Effects of natural disturbances and salvage logging on biodiversity Lessons from the Bohemian Forest
Abstract Severe natural disturbances are common in many forest ecosystems, particularly in the Northern Hemisphere. Attempts to minimize their effects through forest management include salvage logging. In the Bohemian Forest, one of Central Europe's largest continuous forests, windstorms and bark beetle outbreaks have affected stands of Norway Spruce for centuries. Over the past decades, these natural disturbances and their management in the Bavarian Forest National Park and the adjacent Sumava National Park in the central part of the Bohemian Forest have been scientifically studied. Owing to a benign neglect strategy, both windstorms and bark beetle outbreaks have increased stand structural heterogeneity, the amount of dead wood and light availability, which contribute to increased populations of nearly extinct forest specialists. However, the response of a particular taxonomic group or species strongly depends on its relationship to specific legacies that persist after disturbances. Stand climate but not dead wood appears to greatly influence the diversity of epigeal bryophytes, whereas both factors determine the diversity of epixylic bryophytes. Both the amount and heterogeneity of dead wood seems to be more important than stand climate in determining assemblages of wood inhabiting fungi and lichens. To reduce the population density of bark beetles in the management zones of both national parks, storm felled spruces are salvage logged, which alters a variety of these legacies and natural successional pathways. Consequently, the numbers of species of wood inhabiting fungi, saproxylic beetles and epixylic lichens are reduced. Natural levels of biodiversity in salvage logged areas can be preserved by (1) preserving root plates of storm felled trees with partly retained trunks; (2) avoiding soil disturbance by using cable yarding instead of harvesters; (3) retaining sun exposed dry branches of storm felled trees and snags of beetle killed spruces; (4) avoiding logging damage of natural regeneration and of large trees that survive disturbances; and (5) bark scratching instead of debarking to avoid bark beetle outbreaks while maintaining biodiversity. Windstorms and bark beetle outbreaks could be utilized to restore intensely managed forests of Central Europe to their natural composition and structure. Furthermore, experimentally mimicked natural disturbances might help in gaining a mechanistic understanding of how natural disturbances affect biodiversity.