Is it Sufficient? Two Methods to Assess Adequate Sample Size and Minimum Plot Size for Urban Plant Investigations

Determining Adequate Sample Size (ASS) and Minimum Plot Size (MPS) are two fundamental issues in urban vegetation investigations. To estimate ASS and MPS of urban plants, we introduced sampling completeness into MPS calculation and examined the species-area curves method and CV Jack1 (the Coefficient Variation (CV) for the First-order Jackknife Estimator (Jack1)) curves method, based on 54 samples in Chongqing, China. We also tested the effectiveness of extrapolating ASS from CV Jack1 curves, using 180 samples from Chongqing, China, and 222 samples from Xiamen, China. Results showed: (1) The constructed species-area curves fitted logistic function ( R 2 > 0.990); (2) The MPS increased with the sampling completeness, whereas unrecorded species exhibited the opposite trend; (3) Judging by the relative extrapolation error curves of CV Jack1 curve method, when the curve approaching a horizontal asymptote, the relative extrapolation error were all below 5%. The CV Jack1 curve method was found to be a promising approach for extrapolating the ASS. The results and methods in this study provide a theoretical reference for determining appropriate plot sizes and sample sizes of urban plant species richness investigations