Hydrologic feasibility of artificial forestation in the semi-arid Loess Plateau of China

Hydrologic viability in terms of moisture availability is fundamental for ecosystem sustainability in arid and semiarid regions. This study was conducted to examine the regional scale and after-planting variations of soil moisture for planted Black Locust tree (Robinia pseudoacacia L.) plantations in the Loess Plateau of China. 30 sites spanning for 300 km long and 190 km wide in the Northern Shaanxi Province were selected in all. On the regional scale, SMC spatial variability was most closely correlated to rainfall. A large amount of herbaceous cover helped increase the moisture level in the topsoil (0–10 cm), and soil moisture in the deeper layer between 20 and 60 cm below the surface was mostly affected by plantations. The after planting SMC of artificial plantations in areas with sufficient precipitation (mean annual precipitation (MAP) 617 mm) may increase with stand age due to soil water-holding capacity and soil water retention ability improvements after planting. For areas in water shortage (MAP 509 mm), evapotranspiration caused the soil of the plantation to dry up in the first 20 years of growth. Then as the plantation aged, evapotranspiration decreased, and the soil profile recovered gradually. In areas where water was extremely lacking, soil moisture was too rare to be used by trees, and after-planting SMC variation with stand age was insignificant. For the sustainability of artificial ecosystem, the construction of artificial plantations needs to be thoroughly evaluated on regional scale based on the climate conditions (especially rainfall) and soil moisture conditions in arid and semiarid areas.