Combined effects of retention forestry and prescribed burning on polypore fungi.
Retention forestry and prescribed burning aim to alleviate the negative effects of forestry on biodiversity by maintaining the structural elements of natural forests in managed forests. We present the long-term effects of these methods on polypore fungi, a taxonomic group that has been severely affected by forestry. Using a 10-year, large-scale field experiment, we studied how prescribed burning and two different tree retention levels (10 and 50 m3ha-1) affect polypore fungi. We monitored polypore sporocarps on 2767 individually marked trees four times over the study period: in the first autumn after the treatments, and again 2, 4 and 10 years after the treatments. The number of polypore species and records initially increased rather slowly but showed a marked increasing trend towards the end of the 10-year monitoring period. After 2 years, the higher retention sites had an average 8.5 species and the low retention sites 4.5 species per site. After 4 years, the difference was 14 vs. 9 species and after 10 years 26 vs. 19 species. Red-listed species were not found often on the trunks earlier than 10 years after the treatments. Prescribed burning increased the number of polypore species and records along with time. Furthermore, 13 species favoured burned sites, while only six species favoured unburned sites, and the differences in the composition of species assemblages between burned and unburned sites were evident 10 years after the treatments. Synthesis and applications. We show, for the first time, that retention trees can host rich polypore assemblages, and even some red-listed species, and, thus, be useful in conservation of forest biodiversity outside protected areas. Higher retention levels maintain more diverse polypore assemblages. Prescribed burning increases the positive effects of retention forestry by creating substrates that are typical in the early-successional natural forests.