Minimal effects on genetic structuring of a fungus-dwelling saproxylic beetle after recolonisation of a restored forest.
Habitat restoration aims to improve local habitat conditions for threatened species. While such restorations are widespread, rigorous evaluations of their success are rare. This is especially true of those considering species dynamics. Increasingly, deadwood is a target for forest restoration as many species directly and indirectly depend on this resource. In a broadleaf forest in southern Germany, we explored the effect of landscape-wide deadwood restoration on the population genetic structure of the specialist fungus-dwelling saproxylic beetle Bolitophagus reticulatus. Before 2003, the northern area of this forest was intensively logged for more than half a century, while the southern part was less intensively managed. This drove populations of the host fungus Fomes fomentarius, and consequently the beetle, to local extinction in the northern part. Only after the first decade of restoration were both the fungus and its beetles present across all areas of the forest. Using 17 newly developed microsatellite loci, we show that these beetles exhibit population genetic structuring, mainly influenced by the north-south divide. However, the low degree of isolation-by-distance, and the low relatedness of beetles collected from the same trees or fungus, shows that strong dispersal ability is facilitating the recolonisation of these forests on the scale of tens of kilometers. In another 10 years, it is likely that the population will show even less genetic structuring. Synthesis and applications. Through the recolonisation of the fungus Fomes fomentarius and the fungus-dwelling beetle Bolitophagus reticulatus after deadwood restoration, we demonstrate that, while there are many discussions on the optimal spatial distribution of deadwood, just the presence of deadwood can be sufficient to enable recolonisations of specific species. As long as some relict populations of these species are embedded in a once intensively managed forest, increased deadwood (amount and diversity) anywhere will benefit recolonisation of the habitat. However, increasing deadwood diversity should also be encouraged to benefit even more species.