Effects of Afforestation Projects on Tradeoffs between Ecosystem Services: A Case Study of the Guanting Reservoir Basin, China

Evaluating the responses of ecosystem services (ESs) to local land-use changes is critical for understanding the effects of ecological projects related to land planning. Change patterns in the interrelationships between ESs delivered by land-use changes, which are helpful for formulating future strategies, have not been well studied. In this study, we quantified four ESs, namely water yield (WY), water and soil conservation, nonpoint pollution control, and carbon sequestration services, based on the soil and water assessment tool model (SWAT) in the Zhangjiakou section of the Guanting Reservoir watershed, a region with a high concentration of afforestation projects. The impacts of land-use changes on changes in ESs and interrelationships of ESs were investigated by redundancy analysis. The results showed that, along with afforestation, regional water conservation and soil organic carbon content increased by 3.22% and 1.08%, respectively, whereas sediment output, WY, phosphorus output, and nitrogen output decreased by 1.82%, 3.07%, 8.08%, and 12.51%, respectively. Significant tradeoffs of regional ESs were observed between WY and other ESs, while synergies existed between other ESs. Increased areas of evergreen and deciduous forests helped in conserving water, fixing carbon, and regulating runoff. Evergreen forests tended to conserve more water than deciduous forests. With the increase in grassland area, most of the ESs can be improved while introducing fewer tradeoffs compared with those of most of other land-use types. This study provided a better understanding of the effects of afforestation on ESs tradeoffs and benefits to develop better ecological conservation strategies in afforestation regions.