Differences in the soil and hydrology responses of two revegetation chronosequences in the Loess Plateau, China

Vegetation restoration has been widely implemented to restore degraded land. However, vegetation expansion may result in the overconsumption of soil moisture and soil desiccation, which in turn exacerbates land degradation. To ensure the sustainability of ecological restoration, it is necessary to optimise restoration patterns. Two restoration patterns (afforestation with Robinia pseudoacacia L. (RP) and abandoned farmland (AL)) along a revegetation chronosequence (0, 9, 17, 27, and 42 years) were selected to analyse variations in soil and hydrological characteristics on the Loess Plateau, China. The results showed that for the two revegetation types, the soil quality index (SQI) increased markedly (p < 0.05) and the soil loss (SL) and surface runoff (R) decreased significantly (p < 0.05) over time, indicating that vegetation restoration improves soil quality and prevents soil and water erosion. The annual increments of soil moisture storage (Ws) within a 200 cm depth notably decreased during the late restoration stage (> 27 years) for the artificial forest. Moreover, forest also showed increasing actual evapotranspiration (ET) trends and decreasing Ws trends. These results suggest that afforestation might lead to overconsumption of water and soil water depletion during the late restoration stage. Although RP sites had higher SQI (22.2-36.7 %) values and lower SL (47.0-81.4 %) and R (86.5-196.8 %) values when compared with AL sites, the change rates of the SQI, R, and SL at RP sites were stable or decreased over a period of restoration, while these rates showed increasing tendencies under AL sites. These suggests that natural grasslands may be more beneficial than artificial forests during the late restoration stage. Therefore, naturally restored grasslands are highly recommended for sustainable ecological restoration in the semiarid and arid areas of the Loess Plateau or in similar areas elsewhere.