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 pl ots at varying distances from six mid-order streams in Vermont, USA to determine how wide corridors need to be to conserve biological richne ss. Use of stream corridors by most mammal species occurred below or j ust 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 HW M, depending on the stream. Minimum corridor widths of 75-175 m were n eeded to include 90% of the bird species. Thus, no standard minimum co rridor width for conserving species was identified. Virtually all annu al, biennial, non-native and ruderal (weedy) plant species were restri cted to the streamside of HWM, suggesting that annually flooded zones may serve as refugia and travel corridors for these groups. No analogo us relationships were identified for birds or mammals. In summary, dis tribution of species along streams varied greatly by taxon, stream, an d location of the high water mark. Use of a standard corridor width to conserve species is a very poor substitute for individual, stream-spe cific assessment of species distributions.