Forest floor lichen and bryophyte communities in thinned Pseudotsuga menziesii - Tsuga heterophylla forests

Abstract

While a great deal of research has illustrated the importance of late-successional forests for maintaining biodiversity in the Pacific Northwest of North America, over 76% of the forests in the region are less than 100 years old. To preserve landscape-level biodiversity, forest managers are increasingly interested in how young stands can be manipulated to favor late-successional species. We sought to understand how stand-level gradients in canopy structure, particularly those affected by thinning, relate to dominant forest floor bryophyte and lichen species composition and abundance. We sampled forest floor lichen and bryophytes ten years after alternative thinning treatments at two sites in western Oregon. Relationships of forest floor communities to canopy structure were site-specific. At the first site, moss and lichen abundance had small-scale geographic patterns and mosses were negatively associated with epiphytic cyanolichen species richness, however, we found no strong associations between forest floor communities and stand structural characteristics. At the second site, lichens, particularly Cladonia, was negatively associated with canopy cover and was most in thinned plots. Bryophyte abundance was positively associated with Tsuga basal area. This relationship was stronger in the thinned stands, which had a different community composition than those left unthinned. Overall, the forest floor communities were fairly homogeneous at both sites and relationships with stand structural variables were subtle, indicating that thinning did not have a strong impact.