SILLETT, STEPHEN C.*, BRUCE MCCUNE, JERILYNN E. PECK, AND THOMAS R. RAMBO. Department of Biological Sciences, Humboldt State University, Arcata, CA 95521. - Four years of epiphyte colonization in Douglas-fir forest canopies.
In 1995, we installed surface-sterilized Douglas-fir branches with
either rough bark or smooth bark in clearcuts, young forests, and old
growth. Half of the experimental branches were inoculated with
propagules of the epiphytic cyanolichen, Lobaria oregana. In
1997, we concluded that L. oregana was associated with
old-growth Douglas-fir forests because of dispersal limitation;
addition of L. oregana propagules resulted in a marked increase
in establishment rates. In 1999, we revisited the experiment to
determine whether other epiphytes had colonized the tree branches. We
also checked to see if the 1997 results of the experiment persisted.
A total of 26 epiphyte genera (9 bryophytes and 17 lichens) had
colonized the branches. Lichen colonization was generally fastest in
clearcuts. Colonization by alectorioid lichens was rapid in both
clearcuts and old growth but slow in young forests. In contrast,
bryophyte colonization was relatively rapid in all age classes but
slowest in clearcuts. Colonization was generally more rapid on smooth
bark than on rough bark, although Cladonia was more frequent on
rough-barked branches. Bryophytes, cyanolichens, and Sphaerophorus
globosus were more frequent on inoculated branches than on control
branches, implying that the L. oregana propagule mixture used
in 1995 was contaminated with other epiphytes. Like L.
oregana, these species may also be dispersal-limited. The number
of established L. oregana thalli in clearcuts and young stands
decreased from 1997 to 1999, but the number of thalli remained
relatively stable in old growth. After four years, established L.
oregana thalli were larger in clearcuts than in either young
stands or old growth. Overall, the fourth-year results of our
experiment confirm the importance of dispersal limitation as the cause
of old-growth association in L. oregana.
Key words: Douglas-fir, epiphyte, forest canopy, lichen, Lobaria oregana (Lobariaceae), old growth