Soil desiccation trends after afforestation in the Loess Plateau of China

Purpose Soil moisture is the main factor limiting the growth of vegetation in semiarid areas. A large area of the Loess Plateau has undergone vegetation restoration efforts following an afforestation program initiated in 1999. Understanding how soil moisture responded to afforestation is important for long-term sustainability of ecological restoration measures in this area, especially because the tree planted were non-native species. Methods The effects on soil moisture content (SMC) of afforestation (Robinia pseudoacacia and Caragana korshinskii) were measured for different plantation ages (10, 20, 30, and 40 years) on the Loess Plateau. Meanwhile, a comparative with natural restoration grassland for the same age intervals was conducted. Results SMC of R. pseudoacacia plots on south-facing slopes and R. pseudoacacia and C. korshinskii plots on north-facing slopes was lowest when vegetation coverage was greatest after 20 and 30 years, respectively; SMC increases over time following natural grassland restoration; soil moisture consumption of all vegetation types was greater in the shallow soil layer (20-200 cm) than in the deep soil layer (200-500 cm) in each recovery period; and based on a three-way ANOVA, the interaction among afforestation year, vegetation type, and soil depth had significant effects on SMC. Conclusion In response to societal demand for wood, existing plantations should be thinned, with afforested lands located on north-facing slopes being thinned every 10-30 years (approximately 20 years).