Vegetation Destruction and Restoration Effects on Soil Erosion Process on the Loess Plateau

摘要

Vegetation destruction or natural vegetation restoration greatly affects soil erosion process and eco-environmental change. Studies on soil erosion on the Loess Plateau have been focused on soil erosion process and erosion control at severe soil erosion regions where vegetation was completely destroyed. However, there are few available data to quantify effects of vegetation destruction or natural vegetation restoration on soil erosion process. The Ziwuling area on the Loess Plateau, where original vegetation destruction by human activities about 130 years ago, the secondary vegetation restoration during the past about 130 years, and deforestation again, provides an experimental area to quantify effects of vegetation change on soil erosion and eco-environment. The objective of this paper was to use data from field investigation and runoff plot observation to quantify effects of vegetation change on soil erosion. The results showed that before the secondary vegetation restoration, i.e., about 130 years ago, soil erosion conditions in the Ziwuling region were similar to present loessial hilly-gully region of Yan'an-Ansai-Zhidan zone. After the secondary vegetation restoration, soil erosion was very slight, impacts of rainfall and topographical condition on soil erosion were not well obvious, and vegetation effect on soil erosion was predominated. Ephemeral gully erosion at hillslopes and gully erosion at gully slopes or valley ceased, and sediment deposition occurred in ephemeral gully and gully channels during process of the secondary vegetation restoration. Meanwhile, valley erosion and gravitative erosion was almost controlled by vegetation. The soil-erosion was changed from man-made accelerated erosion to natural erosion under ecological balance. Once the secondary forest land was converted to cropland, soil erosion greatly increased, soil erosion rate from a newly deforested land reached 10,000 t/(km~2 · yr) to 24,000 t/(km~2 · yr), which was 787 to 1682 times greater, as compared to woodland. These results show that man-made accelerated erosion play in a cardinal role in the regions where vegetation was completely destroyed by human activities. These finding will help to improve the understanding relationship between vegetation change and soil erosion, and to provide powerful data to make strategies for rehabilitating better eco-environment in the northwestern region of China.