Why is the rainforest lichen Methuselah’s Beard (Usnea longissima) so rare in British Columbia’s inland temperate rainforest?

Coastal (CTR) and inland temperate rainforests (ITR) in western North America share a rich oceanic lichen flora. The distinctive Methuselah’s beard lichen (Usnea longissima) is an exception to this pattern of shared distributions, with very few ITR locations. Does this absence reflect dispersal limitations or climatic intolerance? To answer this question, we transplanted U. longissima thalli from the CTR to three ITR locations, assessing growth rates against reciprocal CTR transplants. Canopy microclimate measurements provided concurrent data on growth conditions. Growth rate responses (length, mass and area) were evaluated after summer and full-year transplants. Notwithstanding extended drought conditions during the summer period, annual transplants at two of the three ITR locations supported growth rates comparable to those at the CTR source U. longissima population, with summer dewfall and autumn rains being major ITR hydration sources. Thalli transplanted to a third ITR site (summer measurements only) in a location transitional to the drier interior plateau lost both mass and length. Based on these findings we suggest that the absence of U. longissima from much of the ITR reflects the combined influence of dispersal limitations and requirements for stands with long site continuity and topographically induced summer wetting of thalli by dewfall.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author