Local adaptation and phenotypic plasticity in two forest understorey herbs in response to forest management intensity

Local adaptation is a common phenomenon that helps plant populations to adjust to broad-scale environmental heterogeneity. Given the strong effect of forest management on the understorey microenvironment and often long-term effects of forest management actions, it seems likely that understorey herbs may have locally adapted to the practiced management regime and induced environmental variation. We investigated the response of <i>Anemone nemorosa</i> and <i>Milium effusum</i> to forest management using a transplant experiment along a silvicultural management intensity gradient. Genets were sampled from sites with contrasting management intensities and transplanted sympatrically, near allopatrically and far allopatrically along the management intensity gradient to test for local adaptation and phenotypic plasticity, as well as to sites where the species were absent to test for recruitment versus dispersal limitations. We then measured survival and fitness traits over two growing seasons. We found only little evidence of local adaptation in <i>A. nemorosa</i> and <i>M. effusum</i>, whereas various traits in both species showed linear plastic changes in response to transplantation along the forest management intensity gradient. Furthermore, <i>A. nemorosa</i> performed worse when transplanted to unoccupied sites, suggesting recruitment limitation, whereas <i>M. effusum</i> performed better in unoccupied sites, suggesting dispersal limitation. Altogether, our results underpin the importance of forest management to indirectly drive phenotypic variation among populations of forest plants.