Analysis Of Normalized Difference Vegetation Index Change And Causes In The Southern Areas Of Taihang Mountains

Vegetation is one of the important indicators of the regional natural ecological environment,the responses of its spatial and temporal distribution and productivity status to the climate changes and indicating the intensity of human activities have been the hotspot of comprehensive research in the earth sciences in recent years.In particular,with the rapid development of remote sensing technology and the integration of geographic information technology,making it possible to monitor vegetation cover changes on a regional scale in a continuous period.Vegetation index is derived from the spectral data of detecting the subsurface conditions of the earth by different bands and calculated by mathematical formula.Normalized Different Vegetation Index(NDVI)was widely used,Which has been proved to be a good indicator of vegetation cover changes,biomass and ecosystem parameters,to assess the vegetation conditions effectively.Therefore,the paper selected the region-northern mountains among southern areas of Taihang Mountain In Jiaozuo,Henan Province,which is sensitive to vegetation changes and studied the spatial and temporal variations of NDVI and the responses of NDVI to the temperature and precipitation,altitude gradients and land use degree during 2000-2015 to explain the mountain vegetation changes.The relevant conclusions are shown in the following four aspects:Firstly,on the spatial pattern of annual NDVI value,there was a gradual increasing trend from the south to the north in the study areas,although the change trend was not significant during the study period,the change trend showed a gradual decreasing trend from the south to the north.The temporal and spatial patterns might be related to the distribution of the vegetation cover type of forest land,cultivated land or residential land.Secondly,under the backgrounds of global climate change,the precipitation decreased and the temperature increased in the study area during 2000-2015.On the responses of vegetation to the the climate factors,the proportion of the negative correlation between NDVI and the temperature,precipitation were 60.66% and 79.72%,and the latter correlation is significantly higher than the former,the annual NDVI was significantly correlated with the extreme low temperature and the extreme high temperature.Thirdly,on the responses of vegetation to the altitude gradient,the annual NDVI showed a increasing trend as the altitude increases in study areas.The decrease of NDVI below 200 m in elevation was mainly caused by the urbanization development and resource exploitation,and the increase of NDVI above 200 m inelevation was mainly related to the ecological construction policy of returning farm land to forest and suitable climate conditions.Finally,on the land use change,the cultivated area and grassland area decreased,while the land for urban construction increased significantly in the research area from 2000 to 2013.On the responses of vegetation to the land use changes,NDVI values of cultivated land and urban construction land both showed a decreasing trend,while NDVI values of woodland and grassland both increased on the certain extent.These are related to the land use type conversion between cultivated land and construction land,the policy of the implementation of mountain closure and forest cultivation and the comprehensive management among the mine geological environment in the research area in recent years.