Effects of forest management on the key fungal decomposer Fomes fomentarius in European beech forests – Lessons from a large-scale experiment

Abstract

Fomes fomentarius (L.) Fr., (commonly known as Tinder fungus) is an abundant fungus in European beech old-growth forests and is important for nutrient cycles, food web dynamics, and biodiversity. The species was heavily reduced during the last centuries by forestry. Modern silviculture strategies in Central Europe aim to balance both the extraction of wood and promoting dead wood habitats. Such an approach is key to sustaining Fomes fomentarius as well as up to 600 saproxylic arthropods associated with the fungus. The aim of this study was to assess how dead wood type in combination with microclimate, resulting from different forest management strategies, affect the presence (occupancy) and abundance (percent cover occupied) of Fomes fomentarius fruit bodies at the stand- and dead wood object-scale. We experimentally extracted a standardized proportion of trees within 50 m by 50 m patches creating stumps, logs, snags, and logs with snags under two microclimate treatments (open canopy gap versus closed canopy) in a random block design. As a control, we defined cut stumps under closed canopies, as this is the common thinning approach in mature beech production forests. We tested the effects of alternative management strategies against the control using Generalized Linear Mixed-effects Models. At the stand-scale, our model revealed a significantly lower occupancy of Fomes fomentarius in control stands compared to treatments in which dead wood was not removed. The average cover of Fomes fomentarius on snags under a closed canopy, at both the stand- and dead wood object-scale, was higher than in control plots. However, effect size was weak at the object-scale. To increase this principal decomposer and boost important microhabitats for many arthropods, silviculture should aim to increase snags while maintaining dense forest canopies. Yet, at landscape scale, diversifying dead wood types and light conditions may boost overall saproxylic diversity.