Maintaining biodiversity in managed forests - Results of beetle and polypore studies in boreal forests

This paper gives a review of several studies where the effects of different forest management methods on polyporous fungi and beetles, and the importance of woodland key habitats (WKHs) for polypore diversity were investigated in different zones of boreal forest in Finland. The total species richness of beetles was relatively well maintained in the seed-tree cut pine forests over the time span of 15 years, but the proportion of rare species had decreased, obviously because the lack of suitable substrate. In the clear-cut spruce forests which were planted for pine the beetle community had changed considerably due to the change of the major tree species and changes in microclimate. Proportion of rare species was low on clear-cuts. The polypore diversity in the seed-tree cut pine forests was relatively well maintained on the pre-logging CWD still 40 years after logging, but on the logging waste only about half of the total species richness was found. In the selectively logged spruce forests neither the forest structure nor the diversity of polypores had returned to natural level in 60-100 years. The results show that there is a time lag of several decades before the real effects of logging are detectable in the saproxylic and saprotrophic communities. WKHs selected on the basis of rich vascular plant flora maintained poorly the characteristic polypore flora of boreal forests. Small (0.2 ha) WKHs covered only about 20% the detected total species richness of polypores. Leaving large-diameter retention trees and CWD in regeneration areas would benefit many saproxylics. It seems, however, difficult to maintain in managed forests the diversity of those saproxylics, which have adapted to the steady, moist microclimate of old-growth spruce forests. Relatively large (0.5-1 ha) unlogged patches of typical old-growth forests would help to maintain both polypore and beetle. diversity of spruce stands.