Dynamics Study On The Formation Mechanism Of Vegetation Pattern

Desertification is one of the most serious environmental and ecological problems today.Vegetation patch pattern is a typical landscape feature in the process of land desertification,and widely exists in arid and semi-arid regions around the world.Therefore,the study of vegetation patch pattern has guiding significance for desertification control and vegetation restoration in arid and semi-arid areas.As the global desertification situation becomes more and more serious,the study of vegetation patch pattern becomes more and more important.There are many researches on the formation mechanism of vegetation patchwork.This paper aims to study the formation mechanism of vegetation patchwork by considering the saturated water absorption effect of vegetation and the convection between vegetation and sand.The main research contents include:The first chapter,it gives the vegetation pattern of biological mechanisms,the corresponding theoretical research method and the corresponding knowledge.In chapter 2,the phenomenon of saturated water absorption in the process of vegetation growth is widely existed but not fully considered.In view of this,a vegetation-water model with saturated water absorption effect is established based on the interaction between vegetation and water.Firstly,the dimensionless model is given.Secondly,the conditions under which Turing instability occurs in the uniform vegetation state and the corresponding Turing parameter region are obtained by means of linear stability theory.Thirdly,multi-scale analysis was used to refine the distribution regions of different patterns within the Turing parameter region.Finally,numerical simulation is used to show the pattern structures of honeycomb,strip,dot strip mixture and dot pattern and the structural transformation among them.The simulation results obtained in this chapter well reproduce the spatial and temporal distribution of vegetation and explain the evolution trend of vegetation in reality,further reveal the relationship between vegetation and spatial and temporal structure and evolution law,and show that the saturated water absorption effect of vegetation can induce the transformation of vegetation patterns.In addition,it was found that the saturated water absorption effect of vegetation could effectively weaken the trend of vegetation pattern transformation and was more conducive to the survival of vegetation in the case of increasing precipitation.This provides a new way to study the mechanism of vegetation pattern transformation.In the third chapter,in some windy and sandy areas,the accumulation effect of vegetation on sand will increase with the increase of vegetation biomass.Therefore,in this paper,we mainly consider the accumulation effect mechanism of a linear action term.In this chapter consider a model with the prevailing wind vegetation-sand diffusion convection,analyzed the bare sand state existence and stability of equilibria and vegetation,gives the system the Turing unstable condition and dispersion relations,through the numerical simulation shows the diffusion induced by vegetation and eventually form irregular stripes,but eventually form convection induced by vegetation and sand sand belt spot diagram structure,indicates the prevailing wind in the desert in favor of the spatial distribution of the vegetation formation rule structure.By simulating the patch patterns with and without wind,it is further verified that the convection caused by the prevailing wind is the driving mechanism for the formation of vegetation banded patch patterns,which is consistent with the vegetation landscape phenomenon observed in some windy and sandy areas,and verifies the correctness of the theory.Chapter 4 summarizes and prospects the research content of this paper.