Negative impacts of afforestation and economic forestry on the Chinese Loess Plateau and proposed solutions

Severe loss of soil and water on the Chinese Loess Plateau (CLP) has caused enormous pressure on social and economic development. To restore the ecological environment and boost the economy, the government has invested heavily in afforestation programmes and encouraged local farmers to plant trees that are economically productive. Although these measures have led to considerable increases in the economic value of forests and some farmers' income, negative effects on the environment, such as deep soil desiccation, soil erosion, and environmental pollution, have increased over time. Our field observations show that non-native forests are not well suited to controlling soil erosion unless a protective ground herb cover is also present. To identify the natural vegetation type on the CLP, pollen records from various topographic units were collected and synthesized. The results show that herbs, mainly from the Poaceae and Asteraceae families, were dominant during both the cold-dry period and warm-humid period. The reason for the dominance of these species is that the moisture in the surface soil is insufficient to sustain forests in the CLP where rainwater infiltrates quickly into the thick, loose loess. The ecological restoration of herbs from the Poaceae and Asteraceae families on the CLP should be considered a priority, and trees can grow well only in areas covered by thin loess deposits with efficient underlying water-resisting layers and a high underground water table. Because Asteraceae are such an important source of medicines, the CLP has great potential to be an important centre for Chinese medicinal herb production. We therefore recommend an expansion of the cultivation of medicinal herbs at the expense of high-value economic trees and pasture grasses, both of which consume large quantities of water.