Effectiveness of re-vegetated forest and grassland on soil erosion control in the semi-arid Loess Plateau

摘要

Afforestation reduces soil loss and minimizes landslide risk worldwide, but little is known on the effectiveness of afforestation policies to control soil erosion with different vegetation types in semi-arid areas. Understanding the effectiveness of distinct re-vegetation types under different physiographic conditions (slope gradient, percentage of vegetation cover and rainfall depth) is essential for better policy formulation. This study examines the benefits of soil erosion control in forests and grasslands using published data. This analysis proves that the benefits of vegetation restoration increase with increasing the vegetation cover and tend to be stable when the coverage exceeds 60%. The benefits on sediment yield reduction are more sensitive (vs. runoff reduction benefit) to rainfall intensity. Regarding slopes and soil erosion control, the highest efficiencies appear in forests on 20-25 degrees slopes and in grasslands on 15-20 degrees slopes. Grasslands can effectively reduce soil erosion, as well as forests with understory grasses. For long-term restoration, a 60% vegetation cover maximizes the benefits of reducing soil erosion and maintaining enough soil water supply that prevents possible soil drought. We propose that future afforestation policies should evaluate in advance the appropriate re-vegetation type; meanwhile, suitable vegetation coverage and local physiographic conditions should be considered. Importantly, promotion of grassland and preservation of forest understory grasses must be enforced in land use policies when considering afforestation to minimize soil erosion. We suggest further research to quantify the efficiency of understory vegetation on soil erosion control, which might provide scientific and practical guidance for afforestation policy in semi-arid areas.