Characteristics of Vegetation Growth in the Farming-pastoral Zone over the North Parts of China Based on MODIS Data

The farming-pastoral zone in the north parts of China lies in the west of Northeast China, the north of North China and the west of Northeast China, the total area is about 1.3 million km².It is an important ecological vulnerable zone in China, and sensitive to the climate change.The research relative to the vegetation ecosystem in this area is important to the ecological construction and sustainable development.The NDVI of NOAA/AVHRR remote sensing data are usually used to reconstruct the ecological condition in recent studies in this area, and the MODIS and SPOT remote sensing data are less used.The MOD17A2 data from 2000 to 2006 with 2004 missing, the Gross Primary Productivity (GPP) of the land product from NASA of USA are used to asses the vegetation growth and its relationship with the climate in the farmingpastoral zone over the north parts of China because of their high spatial resolution.The highest GPP value of every 8 days in the studied area appears in June and the lowest in February, and the annual GPP changes from 0 to 835.4 gC ·m ^-2 with the average of 234.45 gC · m ^-2.Generally the GPP which is higher than 300 gC · m ^-2 distributes in the northeastern area and the forest area.The low GPP, which is lower than 300 gC ·m ^-2, appears in the middle and southwestern area, the grassland and shrub area.The correlation analysis between the GPP of every 16 days and the climate factor, temperature and precipitation at the same time shows that temperature is the main factor affecting the vegetation growth in farming-pastoral zone over the north parts of China, also, precipitation plays an important role.The phonological data of pasture, the emergence date, flowering date and withering data, from three agro-meteorological observation stations, Xilinhaote, Erguna and Yanchi from 2000 to 2006 and its corresponding GPP values are used to make assessment quantitatively on the growth stages of pasture.The GPP of every 8 days in the three stations from 2000 to 2006 shows the annual variation from 2000 to 2006, similar to the variation of the whole farming-pastoral zone over the north parts.The GPP values of the three stations are different, the GPP in Erguna is the highest which shows the regional vegetation growth characteristic in the farming-pastoral zone over the north parts of China.For the average phonological condition of the three stations, the GPP value at the start of flowering stage is the highest, ranging from 10 to 30 gC ·m ^-2, and the GPP values of the emergence stage and withering stage are similar of less than 10 gC ·m ^-2.For the same phonological stage the GPP value is different at different observation stations.Based on the results the MOD17A2 is a useful tool to the vegetation growth research in the farming-pastoral zone over the north parts of China.