Vegetation restoration thresholds under different vegetation types and altitude gradients in the Sichuan-Yunnan ecological shelter, China

Abstract

Determining the threshold for the response of ecosystem services (ESs) to vegetation change is critical for ecological restoration, and once the threshold is exceeded, ESs may be inhibited. Vegetation type and altitude are important factors affecting ESs. However, the nonlinear effects of vegetation change on ESs and their threshold under different vegetation types and altitude gradients are not clear. This study selected the Sichuan-Yunnan ecological shelter as the study area. Four ESs (water yield (WY), carbon storage (CS), soil conservation (SC), and water purification (WP)) were quantified by using the Integrated Valuation of Ecosystem Services and Trade-offs model. The differences in ESs among different vegetation types were identified. Variance analysis was used to explore the spatial differences in ESs under different altitude gradients. The inflection point of the promoting effect of vegetation cover on ESs was taken as the threshold, and elastic analysis was used to determine the impact threshold of fractional vegetation cover (FVC) on ESs. The threshold represents the inflection point at which vegetation cover promotes ESs. The results showed that the CS, SC, and WP of the natural forest were higher than those of the plantation, while the WY was lower than that of the plantation. WY, CS, and SC remained higher in the high-altitude regions, while nitrogen export was higher in the low-altitude regions. FVC was positively correlated with nitrogen export in the low-altitude regions and negatively correlated with WY in the high-altitude regions. FVC had a promoting effect on ESs, and the promoting effect was weakened beyond the threshold. The thresholds of FVC promoting ESs were 0.86, 0.79, 0.85, and 0.83 in natural forest, shrub, plantation, and grassland, respectively. The threshold of FVC promoting ESs in low-altitude regions was larger than that in high-altitude regions. This study can provide a theoretical basis for large-scale ecological management and moderate restoration.