Abstract for poster presented at the Ecological Society of America 84th Annual Meeting. August 8-12, 1999. Spokane, WA.

KEON, DYLAN B., and PATRICIA S. MUIR. Oregon State University, Corvallis, OR 97331-2902 USA. Predicting presence of the sensitive lichen Usnea longissima in managed landscapes.

Usnea longissima is a pendant, epiphytic lichen that has declined significantly in its global range over the last few decades. The U.S. Pacific Northwest remains a stronghold for the species, although U. longissima faces increasing pressure in the region from habitat loss, air pollution, and commercial harvesting. U. longissima has a patchy distribution at both stand and landscape levels, which may result from a lack of suitable habitat, dispersal limitations, or both factors. To address whether the patchy distribution results from a lack of suitable habitat, we collected biotic and abiotic data from an equal number of sites in the Coast Range of Oregon where U. longissima was present and absent to determine habitat requirements for the species. We also used habitat data to develop a model for predicting where U. longissima is likely to occur. While habitat of the two site types differed significantly (p = 0.008), with U. longissima occurrence being associated with older stands (>75 yr), suitable habitats do not appear to be limiting at the landscape level. This suggests that dispersal may limit the species' distribution. Additional work will examine: 1) growth of U. longissima in different habitats, and 2) effective dispersal distance of thallus fragments from an U. longissima population.