ASSESSMENT OF MINIMUM STREAM CORRIDOR WIDTH FOR BIOLOGICAL CONSERVATION - SPECIES RICHNESS AND DISTRIBUTION ALONG MID-ORDER STREAMS IN VERMONT, USA

Bird, mammal and vascular plant species were censused in 200-m long plots at varying distances from six mid-order streams in Vermont, USA to determine how wide corridors need to be to conserve biological richness. Use of stream corridors by most mammal species occurred below or just above the annual high water mark (HWM). Distribution of plant and bird species within corridors was more variable, however, and differed from stream to stream. For example, to include 90% of the streamside plant species, minimum corridor widths ranged from 10 to 30 m above HWM, depending on the stream. Minimum corridor widths of 75-175 m were needed to include 90% of the bird species. Thus, no standard minimum corridor width for conserving species was identified. Virtually all annual, biennial, non-native and ruderal (weedy) plant species were restricted to the streamside of HWM, suggesting that annually flooded zones may serve as refugia and travel corridors for these groups. No analogous relationships were identified for birds or mammals. In summary, distribution of species along streams varied greatly by taxon, stream, and location of the high water mark. Use of a standard corridor width to conserve species is a very poor substitute for individual, stream-specific assessment of species distributions.