Effects and implications of ecological restoration projects on ecosystem water use efficiency in the karst region of Southwest China

Abstract

Large-area ecological restoration projects have been implemented to enhance ecosystem resistance in the karst region of Southwest China since the beginning of the 21st century. Variability in ecosystem water use efficiency (WUE) reflects the responses of vegetation photosynthesis to the water availability. However, whether the restoration projects positively affects ecosystem WUE remains unclear. Therefore, this study aims to evaluate the effect of such projects on ecosystem WUE in the karst and non-karst regions of Southwest China by using time-series satellite-based gross primary production and evapotranspiration data. Results show that (1) afforestation, converted from agriculture land, shrubland and grassland, is a major restoration activity in our study region, the area percentage of which is approximately 93% in karst and non-karst regions; (2) the annual mean ecosystem WUE in the karst region is substantially lower but increased faster than the non-karst region from 2001 to 2015; (3) in the karst area, the increase in the annual ecosystem WUE change rate of ecological restorations is slightly lower but the multiyear accumulative effect is larger during the period of 2001–2015. Therefore, we propose that ecological projects, such as afforestation, positively affects “water costs” of terrestrial carbon sink and effectively improves the fragile karst ecosystem function.