KEON, DYLAN B.* AND PATRICIA S. MUIR. Dept. of Botany and Plant Pathology, Oregon State University, 2082 Cordley Hall, Corvallis, OR 97331. - Factors limiting the distribution of the sensitive lichen Usnea longissima in the Oregon Coast Range: habitat or dispersal?
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