Understanding how stand structure responds to stresses such as drought and pollution could aid forest managers in evaluating silvicultural treatment success, predicting treatment durability, and designing adaptive management approaches. The size-growth relationship (SGR), a measure of growth partitioning among different size trees in a stand, may provide a means of linking stresses impacting individual trees to forest stand development and growth. No study to date has tested SGR’s response to drought and pollution, specifically N deposition, across landscapes. We combined Forest Inventory and Analysis (FIA) stand development and plot-level lichen bioindicator data on N deposition with climate data denoting moisture availability. Using linear regression, we examined SGR, stand structural complexity, individual tree growth and mortality in largely multi-aged, mixed species stands in California, Oregon, and Washington, USA, coniferous and pine-oak forests. Our goals were to determine a) the influence of moisture availability and/or N deposition on SGR, b) whether SGR translates to differences in stand structural complexity over time, and c) the extent to which SGR mediates the impacts of abiotic stress on tree growth and mortality. Consistent with previous research, our results indicated that SGR increased with stand density, indicative of larger trees possessing a disproportionate advantage in aboveground competition for light. SGR declined linearly with stand age, trending over time towards disproportionately slow large-tree growth. SGR strongly increased with low-moderate bioindicated N deposition, which is consistent with past findings that SGR increases with site quality and suggests that N deposition disproportionately increases growth in larger trees. We did not find evidence that drought stress (as indicated by the Palmer Drought Severity Index) influenced SGR. Stands that were already more structurally complex showed further gains in complexity under high SGR (disproportionately rapid large-tree growth), whereas stands that were initially structurally simpler increased in complexity under low SGR (disproportionately slow large tree growth). As such, individual-tree growth and mortality may drive changes in complexity. Our results support the utility of SGR as a predictor of how stress impacts stand structure, but only when accounting for initial structural complexity. Our findings also have implications for the design and durability of silvicultural treatments, given that silvicultural prescriptions often involve the manipulation of tree size distributions. Moreover, these findings underscore the importance of accounting for the historical influence of N deposition on stand development during treatment planning, as well as the likelihood of socioeconomic changes altering N deposition in the future.

了解林分结构如何应对干旱和污染等压力可以帮助森林管理者评估造林处理的成功率、预测处理的持久性和设计适应性管理方法。大小-生长关系 (SGR) 是一个林分中不同大小树木之间生长划分的度量，可以提供一种将影响单个树木的压力与林分发展和生长联系起来的方法。迄今为止，还没有研究测试过 SGR 对干旱和污染的反应，特别是跨景观的氮沉降。我们将森林清查和分析 (FIA) 林分开发和地块级地衣生物指标数据与 N 沉积的气候数据相结合，该数据表示水分可用性。使用线性回归，我们检查了 SGR、支架结构复杂性、在加利福尼亚州、俄勒冈州和美国华盛顿州的针叶林和松橡树林中，个体树木的生长和死亡率主要是多龄、混合树种。我们的目标是确定 a) 水分可用性和/或氮沉积对 SGR 的影响，b) SGR 是否会随着时间的推移转化为林分结构复杂性的差异，以及 c) SGR 介导非生物胁迫对树木的影响的程度生长和死亡率。与之前的研究一致，我们的结果表明 SGR 随林分密度增加，表明较大的树木在地上光竞争中具有不成比例的优势。SGR 随林龄呈线性下降，随着时间的推移趋向于不成比例地缓慢的大树生长。SGR随着低中度生物指示氮沉积强烈增加，这与过去的研究结果一致，即 SGR 随着场地质量的增加而增加，并表明 N 沉积不成比例地增加了较大树木的生长。我们没有发现干旱胁迫（如帕尔默干旱严重程度指数所示）影响 SGR 的证据。在高 SGR（不成比例地快速大树生长）下，结构已经更加复杂的林分显示出进一步的复杂性，而在低 SGR（不成比例地缓慢大树生长）下，最初结构更简单的林分复杂性增加。因此，单棵树的生长和死亡率可能会推动复杂性的变化。我们的结果支持 SGR 作为压力如何影响林分结构的预测因子的效用，但仅限于考虑初始结构复杂性时。鉴于造林处方通常涉及对树木大小分布的操纵，我们的研究结果也对造林处理的设计和耐久性有影响。此外，这些发现强调了在处理计划期间考虑氮沉积对林分发展的历史影响的重要性，以及未来社会经济变化改变氮沉积的可能性。