How does vegetation restoration affect the soil quality on the Loess Plateau? A meta-analysis

Abstract: Soil degradation is one of the biggest environmental problems facing the earth today, with which more than 33% of the earths soil currently degraded. Soil erosion is considered to be one of the dominant and prevalent form of soil degradation in the developing countries. The Loess Plateau is the areas with the most serious soil erosion in China and even in the world. A number of literatures showed that vegetation restoration was one of the most effective measures in controlling soil erosion and preventing soil degradation. But the effects of vegetation restoration across climate, vegetation types and restoration years are not clear. A meta-analysis was conducted and achieved 1731 paired observations from 71 peer-reviewed papers to improve the understanding of the effects of vegetation restoration on soil quality and to identify the factors influencing its changes. The results showed that: (1) The literatures are distributed in various provinces of the Loess Plateau, with the most concentrated distribution in northern Shaanxi Province. In terms of specific data, the relevant data covered several aspects of soil quality indicators, such as Bulk density (n=180), Soil total porosity (n=91), Soil aggregate stability (n=65), Soil organic matter (n=180), Total nitrogen (n=166), Total phosphorus (n=112), Available nitrogen (n=47), Available phosphorus (n=63), Microbial biomass carbon (n=46), Microbial biomass nitrogen (n=29), Microbial biomass phosphorus (n=20), and others. (2) Compared with the farmland, after vegetation restoration on the Loess Plateau, soil bulk density was significantly reduced by 6-10 %, soil total porosity was significantly increased by 12-16 %, soil aggregate stability was significantly increased by 18-24 %, soil saturated hydraulic conductivity was significantly increased by 12-18 %, soil organic carbon and total nitrogen content was significantly increased by 47-55 % and 43-52 %, microbial biomass carbon, nitrogen, phosphorus and enzyme activity were also significantly increased. (3) The effect of vegetation restoration on soil quality mainly depends on soil texture, vegetation type and restoration year. Generally, the effect of forest on soil quality is higher than that of shrub and grass. The effect of vegetation restoration on soil quality increases with the increase of vegetation restoration years. The results of the study provide a basis for the evaluation of the ecological effects of vegetation restoration in the Loess Plateau, and can provide a reference for the selection of reasonable vegetation allocation methods under different restoration conditions, thereby improving soil degradation in arid and semi-arid areas. Keywords: Vegetation restoration; Soil quality; Meta analysis; Loess Plateau