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North China Electric Power University (2018)

Research on the Formation Mechanisms of Aolian-Sand-Vegetation Patterns

张非凡;

Titre : Research on the Formation Mechanisms of Aolian-Sand-Vegetation Patterns

Auteur : 张非凡;

Grade : Doctoral Dissertation 2018

Université : North China Electric Power University

Résumé partiel
Desertificaiton has becoming one of the most serious environmental problems in the world.Vegetation patterns are the typical landscape on desertified lands,and they have been observed widely in arid,semi-arid and semi-humid areas in the whole world.The extensive distribution and the heterogeneity of vegetation patterns contributed to draw the attention of substantial amount of geologists and ecologists.Researches on vegetation patterns can help to understand the potential of related ecological processes,to explore the mechanisms of pattern formation,and promote the understanding of desertificaiton and restoration,and to predict the formation and characteristics of vegetation patterns.These researches can be the guidance for desertification control and ecological restoration.Wind induced sand-vegetation patterns have been observed and described for quite a long time,but exploration of mechanisms on vegetation pattern formation in this situation has been,rare.In this research,we considered six ecological processes including,aeolian sand tranportation in the air,deposited sand movements on the ground,vegetation spread through seed dispersal,the flow of soil water,vegetaion growth and aeolian sand deposition.Based on these processes,a temporal and spatial discrete vegetation-sand model is established.Using this model,the mechanism of wind induced vegetation patterns is explored,and the main results are as follows :(1)Turing-type labyrinth patterns are induced by Turing bifurcation when there is no prevailing wind.While Turing-type regularly banded patterns are formed when prevailing wind exists.Irregular patterns are induced by the Neimark-Sacker bifurcation in the absence of prevailing wind.While irregularly banded patterns are induced by Neimark-Sacker bifurcation when prevailing wind exists.Simulated vegetation patterns are basically the same in type as the observed vegetation patterns in reality.(2)Wind-induced vegetation patterns induced by Turing-Neimark-Sacker coupled bifurcation can be classified into the following five types:coupled bifurcation irregular band patterns,coupled bifurcation labyrinth patterns,coupled bifurcation regular band patterns,coupled bifurcation spot patterns coupled bifurcation crescent-shaped strip patterns.Transitional patterns between these pattern types are more similar to the real patterns.(3)Shannon entropy and contagion index are calculated in this research in the formation of vegetation patterns.The results show that Turing patterns have lower Shannon entropy and higher contagion index than Neimark-Sacker patterns.For coupled bifurcation patterns,the coupled bifurcation irregular band,the coupled bifurcation labyrinth,the coupled bifurcation regular band,the values of Shannon entropy and contagion index in the three type patterns are in the middle of Turing patterns and Neimark-Sacker patterns.However,due to the special effects of coupled bifurcation,coupled bifurcation spotted patterns,coupled bifurcation crescent banded patterns,these two types present lower Shannon entropy than the Turing bifurcation and higher contagion index.(4)Based on the banded vegetation patterns,the characteristics of vegetation pattern under different environmental parameters are studied.The larger the advection intensity(reflecting the strength of prevailing wind),the greater the maximum and mean of vegetation coverage in the pattern ;the smaller the wavelength of the pattern,and the larger the wave number.The longer the time step(reflecting the frequency and time scale of the wind sand activity),the larger the maximum and the mean of the vegetation cover in the pattern,the smaller the wavelength of the pattern and the larger the wave number.

Mots clés : vegetation pattern; sand deposition; coupled bifurcations; pattern stability; self-organization degree;

Présentation (CNKI)

Page publiée le 11 avril 2019