The Influence Of Climate Change On Vegetation Cover In Northeastern China And Four Major Sandy Fields In 1982-2013

Using the Normalization Difference Vegetation Index,we evaluated the temporal and spatial variation of vegetation change in northeastern China and the four major sandy fields with the area during 1981-2013,and examined the influence of climate change on vegetation change.The main conclusions are presented as follows.The vegetation cover in northeastern China has an increasing trend from 1982 to 2013.The NDVI trend has obviously spatial variation.Annual NDVI of northern cropland and forest region has a significant decreasing trend,but in southern shrubland and cropland region has a significant increasing trend.Over the past 32 years,the temperature of northeastern China has significant increasing trend and precipitation has insignificant decreasing trend.Under this warm-dry condition in northeastern China,the response of vegetation to climate varies.Annual temperature and precipitation are all favor vegetation growth in most part of study area,but significant correlation area is limited.We found that temperature in spring and autumn has significant positive correlation with all NDVI.Precipitation in spring and autumn has significant negative correlation with northern cropland.In addition,NDVI-temperature and NDVI-precipitation correlation varies among different vegetation types and different environment conditions.In the northern forest region,NDVI has negative correlation with precipitation but positive with temperature,because it needs much more heat and radiation to meet the need of photosynthesis.In the western grassland region,NDVI has the opposite correlations,because the living environment of grassland is belongs to arid types and water using efficiency is the control factors for grass growth.We also found if annual precipitation is more than 800mm in our study area,NDVI-precipitation correlation coefficient will turn from positive to negative.We then focus on studying the vegetation cover change in the four main sandy fields in this region.In annual trend results,Mu Us sandy land has significant greening trend over the whole sandy region.Otindag sandy land has greening trend in southern part,but browning in northern part.Horqin sandy land has greening trend in eastern part but browning in western part.Hulunbuir vegetation mainly exhibits decreasing trend.Based on the vegetation change results,we evaluate the growing season correlation between sandy vegetation and other 21 different climate factors.Within Horqin,Otindag,and Hulunbuir sandy lands,evaporation has the most significant negative influence on vegetation and surface sensible heat flux has the most significant positive influence on vegetation.Temperature and precipitation are positive with vegetation growth,but sun radiation,wind speed and cloud cover have negative correlation with NDVI in Mu Us sandy land.Correlation between NDVI and climate in Mu Us sandy land is not significant but surface photosynthetically active radiation has significant negative correlation with vegetation growth.By using PCA method to analysis the multiple climate factors,we get four main PCs in quantitative model in each sandy field.PCs in Mu Us and Otindag models are mainly contributed by precipitation and thermal radiation relative factors.PCs in Horqin and Hulunbuir models are mainly contributed by latent heat flux and temperature relative factors.Additional,wind condition is also important for PCs in quantitative models.