Research On Vegetation Pattern Of Forest,Savanna And Treeless Based On Statistical Thermodynamics

The study of the relationship between vegetation pattern and climate factors on a large scale is the challenging questions in ecology.Based on the theory of statistical thermodynamics and the requirements of the thermodynamic paradigm,we use the research results of Hirota,and analyze the global climate data,tree cover data and land use data.In this paper,the research areas include parts of Africa,Australia and South America.We study the large-scale vegetation pattern of forest,savanna and treeless.The results are as follows:(1)According to the derive criterion of vegetation stable state,we identify the state of vegetation particles in each energy grid.The vegetation patterns are established on different scales in Africa,Australia and South America(0.5℃×50mm,1.0℃×100mm and 2.0℃×200mm),and the results have showed the distribution trend of the three vegetation types.The dividing line between vegetation types can be shown objectively and clearly in T-P ecological state space.(2)Under the vegetation pattern of different scales in Africa,the forest generally distribute in the precipitation range of 1700-2100mm,the temperature is between 24℃and 26 ℃.Savanna is in the range of 600-1700mm and 18-28℃.The demand for precipitation is the least in the treeless,which is below 700mm.And treeless is more widely distributed in the temperature range of 16-30℃.(3)Under the vegetation pattern of different scales in Australia,the forest generally distribute in the precipitation range of 2500-4000mm,the temperature is between 25℃ and 28℃.Savanna is in the range of 400-2100mm and 13-28℃.The precipitation of treeless is below 900mm,and the temperature range is 15-29℃.(4)Under the vegetation pattern of different scales in South America,the forest generally distribute in the precipitation range of 1700-3500mm,the temperature is between 24℃ and 27℃.Savanna is in the range of 400-1900mm and 16-28℃.The precipitation of treeless is below 400mm,and the temperature range is 4-20℃.(5)Precipitation is a major driver of past and recent shifts in the extension of tropical forests and savannas.In the space of T-P ecological state,although the range of precipitation and distribution of forest in each continent is very different,we find that the distribution shapes of forest and savanna in each continent are similar,which further indicates that in tropical and subtropical regions,the three alternative states of forest,savanna and treeless are changing in a very common way with the change of precipitation.In this study,the distribution patterns of tropical and subtropical forests,savanna and treeless are objectively presented in the state space of annual mean temperature and annual precipitation.In our theory,the stable state of vegetation system is redefined,which avoids the boundary subjectivity in the study of traditional ecological pattern.This study has some guiding significance for the research of large scale vegetation pattern in the future.