Effects of forest restoration by fire on polypores depend strongly on time since disturbance - A case study from Finland based on a 23-year monitoring period

Fire is increasingly used in management and restoration of forest ecosystems, in order to rehabilitate habitat structure and to create habitats for species dependent on forest fires and dead wood. However, information on the impacts of fire on saproxylic species is scanty, and long-term studies on the effects are almost totally lacking. Here we present results from a long-term field study conducted in eastern Finland in 1988-2011. Two pine-dominated boreal forest stands, a seminatural and a managed one, were intentionally burnt in 1989. We inventoried polypores 1 year before the fire, in the year of burning, and 1, 2, 6, 13 and 22 years after the fire. The short-term effects of fire were destructive for polypore communities. However, species numbers recovered to the pre-fire level 6 years after the fire. After 13 years, the number of species was clearly higher than before the fire, due to the large input of fire-killed dead trees. The number of red-listed species was strikingly high (18 species) in the seminatural stand 13 years after the fire including several species which have earlier been considered as old-growth forest indicators, and remained at high level (17 species) still 22 years after the fire. The number of red-listed species was much lower in the formerly managed stand (6 and 8 species, respectively). We conclude that burning of stands can be a very effective method to create habitats for red-listed polypore species, at least if the stand is located close to high-quality source areas and contains a sufficient amount of large-diameter trunks of different tree species.