Criterion 1: Conservation of biological diversity - Indicator 8: The number of forest dependent species that occupy a small portion of their former range

Abstract

This indicator measures the portion of a species' historical distribution that is currently occupied as a surrogate measure of genetic diversity. Based on data for 1,642 terrestrial animals associated with forests, most species (88 percent) were found to fully occupy their historic range - at least as measured by coarse state-level occurrence patterns. Of the 193 species that have been extirpated from at least one state, 72 percent still occupy less than/equal to 90 percent of their former range. The number of species that now occupy greater than/equal to 80 percent of their former range varies by taxonomic group. Range contraction of this magnitude is most commonly observed among mammals (5.7 percent), followed by amphibians (2.3 percent), and birds (1.4 percent). Geographically, states that have lost the greatest number of animal species are concentrated in the northeastern United States. More refined estimates of geographic range size contraction were obtained for 275 threatened or endangered species. Among this subset of species, animals have undergone a greater degree of range contraction (nearly 50 percent of the species are restricted to less than 25 percent of their historic range) than plants (30 percent of species occupy less than 25 percent of their historic range). For most species, data from which to quantify changes in range occupancy are lacking. Because a species? range is dynamic, a statistically designed inventory that permits an objective and temporally systematic assessment of range occupancy is needed.

Citation

Flather, Curtis H.; Sieg, Carolyn Hull; Knowles, Michael S.; McNees, Jason. 2003. Criterion 1: Conservation of biological diversity - Indicator 8: The number of forest dependent species that occupy a small portion of their former range. In: Darr, David R., coordinator. Data Report: A Supplement to the National Report on Sustainable Forests -- 2003. FS-766A. Washington, DC: USDA Forest Service, Research & Development. Online: http://www.fs.fed.us/research/sustain/