Environmental heterogeneity regulates species-area relationships through the spatial distribution of species

Species-area relationships(SARs), also known as species-area curves, are fundamental scaling tools for biodiversity research. Sampling design and taxonomic groups affect the widely cited forms of species-area curves.However, the influence of sampling design and related environmental heterogeneity on SAR curves is rarely considered. Here, we investigated the SAR among different plant life forms(herbaceous plants, shrubs, and trees) in a 25.2-ha Forest GEO plot, the Wanglang Plot, in Sichuan, southwestern China, using a non-contiguous quadrat sampling method and power-law model. We compared the estimated parameters(the intercept c and the slope z) of the power-law models among different plant life forms, tested whether the SAR curve forms varied with sampling starting location, and assessed the effect of environmental heterogeneity accumulating with sampling area on curve variation. We found a wider range of variations in the SARs. The estimated c, z-values of power SAR were higher for the herbaceous plants than for the woody plants. A wider variation of SARs for the herbaceous plants than those for the woody plants. The selection of sampling starting location affected the SAR curve forms because of the roles of soil and topographic heterogeneity. We concluded that environmental heterogeneity regulates SAR curves sampled from different starting locations through spatial distribution of plant life forms.Thus, we recommend considering the design of sampling starting location when constructing SAR curves, especially in a heterogeneous habitat with unrandom distribution patterns of species.