Forest fragmentation in Fennoscandia: Linking habitat requirements of wood-associated threatened species to landscape and habitat changes

摘要

Fragmentation may occur simultaneously in different spatial and temporal scales. The ecological importance of fragmentation depends both on the scale of fragmentation and on the habitat requirements of the species. The fragmentation of old-growth forests is regarded as one of the most important causes for the recent decline of several forest-dwelling species in Fennoscandia. In Fennoscandia landscape-level fragmentation has proceeded differently in various areas. For example, in eastern Finland mature forest fragmentation was evident very early. By the 1800's, only one third of the landscape was covered by 150 yr old forests. This early fragmentation resulted mostly from the slash-and-burn cultivation practised widely in these areas. In the northern Fennoscandia, however, no such landscape changes have been found before the 1900s. During the 1900's fragmentation has accelerated. Recent results suggest that biological impacts of current landscape-level fragmentation of mature forests may have been overestimated, especially among invertebrate species. Specific habitat requirements of these groups are still poorly known. Instead of requiring mature forests, several wood-associated threatened species may require only dead wood that can occur in any successional stage in both managed and protected areas. Such variability in the habitat requirements allows good opportunities for preservation of the threatened species. Results from current research indicate the need to restore and recreate natural fire-originated early successional stages where the amount of coarse woody debris is high. Promotion of coarse woody debris in young managed forests is potentially a very effective way to sustain populations of several threatened wood-associated species.