A Catastrophe Model to Assess Soil Restoration Under Ecological Restoration in the Red Soil Hilly Region of China

Current methods that utilize simple data or models to evaluate soil restoration under ecological restoration are not sufficiently rigorous. Soil restoration under ecological restoration measures was evaluated in the red soil hilly region of China by applying the catastrophe model. Among 89 soil sites selected, 26 (29.21%) were in the middle lobe, 10 (11.24%) in the upper lobe, and 53 (70.79%) in the lower lobe of the process surface in the Cusp catastrophe model. The catastrophic direction of the 26 unstable soil sites was to the upper lobe of the process surface according to vegetation cover change and fieldwork. There was a significant negative correlation of the variation in bifurcation set (Δ value) with vegetation cover increase, and a higher vegetation cover increase was related to higher unstable probability. The four ecological restoration measures were listed in the order: low-quality forest improvement (LQFI) > arbor-bush-herb mixed plantation (ABHMP) > orchard improvement (OI) > closing measures (CM) according to the proportions of unstable soil sites, which were all higher than no restoration measure, while they were in the order: LQFI < ABHMP < OI < CM according to their Δ values, which were all lower than those of no restoration measure. Farmers' assessment of soil restoration under the four ecological restoration measures was in accordance with the proportions of unstable soil sites and inversely proportional to the Δ value. Therefore, farmers' assessment can prove the evaluation of soil restoration under ecological restoration measures based on catastrophe model.