| According to the investigation scale and the research purpose, the basic conditions for species-area curves on Loess Plateau have been analyzed. Four typical models were adopted in the study: (S=b+alnA,) S=aln(bA+1), S=aAb, S=aA/(1+bA). With the aid of SAS8.1 and MATLAB6.5 system, the first three models were fallen into disuse according to the F value of fitting curves. The model S=aA/(1+bA) was regarded as the standard curve to get second derivative species-area for the communities of Lespedeza davurica (Laxm.) Schindl, Cleistogenes songorica (Roshev) Ohwi, Agropyron cristatum (L.) Gaertn,and Bothriochioa ischaemum (L.) Keng, that is, 3.4 m2, 4.1 m2, 1.4 m2 and 4.8 m2. Since this model fitted all the communities well, it was considered as the best species-area model for the herbage plant communities on Loess plateau. |