Experimentally manipulating forest structure to mimic management strategies: effects on deadwood fungal diversity and decomposition.

Deadwood fungi are extremely diverse and crucial for carbon turnover in forests. To achieve multifunctional forests, we need to better understand the relationships between diversity, management, and ecosystem processes. We tested the effects of forest structure, i.e. canopy cover and deadwood enrichment, on fungal diversity and mass loss of European beech and Scots pine. We additionally assessed the effects of fungal diversity on mass loss. We expected deadwood enrichment to better explain fungal diversity, while canopy cover, alongside fungal diversity, would best explain mass loss. Overall, host tree species was more important than forest structure in explaining diversity. Beech fungal diversity was higher under closed canopies, while pine fungal diversity increased with some types of deadwood enrichment. Surprisingly, beech mass loss was higher in stands without deadwood enrichment, but also where tree crowns were added. Pine mass loss was not affected by forest structure. Effects of fungal diversity on mass loss were significantly related to fungal community composition in pine. Our findings emphasize the need for diverse tree hosts at the forest landscape-scale. However, contrasting diversity and decomposition effects between host trees indicate that stand-scale management strategies should be tailored to tree species to maintain diversity and decomposition processes.