How much is enough – estimating set-aside areas in naturally disturbed forests

Abstract

The amount of naturally disturbed forests in the Northern Hemisphere has increased as a consequence of global change. Natural disturbances, such as wildfires, windstorms and insect outbreaks affect billions of trees and cause significant economic losses. Post-disturbance logging is a common practice globally to 'salvage' some of these economic returns. However, salvage logging can have negative effects on ecosystem functioning and biodiversity. Those taxa, which depend on deadwood (i.e. saproxylic), are most affected. Hence, scientists increasingly encourage the retention of disturbance-affected areas as a main tool to omit the negative effects of salvage logging on biodiversity. However, this retention compels forests managers on balancing between conservation of wood-dependent taxa and capturing economic returns. Therefore, it is important to know, how much biodiversity can be preserved if certain portions (e.g. 50 %) of disturbance-affected stands are salvage logged. We compiled data from published studies from North America (USA, Canada) and Europe (Spain, Switzerland, Germany and Poland) that compared species richness of nine taxonomic groups in salvaged and unsalvaged disturbance-affected forest stands. We modelled the conservation value of disturbance-affected stands with different portions of simulated salvage logging. The conservation value was defined as the sum of species occurring in unsalvaged plots relative to the cover of unsalvaged plots. The results showed that the number of species in unsalvaged plots decreased proportionally to the decrease of unsalvaged plots' cover. Therefore, by retaining 50 % of the disturbance-affected plots, approximately 50 % of the species occurring in unsalvaged plots, mainly deadwood dependent species, was preserved. However, there were differences between the taxonomic groups. For instance, the conservation value of saproxylic taxa (saproxylic beetles, fungi, epixylic mosses and lichens) decreased steeper compared to non-saproxylic taxa (plants, epigaic mosses, spiders, carabids and birds). This finding indicates that depending on the retention strategy decision makers could facilitate different taxonomic groups. In the talk, the effect of different retention scenarios on different taxa will be illustrated. Furthermore, the best strategies for managing naturally disturbed forests will be highlighted.