Effects of resource availability and climate on the diversity of wood‐decaying fungi

Summary 1. Wood‐decaying fungi are crucial for the functioning of forest ecosystems. We tested the hypotheses that on coarse woody debris (CWD), the abundance, diversity and composition of fungi depend more on the amount of available resource than on macro‐ or microclimate, and that on fine woody debris (FWD) more on the microclimate because of the rapid desiccation of thin woody debris. 2. We sampled 7183 dead wood objects with 10 818 fungal samples on 290 plots along four transects, from 650 to 1450 m a.s.l., in the Bavarian Forest National Park, Germany, Overall, we recorded 263 species (54 only on FWD and 71 only on CWD). 3. For each plot, we characterized the macroclimate using field data and a terrain model. Microclimate variables were extracted from remote‐sensing and ground surveys. Resource availability was characterized by measuring the amount, tree species composition, diameter and rotting stage of all dead wood objects. We extracted principal components from each of the three data sets for further analyses. 4. The number of species found per sampled surface area of woody debris indicated that the fungal community on FWD needs a much lower surface area than that on CWD; FWD probably provides more niches per unit surface area than CWD. The abundance of fungi (and therefore also species density) living on FWD and CWD as well as the fungal community composition on CWD were clearly driven by variables characterizing the amount and diversity of the resource. In general, the surface area was the most important factor for abundance of species. In contrast, the community composition on FWD was better predicted by variables characterizing the microclimate. 5. Synthesis . Our results supported the hypotheses that the amount of available resources is more important than macroclimate for fungi living on CWD, and microclimate is more important for fungi living on FWD. Therefore, both dead wood removal and silviculture, which, like logging, open the canopy and increases sunlight exposure, will strongly affect the diversity of wood‐decaying fungi in forests. For the conservation of this important group of organisms in forests, silvicultural strategies are more important than climate.