Long-term Desertification Of The Ordos Plateau, Northern China

Much attention has been paid on historical desertification of the Ordos Plateau, northernChina. Researchers from varies disciplines, including physical science, social science,historical science and so on, have studied independedly this problem in terms of their ownunderstandings of it during the last several decades. However, whether the processes or thedynamics, the problem has so far not been well solved. Therefore, there is a need ofmultidisciplinary study. During the last five years, extensive field work was conducted torestudy this problem, numerous of ancient cities and Neolithic sites have been surveyed andtwo sediment profles related to human activieties were found. Then, together with historicaltexts, archaeological discoveries, historical desertification of Ordos Plateau was reinterpred inthis dissertation. Main achievements are as follows:(1) Study of two sedimentary profiles, namely Erdaochuan (EDC) profile in thesouthwest margin of Mu Us desert and Baoningbu profile in the southeast margin of Mu Usdesert. The results demonstrate that two phases of serious desertification occurred during lasttwo millennia, at the mid-to-late Tang dynasty and late Ming dynasty, respectively. The firstphase last relative short time and environment soon rehabilitated during Song-Yuan period,but the second kept developing until the late 1980s.(2) Interpretation of the environmental significance of ancient cities. Through theinterpretation of distribution pattern within varies historic periods, analysis of remostesensing images, and, most importantly, understanding of eolian sands in ancient city wall,environment of ancient cities at the time they were built were studied. The results present thatsome of ancient cities were built in ever-existing desert, thus the existence of them can not betreated as the signal of lush vegetation environment. On the contrast, desert had been there onthe Ordos Plateau before Qin-Han period.(3) Landscape construction. Based on the results mentioned above, landscape of eachhistorical period was qualitatively constructed.(4) Dynamics of desertification. Together with the studies of climate change, historicalrecords, the reason for the occurring of the two phases of desertification was studied. Theresults show that the desertification occurred at the mid-to-late Tang dynasty is consistentwith climate change, but the second phase, which started at late-Ming dynasty and stopped at late 1980s, is not coincident with climate process; therefore, human activities should haveplayed key role in accelerating this phase of desertification.