Assessing Individual And Local Scale Forest Vulnerability To Mortality From The 2019 Extreme Drought In Central Europe

气候变化正在对全球树木和森林生态系统的健康产生重大影响。对许多地区来说，在未来的气候情景下，干旱事件的频率和强度预计会增加。因此，随着气候变暖和干旱事件变得更加频繁和剧烈，预计森林生长将普遍减少，死亡事件的范围和严重性将增加。虽然干旱事件的影响经常在物种分布的炎热和干燥边缘观察到，但令人震惊的是，最近与干旱有关的死亡发生在气候条件最有利的物种范围的核心地区。全球植被生长模型难以预测被认为气候一般适合该物种的地区的死亡事件，这在确定哪些森林易受干旱影响以及这种脆弱性在不同景观和个别树木之间如何变化方面带来了相当大的挑战。为了解决这个问题，我们迫切需要物种分布核心区域内死亡和生存的个体的详细数据。然而，预测何时何地会发生强烈干旱事件是极具挑战性的，这使得这种响应性数据的收集非常困难。2019年，一场严重干旱事件影响了中欧的森林。2020年春天，很明显，这次干旱事件在欧洲山毛榉（欧洲大陆分布最广泛的阔叶树之一，也是一种重要的林业资源）范围的核心区域内造成了广泛但变化很大的死亡。中欧欧洲山毛榉森林对2019年严重干旱的非凡反应现在为我们提供了一个绝佳的机会，可以更好地预测该物种范围内哪些森林地区面临干旱事件的风险增加。通过在这一极端事件发生后迅速采取行动，在现已死亡的树木的树冠开始失去树枝和倒塌之前，我们可以收集在2019年干旱事件中死亡并幸存下来的单个树木的数据，以确定树木的大小（如直径、高度、树冠大小）、树木的竞争（如树木密度、大小分布）、历史生长模式（由树木年轮确定）和当地地形特征(如坡度、坡向、曲率)影响树木对干旱导致的死亡的脆弱性。我们将详细的实地测量与同样详细的无人机捕获的高光谱和激光雷达数据以及卫星遥感数据相结合，这将使我们能够从森林冠层上方评估树木健康和森林结构。有效利用这一短暂的机会窗口来评估2019年干旱的影响，将使我们能够制定快速评估森林健康和预测大面积森林脆弱性的新方法。本项目收集的数据将使我们能够对当地树木的干旱脆弱性作出现实的预测，并开发遥感方法，以支持这些森林健康预测的验证。2019年中欧干旱事件后造成的情况极为罕见，因此该项目提供了一个重大机会，可以推动亟需的森林健康遥感改进，并提供必要的知识和数据，以改进持续气候变化下的全球森林生长模型。

Climate change is having significant impacts on the health of trees and forest ecosystems globally. For many regions, the frequency and intensity of drought events are predicted to increase under future climate scenarios. Consequently, widespread reductions in forest growth and increases in the extent and severity of die-off events are anticipated as the climate warms and drought events become more frequent and intense. While the effects of drought events have often been observed at the hot and dry margins of species distributions, alarmingly, recent drought-linked die-off has occurred within the core area of species ranges where climatic conditions should be most favourable. Global models of vegetation growth have difficulty predicting die-off events in areas considered to be generally climatically suitable for the species, bringing considerable challenges in identifying which forests are vulnerable to droughts and how that vulnerability varies across landscapes and individual trees. To address this problem, we urgently need detailed data from individuals that die and those that survive intense drought events from within the core regions of the species distribution. However, predicting when and where intense drought events will occur is extremely challenging, making such responsive data collection very difficult. In 2019 an intense drought event impacted forests in Central Europe. In the Spring of 2020, it became clear that this drought event had caused widespread, yet highly variable die-off within the core area of the range of the European beech tree - one of the most widely distributed broadleaf trees on the continent and a key forestry resource. The extraordinary response of the European beech forests in Central Europe to the intense drought in 2019 now provides us with an exceptional opportunity to better predict which forest areas are at an increased risk to drought events within the core of this species range. By acting rapidly in the wake of this extreme event before the crowns of the now-dead trees begin to lose branches and collapse, we can collect data from individual trees that died and survived the 2019 drought event to determine how tree size (e.g. diameter, height, crown size), stand competition (e.g. tree density, size distribution), historical growth patterns (determined from tree rings), and local terrain characteristics (e.g. slope, aspect, curvature) influence the vulnerability of trees to drought-induced mortality. We will pair detailed field measurements with equally detailed drone-captured hyperspectral and LiDAR data and satellite remote sensing data that will enable us to assess tree heath and forest structure from above the forest canopy. Effectively exploiting this short window of opportunity to assess the impact of the 2019 drought will enable us to develop new approaches for the rapid assessment of forest health and to predict vulnerability across large areas of forest. The data collected in this project will allow us to make realistic local forecasts of tree vulnerability to drought and develop remote sensing methods to support the validation of these forest health forecasts. The conditions that have resulted following the drought event in Central Europe in 2019 are extremely rare and so this project provides a major opportunity to drive much needed improvements in remote sensing of forest health and deliver the knowledge and data needed to improve global models of forest growth under ongoing climate change.