Effects of forest management intensity on multi-alpha and multi-beta diversity

Commercial forestry is a major threat to biodiversity. Its effects on forest biodiversity remain unresolved, partly because major management components might have distinct effects on different species groups and their overall diversity. Using a full-factorial deadwood experiment, we investigated the effects of forest management intensity on the diversity of six deadwood-associated species groups (i.e., primary producers, fungal fruit bodies, mycelial fungi, bacteria, archaea and nematodes). We assessed their alpha, beta and multi-diversity along the Hill series (rare (q0), common (q1) and dominant (q2) diversity) and tested them against management intensity, assessed as a composite index comparing tree removal (harvested basal area), deadwood availability (volume), tree species composition (proportion of non-natural species) and stand maturity (diameter at breast height) to unmanaged old-growth forests. Within the management range studied, multi-alpha diversity did not respond significantly to overall forest management intensity, due to contrasting responses of the different species groups. Tree removal potentially increased environmental heterogeneity, thereby promoting alpha diversity. In contrast, multi-beta diversity and the beta diversity of individual species groups, particularly dominant diversity, were strongly altered by tree removal and tree species composition. These components likely act through microclimatic differences and varying resource availability. Deadwood availability had no effect, presumably due to depleted deadwood pools and lacking characterization of deadwood quality within the index. Low- to medium-intensity management can enhance alpha diversity. However, changing tree species composition fundamentally alters communities, particularly dominance patterns, with potential feedbacks on multifunctionality, calling for a mix of integrative and segregated conservation approaches.