Study on the Trend of Vegetation Phenological Change and Its Response to Climate Change in Changbai Mountains

As one of the sensitive indicators in response to climate change, plant phonological change is usually used as an important component of dynamic vegetation models to reflect the dynamic of carbon and water exchange between the land surface and the atmosphere. The phenological change in large scale can not only reflect the seasonal variation patterns of vegetation, but also be an indicator of global climate change. In this study, using the biweekly NOAA/GIMMS NDVI (Normalized Difference Vegetation Index) and meteorological data, we employed the maximum rate of change to extract the phenological change of the vegetation types in Changbai Mountains during 1982-2006, and investigated the possible impact of recent climate change on growing season in three climate zones based on Jingyun Zheng's climatic regionalization. The results were as follows: the onset date of green-up for the vegetation in warm temperate zone was in late April and the onset date of dormancy ended in late October. The length of growing season (LOS) for the vegetation types became shorter with increasing latitude. The earlier onset dates of green-up for all vegetation types were found in three climate zones during 1982-2006, ranging from 0.642 day/yr in Zone I, 0.429 day/yr in Zone II, to 0.371 day/yr in Zone II, which indicates that the earlier onset dates of green-up were significant with a longitude trend of vegetation types. The LOS of the three climate zones became longer during 1982-2006, but the lengthening of growing season demonstrated in different ways in the three climate zones. Temperature had stronger effect on the phenological change. The onset date of green-up was earlier and the corresponding temperature threshold was higher in the low latitude, and the LOS was in significant correlation with the accumulated temperature above 10 degrees C in three climate zones