AIM: Forest net biomass change (ΔAGB; the difference between biomass gain from growth and loss through mortality) determines how forests contribute to the global carbon cycle. Understanding how plant diversity affects ΔAGB in diverse abiotic conditions is crucial in the face of anthropogenic environmental change. Recent studies have advanced our understanding of the effects of plant diversity on growth dependent on the abiotic context, either supporting or rejecting the stress gradient hypothesis. However, we know little about how diversity influences mortality, which prevents us from knowing how diversity affects ΔAGB in diverse abiotic conditions. LOCATION: Across Canada (43–60° N, 52–133° W). TIME PERIOD: 1951–2016. MAJOR TAXA STUDIED: Ninety‐three tree species. METHODS: We modelled the relationships of growth, mortality and ΔAGB with functional diversity that represented niche complementarity, while simultaneously accounting for the influence of functional identity and stand age. RESULTS: Growth and mortality increased, on average, with functional diversity, but the magnitude of the increase in growth was greater than that of mortality, resulting in an increase of ΔAGB. The positive relationship between growth and functional diversity was more prominent in more humid sites than in drier sites. Mortality increased with functional diversity in drier sites but did not increase in wetter sites. The positive relationship between ΔAGB and functional diversity was strengthened with water availability. Moreover, the positive relationship between growth and functional diversity became stronger with temperature, but the positive associations of diversity with mortality and ΔAGB were consistent across the gradient of temperature. MAIN CONCLUSIONS: Our results suggest that higher functional diversity leads to an increase in forest biomass accumulation owing to a greater positive effect of functional diversity on productivity than on mortality. However, in contrast to the stress gradient hypothesis, our findings show that the positive effect of functional diversity is more pronounced in an environment favourable for growth.

中文翻译：

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气候的空间变化改变了加拿大天然林中功能多样性对生物量动态的影响

目标：森林净生物量变化（ΔAGB；通过生长获得的生物量与因死亡而损失的生物量之间的差异）决定了森林对全球碳循环的贡献。面对人为环境变化，了解植物多样性如何影响不同非生物条件下的 ΔAGB 至关重要。最近的研究促进了我们对依赖于非生物环境的植物多样性对生长影响的理解，支持或拒绝压力梯度假设。然而，我们对多样性如何影响死亡率知之甚少，这使我们无法了解多样性如何影响不同非生物条件下的 ΔAGB。位置：加拿大各地（北纬 43–60°，西经 52–133°）。时间段：1951-2016。研究的主要类群：93 种树种。方法：我们模拟了增长的关系，死亡率和 ΔAGB 具有代表生态位互补性的功能多样性，同时考虑了功能特性和林龄的影响。结果：平均而言，随着功能多样性的增加，生长和死亡率增加，但生长增加的幅度大于死亡率，导致ΔAGB增加。生长和功能多样性之间的正相关关系在更潮湿的地方比在干燥的地方更显着。在较干燥的地点，死亡率随着功能多样性的增加而增加，但在较湿润的地点没有增加。ΔAGB 与功能多样性之间的正相关关系随着水的可用性而加强。此外，随着温度的升高，生长与功能多样性之间的正相关关系变得更强，但多样性与死亡率和 ΔAGB 的正相关在整个温度梯度上是一致的。主要结论：我们的研究结果表明，由于功能多样性对生产力的积极影响大于对死亡率的积极影响，更高的功能多样性会导致森林生物量积累的增加。然而，与压力梯度假设相反，我们的研究结果表明，在有利于生长的环境中，功能多样性的积极影响更为明显。