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System descriptions and viability guidelines are based on materials compiled by NatureServe or developed by the Colorado Natural Heritage Program. Funding for the development of these documents was provided in part by the Bureau of Land Management, The Nature Conservancy, and the USDA Forest Service. Maps were produced using the Southwest Regional Gap Analysis Project landcover dataset. Please note that the extent of each system is exaggerated for display at a statewide scale.
Viability specification tables in these documents summarize the factors that contribute to an overall element occurrence (EO) ranking. The estimated viability ranks are: A - excellent, B - good, C - fair, or D - poor. The three primary rank factors (size, condition, and landscape context) are shown in relative order of importance. These factors reflect the present status, or quality of an occurrence and are used as the basis for estimating its long-term viability:
For ecological systems, the term "viability" is used loosely, since systems are comprised of many separate communities and species, each with their own viability. The viability of an ecological system is considered to be the sum of the viability or persistence of the component communities and their ecological processes. More directly, the ranks usually reflect the degree of negative anthropogenic impact to a community (i.e., the degree to which people have directly or indirectly adversely impacted community composition, structure, and/or function, including alteration of natural disturbance processes). Occurrences of adequate size with relatively few impacts would generally be ranked "A", "B", or "C" (at least "fair" viability, with a high probability of long-term persistence), and those with significant degradation would be ranked "D" ("poor" viability, requiring significant restoration work to enable persistence of the occurrence).
Colorado Natural Heritage Program. 2005. Ecological System Descriptions and Viability Guidelines for Colorado. Colorado Natural Heritage Program, Colorado State University, Fort Collins, Colorado.