Nonlinear Stability Analysis Of Vegetation In Arid And Semi-arid Regions

In the arid and semi-arid regions of the world,vegetation becomes fragile duing to the lack of water resources and ecosystems are prone to great changes(such as desertification,system mutation etc).This paper studies the uncertainty in grassland ecosystem simulations caused by parameter uncertainties and the key sensitive parameter combination that leads to the change of ecosystem structure using a grassland dynamics model with temporal and spatial characteristics and conditional nonlinear optima parameter perturbation(CNOP-P)method.The main contents and conclusions are as followsFirstly,the numerical simulation of grassland dynamics model was carried out.The results show that the grassland dynamics model can describe the spatio-temporal changes of grassland ecosystems in arid and semi-arid regions,such as patch structure,and can also show the nonlin-ear characteristics of multi-equilibrium states.This shows that this model can be used to study the uncertainty of physical parameters on the structural changes of grassland ecosystemsSecondly,the uncertainty of physical parameters on grassland ecosystem simulation and its physical mechanism are studied.Taking spots,labyrinths,holes pattern and bare soil as the ground state,7 parameters with physical significance are selected from the model.The results show the joint mode of CNOP-Ps obtained by single parameter optimization is different from the global CNOP-P obtained by multi-parameter simultaneous optimization under the given param-eter range and optimization time.And the latter has a greater impact on grassland ecosystem This effect is reflected in the increase of grass caused by global parameter disturbance,for ex-ample,spot pattern will suddenly become labyrinth pattern,the bare soil will change into spot pattern,and the radius of labyrinth pattern and hole pattern will increase.However,the com-bined mode of single parameter optimization CNOP-Ps calculated by CNOP-P method and the local parameter disturbance of multi-parameter optimization at the same time will has less grass The results are similar under different ground states,different parameter error size and different optimization time.The results of physical mechanism analysis show that the transpiration term which reflects the nonlinear interaction between biomass and water is the main factor leading to the structural change of spot,labyrinth and hole pattern,while the evaporation term is in the case of bare soil.Finally,this paper discusses the key parameter combination and physical mechanism of grassland ecosystem structure change by using the approach of identifying sensitive parame-ters based on CNOP-P method.The experimental results show that the parameter combination obtained by the approach of identifying sensitive parameters combination based on CNOP-P is inconsistent with the parameter combination obtained by the method of ranking sensitive param-eters according to single parameter.Moreover,the former leads to more uncertainty in grassland ecosystem simulation,which will make the increase of grassland biomass more significant and even cause mutation.The number of parameter combinations,the size of error and the optimiza-tion time all affect the uncertainty degree of parameter error on grassland ecosystem simulation The nonlinear interaction between biomass and water reflected in transpiration term in the mod-el is the main factor leading to the structure change of spot,labyrinth and hole pattern,The main reason for the change of bare land structure is the evaporation term.And the difference of growth term,evaporation term and transpiration term is the main reason for the difference of uncertainty degree of grassland ecosystem simulation caused by the two kinds of parameter error.