LAUSR

Abstract Fungal assemblages after a large-scale disturbance can be diverse and have functionally important roles in forests. However, fungi include several functional groups, and the responses of these groups to different forest disturbances is poorly understood. For example, ectomycorrhizal fungi may facilitate the establishment of a new tree cohort while saprotrophic fungi are able to decompose most of the dead organic material that result from the disturbance event. In this study, we examined how functionally different macrofungi respond to two major disturbances: fire (prescribed burning) and different intensities of timber harvest. We used large-scale field experiment where (1) fire and (2) harvest intensity were manipulated simultaneously in a factorial, replicated design. Three levels of harvests and an unharvested control were included, and sites were either burned or not. Fungi were surveyed before treatments in year 2000 and annually over three years (2001–2003) after the treatments. Fungi species were divided into ectomycorrhizal (ECM), saprophyte (SaM) and wood-associated fungi (WAM). The latter group mostly included Aphylloporoid wood-associated species (AWAM) and agarics. We observed also two biotrophic and one parasitic fungus but these were excluded from the assemblage-level analyses due to their rarity. Both number of sporocarps (fruiting bodies) and their biomass were measured. Fungal groups were affected by harvest and fire but the various fungal groups responded in different ways to the treatments. The ECM species were sensitive to timber harvests and disappeared from all the harvested sites. Fire in the unharvested sites did not negatively affect the ECM fungi. The SaM fungi responded quickly after disturbance, and their assemblage composition changed after fire and harvest. Species richness was reduced but fire promoted several pyrophilous SaM species, leading to major compositional changes in SaM species and the formation of distinct assemblages. The WAM species declined after harvests but fire tended to counteract the negative effects of timber harvesting. The results show that fungal groups respond in different ways to major disturbances in boreal forests. Early successional post-disturbance forests contribute to the maintenance of forest biodiversity, especially the specialist SaM species. However, the type of disturbance (fire or harvest) affect fungi in different ways. Understanding the assemblage dynamics of decomposer and other fungi is crucial when estimating how changes in forest disturbance regimes may affect nutrient and carbon cycling, as well as the maintenance of forest biodiversity.