Data from: Climatic stress during stand development alters the sign and magnitude of age-related growth responses in a subtropical mountain pine

The modification of typical age-related growth by environmental changes is poorly understood, In part because there is a lack of consensus at individual tree level regarding age-dependent growth responses to climate warming as stands develop. To increase our current understanding about how multiple drivers of environmental change can modify growth responses as trees age we used tree ring data of a mountain subtropical pine species along an altitudinal gradient covering more than 2,200 m of altitude. We applied mixed-linear models to determine how absolute and relative age-dependent growth varies depending on stand development; and to quantify the relative importance of tree age and climate on individual tree growth responses. Tree age was the most important factor for tree growth in models parameterised using data from all forest developmental stages. Contrastingly, the relationship found between tree age and growth became non-significant in models parameterised using data corresponding to mature stages. These results suggest that although absolute tree growth can continuously increase along tree size when trees reach maturity age had no effect on growth. Tree growth was strongly reduced under increased annual temperature, leading to more constant age-related growth responses. Furthermore, young trees were the most sensitive to reductions in relative growth rates, but absolute growth was strongly reduced under increased temperature in old trees. Our results help to reconcile previous contrasting findings of age-related growth responses at the individual tree level, suggesting that the sign and magnitude of age-related growth responses vary with stand development. The different responses found to climate for absolute and relative growth rates suggest that young trees are particularly vulnerable under warming climate, but reduced absolute growth in old trees could alter the species’ potential as a carbon sink in the future.环境变化对典型年龄相关生长的调控效应仍有待深入解析，究其原因，一方面是在单木水平（individual tree level）上，关于林分发育（stand development）过程中树木年龄对气候变暖的生长响应尚未形成统一认知。为增进我们对多种环境变化驱动因子如何随树木年龄改变其生长响应的理解，本研究依托沿海拔梯度（altitudinal gradient）分布的山地亚热带松树种的树木年轮数据（tree ring data），该梯度覆盖海拔跨度超2200米。我们采用混合线性模型（mixed-linear models），以明确绝对和相对年龄依赖性生长如何随林分发育发生变化，并量化树木年龄与气候因子对单木生长响应的相对重要性。在基于所有森林发育阶段数据构建的参数化模型中，树木年龄是影响树木生长的最关键因子。与之形成鲜明对比的是，当仅使用成熟林分阶段的数据构建参数化模型时，树木年龄与生长之间的关系变得不再显著。这些结果表明，尽管绝对生长量可随树木个体大小的增加持续提升，但当树木进入成熟阶段后，年龄对生长不再具有显著影响。在年温升高的条件下，树木生长受到显著抑制，使得年龄相关的生长响应趋于恒定。此外，幼树对相对生长速率的下降最为敏感，而老树的绝对生长量则在年温升高时受到显著抑制。本研究结果有助于调和此前在单木水平上关于年龄相关生长响应的相悖发现，表明年龄相关生长响应的方向与强度随林分发育进程发生变化。本研究发现的绝对与相对生长速率对气候的不同响应表明，幼树在气候变暖背景下尤为脆弱；而老树绝对生长量的下降，则可能在未来改变该树种作为碳汇（carbon sink）的潜力。