Tree mortality significantly influences forest structure and function, yet our understanding of its dynamic patterns among a range of tree sizes and among different plant functional types (PFTs) remains incomplete. This study analysed size-dependent tree mortality in a temperate forest, encompassing 46 tree species and 32,565 individuals across different PFTs (i.e., evergreen conifer vs. deciduous broadleaf species, shade-tolerant vs. shade-intolerant species). By employing all-subset regression procedures and logistic generalized linear mixed-effects models, we identified distinct mortality patterns influenced by biotic and abiotic factors. Our results showed a stable mortality pattern in evergreen conifer species, contrasted by a declining pattern in deciduous broadleaf and shade-tolerant, as well as shade-intolerant species, across size classes. The contribution to tree mortality of evergreen conifer species shifted from abiotic to biotic factors with increasing size, while the mortality of deciduous broadleaf species was mainly influenced by biotic factors, such as initial diameter at breast height (DBH) and conspecific negative density. For shade-tolerant species, the mortality of small individuals was mainly determined by initial DBH and conspecific negative density dependence, whereas the mortality of large individuals was subjected to the combined effect of biotic (competition from neighbours) and abiotic factors (i.e., convexity and pH). As for shade-intolerant species, competition from neighbours was found to be the main driver of tree mortality throughout their growth stages. Thus, these insights enhance our understanding of forest dynamics by revealing the size-dependent and PFT-specific tree mortality patterns, which may inform strategies for maintaining forest diversity and resilience in temperate forest ecosystems.

中文翻译：

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温带森林植物功能类型 (PFT) 之间树木死亡率的差异：深入了解大小依赖性和 PFT 特定模式


树木死亡率显着影响森林结构和功能，但我们对一系列树木尺寸和不同植物功能类型（PFT）之间的动态模式的理解仍然不完整。这项研究分析了温带森林中与大小相关的树木死亡率，涵盖不同 PFT 的 46 种树种和 32,565 个个体（即常绿针叶树与落叶阔叶树种、耐荫树种与不耐荫树种）。通过采用全子集回归程序和逻辑广义线性混合效应模型，我们确定了受生物和非生物因素影响的不同死亡率模式。我们的结果显示，常绿针叶树种的死亡率模式稳定，而落叶阔叶树种、耐荫树种以及不耐荫树种的死亡模式则呈下降趋势。常绿针叶树种随着尺寸的增大，对树木死亡率的贡献从非生物因素转向生物因素，而落叶阔叶树种的死亡率主要受生物因素的影响，如胸径初始直径（DBH）和同种负密度。对于耐阴物种，小个体的死亡率主要由初始胸径和同种负密度依赖性决定，而大个体的死亡率则受到生物因素（邻居竞争）和非生物因素（即凸度和凸度）的综合影响。 pH值）。对于不耐荫的物种，来自邻居的竞争被发现是树木在整个生长阶段死亡的主要驱动因素。 因此，这些见解通过揭示大小依赖性和 PFT 特定的树木死亡率模式，增强了我们对森林动态的理解，这可能为维持温带森林生态系统的森林多样性和恢复力的策略提供信息。