The sensitive lichen Usnea longissima, formerly a common circumboreal species, has been extirpated from much of its range (e.g., most of Scandinavia). Although the U.S. Pacific Northwest remains a relative stronghold for the species, U. longissima faces increasing pressure in the region from several factors, including habitat loss, air pollution, and commercial harvesting. Usnea longissima has a patchy distribution at both stand and landscape levels, which may result from a lack of suitable habitat, dispersal limitations, or both. We used two approaches in this study. First, data were collected in the Oregon Coast Range from an equal number of sites where U. longissima was present and absent (n = 75 each) to determine habitat requirements for the species. In addition to identifying the variables that define suitable habitat for U. longissima, analysis of the data yielded a model that was used in combination with a GIS to predict suitable habitat for the species. Second, 360 transplants were divided among 12 sites in 4 habitat types within the Oregon Coast Range, and their growth (change in biomass) was measured after one year. Habitat types were based on analysis of the habitat data, and represented a range of suitability for the species, ranging from sites of unlikely suitability where it did not occur through highly suitable sites where the species was abundant. While habitat conditions in the presence and absence sites types differed significantly (p < 0.01), results of the spatial analysis indicate that suitable habitats do not appear to be limiting at the landscape level. Additionally, preliminary data from the transplant experiment indicate that dispersal may play a more important role than habitat conditions in limiting the distribution of U. longissima in the Oregon Coast Range, as the species grew well over a wide range of site conditions.

Key words: dispersal, GIS, habitat, lichen, modeling, Usnea longissima