Structure et biodiversité dans les hêtraies mélangées exploitées et non exploitées : une comparison basée sur le réseau des réserves intégrales françaises | Structure and biodiversity in managed and unmanaged mixed beech forests: a comparison based on the strict forest reserves network in France

In Western Europe, the long history of forest management over the past centuries has shaped both landscape and local scale forest structure, presumably altering the biodiversity of forest dwelling species. In France, the strict forest reserves network has been created to serve as a witness to gauge the effects of management on forest structures and dynamics: it currently covers 0.3% of national territory, distributed over 200 sites representative of the main forest types. However, to date, research comparing biodiversity in managed and unmanaged forests remains strikingly poor in Western Europe, and hardly proposes a broad taxonomic assessment. In order to fill the gap in knowledge in the French context, we studied forest structure and biodiversity in lowland oak-beech-hornbeam forests, and in montane beech-fir-spruce forests. We compared living and dead wood amounts and biodiversity of 6 taxa (vascular plants, saproxylic fungi, birds, bats, carabids and saproxylic beetles) 15 strict forest reserves where forest management has been abandoned for at least 20 years and adjacent managed forests, totalizing 213 plots. Relatively to managed forest, stands in unmanaged forest host larger amounts of old-growth components (deadwood volumes, number of large trees) as well as higher basal areas, whereas other stand characteristics did not differ significantly. Saproxylic fungi responded significantly to management abandonment, their total richness increasing with time since last harvesting. Responses of the other taxonomic groups were less clear and further analyses correlating forest structure with taxa or ecological groups are necessary to better understand the mechanisms associating biodiversity and forest management. The applied outcome of this multitaxonomic approach is to validate indirect biodiversity indicators on a broad gradient of forest management. This project constitutes the first reference for mixed beech forests in France and may help managers to define thresholds in terms of biodiversity oriented measures.