%0 Journal Article
%T GENESES OF DESERTIFICATION IN SEMIARID AND SUBHUMID REGIONS OF NORTHERN CHINA<br>中国北方半干旱和半湿润地区沙漠化的成因
%A Deng Guangrong
%A Jin Heling
%A Chen Huizhong
%A Zhang Chunlai
%A <br>董光荣
%A 靳鹤龄
%A 陈惠忠
%A 张春来
%J 第四纪研究
%D 1998
%I 
%X Through comprehensive analyses of the Quaternary geology, historical literatures and modern observations in northern China. the authors thought that the geneses of desertification are different in different periods and different bine scales.1 Pleistocene The widely spreaded Pleistocene stratigraphic profiles, characterized by alternately overlapped aeolian sand, loess and palaeosol, are the direct evidence of desertification of the Pleistocene in the studying regions. The stratigraphic profile located at Yulin horticultural farm at southeast fringe of Mu Us Desert clearly recorded 15 positive processes, 18 reverse processes and 16 positive-reverse conversion processes since 1.1 Ma B. P. All these processes corresponded to ten thousand to tens of thousand-scale climatic fluctuations revealed by the loess plateau and deep-sea oxygen isotope records, suggeshng that the alternations of the positive and reverse processes of the Pleistocene desertification in the study regions were mainly caused by the climatic changes which were controlled by earth orbit elements, while the influence of human activities were negligible.2 Holocene During the Holocene from 10 000a B. P. to 1900 A. D., the stratigraphic profiles suggests that there were 5 or 6 reverse processes and 6 or 7 posihve processes,with an average cycle of 1 500 a. The climatic changes indicated by the susceptibility in the same period also showed a dry-wet variations with roughly similar cycle.During the historic period, especially in the past 2 000 years the alternations of positive and reverse desertification in semiarid and subhumid regions in China was even more frequent and showed a good agreement with the warm-cold and dry-wet variations in the same period. This suggested that positive and reverse processes of desertification in the period in the studying regions were dominated by a cycle of one hundred years. Therefore the alternations of positive and reverse processes of desertification in the Holocene in the region were also controlled mainly by climate changes. During the Holocene the influence of human activities on desertification has gradually intensified and this is mainly manifested in two respects: First, social production activities destroyed vegetation and top soil, thus causing the positive processes of desertification. Second, through fencing off degraded lands, planting trees and protecting natural environment etc.The desertification in local places was reversed to some extent. However, the former was always predominant. Compared with climate changes. The influences of human activities on desertification only hold a subordinate position, in other words, hUman activities could accelerate or exacerbate the desertification processes caused by climate changes.3 At present Since 1900 A. D. the positive processes and reverse processes of desertification in the studying regions have been alternating at a shoder time-scale and reversed frequency. The development of the positive proc
%K semiarid and subhumid regions
%K geneses of desertification<br>半干旱地区
%K 半湿润地区
%K 沙漠化
%K 成因
%K 中国
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=EA07051745CDC8D89D5F01A3A4CFE6A9&aid=889499A2FB048433&yid=8CAA3A429E3EA654&vid=13553B2D12F347E8&iid=0B39A22176CE99FB&sid=58F693790F887B3B&eid=3986B25773CB6C30&journal_id=1001-7410&journal_name=第四纪研究&referenced_num=53&reference_num=24