This section describes biological resources in the Planning Area. It describes vegetation, invasive species and pest management, fish, wildlife, special status species, and wild horses. Because biological resources are complex and the Planning Area is large, this section does not attempt to provide an encyclopedic description of all vegetation, fish, wildlife, and special status species in the Planning Area. This section and the remainder of this document use common names for species. Appendix K provides a complete list of scientific names for species referenced in this document.

Information in this section is based on plant communities and cover types identified through the Wyoming Gap Analysis performed as part of the National Gap Analysis program between 1991 and 1996. The Wyoming Gap Analysis is the basis for vegetation types that will be used throughout this analysis. The Wyoming Gap Analysis is a product of the University of Wyoming. This data set contains land cover for the entire state of Wyoming at a 1:100,000 scale. This data is useful for providing a broad overview of vegetation resources in the Planning Area, and is suitable for planning purposes at the RMP level of analysis. Each vegetation type consists of several ecological sites. A more accurate and detailed land cover mapping effort was initiated for the Planning Area in 2004; the new land cover data should be available by 2012.

Habitat Fragmentation

As large contiguous blocks of habitat are bisected into smaller blocks, they become isolated from one another by dissimilar habitats and land uses. For example, a contiguous 100,000-acre block of sagebrush habitat is considered fragmented when a major highway is constructed within the habitat, thereby bisecting the block. If, in this example, the highway bisects the 100,000-acre block in half, the result of this fragmentation is two 50,000-acre blocks of sagebrush habitat bisected by a highway. As blocks of habitat are repeatedly bisected into smaller blocks, there can be adverse impacts, including isolation, to individual plant and animal species and communities occupying the habitat. Impacts to biological resources from habitat fragmentation can occur on multiple scales.

Actions that result in habitat loss are exacerbated when fragmentation reduces the size and/or isolates remaining habitat patches below size thresholds necessary to support particular species. For example, some large birds in the Planning Area have large territorial requirements, while some smaller birds in the Planning Area favor habitat areas larger than their territory. These species are area-sensitive, and habitat loss and fragmentation that reduces or isolates their area thresholds likely affects their distribution and abundance in the Planning Area.

With the passage of the Homestead Acts in the 19th Century, early European American settlement of Wyoming introduced people, trails, livestock, agriculture, irrigation, and energy development to the Planning Area, all of which contributed to changes in land management and habitat fragmentation. Subsequent development of the region in the early to mid 1900s included the railroad and a road network to connect population centers. In the late 1900s, ever-increasing rural development of homes and recreational properties further fragmented habitats in the Planning Area. Animal/vehicle collisions resulting from increased traffic in these areas and the risk to private property from wildfire are both consequences and reminders of existing habitat fragmentation conditions within the Planning Area.

Linear features, including roads, railroads, trails, irrigation systems, and ROWs, fragment Planning Area habitat. The network of state highways, county roads, local roads on private and public lands, and railroads dissect much of the Planning Area. The development of irrigation reservoirs and districts with their associated water-distribution systems also has contributed to habitat fragmentation in the Planning Area. Irrigation water also has supported the conversion of native plant communities to hayfields, pasture, and cropland, thereby further fragmenting habitats. Fences can block migration routes for some wildlife species, such as pronghorn, consequently fragmenting their habitats. The conversion of large acreages of sagebrush to predominately grassland communities can fragment habitat for sagebrush-dependent species such as the greater sage-grouse.

Habitat fragmentation in the Planning Area is most prevalent along the linear features identified in the previous discussion; however, fragmentation also occurs at population centers, reservoirs, and other developments where humans live, recreate, and work. For example, the development of private parcels bordering BLM-administered lands has, in some cases, contributed to habitat fragmentation by the conversion to subdivisions or smaller ranchettes. This type of land conversion and habitat fragmentation primarily occurs near the wildland-urban interface. Buildings, roads, fences, and utility corridors associated with residential and commercial developments have all contributed to habitat fragmentation in the Planning Area.

In addition to the linear features and other types of development, conditions on BLM-administered land continue to be influenced by the management of resources and resource uses, including mineral resources; fire and fuels management; forests, woodlands, and forest products; and land resources. Refer to the appropriate sections in this document for additional details regarding existing conditions of these resources and resource uses.

In general, development and the associated construction and maintenance of roads, railroads, well pads, pipelines, and powerlines has fragmented habitat in the Planning Area. In addition, prescribed fires and wildfires have sometimes contributed to temporary habitat fragmentation. Intense and large area burns can temporarily isolate individual species and communities of plants and less mobile species of animals. A frequent fire return interval often associated with invasive species can effectively fragment habitat over the long run. Similar to fire, the habitat fragmenting effects of mechanical vegetative treatments have generally been temporary. Motorized-vehicle use also can contribute to habitat fragmentation through the transportation of invasive species seeds.

Biological Diversity

The Keystone Center defines four elements of biological diversity related to scale (Keystone Center 1991):

Biological diversity is complex, and makes the measurement of existing conditions difficult. Species diversity is the most recognizable and easily understood element of biological diversity, and for this RMP revision is defined as the variety of species found in the Planning Area. In other words, species diversity includes the numbers and distribution of all species. This includes common and plentiful species (e.g., mule deer, elk, and pronghorn) and other less common or rare species (e.g., burrowing owl, mountain plover, and bald eagle). Classifying rare species as sensitive, threatened, or endangered is one way of conserving biological diversity because these classifications heighten awareness and ensure consideration in management actions for conservation of rare species.

Spatial and temporal scales also are important considerations for conserving biological diversity. For example, nonmigratory populations of mammals are sometimes temporarily diminished following a harsh winter and limited food supply. In addition, migratory birds might return to breeding grounds with diminished populations due to the stress factors associated with migration. In these cases, the lower number of individuals of wildlife populations does not necessarily equate to a reduction in biological diversity because the number of individuals ultimately (all else being equal) return to pre-winter levels. For purposes of this RMP and EIS, the BLM considers permanent reductions in the four elements of diversity listed above to be adverse impacts to biological diversity.

Counting the number and relative frequency of species occupying an area over time is one means of identifying reductions in species diversity; however, this approach can be overly simplistic and does not necessarily address the other three elements of diversity. At present, there is no single commonly accepted scientific protocol for measuring biological diversity. Nevertheless, it is generally accepted that “… reducing the number of biological entities in a system or making some of them less abundant reduces diversity” (Langner and Flather 1994).

Climatic factors (e.g., drought) and disease, fire regime, predation, competition, and population cycles all have contributed to the current natural variability in number and relative frequency of individuals, species, and communities of plants and animals in the Planning Area. Other factors include surface-disturbing activities (e.g., road and well pad construction), the physical and chemical environment (e.g., soil nutrients and water), adjacent area vegetation (e.g., croplands), historic vegetation, invasive species, herbivory (e.g., native ungulates and livestock), and the Planning Area’s existing vegetation.

Existing conditions for biological diversity in the Planning Area are a function of physical factors (e.g., soils, geology, air, water, geography, and elevation), natural factors (e.g., climate, fire, drought, disease, and evolution), and human actions. In the context of these physical and natural factors, biological diversity evolved over time to produce the diversity present in the Planning Area prior to European-American settlement. Human actions during the subsequent 150 years changed the pattern, composition, structure, and function of plant and animal communities in the Planning Area. Management challenges for biological diversity include competing resources and resource uses. Management actions to address these challenges are incorporated in the alternatives for physical and biological resources and for fire and fuels management (see Chapter 2).

Vegetation Resources

Climate, geology, soils, elevations, precipitation patterns, and other physical and biological features associated with ecological setting influence the types and mixes of vegetation in the Planning Area. The types and mixes of vegetation in the area form the base for ecosystem processes and functions, such as water cycling, energy capture and cycling, and nutrient cycling, that produce the products and services local, regional, national, and international communities desire. Some of the desirable products and services vegetation supports include clean water, fish and wildlife habitat, livestock forage, recreation, carbon sequestration, and scenery.

As described in Section 3.1.3 Soil, the Planning Area lies within two MLRAs: the Northern Intermountain Desertic Basins – 32, (5 to 9 inch and 10 to 14 inch precipitation zones) and Central Rocky Mountains – 43B, (15- to 19- inch and 20+ inch precipitation zones) (USDA 2008). The following paragraphs described the land use, elevation and topography, climate, and water characteristics of these MLRAs.

Northern Intermountain Desertic Basins

Land use: More than half of this area is federal land; the remainder is a mixture of farms and ranches. Most of the land is used for livestock grazing. The range consists of desert shrubs and short grasses. About 5 percent of the area is irrigated. Most of the acreage is planted for alfalfa and other feed crops, but dry beans, malt barleys, sugar beets, and corn are also grown.

Elevation and topography: The elevation of the area ranges from 3,600 to 5,900 feet amsl. Piedmont plains and pediments slope from the mountains to the stream terraces of the Wind-Bighorn River system. In some places, the plains are eroded to the clay shale bedrock, and areas of badland.

Climate: Average annual precipitation in this area is 5 to 9 inches, with maximum precipitation in spring and fall. Average annual temperature is about 45°F and average freeze-free period is between 120 and 140 days per year.

Water: Low and erratic precipitation provides only a small amount of water to the area. The Wind-Bighorn River and its tributaries bring irrigation water into the area from the bordering mountains. Deep artesian wells provide water for irrigation on the eastern side of the Bighorn Basin.

Central Rocky Mountains

Land use: Almost all this area is federal land administered by the USFS, USDA, and the BLM. Forested areas are used as wildlife habitat, for recreation and watershed management, and for timber production. Meadows on the upper mountain slopes and crests above timberline provide summer grazing for livestock and big game animals. Less than 2 percent of the area is used for agriculture. Forage, grain, peas, and a few other crops are grown in some valleys.

Elevation and topography: The general elevation of the area ranges from 1,300 to 7,900 feet amsl, but in the mountains around the basin, the elevation ranges from 5,000 to 11,000 amsl. High mountains having steep slopes and sharp crests are cut by narrow valleys, most of which have steep gradients. Lakes are common, especially in glaciated areas.

Climate: Average annual precipitation in this area ranges from 24 to 60 inches. Precipitation increases with elevation, with almost 100 inches of annual precipitation in the high mountains. Most of the precipitation during fall, winter, and spring is snow. Summers are dry. Average annual temperature is between 36° and 45°F in most of the area, but is approximately 47°F or more at low elevations. The average freeze-free period is 45 to 120 days, which decreases with elevation. Frost occurs every month of the year on high mountains; some peaks have a continuous cover of snow and ice.

Water: Moderate precipitation in the area and many perennial streams and lakes provide water. Streams and reservoirs supply water to adjoining MLRAs for irrigation and other uses. Springs and shallow wells in the valleys provide water for domestic use and for livestock. Elsewhere, groundwater supplies are small and mostly untapped (USDA 2008).

Table 3-22 summarizes the Wyoming Gap Analysis project of plant communities in the Planning Area. Map 29 shows these plant communities.