关键词: CO₂浓度增高, 水稻, 稗草, 生长, 产量, 竞争

Abstract: From the view of hydrodynamics,this paper studied the acting mechanism of tree,grass and forest litter on slope runoff velocity and kinetic energy.The results showed that slope runoff head loss was related to slope gradient, forest density,net rainfall intensity and slope length.The relationship of water head loss with the distance among trees and the diameter at the ground of tree was E∝（D/b）4/3.The grass on slope turned to be curved with s flowing,and thus,increased the bottom resistance of flow,and reduced the shearing stress of soil surface.Therefore,silt-carrying capacity decreased dramatically.The analysis of actually measured materials of each rainfall, runoff and sediment,and the comparison of Qiaozi eastern gully and Qiaozi west gully in Tianshui city of Gansu Province showed that under same precipitation condition,the runoff,sediment yield,flood peak discharge and maximum sediment transport rate in treated watershed was less than those in untreated watershed,suggesting that vegetation was obviously beneficial to water reservation and water and soil conservation.