The Loess Plateau of China is a region with one of the most severe cases of soil erosion in the world. Since the 1950s, there has been afforestation measure to control soil erosion and improve ecosystem services on the plateau. However, the introduction of exotic tree species (e.g., R. pseudoacacia, P. tabulaeformis and C. korshinskii) and high-density planting has had a negative effect on soil moisture content (SMC) in the region. Any decrease in SMC could worsen soil water shortage in both the top and deep soil layers, further endangering the sustainability of the fragile ecosystem. This study analyzed the variations in SMC following the conversion of croplands into forests in the Loess Plateau. SMC data within the 5-m soil profile were collected at 50 sites in the plateau region via field survey, long-term in-situ observations and documented literature. The study showed that for the 50 sites, the depth-averaged SMC was much lower under forest than under cropland. Based on in-situ measurements of SMC in agricultural plots and C korshinskii plots in 2004-2014, SMC in the 0-4 m soil profile in both plots declined significantly (p < 0.01) during the growing season. The rate of decline in SMC in various soil layers under C korshinskii plots (-0.008 to -0.016 cm(3) cm (-3) yr(-1)) was much higher than those under agricultural plots (-0.004 to -0.005 cm(3) cm(-3) yr(-1)). This suggested that planting C. korshinskii intensified soil moisture decline in China's Loess Plateau. In the first 20-25 yr of growth, the depth -averaged SMC gradually decreased with stand age in R. pseudoacacia plantation, but SMC somehow recovered with increasing tree age over the 25 -year period. Irrespectively, artificial forests consumed more deep soil moisture than cultivated crops in the study area, inducing soil desiccation and dry soil layer formation. Thus future afforestation should consider those species that use less water and require less thinning for sustainable soil conservation without compromising future water resources demands in the Loess Plateau.
Afforestation in the Loess plateau To mitigate soil erosion and improve ecosystem services in the region, trees and shrubs have been planted on the slope lands since the 1950s. A series of large afforestation campaigns, including the Grain-for-Green Program (GFGP) were initiated by the Chinese government at the end of the 1990s to reconvert croplands to forests, shrubs and grass (Cao et al., 2009) Species - Large-scale afforestation operations such as the planting of black locust (Robinia pseudoacacia Linn.), Chinese pine (Pinus tabulaeformis Carr.) and korshinsk peashrub (Caragana korshinskii Kom.)
|Climate change impacts
|Effect of Nbs on CCI
|Reduced water availability
|Soil moisture content (SMC) change over time cm3/cm3/yr
Entire Loess Plateau