关键词: 植被恢复阶段, 减流效益, 减沙效益, 刈割处理

Abstract:

Vegetation coverage can effectively protect soils from erosion by intercepting raindrop impact and retaining runoff. In the loess hilly region of China, vegetation status has been improved since the “Grain for Green” project was launched and as a result, grassland, shrub land, and forestland get greatly increased. Study of the effects of the different restoration stages on runoff and sediment reductions may provide a sound basis for evaluating the environmental effects of vegetation restoration. Natural rainfall is difficult to manipulate and consequently, and soil erosion patterns on slope with different ways of vegetation coverage under natural rainfall condition have not been examined well. Runoff plots integrating different stages of vegetation restoration, including farmland, grassland, shrub land, and forestland were set up on the loess slope of Yangou catchment in Yan’an where the “Grain for Green” project was practiced to examine the runoff and sediment reductions in the different stages of vegetation restoration under natural rainfall condition. The investigation of the accumulative runoff and sediment yields from 2004 to 2008 showed that the runoff and sediment reductions ranked in the order of forestland>shrub land>grassland>farmland. Runoff reduction for forestland was the highest, being only about 10% of runoff from farmland. This implies that farmland was the major sources of soil erosion and sediment. The spatial structure and ground litters on forestland were capable of retaining runoff and thus promoting rainfall infiltration into soil. Sediment yields on grassland, shrub land, and forestland decreased by more than 90% compared with that on farmland in all the years but 2006, in which rainfall was lower. Thus, all the three stages of vegetation restoration had significant sediment reducing effects. On grassland and shrub land, sediment reductions were higher than runoff reductions. Comparison of the runoff and sediment yields on grassland and shrub land before and after vegetation cutting showed that more than 80% of the runoff reductions on grassland and shrub land were attributed to retaining by ground litters on and roots in them. Vegetation removed shrub land had stronger soil anti-erodibility than vegetation removed grassland and sediment yields on the lands increased slightly after vegetation cutting. After vegetation cutting on grassland and shrub land, the remaining roots and ground litters still had considerable soil conserving effects. However, the sediment yields on grassland and shrub land after vegetation cutting increasing indicated that during the initial vegetation succession, the layer near ground surface was still weak in ecological function and needed protecting by closed tendering.

Key words: Restoration stage, Runoff reduction, Sediment reduction, Vegetation cutting treatment