Community structure of polyporous fungi after wildfire in boreal forest

Abstract: Wildfire is a natural disturbance that creates large amounts dead wood and contribute to a landscape of different successional stages, important for biodiversity. The number of wildfires have declined in boreal Fennoscandia due to effective fire suppression. A better understanding of the fire-effects on species communities is necessary to obtain effective conservation. The aim of this study was to compare the community structure of polyporous fungi (polypores) in burned forests with forests with a long history of fire suppression. I studied three different sites in northern Sweden 12 years post fire; (1) a mixed coniferous forest in a landscape highly affected by forestry, (2) an old growth spruce forest in the proximity to high mountains and (3) a pine forest in a large protected area. In each burned area, I measured the coniferous coarse woody debris and surveyed the wood for polypores. The same was done in control areas next to each of the burned areas. The amount and quality of dead wood differed between the burned areas and the control areas. The fires created dead wood but also consumed dead wood of later decay stages, resulting in a shift towards early decay stages in burned areas. In all sites, the community structure of polypores differed between burned and unburned areas but various species contributed to the differences. A few generalists were very abundant in the burned areas compared to the control while several red-listed species found in the controls were few or missing in the burned areas. The red-listed Diplomitoporus crustulinus was not found in the controls but on charred bark on several logs in the burned areas. The shift in community structure is likely due to the difference in amount and quality of dead wood and a dryer microclimate in the burned areas, which is more open and have less ground vegetation. Fire does not necessary increase the local diversity but can increase the diversity on a landscape level. This study indicates that the development of the polypore community post fire is influenced by the traits of the prefire forest and the fire intensity. Many restoration burns is relatively low-intensity fires in pine forests but I show that also intense fires in spruce-dominated forests can be positive for biodiversity.