Severe depletion of available deep soil water induced by revegetation on the arid and semiarid Loess Plateau

Revegetation-induced water deficits in the deep soil (>100 cm) on the arid and semiarid Loess Plateau threaten the sustainability of its ecosystems. However, quantifying changes in deep-soil water status at the regional scale remains challenging. This study represents the first attempt to integrate meta-analysis with the digitization of map data from previous research to evaluate the effects of revegetation on the deep soil water status. A total of 4906 observations from 94 peer-reviewed publications related to soil water changes to a depth of 500 cm in planted forests, planted shrublands, natural grasslands and croplands were synthesized, and two regional-scale evaluation criteria, the stable field capacity (SFC) and the permanent wilting point (PWP), were developed by digitizing the map data. The results indicated that (1) compared with cropland, revegetation more severely depleted the deep soil water availability, and planted forest revegetation resulted in the most serious depletion; (2) the extent of soil water changes was influenced significantly by the tree species planted; Platycladus orientalis was better able to maintain the deep soil water availability than Robinia pseudoacacia and Pinus tabuliformis; (3) the soil water status worsened with time after restoration, particularly at 20 years after restoration; (4) contrary to expectations, deep soil water depletion in forests and shrublands even increased in areas of high rainfall zones (>550 mm) compared to drier zones.; and (5) natural restoration (i.e., grasslands) was a better option than revegetation due to the resultant higher, more stable soil water availability. These results indicate that changes in deep soil water availability must be considered when planning revegetation initiatives.

Automated summary

Artificial revegetation in arid and semiarid areas of the Loess Plateau leads to water deficits in deep soil, especially with forest revegetation showing the most severe impact. The choice of tree species and time since restoration significantly affect soil water status. Surprisingly, deep soil water depletion is even more severe in high rainfall areas, contrary to expectations. Natural restoration, such as grasslands, is a better option as it results in higher and more stable soil water availability.