To alleviate land degradation, China's government is investing huge amounts of money in afforestation. But long-term results indicate that these projects could be exacerbating environmental degradation in arid and semi-arid regions, damaging soil ecosystems, reducing vegetation diversity and cover, and increasing water shortages (S. Cao Environ. Sci. Technol. 42, 1826–1831; 2008).

Although afforestation is potentially important for environmental restoration, China's policy does not take into account the fact that afforestation of arid regions is primarily water-limited, with drought being a major constraint on forest growth. Most of the restoration programmes — including the Three Norths shelter-forest system and regional sand control programmes — involve planting trees in areas where annual precipitation is less than 400 millimetres. In the semi-arid Loess Plateau, water yields have dropped by 30–50% and vegetation cover has decreased by 6.1% as a result (G. Sun et al. J. Hydrol. 328, 548–558; 2006).

The Chinese government has not properly considered local environmental conditions, and this has led to over-planting of trees and the use of unsuitable species. For example, the excessive demand for water by the tree Populus tremula, which accounts for almost half of China's reforestation (J. Liu et al. Proc. Natl Acad. Sci. USA 105, 9477–9482; 2008), negates any potential environmental benefits.

Alongside afforestation, managers should be recreating natural ecosystems to help combat desertification. Large-scale, long-term research is urgently needed to supply data to support a more flexible restoration policy.