Can multi-taxa diversity in European beech forest landscapes be increased by combining different management systems?
Abstract
Forest management greatly influences biodiversity across spatial scales. At the landscape scale, combining management systems that create different stand properties might promote biodiversity due to complementary species assemblages. In European beech forests, nature conservation and policy advocate a mixture of unmanaged (UNM) forests and uneven-aged (UEA) forests managed at fine spatial grain at the expense of traditionally managed even-aged shelterwood forests (EA). Evidence that such a landscape composition enhances forest biodiversity is still missing. We studied the biodiversity (species richness 0D, Shannon diversity 1D, Simpson diversity 2D) of 14 taxonomic groups from bacteria to vertebrates in 'virtual' beech forest landscapes composed of varying shares of EA, UEA and UNM and investigated how γ-diversity responds to landscape composition. Groups were sampled in the largest contiguous beech forest in Germany, where EA and UEA management date back nearly two centuries, while management was abandoned 20-70 years ago (UNM). We used a novel resampling approach that created all compositional combinations of management systems. Pure EA landscapes preserved a maximum of 97.5% γ-multidiversity (0D, 1D) across all taxa. Pure and mixed UEA/UNM landscapes reduced γ-multidiversity by up to 12.8% (1D). This effect was consistent for forest specialists (1D: -15.3%). We found only weak complementarity among management systems. Landscape composition significantly affected γ-diversity of 6-9 individual taxa, depending on the weighting of species frequencies with strongest responses for spiders, beetles, vascular plants and birds. Most showed maximum diversity in pure EA landscapes. Birds benefited from UNM in EA-dominated landscapes. Deadwood fungi showed highest diversity in UNM. Synthesis and applications. Our study shows that combining fine-grained forest management and management abandonment at the landscape scale will reduce, rather than enhance, regional forest biodiversity. We found an even-aged shelterwood management system alone operating at intermediate spatial scales and providing stands with high environmental heterogeneity was able to support regional biodiversity. However, some taxa require certain shares of uneven-aged and unmanaged forests, emphasizing their general importance. We encourage using the here presented resampling approach to verify our results in forest landscapes of different composition and configuration across the temperate zone.