Numerous studies have reported that observed species shifts in mountain areas lag behind expectations under current warming trends, however, the mechanisms remain poorly understood. One important mechanism might be microclimatic heterogeneity causing migration of species to cooler conditions under closed forest canopies, but evidence is scarce. We here compared the distributions of 710 species (11 taxonomic groups including fungi, plants, and animals) along an elevation gradient (287–1419 m a.s.l.) in a temperate low mountain range between 2006–2008 and 2016–2017 to address this open question. We characterized each species' distribution (peak and breadth) based on their abundance along two environmental gradients: elevation and canopy cover. We then analysed changes in species' distribution peaks, asking whether shifts in canopy distribution and initial distribution characteristics explain variation in elevational distribution shifts. Across all taxa, the mean shift in elevational distribution peak was + 35.3 m (i.e. upslope). Species' baseline distribution peaks were strong predictors of elevational distribution shifts with stronger upslope shifts in low‐elevation and open‐forest species. Even though we observed considerable variation in the responses among species, canopy distribution shifts had a significant negative effect on elevational distribution shifts overall and in six taxonomic groups. We suggest that this is related to cooler microclimatic conditions under closed compared to open forest canopies. Shifts to closed‐canopy forests may thus partly compensate for elevational distribution shifts, highlighting the conservation value of heterogeneous landscapes featuring microclimatic refugia. Yet, it is likely that other mechanisms, such as habitat limitation, are also at play. Future studies need to quantify the potential of microclimatic refugia under accelerating forest dynamics, considering the interplay of canopy cover and other factors driving microclimate, and to illuminate the complex climate change response mechanisms among species and taxonomic groups.

中文翻译：

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到顶峰还是黑暗中？山地森林海拔与冠层覆盖分布变化的关系


大量研究报告称，在当前的变暖趋势下，观察到的山区物种转移落后于预期，然而，人们对其机制仍然知之甚少。一个重要的机制可能是小气候异质性导致物种迁移到封闭森林树冠下的凉爽条件下，但证据很少。我们在这里比较了 2006-2008 年和 2016-2017 年间温带低山山脉沿海拔梯度（海拔 287-1419 米）的 710 个物种（包括真菌、植物和动物在内的 11 个分类群）的分布，以解决这个悬而未决的问题。我们根据每个物种在两个环境梯度上的丰度（海拔和树冠覆盖率）来表征每个物种的分布（峰值和宽度）。然后，我们分析了物种分布峰值的变化，询问树冠分布和初始分布特征的变化是否解释了海拔分布变化。在所有分类群中，海拔分布峰值的平均偏移为 + 35.3 m（即上坡）。物种的基线分布峰值是海拔分布变化的有力预测因子，在低海拔和开阔林物种中，上坡变化更强。尽管我们观察到物种之间的响应存在相当大的差异，但树冠分布变化对整体和六个分类群的海拔分布变化产生了显着的负面影响。我们认为，与开放的森林树冠相比，这与封闭条件下凉爽的小气候条件有关。因此，向封闭树冠森林的转变可能部分补偿了海拔分布的变化，突出了以微气候避难为特征的异质景观的保护价值。 然而，其他机制，如栖息地限制，很可能也在起作用。未来的研究需要量化在加速森林动力学下小气候避难所的潜力，考虑树冠覆盖和其他驱动小气候的因素的相互作用，并阐明物种和分类群之间复杂的气候变化响应机制。