A Multi-Criteria Assessment of the Irreplaceability and Vulnerability of Sites in the Greater Yellowstone Ecosystem

Authors(s): R. F. Noss, C. Carroll, K. Vance-Borland and G. Wuerthner

Publication: Submitted to Conservation Biology

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Publication Date: 0000-00-00

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Abstract: We conducted a systematic conservation assessment of the 10.8 million ha Greater Yellowstone Ecosystem (GYE), employing the three tracks of special elements (e.g., rare species and communities) protection, habitat representation, and protection of critical areas for focal species (grizzly bear [Ursus arctos], wolf [Canis lupus], and wolverine [Gulo gulo]). The GYE is distinct in that large core refugia lie in close proximity to a rapidly growing human population. Using a site-selection algorithm, combined with GIS-based biological and habitat data and static (habitat suitability) and dynamic (population viability) modeling of focal species, we identified sites within the GYE that are biologically irreplaceable and vulnerable to degradation. Irreplaceability scores were assigned to 43 megasites (aggregations of planning units) on the basis of 9 criteria corresponding to quantitative conservation goals. Interviews and a workshop with experts supplemented quantitative data in determining vulnerability scores. Existing protected areas constitute 27% of the GYE. Our proposed megasites would expand protection by 43% (i.e., to 70% of the region) and increase protection of known occurrences of the most highly imperiled species by 71% (to 100%) and of all special elements by 62% (to 92%). They would also significantly increase representation of vegetation types, physical habitats, and aquatic habitats, and capture the most critical areas for the focal species. The most efficient course would be to protect first the megasites ranked highest in irreplaceability and vulnerability (i.e., the upper right quadrant in a graph of irreplaceability vs. vulnerability), but real-world conservation must follow an informed opportunism, with explicit recognition of the trade-offs involved. Introduction Systematic planning on a regional scale has become the standard approach for conservation organizations and agencies worldwide (Noss 1983; Pressey 1994; Dinerstein et al. 1995; Noss et al. 1997; Ricketts et al. 1999; Groves et al. 2000). Systematic conservation planning is superior in many ways to opportunistic or politically-biased approaches, which have resulted in a skewed distribution of protected areas (Pressey et al. 1993; Scott et al. 2001). Among the key attributes of systematic conservation planning are explicit goals, quantitative targets, objective methods for locating new reserves to complement existing ones, and rigorous criteria for implementing conservation action (Margules & Pressey 2000). The Greater Yellowstone Ecosystem (GYE) was first defined as the area necessary to sustain the disjunct Yellowstone population of grizzly bears (Ursus arctos; Craighead 1979). Today, the GYE is the southernmost area in North America that still contains the full suite of native carnivores, along with intact watersheds, mountain ranges, and other wilderness qualities (Clark et al. 1999). Although the GYE is not considered a biological hotspot at a global or continental scale (Ricketts et al. 1999; Myers et al. 2000), it presents an opportunity that most hotspots, which are largely in tropical, subtropical, and Mediterranean climates, do not-to conserve a full suite of native species within a reasonably intact ecosystem. Nevertheless, biodiversity in the region is threatened. The GYE's scenic qualities have attracted a burgeoning human population, the impacts of which now rival the traditional threats of resource extraction. For instance, growth rates for the 20 counties within the GYE averaged 14% between 1990 and 1999 and ranged up to 66% (Greater Yellowstone Coalition, unpublished data). A 1991 study found more than a million acres in the GYE already subdivided (Harting & Glick 1994). The GYE may be unique in the western United States in that large core refugia lie in close proximity to a rapidly growing human population. We conducted a conservation assessment of the GYE to serve four well-accepted goals of conservation (Noss & Cooperrider 1994): 1) Represent all kinds of ecosystems, across their natural range of variation, in protected areas; 2) Maintain viable populations of all native species in natural patterns of abundance and distribution; 3) Sustain ecological and evolutionary processes within their natural ranges of variability; and 4) Build a conservation network that is adaptable to environmental change. In pursuit of these goals we integrated three common approaches of conservation planning (albeit these approaches usually have been pursued separately rather than jointly): 1) Protection of special elements-identifying, mapping, and protecting rare species occurrences (particularly hotspots where occurrences are concentrated), imperiled natural communities, and other sites of high biodiversity value; 2) Representation of a full spectrum of habitat types (e.g., vegetation, abiotic habitats, aquatic habitats) in protected areas; and 3) Conservation of focal species-identifying and protecting critical habitats of area-limited, sensitive species. Assessments that consider the needs of focal species can address issues of habitat area and configuration that otherwise are ignored. Together, these three tracks constitute a comprehensive approach to conservation planning (Noss et al. 1999). Using a site-selection algorithm (Andelman et al. 1999) applied to several classes of conservation targets within the three tracks described above, we identified sites within the GYE that have the most to lose if not protected. To identify high-priority sites, we relied on two key concepts: irreplaceability and vulnerability (Pressey et al. 1994; Margules & Pressey 2000; Pressey & Cowling 2001). Irreplaceability provides a quantitative measure of the relative contribution different areas make to reaching conservation goals, thus helping planners choose among alternative sites in a portfolio. As noted by Pressey et al. (1993), irreplaceability considers the potential contribution of a site to achievement of a conservation goal and the extent to which options for achieving the goal are narrowed if the site is not conserved. We assessed vulnerability on the basis of expert opinion and consensus about the threats faced by each site, taking into account quantitative data where available. Our findings provide a template for making conservation decisions with awareness of the trade-offs involved. Study Area We defined the study area boundaries (Fig. 1) in consultation with the Greater Yellowstone Coalition, with consideration to mountain ranges, watersheds, wildlife migration routes, and other features. The core of this 10.8 million ha region is the 890,000 ha Yellowstone National Park (YNP), 134,000 ha Teton National Park and John D. Rockefeller Memorial Parkway, and an additional 1.6 million ha in federally designated wilderness. As a high mountainous region 1300 km from the moderating effects of the Pacific Ocean, the GYE's climate is cold continental. Precipitation varies with elevation and rain-shadow effects. For example, the southwest corner of YNP may receive > 200 cm annual precipitation, whereas areas below the east slope of the Yellowstone Plateau receive as little as 15 cm (Despain 1990; Merrill & Jacobson 1997). The GYE is intersected by two major climatic regimes: a summer/dry-winter/wet regime characteristic of the Pacific Northwest and a winter/dry-summer/wet regime typical of the Southwest and southern Plains. Areas to the south and east of YNP receive proportionally more precipitation in summer, particularly by summer monsoon thunderstorms (Despain 1987; Whitlock & Bartlein 1993). Hence, aspen (Populus tremuloides) and willows (Salix spp.), which require abundant water during the growing season, are more abundant in the southern portions of the GYE. Lower elevations of the GYE are generally treeless except along streams and are dominated by grass-shrub communities (e.g., bluebunch wheatgrass [Pseudoroegneria spicata], Idaho fescue [Festuca idahoensis], big sagebrush [Artemisia tridentata]). Riparian trees include one of three species of cottonwood (Populus). Many riparian communities have been affected negatively by livestock and dams (Merigliano 1996). Ponderosa pine (Pinus ponderosa), Douglas-fir (Pseudotsuga menziesii), or Rocky Mountain juniper (Juniperus scopulorum) delineate the lower tree line. Ponderosa pine is relatively scarce in the region, occurring where summer precipitation is highest (Knight 1994). Throughout most of the GYE, Douglas-fir is the dominant low elevation tree, intermixing with aspen at higher elevations. Limber pine (P. flexilis) occurs throughout on dry windy sites. Engelmann spruce (Picea engelmannii), subalpine fir (Abies lasiocarpa), and lodgepole pine (P. contorta) compose mid-elevation forests. Spruce-fir forest would dominate more of the area were it not for stand-replacement fires that favor lodgepole pine. At the highest elevations whitebark pine (P. albicaulis) is common. Extensive tracts of alpine tundra occur above timberline (Knight 1994).

Keywords: Greater Yellowstone Ecosystem, Grand Teton National Park, Yellowstone National Park, John D. Rockefeller Memorial Parkway, Teton County, Jackson Hole, Bridger-Teton National Forest, habitat, animal, mammal, Ursidae, Ursus arctos horribilis, bear, grizzly bear, Canidae, canine, wolf, Canis lupus, wolverine, Gulo gulo, suburban area, population, mortality, wildlife, management, carnivore