Influence of overstory removal on growth of epiphytic mosses and lichens in western Oregon.

Will old-growth-associated epiphytes survive if the forest canopy is opened around them by thinning or partial harvest? If old-growth association is due to a species' environmental tolerances, it may not survive in the relatively open stands that result from such treatments. If, however, old-growth association is due to dispersal limitations rather than environmental tolerances, retention of host trees as refugia and sources of inoculum might carry populations of old-growth-associated epiphytes into young stands. We studied growth rates of lichen and moss transplants in a Douglas-fir (Pseudotsuga menziesii) forest (tree ages approximately 55 yr) in western Oregon for nine months before and 27 months after moderate thinning, creation of 0.4-ha patch cuts, and in control areas. We also assessed moss sporophyte production. We contrasted responses of one moss species, Isothecium myosuroides sensu lato, which is ubiquitous in forests of varying ages, with those of another moss, Antitrichia curtipendula, and a lichen, Lobaria oregana, which are both associated with old-growth forests. Both old-growth associates grew faster in thinned areas and patch cuts than in controls, while Isothecuim grew most slowly and produced fewest sporophytes in patch cuts. These species are likely to survive in remnants, assuming they can remain attached, and may be successful in young stands if they can disperse and establish there. Our results suggest that logging with green-tree retention and other silvicultural practices that preserve trees or shrubs hosting the species studied here are likely to encourage these species' development in managed forests.