Anthropogenic climate change pushes forest ecosystems globally beyond their limits. Widespread events of forest die-off have been attributed to direct and indirect impacts of increasingly frequent and intense droughts. Here, we focus on an extensive mortality event in Norway spruce (Picea abies (L.) H. Karst.) and European beech (Fagus sylvatica (L.)) forests in Germany, following the successive 2018 – 2019 hot droughts. To examine whether this die-off indeed attributed to observed trends in drought occurrence and intensity, we sampled 143 beech and 186 spruce trees at three low-elevation sites (Spessart, Hassberge, Fichtelberg) with different edaphic properties in northern Bavaria. We analysed long-term hydroclimatic sensitivity and growth responses to extreme events of five site- and species-specific tree-ring width chronologies, including a reference site for each species. Growth of beech was sensitive to drought in April to June, whereas spruce growth was strongly related to drought during June to August, except at slightly higher elevations at the Fichtelberg site, where a summer temperature signal was observed. Trees at the Spessart and Hassberge sites showed an increased response to hydroclimatic conditions in April following the extreme drought in 1976 and from the 1990s onwards at the Fichtelberg site. Spruce bark beetle (Ips typographus L.) outbreaks during the 2018 drought accelerated the high mortality rates in around 50% of the trees at the Spessart and Hassberge site. In 2018, around 7% of all beech trees died at the Hassberge site, the site with the highest clay content. Our results suggest that these widespread mortality events can be attributed to an increasing drought sensitivity and were accelerated by the consecutive recent drought years. Sustainable forest management practices for these ecologically and economically important tree species are required to mitigate the effects of global warming in the future.

人为气候变化使全球森林生态系统超出其极限。森林死亡的广泛事件归因于日益频繁和严重干旱的直接和间接影响。在这里，我们集中讨论挪威云杉（Picea abies（L.）H. Karst。）和欧洲山毛榉（Fagus sylvatica）的广泛死亡事件。(L.)) 德国的森林，经历了 2018 年至 2019 年的连续干旱。为了检查这种死亡是否确实归因于观察到的干旱发生和强度的趋势，我们在巴伐利亚北部具有不同土壤特性的三个低海拔地点（Spessart、Hassberge、Fichtelberg）对 143 棵山毛榉和 186 棵云杉树进行了采样。我们分析了五个特定地点和特定物种的年轮宽度年表的极端事件的长期水文气候敏感性和生长响应，包括每个物种的参考地点。山毛榉的生长对 4 月至 6 月的干旱敏感，而云杉的生长与 6 月至 8 月的干旱密切相关，但 Fichtelberg 站点海拔略高的地方除外，在那里观察到了夏季温度信号。在 1976 年和 1990 年代之后，在 1976 年极端干旱之后，Spessart 和 Hassberge 站点的树木在 4 月份对水文气候条件的反应有所增强。云杉树皮甲虫 (Ips Typgraphus L.) 2018 年干旱期间的爆发加速了 Spessart 和 Hassberge 站点约 50% 树木的高死亡率。2018 年，大约 7% 的山毛榉树在 Hassberge 遗址死亡，该遗址的粘土含量最高。我们的研究结果表明，这些广泛的死亡事件可归因于干旱敏感性的增加，并且在最近的连续干旱年份加速了。需要对这些在生态和经济上具有重要意义的树种进行可持续的森林管理实践，以减轻未来全球变暖的影响。