Changes in satellite-derived vegetation growth trend in temperate and boreal Eurasia from 1982 to 2006

Monitoring changes in vegetation growth has been the subject of considerable research during the past several decades, because of the important role of vegetation in regulating the terrestrial carbon cycle and the climate system. In this study, we combined datasets of satellite-derived Normalized Difference Vegetation Index (NDVI) and climatic factors to analyze spatio-temporal patterns of changes in vegetation growth and their linkage with changes in temperature and precipitation in temperate and boreal regions of Eurasia (>23.5 degrees N) from 1982 to 2006. At the continental scale, although a statistically significant positive trend of average growing season NDVI is observed (0.5 x 10(-3) year (1), P = 0.03) during the entire study period, there are two distinct periods with opposite trends in growing season NDVI. Growing season NDVI has first significantly increased from 1982 to 1997 (1.8 x 10(-3) year(-1), P < 0.001), and then decreased from 1997 to 2006 (-1.3 x 10(-3) year(-1), P = 0.055). This reversal in the growing season NDVI trends over Eurasia are largely contributed by spring and summer NDVI changes. Both spring and summer NDVI significantly increased from 1982 to 1997 (2.1 x 10(-3) year(-1), P = 0.01; 1.6 x 10(-3) year(-1) P < 0.001, respectively), but then decreased from 1997 to 2006, particularly summer NDVI which may be related to the remarkable decrease in summer precipitation ( 2.7mm yr(-1), P = 0.009). Further spatial analyses supports the idea that the vegetation greening trend in spring and summer that occurred during the earlier study period 1982-1997 was either stalled or reversed during the following study period 1997-2006. But the turning point of vegetation NDVI is found to vary across different regions.