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Can't see the trees for the forest: complex factors influence tree survival in a temperate second growth forest

机译：看不到森林的树木：复杂的因素影响温带二次生长森林中树木的生存

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Forest decline is a widespread, well‐recognized problem, but studies reporting decreases in tree survival have been largely limited to relatively rare old‐growth forests or low‐diversity systems, and to models which are species‐aggregated or cannot easily accommodate yearly climate variables. We created survival models for a multispecies second‐growth forest in the Sierra Nevada of California using a hierarchical state‐space framework. We accounted for a mosaic of measurement intervals and random plot variation, and we directly included yearly stand development variables alongside climate variables and topographic proxies for nutrient, water, and light availability. Our model captured the expected dependence of survival on tree size, but revealed different relationships between size and survival for each species. At the community level, including stand development variables accounted for decreasing survival time trends, but species‐specific models demonstrated a diversity of factors influencing survival, including time trends, fundamental niche limitations, and the impact of competition. Our results on time trends and competitive performance showed local exceptions to existing theories of Sierran forest dynamics, with some shade‐tolerant species increasing in survival over time and others performing better than expected under more crowded conditions. Within species, low survival was concentrated in susceptible subsets of our population and single estimates of annual survival rates did not reflect this heterogeneity in survival.
机译：森林退化是一个广为人知的普遍问题，但是报告树木存活率下降的研究在很大程度上限于相对稀少的老龄森林或低多样性系统，以及物种聚集或无法轻松适应年度气候变量的模型。我们使用分层的状态空间框架为加利福尼亚内华达州的一个多物种第二生林创建了生存模型。我们考虑了测量间隔和随机样地变化的镶嵌关系，并且直接将年度林分发展变量以及气候变量和营养，水和光的可利用性的地形代理包括在内。我们的模型捕获了预期的生存对树木大小的依赖性，但是揭示了每个物种的大小与生存之间的不同关系。在社区一级，包括林分发展变量导致生存时间趋势减少，但特定物种模型显示出影响生存的多种因素，包括时间趋势，基本生态位局限性和竞争影响。我们关于时间趋势和竞争绩效的结果表明，现有的赛尔兰森林动力学理论存在局部例外，一些耐荫树种的生存时间随着时间的推移而增加，而另一些在较拥挤的条件下表现优于预期。在物种内部，低存活率集中在我们种群的易感子集中，对年存活率的单一估计并不能反映这种存活率的异质性。

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