CREAF, Cerdanyola del Vallès, Spain.
Unitat d'Ecologia, Univ. Autònoma Barcelona, Cerdanyola del Vallès, Spain.
Glob Chang Biol. 2020 May;26(5):3134-3146. doi: 10.1111/gcb.15042. Epub 2020 Mar 13.
In recent decades, many forest die-off events have been reported in relation to climate-change-induced episodes, such as droughts and heat waves. To understand how these extreme climatic events induce forest die-off, it is important to find a tool to standardize the climatic conditions experienced by different populations during a specific climatic event, taking into account the historic climatic conditions of the site where these populations live (bioclimatic niche). In this study, we used estimates of climatic suitability calculated from species distribution models (SDMs) for such purpose. We studied forest die-off across France during the 2003 heatwave that affected Western Europe, using 2,943 forest inventory plots dominated by 14 single tree species. Die-off severity was estimated by Normalized Difference Vegetation Index (NDVI) loss using Moderate-resolution Imaging Spectroradiometer remote sensor imagery. Climatic suitability at the local level during the historical 1979-2002 period (HCS), the episode time (2003; ECS) and suitability deviance during the historical period (HCS-SD) were calculated for each species by means of boosted regression tree models using the CHELSA climate database and occurrences extracted from European forest inventories. Low HCS-SD and high mean annual temperature explained the overall regional pattern of vulnerability to die-off across different monospecific forests. The combination of high historical and low episode climatic suitability also contributed significantly to overall forest die-off. Furthermore, we observed different species-specific relationships between die-off vulnerability and climatic suitability: Sub-Mediterranean and Mediterranean species tended to be vulnerable in historically more suitable localities (high HCS), whereas Euro-Siberian species presented greater vulnerability when the hot drought episode was more intense. We demonstrated that at regional scale, past climatic legacy plays an important role in explaining NDVI loss during the episode. Moreover, we demonstrated that SDMs-derived indexes, such as HCS, ECS and HCS-SD, could constitute a tool for standardizing the ways that populations and species experience climatic variability across time and space.
近几十年来，许多森林死亡事件都与气候变化引发的干旱和热浪等事件有关。为了了解这些极端气候事件如何导致森林死亡，重要的是找到一种工具来标准化不同种群在特定气候事件期间经历的气候条件，同时考虑到这些种群生活地点的历史气候条件（生物气候位）。在这项研究中，我们为此目的使用了物种分布模型（SDM）计算的气候适宜性估计值。我们使用 14 种单木种主导的 2943 个森林清查样本来研究法国在 2003 年热浪期间的森林死亡情况，该热浪影响了西欧。使用中等分辨率成像光谱仪（MODIS）遥感图像计算归一化差异植被指数（NDVI）损失来估算死亡率严重程度。使用 CHELSA 气候数据库和从欧洲森林清查中提取的发生情况，通过提升回归树模型为每个物种计算了历史时期（HCS）、事件时间（ECS）和历史时期（HCS-SD）的局部水平的气候适宜性。低 HCS-SD 和高平均年温度解释了不同单种森林在整个区域的易损性模式。高历史和低事件气候适宜性的组合也对整体森林死亡有显著贡献。此外，我们观察到易损性和气候适宜性之间的不同物种特异性关系：亚热带和地中海物种往往在历史上更适宜的地方（高 HCS）易受影响，而欧洲西伯利亚物种在热干旱事件更剧烈时则表现出更大的脆弱性。我们证明，在区域尺度上，过去的气候遗留物在解释事件期间的 NDVI 损失方面起着重要作用。此外，我们证明，SDM 衍生的指标，如 HCS、ECS 和 HCS-SD，可以作为一种工具，用于标准化种群和物种在时间和空间上经历气候变异性的方式。
