ASSESSING CONSERVATION VALUE OF STREAM COMMUNITIES - A COMPARISON OF APPROACHES BASED ON CENTERS OF DENSITY AND SPECIES RICHNESS

1. We used a recently developed Index of Centres of Density (ICD) to a ssess conservation value of thirty-nine sites in the upper Clinch Rive r drainage of Virginia and Tennessee, U.S.A. The ICD incorporates info rmation on the population density of each species at a site relative t o sites throughout the region. 2. Value assessments based on the ICD w ere compared to those based on species richness. Species richness at s ites was not related to ICD scores, but collective species lists from high-ranking sites were similar for both approaches. All sites with ra re species had either a high ICD score or high species richness. 3. Fo ur community types (defined by physiography and stream size) were bett er represented in sites with high-ranking ICDs than in sites with high -ranking species richness. Sites with high ICD scores were distributed uniformly throughout the region. 4. The ICD is a more powerful tool t han species richness for assessing conservation value because the ICD identifies areas with regionally rare species, especially viable popul ations, or distinctive communities, all of which are key components of a region's biodiversity.