Abstract:

Due to terrain complexity and deficiency of the arable land,local population has produced a heavy pressure to resources and environment in the mountainous region of southern Gansu.Peasants live in poverty.It is provided with important signification to study on the optimum human population size for reconstruction after the earthquake disaster,poverty alleviation and protection of the ecological security of the upper Yangtze River.Based on two indexes,per capita grain and economic level, this paper estimated local human carrying capacity on three levels,the subsistence life, the relative ample life and the welloff life, and measured the relationship between population and agricultural resources.Meanwhile,on the basis of terrain complexity,we estimated the labor number and the population size that they could support.The result shows that total population size is overloaded even at the subsistence level in this region.Taking welloff life as a standard,the optimum population size is 135 million,which is about a half of the existing population.Labor forces of 1.008 1 million are needed to make use of present arable land and forestland for production activities,and the population that they can support is 1.915 4 million.The total population will be 2.310 3 million when the population in towns is included.This population size is a level low enough to realize subsistence life,but too high for relative ample life and even more difficult to realize welloff life. The strange circle existing among “population—farmland—labor force” has determined arduousness and complexity to realize the target of welloff life in the mountainous region.Therefore,innovation thoughts and multiple measurements are needed for reconstruction after the earthquake disaster and regional sustainable development in this region.

Key words: terrain complexity/ support coefficient/  optimum population scale/  human carrying capacity/ the mountainous region of southern Gansu