Analysis Of History Of Vegetation Reclamation And Eco-enviromental Transition Of Temperate Grassland In Northern China

China is resourceful with 4×10~8 hm~2 of natural grassland covering 40.9% of national land area. In northern China, 1.67×10~8 hm~2 of temperate grassland, almost covering 41% of the national grassland area, are presented as zonal distribution from northeast to southwest mainly distributed in northern and western China, This range from northwest desert to southeast agricultural district forms a natural green ecological shelter and wildlife habitat, and also conventional region of animal husbandry in northwest China. Northern temperate grassland comes into being after long-term geologic origin and changes with climatic variations and human actions. Good research of history of evolutions in northern temperate grassland can complement and construct theoretical frame of history of grassland' happenings in China and provides important academic value. At the same time, it may summarize historical experiences and lessons and guides us to utilize grassland rationally and achieve more ecological, economic and social benefits.In order to explain the variation of grassland vegetation reclamation and ecological environment, a large amount of historical information was referred to study relationship between historical changes of climate and grassland vegetation, effects of population increase and social factors on the grassland vegetation reclamation. Results show that northern temperate grassland came into being in Miocene (about 7 to 10 million years ago) and strenuous evolution happened to ecological environment of grassland during the thousands years of human action. Natural climate condition has had large influence on original vegetation components; and the improvement of productivity, the increase of population especially in agricultural district, policies in all of dynasties, wars and other anthropogenic factors had leaded to deforestation, land reclamation and reclamation of the grassland vegetation and abandon of the land reclaimed, therefore caused a series of variation of grassland ecological environment. From Neolithic period to Ming Dynasty, northern temperate grassland experienced periodic changes from warm to cold and from dry to humid. It seems generally that it is shorter and shorter during warmer period and lower and lower in the temperature of this period; dry and cold period is opposite, decreasing grassland area and deteriorated grassland ecological environment were characteristic of the periodic change. but theoretically, the climate of northern grassland in china will become warm following one hundred years, the rainfall of the northwest will increase and that of the ease will reduce to some extent ; apart from the anthropogenic factors, the grassland will also have a tendency of expansion.