Balancing the Risk: Heritability of Leaf Phenology and Frost Resistance in the Dominant Temperate Forest Tree European Beech.

Ongoing climate change is increasingly affecting forest ecosystems. European beech, the naturally dominant tree species of Central Europe, has suffered in recent dry years. Due to its frost sensitivity and conservative spring leaf out behavior, it is also less able to profit from generally prolonged growing seasons due to climate warming, compared to other species. Its potential to maintain its competitiveness depends on its capacity to adapt to the changing environmental conditions; otherwise, the species might lose its dominance and face shifts in its distribution range. Generally, the capacity to adapt by selection depends on phenotypic variation of traits and their heritability in a population or species. Here, we aimed to quantify heritability of a set of relevant phenological and physiological traits. Based on 961 half-sib seedlings, originating from mother trees with early, intermediate, and late leaf out from a natural forest stand in north-east Germany, we measured spring (leaf out date) and autumn (leaf senescence) phenology as well as the frost tolerance of buds in late winter and of leaves in spring. Narrow-sense heritabilities were calculated by animal models and half-sib analysis. The European beech seedlings revealed a medium heritability in spring phenology (h 2: 0.48 and 0.57 for two consecutive years) and autumn leaf senescence (h 2: 0.35). The physiological traits leaf and bud frost tolerance had a low heritability (h 2: 0.13; h 2: 0.12, respectively). This demonstrates a considerable capacity to adapt spring and autumn phenology if the selective pressure increases. The possibility of a paralleled adaptive evolution of frost tolerance, however, remains questionable.