The sensitive lichen Usnea longissima Ach. has a limited, patchy distribution across forested landscapes in the U.S. Pacific Northwest. To gain insight into whether the current distribution within the Oregon Coast Range has resulted from a lack of suitable habitat or from dispersal limitations, we measured growth of U. longissima transplants placed in four habitats. Transplant study site locations and habitats were determined through an accompanying study that identified significant U. longissima habitat characteristics, based on the present distribution of the species, and used predictive modeling to identify areas of apparently suitable habitat within the study area. Transplants were placed in 12 sites, comprised of three replicates of the four habitats. Ninety transplants were placed in each habitat (n = 360). Growth was measured as changes in biomass and length after one year. Transplants grew in all habitats, particularly in sites where habitat was predicted to be least suitable for U. longissima. Although transplants in those sites had mean biomass increases that were 2.7 to 4.6 times greater than those of transplants placed in the other three habitats, their overall rate of attrition was 1.5 to 1.8 times higher than transplants in the other three habitats. Increases in length were also greatest in sites where habitat was predicted to be least suitable. The fact that the transplants grew well in all habitats and actually thrived in sites where habitat was predicted to be least suitable indicates that dispersal limitations may play a more significant role than the availability of suitable habitat in determining the distribution of U. longissima in the Oregon Coast Range. These findings underscore the importance of green tree retention during timber harvests. Trees containing U. longissima should be retained so that they may inoculate the regenerating stand with U. longissima fragments. It is also recommended that stands harboring significant populations of U. longissima (typically old stands) be preserved as source locations of this dispersal-limited species.
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