| Soil erosion in the Loess Plateau has always been the focus of attention.Studying the relationship between plant community succession and runoff erosion is the core of revealing the mechanism of vegetation inhibiting erosion.In the changing plant community environment,the changes of aboveground and underground ecological structure in the process of community secondary succession are analyzed,to clarify the coupling and feedback between plant community succession process and slope hydrological process,division of soil erosion forms,to analyze the soil and water conservation potential of vegetation and establish the evaluation system of vegetation erosion resistance and control ability were hot topic in the study of soil and water loss dynamic mechanism and vegetation regulation principle.This study in the loess plateau farmland slope plant community as the research object,through field investigation,sampling and runoff simulation test,the system to study the changes in plant community structure and function in the process of ecological succession,and preliminarily probes into the development of plant community succession of slope runoff control mechanism,illuminates the plant community ecological factors in the erosion of the comprehensive function and its attribution,based on high precision terrain slope information,divides the changing form and background conditions of soil erosion in the form of plant community structure is analyzed in the erosion effect.This research obtained the following main conclusions:(1)The succession and development sequence of plant community in the study area was determined.The early stage of succession(0-2 years)is characterized by the invasion of annual compositae,the middle stage of succession(8-16 years),the gradual emergence of perennial gramineae as the dominant species,and the late stage of succession(22-40 years),the simultaneous emergence of leguminous shrubs and deciduous small trees.The results of vegetation important value showed that the main succession species were perennial herbaceous plants(249.4).The succession of plant communities in the study area was accompanied by a large degree of energy collection and accumulation,and was still in a rapid recovery period during the 1-40 years of succession.(2)The fractal dimension of root structure and the ecological niche index of root ecological function were proposed based on nonlinear theory.The fractal dimension of root length decreased from 2.99 to 2.67,which objectively demonstrated that community succession promoted gradually complete and complex root structure during the 1-40 years of plant community development in the study area.The distribution of root niche index in vertical dimension,horizontal dimension and index latitude increased from 6.18 to 8.91,and the ecological function of root system increased significantly with the succession development of plant community.(3)The influence of plant community succession on the dynamic characteristics of slope runoff was analyzed.The average flow velocity of slope runoff decreased from 0.203-0.266 m/s to 0.078-0.180 m/s and the runoff resistance coefficient increases 12.5 times in 1-40 years of succession development of plant community.The runoff flow pattern is mainly affected by the underground and overground parts of the plant community.The vegetation important value(0.87),species number(0.84),humus quantity(0.82)and micro-aggregate content(0.79)have a high correlation degree for the deceleration(velocity),energy dissipation(power)and resistance increase(resistance coefficient)of slope runoff.The fine root length(root length density)per unit soil is an important factor affecting runoff shear force.The complexity of root structure(fractal dimension)is the main reason to improve soil shear strength.(4)The mechanism of plant community succession on slope water and sand resistance control was revealed.The average yield and sediment yield decreased by 1.58 and 20.97 times,respectively,during the succession of plant communities from 1 to 40 years.When the dominant species were replaced each time,the runoff and sediment yield decreased,and the cumulative runoff and sediment yield slope decreased by 0.79 L/min and 17.4 g/min,respectively.Runoff sediment concentration decreased step by step with the succession of plant community,from about 10.27 g/L to 0.58 g/L.The flow reduction benefit of plant community succession development was mainly affected by the change of root length density(0.81),and the sediment reduction effect was mainly affected by soil structure characteristics.Micro aggregate(0.88)is the main source of sediment in erosion process.The root structure and function are the precursor factors that affect runoff sediment concentration.The important value of vegetation(0.81)and species number(0.80)play the role of filtering sediment flow,which is the objective factor to reduce runoff sediment concentration,while the thickness of sediment particles in the sediment flow(D50,0.81)is the subjective factor to affect runoff sediment concentration.(5)The evaluation system of slope core terrain factor was established.Succession of plant communities reduced the range of topography before and after erosion.In the relationship between the slope topography and the amount of erosion,four types of erosion patterns,namely slight breakage,severe breakage,slight deposition and severe deposition,were identified Sediment deposition index is constructed,and it is highly correlated with fractal dimension of root length,root niche index,important value of vegetation and median grain size D50 of soil particles,which can be expressed by linear formula Y=AX+B.It was found that the main plants affecting the erosion pattern were compositae and annual herbaceous plants,and the representative species were Artemisia capillaris,Artemisia scoparia,Carduus nutans,Sonchus oleraceus,Artemisia sacrorum,and Setaria viridis.The regression model was established and passed the significance test(P<0.01).The regression model passed the significance test(P<0.01).When the vegetation importance of representative species doubled,the sediment deposition increased by 13.1-34.2%. |
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