Growing-season normal difference vegetation index,NDVI,response to climate changes and increased carbon dioxide concentration in frozen areas of Northeast China during 1982 ～2008

Based on GIMMS and MODIS remote sensing data from 1982 to 2008,we analyzed the spatial-temporal characteristics of vegetation Normal Difference Vegetation Index NDVI during the growing-season. We then explored the responses of NDVI to climate changes and the increased carbon dioxide concentration for different vegetation types in different frozen regions. The average growing-season NDVI value in different frozen regions is: continuous permafrost region mostly continuous permafrost region seasonal frozen earth region segregated permafrost region. For vegetation types, the average growing-season NDVI value is: forests shrubs marshes farmlands grasslands. The average annual growing-season NDVI value of forests is 0. 61,and that of grasslands is 0. 46. The past 27 years can be divided into three stages based on the annual variability of average growing-season NDVI: ①1982 ～ 1990,slight increase stage,②1990 ～ 2000,slow decrease stage,③2000 ～ 2008,obvious increase stage. The continuous and mostly continuous permafrost region experienced significantly increased vegetation NDVI from 1982 to 2008 (p 0. 05) . The NDVI values of forests had significant increasing trends,but other vegetation types showed no significant trends. In the past 27 years,the study area saw significantly increased air temperature,declined precipitation,and increased carbon dioxide concentration. The average growing-season NDVI for the whole study region was significantly positively correlated with annual average air temperature (p 0. 05) . It could be summarized that,in the frozen areas of Northeast China,the climatic factor controlling the growing season vegetation NDVI was temperature. Vegetation growing-season NDVI was effected by annual average temperature as follows: forests marshes scrubs farmlands grasslands; and by precipitation: forests marshes grasslands scrubs farmlands; by carbon dioxide concentration: forests marshes grasslands farmlands scrubs.