The future trajectory of global forests is closely intertwined with tree demography, and a major fundamental goal in ecology is to understand the key mechanisms governing spatio-temporal patterns in tree population dynamics. While previous research has made substantial progress in identifying the mechanisms individually, their relative importance among forests remains unclear mainly due to practical limitations. One approach to overcome these limitations is to group mechanisms according to their shared effects on the variability of tree vital rates and quantify patterns therein. We developed a conceptual and statistical framework (variance partitioning of Bayesian multilevel models) that attributes the variability in tree growth, mortality, and recruitment to variation in species, space, and time, and their interactions – categories we refer to as organising principles (OPs). We applied the framework to data from 21 forest plots covering more than 2.9 million trees of approximately 6500 species. We found that differences among species, the species OP, proved a major source of variability in tree vital rates, explaining 28–33% of demographic variance alone, and 14–17% in interaction with space, totalling 40–43%. Our results support the hypothesis that the range of vital rates is similar across global forests. However, the average variability among species declined with species richness, indicating that diverse forests featured smaller interspecific differences in vital rates. Moreover, decomposing the variance in vital rates into the proposed OPs showed the importance of unexplained variability, which includes individual variation, in tree demography. A focus on how demographic variance is organized in forests can facilitate the construction of more targeted models with clearer expectations of which covariates might drive a vital rate. This study therefore highlights the most promising avenues for future research, both in terms of understanding the relative contributions of groups of mechanisms to forest demography and diversity, and for improving projections of forest ecosystems.

中文翻译：

---

全球森林树木人口统计变化的主要轴


全球森林的未来轨迹与树木人口统计密切相关，生态学的一个主要基本目标是了解控制树木种群动态时空模式的关键机制。虽然以前的研究在单独确定这些机制方面取得了实质性进展，但由于实际限制，它们在森林中的相对重要性仍不清楚。克服这些限制的一种方法是根据机制对树木生命率变异性的共同影响对机制进行分组，并量化其中的模式。我们开发了一个概念和统计框架（贝叶斯多级模型的方差划分），将树木生长、死亡率和补充的变异性归因于物种、空间和时间的变异及其相互作用——我们称之为组织原则（OPs）的类别）。我们将该框架应用于 21 个森林地块的数据，覆盖约 6500 个物种的超过 290 万棵树。我们发现，物种之间的差异，即物种 OP，被证明是树木生命率变异的主要来源，仅解释了人口统计差异的 28-33%，以及与空间相互作用的 14-17%，总计 40-43%。我们的结果支持这样的假设：全球森林的生命率范围相似。然而，物种之间的平均变异性随着物种丰富度的增加而下降，这表明不同的森林在生命率方面的种间差异较小。此外，将生命率的方差分解为提议的 OP 显示了树木人口统计学中无法解释的变异性（包括个体变异）的重要性。 关注森林中人口差异的组织方式可以促进更有针对性的模型的构建，并对哪些协变量可能驱动生命率有更​​清晰的预期。因此，本研究强调了未来研究最有希望的途径，无论是在了解机制组对森林人口统计和多样性的相对贡献方面，还是在改进森林生态系统的预测方面。