Estimating non-linear effects of natural and anthropogenic factors on ecological resilience: evidence from the southern hilly areas

Ecological resilience is the key indicator for measuring the ability of the ecosystem to return to a stable state after natural and anthropogenic disturbances. Revealing change in ecological resilience is crucial for ecological restoration in southern hilly areas. However, the non-linear effects of factors on ecological resilience were not clear in previous studies. This study used the Restricted Cubic Spline (RCS) regression to examine the variables of ecological resilience in the province of Hunan and proposed an ecological resilience evaluation framework based on the structure and function of ecosystems. The results showed that ecological resilience had increased from 2000 to 2020, illustrating a significant spatial heterogeneity of regions. The RCS results indicated that natural and anthropogenic factors had nonlinear relationship with ecological resilience, and thresholds varied over the period (e.g., in 2000, DEM ≥ 459.00 m, SP ≥ 6.09°, TEM ≤ 16.89 °C, PRE ≥ 1361.44 mm, etc.; in 2010, DEM ≥ 467.76 m, SP ≥ 6.22°, TEM ≤ 17.07 °C, PRE ≥ 1404.25 mm, etc.; DEM ≥ 511.57 m, SP ≥ 11.76°, TEM ≤ 17.52 °C, PRE ≥ 1500.00 mm, etc.). This study provided a new perspective on structure-function relationship in ecological resilience, while also considering ecological protection policy on anthropogenic factors to delineate priority areas for ecological restoration.