Data from: Checkerboard score-area relationships reveal spatial scales of plant community structure

Identifying the spatial scale at which particular mechanisms influence plant community assembly is crucial to understanding the mechanisms structuring communities. It has long been recognized that many elements of community structure are sensitive to area; however the majority of studies examining patterns of community structure use a single relatively small sampling area. As different assembly mechanisms likely cause patterns at different scales we investigate how plant species co-occurrence patterns change with sampling unit scale. We use the checkerboard score as an index of species segregation, and examine species C-score-sampling area patterns in two ways. First, we show via numerical simulation that the C-score-area relationship is necessarily hump shaped with respect to sample plot area. Second we examine empirical C-score-area relationships in arctic tundra, grassland, boreal forest, and tropical forest communities. The minimum sampling scale where species co-occurrence patterns were significantly different from the null model expectation was at 0.1 m2 in the tundra, 0.2 m2 in grassland, and 0.2 Ha in both the boreal and tropical forests. Species were most segregated in their co-occurrence (maximum C-score) at 0.3 m2 in the tundra (0.54 m by 0.54 m quadrats), 1.5 m2 in the grassland (1.2 by 1.2 m quadrats), 0.26 Ha in the tropical forest (71 m by 71 m quadrats), and a maximum was not reached at the largest sampling scale of 1.4 Ha in the boreal forest. The most important finding is that the dominant scales of community structure in these systems are large relative to plant body size, and hence we infer that the dominant mechanisms structuring these communities must be at similarly large scales. This provides a method for identifying the spatial scales at which communities are maximally structured; ecologists can use this information to develop hypotheses and experiments to test scale-specific mechanisms that structure communities.

明确特定机制影响植物群落构建的空间尺度，对于解析塑造群落结构的核心机制至关重要。长期以来学界已达成共识：群落结构的诸多特征对取样面积具有敏感性；但当前绝大多数探究群落结构格局的研究，仅采用单一且相对偏小的取样区域。鉴于不同的群落构建机制大概率在不同尺度上塑造群落格局，本研究旨在探究植物物种共存格局如何随取样单元尺度发生变化。本研究以棋盘格得分（checkerboard score）作为物种分隔程度的量化指标，并通过两种方式分析物种C得分与取样面积的关系格局：其一，通过数值模拟证明，取样样方面积与C得分之间的关系必然呈驼峰形曲线；其二，针对北极苔原、草原、寒温带针叶林以及热带森林群落，分析其实证层面的C得分-取样面积关系。当物种共存格局与零模型（null model）预期存在显著差异时，各群落的最小取样尺度分别为：苔原群落0.1平方米，草原群落0.2平方米，寒温带针叶林与热带森林群落均为0.2公顷。物种共存的分隔程度（即C得分最大值）在苔原群落中出现在0.3平方米（0.54米×0.54米样方），草原群落在1.5平方米（1.2米×1.2米样方），热带森林群落在0.26公顷（71米×71米样方）；而寒温带针叶林群落在最大取样尺度1.4公顷时仍未达到C得分峰值。本研究最核心的发现为：上述四类群落中，主导群落结构的空间尺度远大于植物个体的体型尺寸，据此可推断，塑造这些群落的核心机制必然作用于同等尺度的空间范围。本研究为识别群落结构达到最大化的空间尺度提供了可行方法；生态学家可借助该结论提出假说、设计实验，以验证调控群落结构的尺度依赖性机制。