In recent decades, climate change has disrupted forest functioning by promoting large-scale mortality events, declines in productivity and reduced regeneration. Understanding the temporal dynamics and spatial extent of these changes is critical given the essential ecosystem services provided by forests. As the most widespread tree species in North America, quaking aspen (Populus tremuloides) is well suited for studying the dynamics of tree populations during a period of unprecedented climate change. Synthesizing continent-wide data, we show that mortality rates of mature aspen stems have increased over the past two-to-three decades, while relative gains in aspen basal area have decreased during the same period. Patterns were pervasive across multiple stand size classes and composition types in western North America biomes, suggesting that trends in demographic rates were not simply a reflection of stand development and succession. Our review of the literature revealed that increased aspen mortality and reduced growth rates were most often associated with hotter, drier conditions, whereas reduced recruitment was most often associated with herbivory. Furthermore, interactions between climate and competition, as well as climate and insect herbivory, had important, context-dependent effects on mortality and growth, respectively. Our analyses of aspen across its entire geographic range indicate that this important tree species is experiencing substantial increases in mortality and decreases in population growth rates across multiple biomes. If such trends are not accompanied by increased recruitment, we expect that the reduced dominance of aspen in forests will lead to major declines in the many essential ecosystem services it provides.

近几十年来，气候变化导致大规模死亡事件、生产力下降和再生减少，从而破坏了森林的功能。鉴于森林提供的基本生态系统服务，了解这些变化的时间动态和空间范围至关重要。作为北美分布最广的树种，颤杨（Populus tremuloides）) 非常适合研究前所未有的气候变化时期树木种群的动态。综合整个大陆的数据，我们表明成熟的白杨茎的死亡率在过去的两到三年内有所增加，而同期白杨基部面积的相对增长却有所下降。模式在北美西部生物群落的多个林分大小类别和组成类型中普遍存在，这表明人口率的趋势不仅仅是林分发展和演替的反映。我们对文献的回顾表明，白杨死亡率增加和生长速度降低最常与更热、更干燥的条件有关，而减少补充最常与食草有关。此外，气候与竞争之间的相互作用，以及气候和昆虫食草，分别对死亡率和生长具有重要的、依赖于环境的影响。我们对整个地理范围内的白杨进行的分析表明，这种重要的树种在多个生物群落中的死亡率大幅上升，人口增长率下降。如果这种趋势没有伴随着增加的补充，我们预计白杨在森林中的主导地位下降将导致它提供的许多基本生态系统服务的大幅下降。