KEY ECOLOGICAL FUNCTION OF CHARCOAL FROM WILDFIRE IN THE BOREAL FOREST

Wildfire is a major disturbance factor in boreal forests where it is i mportant in rejuvenating soil properties and encouraging tree regenera tion and growth. However, the mechanisms behind these effects are poor ly understood and little is known as to the ecological effects of char coal produced by wildfire in these ecosystems. In this study we firstl y quantified the mass of charcoal in a chronosequence of twelve forest sires in northern Sweden and found charcoal mass in soil to vary from 984 to 2074 kg ha(-1); these levels appear to be sufficient for charc oal to have important ecological effect through its sorptive abilities . We then investigated the ability of charcoal from 32 forest stands ( representing a range of ages from 1 to 350 yr since last fire) to adso rb phenolic compounds produced by the late successional dwarf shrub Em petrum hermaphroditum: phenolic compounds from this species have previ ously been shown to have important phytotoxic effects in boreal forest s. Charcoal in soil from forests younger than 100 yr was very effectiv e at reducing these effects while older charcoal was not, suggesting t hat the sorptive ability is likely to be most important in earlier-suc cessional forests. Experimental reheating of deactivated older charcoa l From soil showed that temperatures above 450 degrees C could reactiv ate charcoal. A microcosm experiment also revealed that soil microbes could effectively reactivate young charcoal that had been saturated wi th phenolics, Finally we investigated the effects of artificially made charcoal on soil microbial properties at six sites. The microbial bio mass was consistently enhanced in humus when it was placed adjacent to charcoal particles. Decomposition of plant litter was sometimes also affected by being in the proximity of charcoal but the direction of th ese effects was unpredictable. We conclude that charcoal might catalys e important ecological soil processes in the proximity of charcoal but the direction of these effects that diminish as succession proceeds, and ultimately may have important long-term consequences for stand pro ductivity and ecosystem function, especially in forests under strict f ire control.