The Gap Analysis Program brings together the problem-solving capabilities of federal, state and private scientists to tackle the difficult issues of land cover mapping, vertebrate habitat characterization, assessment and biodiversity conservation at the state, regional and national levels. The program seeks to facilitate cooperative development and use of information. The gap analysis process provides an overview of the distribution and conservation status of actual vegetation and terrestrial vertebrates. Digital map overlays in GIS are used to identify individual species, species-rich areas and vegetation types that are not represented or are underrepresented in existing management areas. It functions as a preliminary step to more detailed studies needed to establish actual boundaries for potential biodiversity management areas. These data and results are then made available to institutions as well as individual land owners and managers so that they may become more effective stewards through more complete knowledge of the management status of these elements of biodiversity. GAP, by focusing on higher levels of biological organization, is likely to be both less costly and more likely to succeed than conservation programs focused on single species or populations (Scott et al. 1993).
Biodiversity inventories can be visualized as “filters” designed to capture elements of biodiversity at various levels of organization. The filter concept has been applied by The Nature Conservancy, which established Natural Heritage Programs in all 50 states, most of which are now operated by state government agencies. The Nature Conservancy employs a fine filter of rare species inventory and protection and a coarse filter of community inventory and protection (Jenkins 1985, Noss 1987). Community-level (coarse filter) protection is a complement to, not a substitute for, protection of individual rare species. Gap analysis is essentially an expanded coarse filter approach (Noss 1987) to biodiversity protection. The vegetation types mapped in GAP serve directly as a coarse filter, the goal being to assure adequate representation of all types in biodiversity management areas. By using landscape-sized samples (Forman and Godron 1986) as an expanded coarse filter, gap analysis searches for and identifies biological regions where unprotected or underrepresented vegetation types and animal species occur. A second filter uses combined species distribution information to identify sets of areas in which all, or nearly all, mapped species are represented. Additional data layers can be used for a more holistic conservation evaluation. These could include indicators of stress or risk (e.g. human population growth, road density, rate of habitat fragmentation, distribution of pollutants) and the locations of habitat corridors that allow for natural movements of wide-ranging animals or the migration of species in response to climate change.
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