Siitonen, J. (2001): Forest management, coarse woody debris and saproxylic organisms: Fennoscandian boreal forests as an example. Ecological Bulletins 49: 11-41.

Forest management, coarse woody debris and saproxylic organisms: Fennoscandian boreal forests as an example
Juha Siitonen

A conservative estimate for the total number of species dependent on dead-wood habitats is 4000-5000 within the area of Finland, which accounts for 20-25% of all forestdwelling species. A large body of data concerning the average amounts of coarse woody debris (CWD) in both natural and managed forests has accumulated during the 1990s in Fennoscandia, including results from national forest inventories. The average volume of CWD in old-growth forests is generally 60-90 m3ha-1 in southern Fennoscandia, and declines to 20 m3ha-1 close to the timberline. Available data and modelling results indicate that the volume is even much higher following disturbance, and only slightly lower in mature natural forests. In managed forest landscapes the average volumes vary between 2 and 10 m3ha-1 depending on the region. This means that the average amount of CWD at the landscape level has probably been reduced by 90-98%. General species-area relationships suggest that such a reduction in available habitat might lead to the disappearance of > 50% of original saproxylic species in managed forests in the long term. Several recent studies have shown that the number of saproxylic species per stand depends on the amount of CWD, and also on the average size and decay stage of dead trunks. These relationships can be explained by either higher habitat diversity (more different niches) or larger population sizes of individual species (lower risk for local extinction) with increasing amount of CWD. A third important factor explaining local species richness of species living in ephemeral habitat patches, i.e. dead trees that decay away, is the spatiotemporal continuity of suitable host trees. Important theoretical and practical issues for conservation, management and research include, for instance, how well the remaining high-quality patches (e.g. old-growth fragments, key habitats) can secure the regional persistence of saproxylic species, and how much, what kind, and where CWD should be retained in the ordinary managed forests in order to maintain most of the species.