Research On Dynamic Model And Patterns Of The Competition Between Vegetation And Erosion

The study on the co-evolution of vegetation and erosion by using dynamic models is the frontier and hotspot of current research of ecosystem.In this thesis,based on the interactions between slope erosion and vegetation,a dynamic model of vegetation-erosion competition was established,and the dynamic process of vegetation-erosion under different rainfall conditions was studied.The spatial distribution pattern and evolution process of vegetation under the influence of slope erosion were revealed.The main research results are as follows:(1)Based on the classic empirical formula of soil erosion and the Thornes model,a new dynamic model of vegetation-erosion competition was established based on the interactive mechanism between vegetation and erosion.By using the method of nonlinear dynamic analysis and simulations,it was found that the vegetation and erosion can coexist as equilibrium,and the influence of the equilibrium on the dynamically changing process of vegetation and erosion was revealed.(2)Via the analysis of vegetation-erosion dynamic process under different parameters and rainfall circumstances,it was found that in the case of temporally uniform rainfall the equilibrium is sensitive to the parameters of soil grain density and permeability.The erosion amount exhibits ladder shaped increase in the case where rainfall changes monthly and sudden rise in the case where rainfall shows extreme changes annually.The results revealed various processes in the dynamics of vegetation and erosion under different rainfall conditions.(3)Introducing the processes of convection and diffusion into the vegetation-erosion dynamic model,the research found that under the impact of soil erosion,three states may present on the slope:homogeneous vegetation,banded vegetation and bare ground.Through analysis of the transition process of vegetation state under the influence of parameters,it was revealed that the degradation mechanism of vegetation spatial pattern under the process of erosion as well as the co-evolution of the vegetation and erosion under interactions.(4)Considering the extreme situation where the diffusion process of soil erosion on slopes dominates the adcevtion.the multi-scale analysis method found that vegetation can present a variety of spatial distribution patterns such as spots,stripes.and bands,and that the enhancement of cross-diffusion promotes the transition of vegetation pattern from dots to bands.The change of vegetation state reveals the multi-stable state of vegetation and erosion and the self-regulation mechanism of vegetation under erosion stress.Based on the competitive dynamic model of vegetation and erosion,this thesis studied the dynamic process of vegetation and erosion under different parameters and rainfall conditions,and explored various self-organized spatial distribution patterns that vegetation may exhibit under the influence of erosion on slopes,providing a theoretical basis for the restoration and the prediction of ecosystem evolution process.