Driving Forces and Ecological Restoration Revelation in Southwest China Based on the Divergence Characteristics of Ecosystem Compound Use Efficiency

Abstract

Ecosystem carbon use efficiency (CUE), water use efficiency (WUE), and light use efficiency (LUE) are critical parameters for estimating CO2 uptake, water circulation, and ecosystem balance. Research on the change trends of individual use efficiency has matured; however, studies on the spatiotemporal heterogeneity and driving mechanisms of divergence patterns for multi-use efficiencies capability are limited. Therefore, taking southwest China as an example, this study constructed a compound use efficiency (COM) through CUE, WUE, and LUE. Based on the spatiotemporal patterns and divergence characteristics analysis of water–carbon–light use efficiencies, the scale effects and driving mechanism of its divergence characteristics for COM at the optimal scale were clarified. The results revealed that the average value of CUE, LUE, WUE, and COM were 0.49, 0.7 gC m−2 MJ−1, 2.31 gC kg−1 H2O, and 0.87, respectively. Apart from CUE, the LUE, WUE, and COM parameters exhibited a fluctuating upward trend. Statistically, there was a high COM in karst and ecological restoration regions, reflecting the strong adaptability of karst vegetation and the effectiveness of ecological restoration; as the elevation rose, COM increased and then decreased, with the highest value at the elevation of 3000 m; the lowest COM was found in grassland, refuting the inference that it can be used as an optimal vegetation type for China’s Grain to Green program from the perspective of use efficiency. Sub-basin was the most optimal divergence scale, and although temperature and elevation were the dominant single force causing COM divergence, the couplings of precipitation and population density and elevation and population density had more controlling impacts than a single force. These findings enrich the understanding of ecosystem use efficiency and are beneficial for the improvement in ecological restoration strategies in karst landscapes.