Site conditions rather than provenance drive tree growth, climate sensitivity and drought responses in European beech in Germany

Ongoing climate change and associated extreme events strongly impact the growth and vitality of forest ecosystems in Europe. Because of its’ high drought sensitivity, European beech, which is considered as climax tree species in large parts of Central Europe, may specifically suffer. Hence, recent studies increasingly focus on the resistance and resilience of beech growth to climate change. Intra-specific variations in growth responses by comparing different beech provenances, however, received less attention, as did the question whether provenance selection can be used to mitigate potential future negative impacts of climate change. Therefore, we here investigated 24 provenances belonging to the International Beech Provenance Trial growing at three sites in Germany along a latitudinal gradient (study sites are referred to as ’North’, ‘Center’, ‘South’). Specifically, we compared tree-ring width (TRW), diameter breast height (DBH), climate-growth relationships, as well as drought resistance and resilience in the extreme years 2003 and 2018. Large differences in growth performance were observed between the three study sites. At site North, beech trees showed the highest DBH and TRW. Tree growth was predominantly driven by previous-year October and current-year winter temperature, whereas growth at sites Center and South was significantly impacted by summer SPEI and constrained by precipitation in late winter and early June, respectively. Overall, drought responses in 2003 were less variable than in 2018. We found increasing resistance and decreasing resilience from the wetter North to the drier South, but with minimal differences between the Center and the South. Whereas differences between study sites were large, provenance differentiation within sites was comparably low, substantiating that beech is a highly plastic tree species. Even though some provenances were found to perform slightly better or worse, differences were not statistically significant and show unclear patterns. Hence, we conclude that climate change will affect beech forests in Europe mainly depending upon site conditions, and that provenance selection may not ensure superior growth performance.