太仆寺旗2000-2008年EVI对气候及土地利用变化的响应

以位于北方农牧交错带的太仆寺旗为研究区,利用2000-2008年MODIS-EVI数据和周边45个气象站点同期月气温、降水资料,分析了近10 a该区EVI的时空变化及年最大EVI与气候因子的相关性。结合2000年和2005年的土地利用数据,分析了各地类EVI对气温、降水变化的响应及各地类变化过程对EVI变化的影响。结果表明:年最大EVI与6-7月平均气温呈显著负相关,与同期总降水呈显著正相关,相关系数均大于0.9;各地类EVI与气候因子相关性差异明显,退耕前,仅草地EVI对气候变化敏感,退耕后,耕地、林地EVI与气候因子相关性显著增强;耕地变草地、林地变耕地分别导致EVI减小2.27%和1.42%,林、草相互转变导致EVI分别减小0.71%和0.67%,说明退耕还林还草等措施未必促进植被恢复,受其他自然及人为因素影响。

Responses of EVI to Climate and Land-use Variation in Taips County from 2000 to 2008

The farming-pastoral zone in northern China has become one of the most vulnerable eco-regions due to the comprehensive effects of climate changes and human activities.As an integral component of ecosystem,vegetation cover dynamics indicated by various vegetation indices from long time series remote sensing data could be used to reflect the ecological and environmental changes.`The Grain for Green Project is widely put forward by converting farmland into forests and grasslands,the evaluation of which as a result has become the hot spot of ecosystem researches.Identifying the distinctive impacts of climatic factors and land use management disturbances could help to make more objective assessment of vegetation restoration and guiding the follow-up ecological constructions.This study used Taips County,a typical region in the farming-pastoral zone,as the study area.Based on the data of MODIS-EVI,monthly mean air temperature and precipitation obtained from the nearby 45 weather stations,the spatial-temporal patterns of vegetation cover from 2000 to 2008 were explored.The correlation coefficients between the annual maximal EVI over the whole region and the climatic variables of different months during the growing periods were calculated.Together with the land use data in 2000 and 2005,when northern China was experiencing fast land use shift,we further analyzed the correlation between EVI and climatic variables for different land use types.And EVI changes caused by land use transitions were also studied.The results indicated that from 2000 to 2008,the annual maximal EVI fluctuated with an increasing trend and the vegetation in middle-east of the region grew better than that in the southwest.The average EVI over the whole region of July had a negative correlation with the mean air temperature of June and July and a positive correlation with the total precipitation of the two months.The correlation coefficients were both higher than 0.9,suggesting delayed and accumulative effects.The correlation between EVI and climatic variables of different land use types differed significantly.Before farmland conversions,only the EVI of grasslands had negative correlations with precipitation while after the abrupt land use changes from farmland to forests and grasslands,the EVI of farmland and forests both had higher correlation coefficients than grasslands,interpreting the non-identical results of intensive and extensive land use managements.Different land-use transition patterns resulted in different EVI changes.EVI decreased 2.27% and 1.42% respectively when farmland converted into grassland and forests converted into cropland.The inter-transitions between forests and grasslands also resulted in EVI decrease,pointing out the great uncertainties of environmental protective policies and vegetation restoration projects in case of other natural and human influences.