Dynamics Modeling And Spatiotemporal Complexity Of Vegetation Evolution In Arid And Semi-arid Regions

In recent decades,under the joint influence of global warming and human activities,vegetation degradation,soil erosion and land desertification have become increasingly serious in arid and semi-arid regions,which have posed a serious threat to human survival and sustainable development of ecological environment.Therefore,it is very important and urgent to restore and protect the surface vegetation.Vegetation pattern can not only depict the structure and distribution of vegetation in different time horizons,but also warn land desertification.Many scholars have devoted themselves to studying the dynamics of vegetation pattern in arid and semi-arid regions.At present,the research on dynamic modeling of vegetation pattern mainly focuses on considering the local effects of vegetation and water resources,focusing on the suitability of solutions,traveling wave solutions,local solutions,global solutions and so on.Moreover,due to the difficulties in obtaining real data of climate elements,studies on the spatiotemporal complexity of vegetation combined with real data are still in the initial stage.However,the absorption of water resources by vegetation is not a simple local process,so the reaction-diffusion equation with nonlocal effect is used in this paper to accurately describe the nonlocal water absorption process of vegetation.Using linear and nonlinear analysis methods combined with climate factor data to study the dynamics of vegetation evolution,the research results can not only reveal the internal mechanism of vegetation pattern formation and obtain the leading factors of its formation,but also provide scientific basis for formulating reasonable vegetation restoration and protection strategies in arid and semi-arid regions.In this paper,a series of dynamic models of vegetation evolution with nonlocal effects in arid and semi-arid regions are constructed theoretically,and the temporal and spatial complexity of vegetation evolution is described based on mathematical analysis and numerical simulation.At the same time,the vegetation evolution dynamics in Altay region of Xinjiang was studied by using the vegetation model with climate elements and nonlocal effects.The main research contents are as follows.(1)Establishment of vegetation dynamics model with nonlocal effect and analysis of pattern dynamics.Using Turing instability analysis,the conditions for generating vegetation pattern were obtained.The results show that with the increase of the intensity of nonlocal effect,the stripe pattern width of the pattern becomes smaller,and then a dotted mixed pattern appears,which eventually evolves into a high-density spot pattern.This indicates that the vegetation gradually evolved from low-density stripe distribution to high-density point distribution.The nonlocal effect increased the vegetation biomass,that is,the nonlocal effect had a positive effect on the increase of vegetation biomass.(2)Establishment and spatiotemporal dynamics analysis of vegetation dynamic model with coupling of soil water diffusion and nonlocal effect.Using linear stability analysis and Turing instability theory,the formation conditions of vegetation pattern determined by several inequalities were obtained.At the same time,the amplitude equation of the system is obtained by using the multi-scale analysis method,and different steady-state solutions of the amplitude equation correspond to the steady-state patterns of vegetation with different structures.It is found that both the nonlocal effect of vegetation and the feedback of soil water diffusion can cause the phase change of vegetation pattern.The change of nonlocal effect intensity will lead to mixed vegetation pattern structure.The enhancement of feedback intensity of soil water diffusion will induce vegetation patterns with different structures.Whether the intensity of nonlocal effect increases or the feedback intensity of soil water diffusion increases,the isolation between vegetation patches will increase.(3)Establishment and spatiotemporal complexity of vegetation dynamic model with nonlocal effect and root hydrotropism.The global weak solution of the model is given,the Turing bifurcation conditions and the specific range of Turing region are obtained.The spatial distribution of vegetation in the study area was analyzed quantitatively.It is found that there is a threshold value of root hydrotropism intensity.Appropriate root hydrotropism intensity can increase vegetation density within the threshold range,but the isolation degree between vegetation patches will gradually increase with increasing root hydrotropism intensity,and the region is prone to desertification.When the root hydrotropism intensity exceeds the threshold,vegetation pattern will not be generated,and desertification will occur in the study region.(4)Establishment of vegetation dynamics model with nonlocal effect coupled with climatic factors and study of pattern characteristics.Under the influence of global warming,Altay region of Xinjiang was taken as the study area,and the corresponding climate element areas of vegetation pattern were obtained.The results show that the increase of rainfall will increase the biomass of vegetation.However,with the increase of temperature,the biomass of vegetation will decrease,and the pattern structure of vegetation will change from high-density point structure to strip structure.Of course,the established model can also be extended to other arid and semi-arid regions,and the vegetation evolution dynamics can be studied by combining the real climate data of other regions.