| Oasis is the specific landscape and is the best part in arid regions. The formation and evolution of the cultivated oasis are the results of the change of natural environment combine with humanistic activities, the macro-scene of remaking nature, as well as the intuitive refection of the relation between human and land. Reconstructing the cultivated process of the oasis and its spatial changes, discussing the factors like population and cultivated lands, and analysing the driving mechanism of the oasis evolution is significant for recognizing the process and the rules of environmental changes in arid regions under the impact of human activities. Meanwhile, it will also provide important references for the optimization of control and management mode for ossification.The Heihe River basin, which locates in the northwest of China, has a long history of water and land resources development and its spatial distribution changed dramatically during the long cultivated process. It is one of a typical region of water and land utilization of the oasis. Some oases formed to stable artificial oases after long transformation, while others converted into deserts. Nowadays ecological degradation has brought serious disasters in the regional development. However, theses problems did not occur in a short period of time, but had a close relationship to the long water and land utilization. Therefore, taking the Heihe River basin as the study area, using the multiple sources of data like remote sensing images, as well as using the3S technology and the multidisciplinary approach, the ancient sites were investigated and the high resolution series of oasis evolution were reconstructed with the scale of1:100,000based on the dynasties after the implementation of several intensive field surveys and archaeological investigations. Meanwhile, the spatial-temporal process of oasis evolution was discussed. Then the main driving factors that affected the oasis evolution were determined and the inner mechanism was discussed. Finally, the experiences and lessons of the oasis development were proposed to provide the references for the optimal resource allocation in modern times. The main conclusions can be shown as follows:(1) Overall, the main shapes of the ancient cities are single ones with the shape of square and rectangle and the combined ones are rare. The area of all the cities was a clumped distribution both in the peak and in the low value, with50%of them lower than2×104m2and30%higher than10×104m2. Seen from the evolution of times, the city areas increased in a fluctuating tendency and the spatial distribution changed from clustering in the entire basin to radial distribution in the midstream.(2) The areas of the cultivated oasis in the seven dynasties named Han, Jin, Tang, Yuan, Ming, Qing and the Republic of China, which can be reconstructed, were about1703、1115、629.614、964、1205and1917km2, experiencing the process of decreasing firstly and increasing later.(3) The oasis in the Heihe River basin transferred to the midstream and upstream and distributed in the plains. In the early periods like the Han, and Jin, the oasis distributed both in the midstream and in the downstream, especially in the downstream. But soon the oasis in the terminal regions decreased gradually and the centre transferred to the midstream. During the Ming, Qing and the Republic of China, the oasis mainly distributed in the midstream, showing an expansion trend to outward and to around in radial way. The range expanded from the high plains in the Hexi Corridor to the alluvial fan near the mountains in the south. The oases with excellent natural conditions lasted for a long time, while the oasis in the terminal regions changed frequently and was usually abandoned after exploitation, which indicates the high dependency of the oasis to the water resources.(4) The spatial-temporal changes of the oasis in different regions differ notably. The main oases along the large rivers which included Shandan-Minle, Ganzhou-Linze-Gaotai, Jiuquan and Jinta-Dingxin shrank from the Han Dynasty to the Yuan Dynasty and expanded since the Ming Dynasty. The oasis areas since the Ming Dynasty were much larger than that of before the Ming Dynasty, showing a trend of expansion. However, the oases along the small rivers like the Maying River shrank since the Han Dynasty and were abandoned in the Yuan Dynasty finally. Since the Ming Dynasty, the oases recovered gradually, with their scale much smaller than that of in the early periods like Han and Jin, showing a trend of recession. (5) The oasis evolution in the Heihe River basin was affected by both natural factors and socio-economic factors. Among them, the climate and its change altered the oasis change through altering the factors like the water resources, river systems, deserts in the form of changes of temperature and rainfall, which is the main natural factor. Considering the importance and particularity in the respect of political and military position in historic periods, the political situation can be regarded as the premise as well as the core socio-economic factor in the oasis evolution.(6) From the time, the effects of the natural factors were more significant from the Han to the Yuan Dynasty. Although having the prosperous condition of oasis development in the Han Dynasty, the disturbance from the human beings was not prominent due to the first time for the large-scale development. From the Wei-Jin to the Yuan Dynasty, the population decreased and the cultivation was in a recession. Since the Ming and the Qing dynasties, the development of the oasis enhanced markedly with the increase of the population. Thus the humanistic factors were more remarkable.(7) There are several revelations for the oasis development and evolution. The first step for oasis development and economic growth is to maintain the stability of the political situation. In order to ensure a sound ecosystem and a sustainable use, the advice of development coexisting with protection under the ecological securities restraint of water resources was presented. When the human beings are well satisfied, reasonable industrial structure adjustment and transformation are the only way for the development of the oasis. |
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