Ecological effects of establishing a 40-year oasis protection system in a Northwestern China Desert

Abstract

Aims: Desertification around oasis areas is a serious problem in semi-arid and arid regions, which is expected to continue into the future due to a rapidly increasing human population. Oasis protection systems are created to reverse desertification by recovering degraded soil and vegetation properties and improving ecosystem services. Most research has focused on the short-term effects of a single restoration practice using an individual vegetation or soil metric, while more complete assessments along a gradient of an entire oasis protection system have seldom been studied. In this study, soil and vegetation properties were measured along a 40-year oasis-protection system to assess the effectiveness of increasing land protection belts along a gradient from prohibiting grazing, to fencing shrubland, to establishing shrub- and tree-plantations in northwestern China. Methods: Three sites in each belt of the oasis-protection system were selected to measure soil texture, soil organic carbon, total nitrogen, total phosphorus, pH, electrical conductivity, and eight ions under the plant canopy and in the inter-canopy area, as well as to investigate plant community composition, diversity and productivity. Wind velocity and sand transportation rates were measured in each of the five belts during storm events. Results: Compared with shifting dunes in unprotected desert settings, the wind velocity and sand transportation rate decreased by 75 and 98%, respectively, when spring storms passed through the most protected plantation belts in the oasis system. Soil organic carbon, total nitrogen, total phosphorus significantly increased, along with the silt and clay contents, across the protection gradient, and reached their highest levels at the shrub- and tree-plantation belts. Similarly, the density, cover, and biomass of herbaceous plants also increased along the gradient. Despite these positive effects, there was a significant increase in soil salinity, sodicity, and desiccation at the shrub- and tree-plantation belts, which may negatively affect the future sustainability of the oasis-protection system under a predicted future drier and warming climate. Conclusions Although shrub and tree plantations improve soil fertility and favor the development of the herbaceous plant community, their environmental consequences (i.e., soil salinization and desiccation) need to be evaluated in the context of ecosystem restoration over the long-term, especially in arid regions.