Sampling origins and directions affect the minimum sampling area in forest plots

The minimum sampling area (or minimum area), representing the smallest space that reflects the species composition and characteristics of a plant community, is estimated using species-area relationships (SARs) for designing and managing biodiversity conservation. However, the sampling design’s effect on the determination of the minimum area has rarely been systematically evaluated. In this study, we used tree census data from three forest dynamic plots of 25–60 ha in different climatic zones in China to calculate the minimum areas of woody plants in the plots and analyze the effects of species richness and topographic heterogeneity on the areas by changing sampling origins and directions. Our findings reveal that the estimated size of the minimum areas varied significantly with sampling origins and directions, with a difference of approximately 1.5–2 times in forest plots. Topographic heterogeneity affected the minimum area through changes in species composition, while species richness had only a weak impact. These results suggest the importance of considering the sampling origin and direction design when utilizing SARs to estimate the minimum area and species diversity in plant communities, which contributes to a better understanding of vegetation characteristics and the minimum area required for censuses in heterogeneous habitats.

Methods
All woody plant individuals with a DBH > 1 cm in the plots were mapped, tagged, and identified.