The Relationship Between Vegetation Structure And Slope Total Runoff-Sediment Yield In The Hilly Area Of Loess Plateau,China

For a long time,vegetation restoration and reconstruction has been considered as a fundamental measure in reducing soil erosion and improving ecological environment.The primary problem faced in vegetation restoration and reconstruction is the question of what kind of vegetation system to build.Because vegetation often consists of different species with different structural and trait characteristics.With different species composition and structure,vegetation tends to have different water and sand retention efficiency as well.Therefore,it is of great significance to study the relationship between vegetation structure and sand production,and to clarify the structural characteristics of vegetation systems with high water and sand storage efficiency,in order to select the appropriate vegetation system.However,this is not an easy task in practice,because it is very difficult to use which vegetation parameters can reasonably express the structural characteristics.The vast majority of existing studies have used vegetation coverage or its derived indicators when analyzing the relationship between vegetation and soil erosion.The study shows that vegetation parameters based on vegetation coverage do not effectively express the structural characteristics of vegetation,and overemphasis on the relationship between vegetation coverage and soil erosion will lead to a restoration model that simply aims to increase vegetation coverage,ignoring the role of vegetation structure,which will lead to the phenomenon of "green from a distance but yellow water flow from a close distance".This will lead to the phenomenon of "green from afar but yellow water from close up".Therefore,exploring other parameters besides vegetation coverage that can effectively express structural characteristics is still very important from a theoretical and practical standpoint.To this end,in this paper,on the basis of vegetation coverage,we introduced parameters such as species diversity,structured vegetation index(to quantify the hierarchical structure of vegetation communities),plant functional traits and functional trait diversity index(to characterize the trait structure of plant communities),and used artificial rainfall simulation experiments in the field to explore the response relationship between vegetation community structure changes and sand production,and obtained the following main conclusions:Compared with herbaceous communities and forest communities,shrub communities had better soil and water conservation ability,and performed better in terms of prolonging runoff start time and reducing the total sediment yield.In addition, the total sediment yield decreased with the increase of runoff start time,and there was a significant positive correlation between total runoff yield and total sediment yield.In terms of runoff rate and sediment loss rate,the variation of runoff rate among different vegetation communities was small,and the variation of sediment loss rate maximum was large.Compared with the average maximum sand production rate of shrub communities,the average maximum of sediment loss rate of herbaceous communities and forest communities increased by 53.82% and 107.01%,respectively,which also indicated the good sand reduction ability of shrub communities.The differences in vegetation parameters under different vegetation community types were compared,and it was found that the vegetation coverage and stratified vegetation cover index were significantly higher in shrub communities than in herbaceous communities and forest communities.Species diversity indices did not differ significantly among vegetation community types.Among the community trait values,leaf volume was significantly higher in forest communities than in herbaceous communities and shrub communities;root tissue density was significantly higher in shrub communities than in herbaceous communities.For the functional diversity index,the functional richness index and functional divergence index of forest communities were significantly higher and lower than those of herbaceous communities,respectively.Vegetation parameters are important indicators for assessing the soil and water conservation capacity of vegetation.Vegetation coverage and stratified vegetation cover index were significantly correlated with the runoff start time,the runoff end time,and the total sediment yield.Among the species diversity indices,Simpson index and Shannon-Wiener index significantly influenced the total sediment yield.Among the investigated community trait values,specific root length and specific leaf area were strongly correlated with total sediment yield,and root tissue density significantly influenced the runoff start time.For the functional diversity indices,functional richness index was significantly negatively correlated with total runoff yield,and a highly significant negative correlation between functional divergence index and total sediment yield.By constructing a multiple linear regression equation,it was concluded that vegetation coverage,stratified vegetation cover index and root tissue density jointly explained 35.40% of the variation in the runoff start time,with vegetation coverage and root tissue density contributing more to prolonging the runoff start time.The stratified vegetation cover index was important for prolonging the end time of flow production,and together with vegetation coverage explained 23.93% of the variation in the runoff end time.The Simpson index,Shannon-Wiener index and functional richness index together explained 50.23% of the variation in total runoff yield.In addition,vegetation coverage,stratified vegetation cover index,specific leaf area,specific root length and functional divergence index together explained 56.26% of the variation in total sediment yield,and the specific leaf area contributed relatively least to the reduction of sediment production.