Abstract:Landscape fragmentation leads to patch size and shape changes, and many studies proved that patch size and patch shape have important influence on species diversity. The Sanjiang Plain is the largest freshwater wetlands in China. However, the wetland had been fragmented into a patchy mosaic of isolated remnants as a result of anthropogenic activity since the 1950s. In this study, the patch characteristics and plant species richness on wetland remnants in the Bielahong River basin, a typical region in the Sanjiang Plain, were investigated. The study results show that the wetland had been seriously fragmented into small wetland remnants under the intense anthropogenic activity. Most remnant patches are less than 2hm2, with regular shape and simple boundary. Three indices of patch shape complexity, including shape index (SI), fractal dimension (Fd) and the number of shape characterizing points (NSCP), are uncorrelated with patch size and plant species richness, but plant species richness is significantly associated with path size, perimeter and the ratio of perimeter and area (P/A). As patch size controls the variance of patch perimeter and P/A, it is the main determinant of plant species richness. Although the NSCP proposed by Moser et al. is a good predictor for plant species richness in agricultural landscape, it was not applicable in the regular wetland remnants. However, exploring the mechanisms for the significant species-area relationship would help us understand species diversity pattern in wetland remnants, which needs to be considered in further studies.