Abstract: The manner in which species richness increases with increasing sampling area is among the important laws of ecology. However, forms and parameters of the species–area relationships vary depending on sampling methods, climate, and spatial scales. Because the species–area relationships connect biodiversity at different scales, they are used for estimating species richness at local or regional scales, and for assessing regional biodiversity losses. Here, we review recent developments in the forms, spatial variation in parameters, applications, and scale-dependence of species–area relationships. As a case study, we used species–area rela-tionships to estimate number of plant species in different regions of the Qinling Mountains, and found that the well-consistent estimated and recorded numbers of species were achieved for different nature reserves in the Qinling Mountains.