one occurrence.5
2. Identify the minimum total area of sites needed to represent at least one occurence.
3. Identify the minimum number of sites needed to represent at least 5% of the total regional extent.6
4. Identify the minimum total area of sites needed to represent at least 5% of the total regional extent.
In the test application they describe, Pressey et al. seek to ensure representation of 248 land systems7across 1885 potential conservation sites in an area of 325,000 km
. They find that a minimum of 54 sites (2.86% of the total) and an area of 12084 km (3.72% of the total) are needed to represent at least one occurrence of each land system. They find that a minimum of 126 sites (6.68% of the total) and an area of 25887 km (7.96% of the total) is needed to represent at least 5% of each land system.
In addition to deciding on the size, number, and spatial configuration of units to be included in a conservation reserve system, conservation managers must make several additional layers of decisions:
- How frequently must the status of populations/communities be monitored?
- Is it necessary to manipulate the habitat to, for example, preserve early successional environments?
- Should an effort be made to exclude/remove invasive exotics?
We won't talk specifically about these questions, since we've been talking about them all semester. Beside, there are few, if any, general principles that can be applied to all reserves. Rather, good biological judgement based on the best natural history information available is always required, as is a clear sense of what the priorities are.
In designing nature reserves there's a lesson from landscape ecology that is especially important to remember. I suppose you could call it ecology's relativity principle:
- There is no single, universally applicable spatial or temporal scale appropriate for understanding all ecological processes. The scale that is appropriate depends on the process you are trying to understand.
- Population dynamics of Arabidopsis thaliana vs. population dynamics of Quercus rubra
The application of this principle to design of nature reserves is quite straightforward:
- There is no single size, no single scheme of management, no single means of protection that is universally applicable to all conservation reserves. The appropriate size, the appropriate management scheme, and the appropriate means of protection depend on the purpose for which the reserve was established.
Unfortunately, we don't have time this semester for a lecture focusing specifically on landscape ecology and remote sensing, but let me mention a few principles that might have been covered in such a lecture that are especially relevant to design of reserves or reserve systems:
- Remote sensing - Landsat thematic mappers, SPOT, and all that - means that it is now possible to use very sophisticated techniques to identify areas of conservation concern and the threats to which they may be subject.
- The middle level of spatial and temporal scales - those that span decades or centuries rather than millenia and areas from a few hectares to a few tens of square kilometers - are often the most relevant for conservation purposes.
- They are the time scales over which many ecological processes happen, and especially those ecological processes over which human beings may hope to have some influence.
- They are the spatial scales over which management schemes can have a direct impact.8
- Gap analysis - A national program using remote sensing data to identify ``gaps'' in conservation coverage. Quoting from their web page:
The mission of the Gap Analysis Program (GAP) is to provide regional assessments of the conservation status of native vertebrate species and natural land cover types and to facilitate the application of this information to land management activities. This is accomplished through the following five objectives:
- map the land cover of the United States
- map predicted distributions of vertebrate species for the U.S.
- document the representation of vertebrate species and land cover types in areas managed for the long-term maintenance of biodiversity
- provide this information to the public and those entities charged with land use research, policy, planning, and management
- build institutional cooperation in the application of this information to state and regional management activities.
Nature reserves have often been established, at least by private organizations like the Nature Conservancy, for the protection of identifiably rare and endangered species. In so doing, they may have failed to help prevent the general biotic impoverishment that accompanies the conversion of natural ecosystems to human-dominated ones. The importance of gap analysis is less in its conceptual novelty than in the emphasis it helps to place on protection of diverse ecosystems, even if that diversity is composed primarily of non-endangered species. It is also a systematic, planned attempt to put together a system of reserves that make sense, rather than making piecemeal decisions on individual pieces of property.
There is a large potential problem, however. The Gap Analysis program presumes that vegetation cover and predicted vertebrate distribution will be a good surrogate for diversity in other groups. How likely is this? Well, Prendergast and colleagues [8] looked at the distribution of five groups on the island of Britain:
- butterflies,
- dragonflies,
- aquatic plants,
- breeding birds, and
- liverworts.
In a 10km grid that covered all of England, Wales, and Scotland they recorded the number of species in each group.9The survey included a total of 2500 tracts. They then ranked separately for each taxonomic group each tract into the 5% with the highest number of species and the 5% with the lowest number of species. How much ``hot spot'' overlap was there between taxonomic groups?
- Butterflies and birds share only 10% of hot spots.
- Butterflies and dragonflies share 34% of hot spots, the greatest overlap found.
- None of the 2500 tracts is a hotspot for all five groups. Liverwort hot spots are concentrated in western Scotland. Dragonfly hot spots are concentrated in southern England.
- Protecting tracts with a high diversity may not protect rare species. 16% of rare birds were found in cold spots.
- Dobson et al. [2] did a similar analysis using their data on the distribution of endangered species in the United States.
- Remember that they divided their data into 11 taxonomic groups.
- In the 2858 counties included in their study only two are hot spots for three groups: San Diego, California (fish, mammals, and plants) and Santa Cruz, California (arthopods, reptiles and amphibians, and plants).
- Only nine counties are hotspots for two groups: Hawaii, Honolulu, Kauai, and Maui, Hawaii; Los Angeles and San Francisco, California; Highlands and Monroe, Florida; and Whitfield, Georgia.
So after that long-winded, general introduction I'm going to step back a bit further than I already have from reality, and to talk a little about the history of thinking about reserve design. I do this for three reasons:
- The theory of reserve design began with applying principles of island biogeography a lá MacArthur & Wilson. It's a good chance to see what is now widely regarded as a false start in conservation biology and how it emerged from a reasonably well-established theoretical and empirical base. It serves as a check to our egos, lest we begin to think that we really do understand everything.
- The theory of island biogeography is the basis for many of the estimates of contemporary extinction rates that I quoted in my first lecture many weeks ago. It's important to understand where these estimates come from and to get some sense of their reliability.
- Finally, all though the theory of island biogeography does have limited applicability to the design of nature reserves, there are a couple of important principles that emerge from it that are worthy of consideration.
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