Drought-induced tree mortality of European beech affected by legacy effects and small-scale heterogeneity in soil properties and tree neighbourhood composition

由于气候压力及其对食草动物和病原体动态的影响，森林正面临越来越大的压力，主要是干旱事件的强度和频率增加。最近的一个例子是欧洲山毛榉（Fagus sylvatica L.）的区域性枯死，这表明气候压力的增加如何影响森林的未来。在2018/2019年严重的中欧干旱之后。这种剧烈的和前所未有的反应，这一主要的欧洲阔叶树种，自然会主导中欧森林植被表明，下降的生命力与下降的增长稳定性相结合的螺旋式下降-质疑设想的突出作用，这一物种的气候变化减缓。在那里，具有强烈干旱反应直至死亡的个体出现在重要且似乎未受影响的个体旁边。我们认为，各种非生物和生物因素的复杂相互作用可能是导致山毛榉林分内干旱响应分布不均匀的原因。虽然非生物因素的小规模异质性，主要是土壤特性，驱动了林分内土壤水分可用性的变化，种内竞争作为一个关键的生物因素可能会进一步介导遗产效应和干旱引起的死亡率。因此，旨在通过联合分析对历史气候变化的生长响应以及沿气候梯度沿着的细尺度土壤和结构因素，解开干旱引起的欧洲山毛榉树木死亡率的驱动因素，以应对2018/19年严重的干旱和热浪。具体来说，我们的目标是i）通过历史高分辨率遥感产品确认树木生命力和树冠状况的视觉分类，ii）描述每棵树的地形，土壤，结构和竞争状态的小尺度变化，iii）通过来自径向生长的衰退指标量化和比较树木之间的生命力损失，iv）通过建立干旱相关的欧洲山毛榉分布范围内的生长衰退和恢复模式的地理背景，制定一项新的风险评估战略，以及（v）提供一个经实地验证的干旱预测框架-在给定的土壤和结构条件下，这种经济和生态上重要的树种的敏感性。

Forests are facing increasing pressure due to climatic stress and its influence on herbivore and pathogen dynamics, mainly through increased intensity and frequency of drought events. A recent example of how increasing climate stress can shape the future of forests is the regional die-back of European beech (Fagus sylvatica L.) after the severe Central European drought of 2018/2019. This drastic and unprecedented response of this major European broad-leaved species that would naturally dominate Central European forest vegetation suggests a downward spiral of decreasing vitality in combination with decreasing growth stability — questioning the envisioned prominent role of this species for climate change mitigation.The sites affected by beech die-back exhibit a high heterogeneity, where individuals with strong drought responses up to mortality occur next to vital and seemingly unaffected individuals. We propose that complex interactions of various abiotic and biotic factors might be responsible for this uneven distribution of drought response within beech stands: while small-scale heterogeneity in abiotic factors, predominantly soil properties, drives the variability of soil water availability within the stand, intra-specific competition as a critical biotic factor might further mediate legacy effects and drought-induced mortality.The proposed project, therefore, aims at disentangling the drivers of drought-induced tree mortality in European beech in response to the severe 2018/19 drought and heatwave by a joint analysis of growth-responses to historic climatic variability and fine-scale edaphic and structural factors along a climatic gradient. Specifically, we aim to i) confirm the visual categorization of tree vitality and crown condition by historical high-resolution remote sensing products, to ii) describe small-scale variability in the topographic, edaphic, structural and competitional status of each tree, to iii) quantify and compare the loss of vitality among trees through decline indicators derived from radial growth, to iv) develop a novel strategy for risk assessment through establishing the biogeographic context for drought-related patterns of growth decline and recovery across the distributional range of European beech, and (v) to provide a field-validated framework for predicting the drought-sensitivity of this economically and ecologically important tree species under given edaphic and structural conditions.