Lichen diversity on stems, slash and stumps in managed boreal forests

The shortage and low diversity of coarse dead wood in managed forests are major threats to wood living organisms. Increasing harvest of slash and stumps for biofuel may further decrease the amounts of dead wood. The aim of this thesis was to predict the impact of forest fuel harvest on lichen diversity in a managed forest landscape. First, lichen diversity was compared between the stem and slash fractions within living mature trees. Comparisons were also made between slash and stumps created at final felling. The effects of local factors on the species composition and richness of lichens and bryophytes on stumps were analyzed. Finally, colonization and extinction dynamics of epixylic lichens on stumps were examined. Lichen species composition differed between the stem and the slash fractions, indicating that slash harvest removes lichen communities other than those removed with stems. The lichen flora on slash changed from freshly created slash with bark to decorticated slash. There were compositional differences between decorticated slash and stumps created at final felling. The majority of species found on both substrates were more frequent on stumps, on which eight rare species were found. Lichen richness on stumps increased with presence of irregularities on the cut surface. Metapopulation processes structure the local epixylic lichen community. Connectivity and stump quality affected the probability of stump colonization by epixylic lichens. The extinction risk of local populations was mainly explained by variables describing patch quality. The effects of slash harvest are probably of minor importance to the overall lichen diversity in the study area. However, stumps may be important since 1) the majority of the epixylic lichens found have a preference for less shaded environments, 2) we found eight rare lichen species on the cut surface, and 3) stumps constitute the major part of coarse dead wood in these kinds of stands. The relative importance of stumps to the regional persistence of species in managed forests will depend on the availability of other types of coarse dead wood which depends on, e.g. geographic region, present and past land use, and forest type