Determinants of plant species richness in different wetland types along a hydrological gradient: implication for conservation

The loss of biodiversity caused by wetland degradation is a hot issue in ecology. It is known that hydrological degradation is the pri- mary reason resulting in wetland degradation, but little is known about the relationship between plant species richness and environmental factors in dif- ferent wetland types along a hydrological gradient. According to the gradient from high to low water level, wetland remnants in the Sanjiang Plain of northeast China were classified into three wetland types, which were permanently inundated marsh- es (PIM), seasonally inundated marshes (SIM) and wet meadows (WM) respectively. In this paper, we aimed to identify the determinants of plant species richness in the three wetland types and discern the transition of the determinants along a hydrologi- cal gradient. Plant species richness as well as area, habitat heterogeneity and resource availability was investigated in 51 wetland remnants, which were composed of 6 PIM, 25 SIM and 20 WM. Aver- agely, the area of wetland remnants occupied by PIM, SIM and WM was 0.35 ± 0.17 ha, 2.81 ± 2.88 ha and 1.34 ± 1.18 ha respectively. Aggregating the species in each wetland type, there were 67, 244 and 170 species recorded in PIM, SIM and WM. The determinants of species richness varied in different wetland types: standing water depth in PIM, area and water heterogeneity in SIM, and soil fertility and area in WM. With the decreasing water level, the influence of hydrological condi- tion on species richness in the three wetland types declined while the impact of area and soil fertil- ity gradually increased. Thus, hydrological condi- tion was probably responsible for the transition of the determinants of species richness in different wetland types. Moreover, the habitat specialists of wetland would be lost when PIM or SIM degraded to WM. In order to conserve and restore plant di- versity, specific measures should be taken includ- ing preventing area loss for all wetland remnants, managing the hydrological process for PIM and SIM, and regulating soil nutrient for WM.