Fagus sylvatica L. (European Beech) is the dominant tree species over large areas of Western and Central Europe. Yet, due to its drought susceptibility and low seed dispersal capability, it is expected to suffer from climate change. Across its large distribution range, F. sylvatica shows only low genetic adaptation to its local environments. Implications of its high phenotypic plasticity for species persistence in the face of future climatic changes, however, are not fully understood yet. We conducted a fully reciprocal transplantation experiment across a Europe-wide gradient, reaching from the dry (Spain) to the cold distribution edge (Sweden, Poland) of the species. At 12 different sites inside and outside of the natural distribution range, we planted in total over 12.000 beechnuts collected from known mother trees. We sampled morphological, fitness- and stress-related traits during the year of establishment and in the subsequent years. We compared different potential sources of phenotypic plasticity in F. sylvatica, namely within single mother trees, within single stands or provenances, and across different provenances under the contrasting climates of the translocation sites.
Results/Conclusions
Comparing phenotypic responses at the provenance level, seedlings of F. sylvatica expressed only little differences in phenotypic plasticity for several traits. All studied provenances showed a comparable phenotypic responsiveness to the various environmental conditions of the gradient. Most interestingly, we found that the full phenotypic variation was already present within the offspring of each mother tree. This finding implies surprisingly high phenotypic plasticity per mother tree and, hence, indicates high potential to respond to climate change. This high within-tree variation could presumably also be a basis for potential local adaptation, once the evolutionary pressure is increasing and slightly less plastic individuals would be sorted out. Overall, we suggest, that F. sylvatica has a high capacity to buffer the impact of future climatic changes by phenotypic plasticity and can possibly also enable long-term genetic adaptation by its within-stand variation in phenotypic plasticity.