Spatio-temporal Dynamic Of NDVI And NPP In The Black-soil Area Of Northeast China

As an important component of terrestrial ecosystems,vegetation plays an important role in many fields such as climate regulation,soil and water conservation.Therefore,monitoring the growth and dynamics of vegetation responding to climate change have an important significance in the study of global climate change.The northeast black soil area locates in northeast China and is sensitive to climate change,which is one of the sensitive areas for dynamic research of vegetation in northeast China.Exploring the dynamics variation of vegetation in the study area and its response mechanism to the global climate change has a significant indicative function.Using the dataset of MODIS NDVI to interpolate the dataset of GIMMS NDVI could acquire long-term dataset of NDVI,after consistency check,applying CASA model simulated the NPP dataset of vegetation over the black-soil area of the Northeast China from 1982 to 2016.Based on the linear regression model,calculating the long-term dynamic change trend of NDVI and NPP of vegetation in the study area in multiple spatial scales and different seasons.Meanwhile,combined with meteorological factors(temperature and precipitation),study the dynamics of NDVI and NPP of vegetation in the study area and its response to the climatic factors.Results showed that:(1)Based on the linear regression model,the time series of GIMMS NDVI dataset got extended through MODIS NDVI dataset,and the consistency test was carried out.And also,the reliability of multi-year NPP dataset simulated by CASA was proved.(2)Regionally,the NDVI during the growing season presented three different trends across these years(first increase,then decrease,and finally increase).Under the joint effect of temperature and precipitation,the regional vegetation growth showed obvious seasonal difference.From the scale of pixel,the NDVI exhibited a general increasing trend.The increasing vegetation types mainly included grasslands,forests,and crops;and the cities of Hegang,Suihua,and Changchun experienced significant vegetation growth.The mean NDVI of mult-years had a close correlation with temperature and precipitation over the same period.Over the regions where are mainly covered by arable lands,the vegetation NDVI was positively related to air temperature,while it had a significant positive correlation withprecipitation over the edges of the plains and mountains,where the dominant vegetation types are forests and grasslands.(3)At the regional scale,the annual average NPP of vegetation in growing season and summer is higher than spring and autumn.The NPP value of vegetation in spring has been rising from 1982 to 2016,and the significance gradually increases with the extension of time.The NPP of vegetation in 1982-2016 has a certain correlation with the temperature and precipitation in the same period,and the correlation has some differences among the six stages.At the pixel scale,the average NPP of vegetation in the black soil region of Northeast China showed a significant upward trend.The overall trend in six periods was to improve.In Qiqihar,Changchun and Heihe,the main vegetation types were grassland and agricultural vegetation.The NPP value of many years was positively correlated with temperature and precipitation in the same period,and the regional correlation was collectively affected by vegetation types,topographic factors and climatic strips.