Ecological effects of establishing a 40-year oasis protection system in a northwestern China desert

摘要

Oasis-protection systems are created globally to reverse land degradation in drylands and improve ecosystem condition. This study assessed the effects of a 40-year oasis-protection system on soil physicochemical and plant community properties along a gradient from prohibited grazing to fenced shrublands, to shrub- and tree plantation belts in arid northwestern China. We found that compared with shifting dunes in unprotected desert settings, the wind velocity and sand transportation rate decreased by 75 and 98% when spring storms passed through the most protected shrub- and tree- plantations in the oasis-protection system, respectively. The fraction of silt and clay content, and soil carbon, total nitrogen, and total phosphorus significantly increased along the protection gradient, and reached their highest levels at the most protected belts. Meanwhile, an annual herbaceous plant community developed, and the densities, covers, and biomasses of herbaceous plant species increased with soil nutrients along the gradient. However, a significant increase in soil salinity, sodicity, and desiccation occurred at the shrub- and tree plantation belts, and shrub and tree species introduced in the plantations failed to regenerate after 40 years. Our results demonstrate that the positive effects of oasis-protection systems need to be weighed against the long-term negative consequences of soil salt accumulation and desiccation that can occur in frequently used shrub- and tree plantations, which limits future plant regeneration and ecosystem recovery.