The Response of Typical Vegetation Growth to Climate Conditions in North Tibetan Plateau

Based on the scanned and georeferenced vegetation map of North Tibetan Plateau from 1：1000000 China Vegetation Atlas and grassland resource map of the North Tibetan Plateau, alpine steppe in the western North Tibetan Plateau, alpine meadow in the central North Tibetan Plateau and alpine shrub meadow in the eastern North Tibetan Plateau are selected as three most typical vegetation types in the North Tibetan Plateau. First, the climate conditions in North Tibetan Plateau are analyzed. Secondly, the ten-day mean temperature and precipitation and SPOT VEGETATION ten-day maximum composite NDVI (normalized difference vegetation index) of three typical vegetation regions from 1999 to 2001 are studied. Finally, the relationships between vegetation growth based on the SPOT VEGETATION ten-day maximum composite NDVI and the ten-day mean temperature and ten-day precipitation as two key climate variables that affect vegetation growth in these regions are analyzed. The spatial distribution of the precipitation decreases from southeast to northwest and that of the temperature decreases from south to north in the North Tibetan Plateau. Contrary to the precipitation, evaporation is higher in west than that in east in the North Tibetan Plateau. SPOTV EGETATION NDVI variations can represent the three typical vegetation growth patterns. In two important vegetation growth periods, the date of the green-up initiation and withering of vegetation represented by NDVI is consistent with the vegetation growth phases by calculating from accumulated temperature. The coefficients between NDVI and corresponding temperature from 1999 to 2001 in the alpine steppe is 0.66, in alpine meadow 0.81, and in alpine shrub meadow 0.79, while the coefficients between NDVI and precipitation in three different vegetation types are 0.53, 0.68 and 0.54, respectively. It means that NDVI variations in the North Tibetan Plateau are more sensitive tothe temperature than to precipitation. Because of the high altitude and frigid climate in the North Tibetan Plateau, the impact of the temperature on the vegetation growth markedly is higher than that of the precipitation. The temperature is the main confining factor for vegetation growth in the North Tibetan Plateau. Response degree of three typical vegetations to climate variations in the North Tibetan Plateau from high to low arealpine meadow, alpine shrub meadow and alpine steppe, respectively .