Introduction
Thou shalt conserve biodiversity. - Al Gore
1.1 Background
The loss of biological diversity remains one of mankind's most significant ecological problems. Traditional responses to increased loss of biodiversity in the United States have concentrated on rescuing individual species under the Endangered Species Act. Effort expended on a species-by-species basis, however, has been criticized as inefficient, expensive, and biased toward species with broad public appeal (Pitelka 1981, Scott et al. 1987, Noss 1991). The goal of biodiversity conservation is to reverse the processes of biotic impoverishment at each level of organization - genes, species, ecosystems and landscapes - and is concerned with ecological and evolutionary processes as much as species diversity and composition (Scott et al. 1993). Thus, biological conservation represents a significant step beyond rare and endangered species conservation (Noss 1991, Scott et al. 1991).
Most conservationists agree that the best strategy for conserving biodiversity is to manage for native species in natural landscapes that are sufficiently large to maintain both species and natural processes, and that are linked to allow genetic interchange (Noss 1983, McNeeley 1994). This approach requires planning for a cohesive, representative system of areas managed for the maintenance of long-term biodiversity. We view these areas as management areas rather than reserves because management for the maintenance of biodiversity does not necessarily preclude land management. Implementation of such a plan first requires knowledge of the patterns and dynamics of elements of biodiversity in a state-wide to regional context. Gap analysis has emerged as a rapid and efficient method for characterizing the state-wide distributional patterns and the current conservation status of two elements of biodiversity - actual vegetation types (hereafter called land cover types) and terrestrial vertebrate species.
1.2 The Gap Analysis Concept
Inventories of biodiversity 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 (TNC), which has established Natural Heritage Programs in all 50 states. The Nature Conservancy employs a fine filter approach for rare species inventory and protection and a coarse filter approach for community protection (Jenkins 1985, Noss 1987). It is postulated that 85-90% of species and land cover types can be protected by the coarse filter, without having to inventory or plan for those species individually. A fine filter is then applied to the remaining 10-15% of the species and plant communities to ensure their protection (Scott et al. 1993).
Gap analysis is essentially an expanded coarse-filter approach to biodiversity protection (Noss 1987). It uses actual land cover types (mapped from satellite imagery) and existing survey and species-habitat information to identify unprotected species, plant communities, and sites of high biodiversity value that may merit consideration for the long-term maintenance of native species and natural ecosystems before they become critically rare. Thus, it is expected to reduce the rate at which species require listing as threatened or endangered. Those species already imperiled will still require individual efforts to assure their recovery. The community-level (coarse filter) approach of gap analysis is a complement to, not a substitute for, protection of individual rare species and functions as a preliminary step to the more detailed studies needed for biodiversity planning.
The land cover types mapped in gap analysis serve directly as a coarse filter, with the goal of assuring adequate representation of all ecosystems in biodiversity management areas. The major role of vertebrates in gap analysis is to represent faunal diversity. This use implies a high correlation between vertebrate richness and overall biodiversity. While it has been suggested that vertebrates often provide a protective umbrella for other taxa (Murphy and Wilcox 1986), recent comparisons of geographical coincidences in species rich areas among taxonomic groups have not always supported this relationship (Prendergast et al. 1993, Saetersdal et al. 1993, Lawton et al. 1994). In fact, emphasis on vertebrate species has resulted from a greater amount of information on these taxa. As more information on other taxa become available similar analyses can be conducted. Also, because the spatial scale at which organisms use the environment differs tremendously among species, and depends on body size, food habits, mobility, and other factors, no coarse filter will be a complete assessment of biodiversity protection status and needs. Species that fall through the pores of the coarse filter, such as endemics and wide-ranging animals, can be captured by the safety net of the fine filter.
In assembling information to conduct a gap analysis, the Gap Analysis Program (GAP) 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 methods, and biodiversity conservation at the state, regional and national levels. The program seeks to facilitate cooperative development and use of information, so that institutions, agencies, and private land owners and managers may be more effective land stewards.
1.3 Objectives Of Gap Analysis
There are four major objectives of the gap analysis program: (1) map land cover as closely as possible to the alliance level (Jennings 1993), (2) map the state-wide distribution of those terrestrial vertebrate species for which adequate information on habitat associations and mapped habitat variables is available, (3) document the occurrence of land cover types and terrestrial vertebrate species that are inadequately represented in areas managed for biodiversity conservation (i.e., "gaps"), and (4) make all information developed available to users in a readily accessible format.
1.4 State Goals For Gap Analysis
To meet the above objectives, it was necessary for gap analysis to be conducted at the state level yet to maintain consistency with national standards. The Wyoming Gap Analysis Project (WY-GAP) was initiated in 1991 as a cooperative effort among many state, federal, and private agencies all of whom contributed to the success of the project. Since none of the databases needed for the Wyoming gap analysis were available on a state-wide basis at the initiation of the project, we worked closely with our state cooperators to share data and resources to compile the necessary state-wide information system described in this report. In compiling these databases, we have maintained the integrity and documentation of the source files, and have developed a re-distribution policy for data containing sensitive species data.
Recognizing that WY-GAP databases would be the most comprehensive source of state-wide, GIS maps of biological resources for the near future, the data were organized in a manner that would facilitate other uses of the information within the state, while also meeting the requirements of the national program. Additionally, our goal has been to gain acceptance of the information through a state-wide review process. We have found that the WY-GAP databases have already been useful for several state-level analyses, but due to the scale at which the information was developed, we caution against inappropriate uses of the data (see Chapter 7) and suggest that the most appropriate uses of these data sets are to address landscape or state-wide analyses and to provide context for a smaller areas.
1.5 General Caveats
Overall limitations of the gap analysis approach must be recognized so that additional studies can supplement the results of the Wyoming gap analysis. Specific limitations of the data inputs are described in the subsequent chapters of this report. The following are a list of general caveats in the use of gap analysis results. First, results of the gap analyses were derived from remote sensing and predictive models and are used to make general assessments about conservation status. Any decisions based on the data must be supported by ground-truthing and more detailed analyses.
Second, the static nature of gap analysis data limits their utility in conservation risk assessment. Our databases provide a snapshot of a region in which land cover and land stewardship are both very dynamic, but provide the basis for establishing changes in these elements through time. Third, gap analysis is not a substitute for a thorough national biological inventory. As a response to rapid habitat loss, gap analysis provides a quick assessment of the distribution of vegetation and associated species before they are lost. As such, it provides immediate focus and direction for a national program to maintain biodiversity. The process of improving knowledge in systematics, taxonomy, and species distributions is lengthy and expensive, but must be continued and expedited to provide the detailed information needed for a comprehensive assessment of our nation's biodiversity. Maps of land cover and species distributions developed by gap analysis projects can be used to make such surveys more cost-effective by stratifying sampling areas according to expected variation in biological attributes.
1.6 How This Report Is Organized
The organization of this report follows the general chronology of the project's development, beginning with the production of the individual data layers including land cover (Chapter 2), predicted vertebrate species distribution (Chapter 3), and land stewardship (Chapter 4), followed by analysis of the data (Chapter 5), management implications and current directions (Chapter 6), and ending with how to acquire and use GAP data (Chapter 7). The format diverges from standard scientific reporting by embedding results and discussion sections within individual chapters. This approach was taken to allow the individual data products to stand on their own and to provide data users with a concise and complete report for each product.
1.7 Study Area
The project study area includes the entire state of Wyoming and portions of Montana and Idaho which fall within the bounds of Yellowstone National Park (Map. 1.1). Clark and Stromberg (1987) and Knight (1994) have described the physiographic setting, climatic patterns, vegetation, and general faunal distributions of Wyoming in detail. Generally, Wyoming straddles the Continental Divide and has abrupt topographic relief created by alternating basins and mountain ranges. Thirty-seven percent of Wyoming's land base is above 2,134 m (7,000 ft) elevation with the highest point (4,207 m) at the summit of Gannett Peak in the Wind River mountains. The lowest point in Wyoming (930 m) occurs where the Belle Fourche River flows into South Dakota. Major mountain ranges are generally oriented in a north-south manner. The Absaroka, Beartooth, Gros Ventre, Teton, Wind River, Salt River, and Wyoming mountain ranges are in the northwest part of the state. The Bighorn Mountains are in the northcentral part of the state, the Sierra Madre, Medicine Bow, and Laramie Ranges in the southeast, and the Black Hills are in the northeast. Smaller east-west oriented ranges including the Owl Creek, Green, Rattlesnake, Ferris, Seminoe and Shirley mountains occur near the middle of the state. Internal basins and eastern plains are rolling to flat and the eastern plains are part of the Great Plains.
Vegetation of Wyoming includes sagebrush, greasewood, and saltbush shrublands in the intermountain basins, grasslands on the Great Plains, juniper and mountain mahogany shrublands in the foothills, and forest and alpine meadows in the mountains (Knight 1994). The climate of Wyoming varies considerably from semiarid in lower to middle elevations, to wetter, colder conditions in the mountains. Across Wyoming, precipitation varies ten fold from 15 to 150 cm each year. In general, the intermountain basins in the western two thirds of the state are drier, with averages of 15-30 cm/yr, than the Great Plains region to the east, with an average of 30-40 cm per year. The foothills and mountains receive 40-150 cm/yr.
Map 1.1. Major roads, rivers and topographic features in Wyoming (map unavailable).