Dynamic Changes of Stipa bungeana Steppe Species Diversity as Better Indicators for Soil Quality and Sustainable Utilization Mode in Yunwu Mountain Nature Reserve, Ningxia, China

摘要

Due to serious degradation of typical Stipa bungeana steppe community on the Loess Plateau, a 26-year (1982-2007) experiment has been carried out by methods of forbidden grazing, cutting, and rotational grazing. Our results show that the process of succession of long-term enclosed S. bungeana community can be divided into two stages: 1980-1996, the forward succession stage, when the species diversity and biomass reach the peak (33.7 species/m~2 and 1349.41 g/m~2, respectively); 1997-2007, the slow succession stage, when the gradually thickening of litter layer (litter depth reaches 3-5 cm) directly causes the reduction of species diversity and biomass to 19.1 species/m~2 and 863.19 g/m~2, respectively. While under the cutting and rotational grazing methods, grassland succession can be divided into four stages: 1st-5th year, the continuing growth stage; 6th-9th year, the vigorous competing stage; 10th-15th year, the aggregation growth stage of constructive species with biomass reaching the peak (1444.19 g/m~2); and 16th-23rd year, stable growth stage of constructive species, which form sub-climax and are eventually dominated by S. bungeana, with the species diversity and biomass of 25-27 species/m~2 and 956.76-1165.35 g/m~2, respectively. The constructive species suddenly change in the 24th year, and the population of S. grandis increases rapidly to 21 m~2 accounting for 25% of the total plant population. Long-term enclosure leads to decreased species diversity and biomass and is not beneficial for grassland renewing. The species diversity and biomass of degraded grassland continuously decrease to 10 species/m~2 and 392.1 g/m~2 due to long-term artificial failure and transitionally grazing, leading to harden soil with slow rainfall infiltration, where plants can only sustain life under the drought condition. Therefore, reasonable cutting and rotational grazing are the methods of choice for the gradual increase of species diversity and promotion of the natural renewal and forward succession of the grassland on Loess Plateau. These results provide reliable information for the diversity dynamic change as better indictors of soil quality and sustainable utilization mode.