A multi-method framework for unveiling nonlinear and interactive drivers of vegetation restoration: a case study in...

Large-scale ecological restoration projects (ERPs) have become crucial strategies for fragile regions to mitigate degradation and enhance ecosystem services. However, conventional evaluations of ERP effectiveness often rely on a single model, which is insufficient to capture nonlinear relationships and the interactive effects of multiple driving factors during the restoration process. To address this limitation, this study develops a comprehensive analytical framework that integrates the Generalized difference-in-differences, vine copula model, and piecewise structural equation modeling. By combining spatial analysis with econometric techniques, this framework not only identifies the direct and indirect effects of vegetation change but also characterizes its complex nonlinear response mechanisms. When applied to the karst peak-cluster depression in southwest China, a representative fragile ecosystem, the results reveal that ERPs significantly enhanced regional greening across geomorphic units from 1991 to 2020, though the effectiveness varied markedly among regions. Furthermore, the combined effects of extreme drought and heat greatly increased degradation risks, underscoring the region's high sensitivity to climate fluctuations. Human activity intensity displayed a nonlinear relationship with greening, characterized by the most favorable restoration conditions occurring in low-disturbance zones such as the urban-rural fringe. Moreover, soil thickness was identified as a key constraint on vegetation recovery in karst landscapes. Overall, this study provides a novel methodological framework that integrates spatial analysis, econometrics, and probabilistic modeling to unravel the complex driving mechanisms of vegetation dynamics. The framework not only deepens understanding of karst ecological restoration but also provides transferable guidance for ecological planning and adaptive management in other fragile ecosystems.