Effect of Rocky Desertification Control on the Nonlinear Trends of Gross Primary Productivity in Southwest Karst Areas, China

ABSTRACT Monitoring trends in gross primary productivity (GPP) is essential for assessing changes in carbon sinks. The implementation of rocky desertification control in karst areas has led to an increase in GPP. However, its impact on the nonlinearity of GPP increase has not been determined. Based on the ensemble empirical mode decomposition (EEMD) method, this paper analyzed the nonlinear trend of GPP in the Karst region of southwest China from 1982 to 2018 and clarified the impact of rocky desertification control on the nonlinear trend of GPP, the results show that: (1) The Mann–Kendall method found that 47.17% and 50.11% of the study areas showed nonsignificant change and significant increase in GPP, however, 6.72% and 8.58% of the regions with nonsignificant change and significant increase respectively show the trend reversal from increase to decrease with EEMD method, moreover, 2.94% and 4.19% show the trend reversal from decrease to increase, respectively; (2) Rocky desertification control changed GPP more significantly in rock desertification area than nonrocky desertification area. With the aggravation of rocky desertification, the control effect becomes better, which is reflected in the increasing proportion of monotonic increases in GPP. However, for severe rocky desertification areas, the effect of governance is more reflected in the large proportion of GPP from reduction to increase. (3) The control effect is better, but the risk of carbon sink reduction is higher in changed rocky desertification areas than those in unchanged rocky desertification areas. In the meantime, the mitigation of rocky desertification can favor the increasing of GPP in the areas with severe and moderate rocky desertification, while it can just reduce the risk of decreasing of GPP in the areas with potential and slight rocky desertification. Overall, this study enhances our understanding of the impact of rocky desertification control on carbon cycle processes in both changed and unchanged rocky desertification areas.