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.明确调控植物群落构建的特定机制所对应的空间尺度，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：群落结构的多项特征对采样面积具有敏感性；然而当前绝大多数针对群落结构模式的研究，仅采用单一且相对偏小的采样区域。由于不同的群落构建机制往往会在特定空间尺度上形成对应的群落模式，本研究旨在探究植物物种共存模式如何随采样单元尺度发生变化。本研究以棋盘得分（checkerboard score）作为物种分隔度的量化指标，并通过两种路径分析物种C得分-采样面积的变化模式。其一，通过数值模拟证实：采样面积与C得分之间的关系必然呈驼峰状分布。其二，针对北极苔原、草原、寒温带针叶林以及热带森林群落开展实证分析，探究其C得分-采样面积的实际关联模式。物种共存模式与零模型预期存在显著差异的最小采样尺度分别为：苔原群落0.1 平方米（m²）、草原群落0.2 平方米（m²），寒温带针叶林与热带森林群落均为0.2 公顷（Ha）。各群落中物种共存分隔度最高（即C得分达到峰值）的采样尺度分别为：苔原群落0.3 平方米（m²，对应0.54 m × 0.54 m的样方）、草原群落1.5 平方米（m²，对应1.2 m × 1.2 m的样方）、热带森林群落0.26 公顷（Ha，对应71 m × 71 m的样方）；而寒温带针叶林群落的最大C得分在本次研究设置的最大采样尺度1.4 公顷（Ha）内仍未出现。本研究最重要的发现在于：上述各群落的群落结构主导尺度相较于植物个体体型明显偏大，据此可推断，塑造这些群落的核心机制同样作用于较大的空间尺度。该研究提出了一种可用于识别群落结构达到最大化的空间尺度的方法，生态学家可借助该方法构建相关假说与实验，以验证调控群落结构的尺度依赖型机制。