Massive afforestation and reforestation programs have been implemented around the world to restore degraded land and respond to climate change. Many studies suggest that such large-scale campaigns may be counterproductive if there is insufficient water to sustain the trees, especially in dryland. However, we suggest the large-scale afforestation may become a new problem even in humid regions with abundant water, and that the problem will be exacerbated by climate change. To test this hypothesis, we compared the water surplus (evapotranspiration) of natural vegetation and planted trees in 15 provinces of southern China using eight evapotranspiration models. The planted forests consumed considerably more water than natural vegetation, thereby utilizing water that would otherwise be available to support other uses. It may raise water conflicts among sectors in climatic change. We found that if artificial restoration by afforestation or reforestation were replaced by restoration of the natural vegetation, water-use efficiency would improve by 9.97-16.34% in different regions. Uncritical acceptance of large-scale planting of woody vegetation may therefore reduce the ecosystem’s resilience against climate change in the short term and increase the long-term risks of water conflict in society in long run if major climatic shifts over. It is therefore necessary to carefully assess whether the benefits of the planted forests outweigh the potential negative environmental and socioeconomic consequences.
Afforestation … afforestation in southern China has been achieved on the lands which were almost covered by grass and steppe vegetation, especially in mountainous regions
|Climate change impacts||Effect of Nbs on CCI||Effect measures|
|Reduced water availability||Negative||Water surplus (WS = Precipitation - evapotranspiration of afforested plots)|
the 15 provinces of southern China