Drivers of species and genetic diversity within forest metacommunities across agricultural landscapes of different permeability

Context Habitat fragmentation and land use intensification are major threats to biodiversity worldwide, affecting both species (SD) and genetic (GD) diversity. It remains unclear whether SD and GD respond to the same components of landscape changes and to what extent they correlate in fragmented systems. Objectives We explore the role of current and historical patch and landscape features on SD and GD, in and between forest fragments, along a gradient of landscape matrix permeability. We seek the circumstances under which SD and GD correlate. Methods Within three contrasted agricultural landscapes of northern France, we assessed vascular plant SD and the GD of two plant species with contrasted life history traits in all forest fragments. Species richness and expected heterozygosity were taken as proxies for SD and GD respectively. Using regression and correlation analyses, we explored relationships between SD/GD and local, landscape and historical factors; and between SD and GD. Results When landscape permeability is above a certain threshold, SD and GD appear to be patterned by the same processes, which results in a positive SD-GD correlation. This permeability threshold is species-specific, depending upon species’ dispersal traits and niche width. The SD-GD correlation depends upon current and past landscape permeability, so that the lack of correlation emerges as the rule in weakly permeable landscape matrices, especially when fragments are small. Conclusions Landscape matrix permeability and patch features drive SD and GD of vascular plants within and between forest fragments. A generalist, fast-colonizing species better reflects diversity patterns in fragmented forests.