Reconstructing Historical Cropland Spatial Distribution Of Valley In Tibetan Plateau

Land Use/Cover Change which caused by human Activities is one of the main reasons for changing in the Earth’s natural ecosystems, it is the key factor that impact climate Change of regional and global too, has become one of the core areas in study of Global ecological change. The study in reconstructing historical land use / cover change especially in the past 300 years not only can reveal the evolution of the relationship between people and land of historical periods very well, but also can provide a theoretical basis for simulating past climate change process and diagnosising climate formation mechanism. However the high-resolution and high-precision land cover data is the key to analysis the environmental effects(especially the climate effects)Profoundly.Tibetan Plateau is a fragile, sensitive area for global change, it affected by human activities and global climate change easily, analysis its land use / cover change during the historica is significant for understanding the regional and global environmental change. In this paper, we design a methods to reconstruct historical cropland spatial distribution of valley in Tibetan Plateau basis on the existing methods, select the Yellow River-Huangshui River valley as case, reconstructed its farmland pattern evolution in the Qing Dynasty and analyzes the driving mechanism. Draw the following conclusions:(1) Plateau due to its special geographical location and the harsh natural conditions, the impact of human factors on the distribution of cropland spatial is small, cropland spatial distribution is mainly limited by natural environment, and this limitation is particularly prominent when agricultural technological backwardness in the historical period, the method in this article just from this perspective.The results show that cropland spatial distribution which reconstruced by the method is more in line with the historical actual cropland spatial distribution in Tibetan Plateau.(2) Select the Hehuang valley which has long history as a case, we reconstructed its cropland spatial use the model that designed in paper. Hehuang valley is a gathering place for minorities, there are six kinds of cropland in the Hehuang valley and they are also classified two grops based on the nation of cultivators, one grop is named Tun, Ke, Qiu, Zhan, Ken land which are cultivated by the soldiers, the other is named Fan land which are cultivated by the minority. The cultivated area of Hehuang valley has significant volatility in Qing dynasty, 1726-1772, 1806-1845 cultivated area in a increasing stage and until 1845 it having a peak.(3) The change of Tun, Ke, Qiu, Zhan, Ken land is different from Fan land, the relationship of them is as one falls, another rises, it is related the natural conditions of Hehuang valley and government policy closely. Secondly, the area of Fan land occupies larger proportion, this is determined by the geographical conditions and its geographical distribution.(4) The reconstruction of cropland spatial distribution of Yellow River-Huangshui River valley in Qing dynasty shows that although Yellow River-Huangshui River valley has larger area, but less arable land as the limited of natural environmental conditions. the cropland in the space are mainly distributed near the Huangshui River and its tributaries Beichuan River,the middle and lower reaches of Datong River and the Huanghe River. Among them cropland distributed denser in the north of the Hehuang valley consisted by the basin of Huangshui river and the tributary area of Datong river.(5) Under the dual impact of natural environmental conditions and political structure, the cropland fraction of the Yellow river-Huangshui river valley is low as a whole, cropland experienced wasteland reclamation stage(1726-1772), abandoned stage(1772-1806),reclamation stage(1806-1845) and the stage of abandoning cultivation again.the change of cropland area has the consistency of cropland fraction.(6) The cropland spatial distribution mainly affected by government policies, wars, natural disasters, climate change and other natural factors in.