中文摘要：

以位于农牧交错带南部的甘肃省环县为研究区域,采用因子分析法,以1949-2013年共65年的16个社会经济和自然因子的统计数据为样本,研究了环县土地沙漠化过程中驱动因素的时间变化。结果表明：1）1949~1979、1980~1999和2000~2013年3个时间段人类活动对土地沙漠化驱动作用的贡献率分别为46.21%、36.25%和44.79%;自然因素的贡献率在1949~1979年为26.45%,比1980~2000年高11.32%,比2000~2013年高4.87%;1980~1999年综合因素贡献率为30.77%,分别比1949~1979年和2000~2013年高21.41%和12.18%。2）人为因素是3个时间段引起环县土地沙漠化发生和逆转的主要因素,气候变化对沙漠化的影响相对较小,其中人为因素的影响主要是人口数量急剧增加、农业人口过大,过度垦殖导致土地不合理的利用,超载放牧引起草场大面积退化;自然因素的影响主要是气温的持续升高、降雨量减少、蒸发量增加、空气相对湿度下降,导致干旱和土壤干层的发育,抑制了植物的生长,降低了植被覆盖度及土壤的抗冲蚀能力;而较强而持续的风力及暴雨量的增加加速了土壤侵蚀。3）1980年土地联产承包制和2000年退耕还林（草）政策的实施并未使人为因素的影响明显变化;3个时间段自然因素的贡献率不断下降,综合因素的贡献率增加。

英文摘要：

Taking the Huan County of Gansu province located in the south part of agriculture pasture ecotone as research area, temporal variation of driving factors of land desertification for the last 65 years was analyzed using principal component analysis based on 16 statistical data of social and economic factors.from 1949 to 2013. Re- sult show that： （1） The process of desertification in Huan county for last 65 years could be divided into three time phases, including 1949 - 1979, 1980 - 1999 and 2000 - 2013 according to the contribution rate of human activity factors to land desertification 46.21% ,36.25% and 44.79%, respectively. Natural factors contribution rate from 1949 to 1979 was 26.45% , it was 11.32% higher than that of 1980 - 2000 and 4.87% higher than that of 2000 ~ 2013. Furthermore, Comprehensive factors contribution rate from 1980 to 1999 was 30.77%, it was 21.41% and 12.18% higher than that from 1949 to 1979 and from 2000 to 2013, respectively. （2） The in- fluence of climate change on desertification was relatively small, but the human activity was the much more active factor to the desertification and reverses desertification. It mainly incarnated on the changes of the dramatically - increased population and agricultural population, unreasonable landuse caused by excessive reclamation as well as pastures degradation induced by overgraze ; Moreover, the influence of natural factors mainly incarnated on the changes of temperaturesfising, lower rainfall, increased evaporation and decreased sir relative humidity which may led to soil drought and development of soil dried layer, inhibition of plant growth and vegetation coverage as well as the ability to resist erosion of the soil. However, factors for accelerating soil erosion were the strong and consistent wind and storm rainfall. （3） The implementation of land combined contract system in 1980 and the policy of returning farmland to forest （grass） in 2000 have little impact on the influence of human factors ; as for the three phases, contr