Does Afforestation Promote Soil Organic Carbon Sequestration and Soil Water Depletion? Case Study of Robinia Pseudoacacia Forests on the Loess Plateau

Afforestation is a common and effective method for restoring degraded ecosystems worldwide. Robinia pseudoacacia is a main non-native tree species that has been widely planted in the Loess Plateau for revegetation. However, suitability and sustainability of R. pseudoacacia must be considered due to its uncertainty on soil water consumption and carbon sequestration. We aimed to analyze dynamic effects of R. pseudoacacia forest on soil carbon storage (SCS) and soil water storage (SWS) in this study. The relationship between soil water content (SWC) and soil organic carbon (SOC) and influencing factors on the 0–500 cm profile of the chronosequence from 10–50-year-old plantations was investigated. Results showed that dynamics of soil water storage (SWS) and soil carbon storage (SCS) on time scale may be divided into reduction (the initial 20 years after afforestation) and recovery (the 20–50 years after afforestation) processes. SCS had a net cumulative effect relative to wasteland (WL) at 50 years after afforestation while SWS remained in deficit. Additionally, SOC of R. pseudoacacia forest increased with the increase of SWC and showed a significant (p < 0.05) positive correlation in the 0–100 cm layer. These findings suggested that SWC and SOC in the process of vegetation growth were likely two dependent processes with a complementary relationship. Additionally, stand density made greatest contributes to the dynamic of SWS and SCS through changing vegetation, soil and litter characteristics (eg., coverage, understory vegetation coverage, and litter biomass). The results of this study can guide forest managers on how to maintain the carrying capacity of forest water and nutrient resources