Dispersal limitations of epiphytic lichens result in species dependent on old-growth forests

Epiphytic lichen biomass accumulates slowly in forest canopies. We evaluate d three alternative hypotheses for the slow accumulation of epiphytic liche ns, using two experiments in tree crowns from 15 Douglas-fir forest stands representing three age classes: old growth, young, and recent clearcuts. Th e first experiment evaluated whether forest age, bark roughness, or dispers al rate limits the establishment of the dominant old-growth-associated lich en, Lobaria oregana. Surface-sterilized branches with either rough or smoot h bark were repeatedly inoculated with propagules and compared 1 yr after t he last inoculation. Dispersal affected rates of establishment: inoculated branches had 27 x more newly established thalli than controls. Establishmen t on smooth bark was highest in clearcuts, intermediate in young forests, a nd lowest in old growth. There was as much or more establishment of sown pr opagules on smooth-barked branches as on rough-barked branches in all age c lasses. In the second, transplant-performance experiment, Lobaria oregana g rew as rapidly in young forests as in old growth but lost biomass and suffe red more injuries in clearcuts. In contrast, L. pulmonaria performed at lea st as well in clearcuts as in young forests and old growth. Poor dispersal and establishment limit the development of L. oregana populations in Dougla s-fir forests. Particular substrates and microenvironments found only in ol d growth are not essential for Lobaria establishment and growth. Maximizing the number and dispersion of remnant trees in cutting units should maximiz e the rate of accumulation of L. oregana biomass in the regenerating forest . The single most important action promoting the accumulation of old-growth -associated epiphytes will be the retention of propagule sources in and nea r all cutting units.