Species turnover (β-diversity) along elevational gradients is one of the most important concepts in plant ecology. However, there is a lack of consensus about the main driving mechanisms of tree β-diversity at local scales in very diverse ecosystems (e.g., Andean mountains), as well as how the sampling effect can alter β-diversity estimations. Recently, it has been hypothesized that patterns of change in β-diversity at local scales along elevational gradients are driven by sampling effects stemming from differences in the size of the species pool rather than by underlying community assembly mechanisms. Thus, we aim to evaluate the relative extent to which sampling effects, such as species pool size, grain size, and tree size cut-off, determine species sorting, and thus, the variability of β-diversity at local scales along elevational gradients in the northwest of Colombia. Using 15 1-ha permanent plots spread out along a 3000 m elevational gradient, we used standardized β-deviation to assess the extent to which either sampling effects or the community assembly mechanisms determine the changes in species composition at local scales. Standardized β-deviation was measured as the difference between the observed and null β-diversity divided by the standard deviation of the null β-diversity. We found that the magnitude of change in local β-deviation along the elevational gradient was significant and dependent on the employed spatial grain size and tree size cut-off. However, β-deviation increased with elevation in all sampling designs, which suggests that underlying community assembly mechanisms play a key role in shaping local β-diversity along the elevational gradient. Our findings suggest that grain size enlargement and the inclusion of trees with small diameters will improve our ability to quantify the extent to which the community assembly mechanisms shape patterns of β-diversity along elevational gradients. Overall, we emphasize the scale-dependent nature of the assessment of β-diversity. Likewise, we call for the need of a new generation of enlarged forest inventory plots along gradients of elevation in tropical forests that include small individuals to improve our understanding about the likely response of diversity and function to global change.

中文翻译：

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谷物和截留尺寸在塑造哥伦比亚西北部海拔梯度上的树木β多样性中的重要性

沿海拔梯度的物种周转率（β-多样性）是植物生态学中最重要的概念之一。但是，对于非常多样化的生态系统（例如，安第斯山脉）中局部尺度上树木β多样性的主要驱动机制，以及采样效果如何改变β多样性估计，尚缺乏共识。最近，有一种假设认为，沿海拔梯度的局部尺度上β多样性的变化模式是由物种库大小差异引起的采样效应驱动的，而不是由潜在的群落组装机制驱动的。因此，我们旨在评估采样效果（例如物种库大小，谷物大小和树木大小截止）的相对程度，以确定物种的分类，因此，β多样性在哥伦比亚西北部沿海拔梯度的局部尺度变化。利用沿3000 m海拔梯度分布的15个1公顷永久性样地，我们使用标准化的β偏差来评估采样效果或群落聚集机制决定局部尺度上物种组成变化的程度。标准化β偏差的测量方法是，将观察到的β多样性与无效β多样性之间的差异除以无效β多样性的标准偏差。我们发现，沿高度梯度的局部β偏差的变化幅度是显着的，并且取决于所采用的空间粒度和树木大小的截止值。但是，在所有采样设计中，β偏差都随高度的增加而增加，这表明潜在的社区聚集机制在塑造沿海拔梯度的局部β多样性方面起着关键作用。我们的发现表明，晶粒尺寸的扩大和小直径树木的包容将提高我们量化群落组装机制沿海拔梯度塑造β多样性模式的程度的能力。总体而言，我们强调β多样性评估的规模依赖性。同样，我们要求在热带森林中沿海拔梯度形成新一代的扩大的森林资源积蓄图，其中包括小个体，以增进我们对多样性和功能对全球变化的可能反应的了解。我们的发现表明，晶粒尺寸的扩大和小直径树木的包容将提高我们量化群落组装机制沿海拔梯度塑造β多样性模式的程度的能力。总体而言，我们强调β多样性评估的规模依赖性。同样，我们要求在热带森林中沿海拔梯度形成新一代的扩大的森林资源积蓄图，其中包括小个体，以增进我们对多样性和功能对全球变化的可能反应的了解。我们的发现表明，晶粒尺寸的扩大和小直径树木的包容将提高我们量化群落组装机制沿海拔梯度塑造β多样性模式的程度的能力。总体而言，我们强调β多样性评估的规模依赖性。同样，我们要求在热带森林中沿海拔梯度形成新一代的扩大的森林资源积蓄图，其中包括小个体，以增进我们对多样性和功能对全球变化的可能反应的了解。