Plant Community and Succession in Lowland Grasslands under Saline-Alkali Conditions with Grazing Exclusion

Rangeland degradation poses a serious environmental and economic problem in northern China. This study investigated soil conditions and plant community patches prior to and after grazing exclusion in Youyu County, Shanxi Province. The soil at this site has a pH of 8.2 to 10.1 and electrical conductivity of 0.4 to 5.9 dS m(-1). With the exception of bare patches, the patches were named after the dominant species, that is, Artemisia anethifolia Weber ex Stechm. (AA), Phragmites australis (Cav.) Trin. ex Steud. (PA), Puccinellia distans (Jacq.) Parl. (PD), Chloria virgate Sw. (CV), and Leymus secalinus (Georgi) Tzvel. (LS) with increasing biomass production, Shannon-Wiener index (H'), evenness index (V'), degree of succession (Ds), and patch shape parameters. Canonical correlation analysis was used to explain the relationships between soil variables and biological, and between soil variables and shape variables of the community patches. The soil canonical variable was represented by soil moisture, organic matter, and bulk density with a standardized canonical coefficient of 1.09, 0.79, and -0.69, respectively. The plant canonical variable was represented by biomass production with correlation coefficient of 0.96 (P = 0.0021). A total of 73.0% of the variance standardizing the measuring units of the plant variables were explained by the soil canonical variable, indicating that the first latent soil variable could be used to predict the latent plant variable. Open grazing (90% biomass removal) contributed to the deterioration of the grassland. Over a 2-yr period, grazing exclusion did not increase the H' but it did increase biomass production. Therefore, correcting soil problems is needed in addition to reducing the grazing stock.