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within a particular country or region, first identify and classify the various elements of biological diversity in several ways. Then examine the existing and proposed systems of protected areas and other land-management units that help conserve biological diversity. Finally, using various classifications, determine which elements (e.g., major ecosystems, vegetation types, habitat types, species) are unrepresented or poorly represented in the existing system of conservation areas. Once this is known with reasonable precision, priorities for the next set of conservation actions can be established. The process continues indefinitely, and the conservation system is refined as land use changes and as better information about the distribution and status of species and ecosystems is obtained.
In practice, this process usually entails comparing and analyzing many different sets of information by using maps or computers to identify, for example, the gaps in coverage. Many countries have begun this process, but unfortunately, very few have attempted it in a thorough, systematic fashion with defined conservation objectives. Notable exceptions include Great Britain, Peru, Australia, and South Africa (Specht et al., 1974).
The example from Australia illustrates the process well. By the mid-1970s, there was an adequate description of the major vegetation types found throughout Australia. A comprehensive review of the various park and reserve systems was begun to determine which vegetation types were already represented and seemingly adequately protected. The thoroughness of this effort varied considerably from state to state, but by the late 1970s and early 1980s, it was becoming possible to make more objective statements about which vegetation types were poorly represented in the national and state systems and therefore which ones needed conservation attention first. The state of Queensland has taken this broad-scale analysis one step further (Sattler, 1986). The Queensland National Parks and Wildlife Service recently completed mapping the vegetation of Queensland’s 90 national parks, environmental parks, fauna reserves, and scientific reserves larger than 1,000 hectares, and it now is analyzing gaps in the representation of vegetation types by protected areas. As these are identified, steps will be taken to protect or otherwise conserve good representative examples of the highest-priority vegetation types (Sattler, 1986).
AN UNDERLYING CONCEPT
An important concept underlies the gap analysis process: by ensuring that all vegetation types are well represented in a system of conservation areas, it is assumed that much if not most of the biological diversity (species and ecosystems) will be protected. Systems in practice verify this, e.g., in much of the United States, Australia, and Europe, but in addition, special efforts must be made to ensure the protection of particularly critical species and ecosystem types.
Debates continue to rage among biologists about the minimum critical sizes of populations and ecosystems that are necessary to conserve the biota over the long term. A very practical question emerges from these debates: should a particular ecosystem type already represented in the system of conservation areas be better represented, or should the next conservation effort be aimed at conserving other