Dynamics Of Grassland Growth And Its Response To Climate Change On Tibetan Plateau

The Tibetan Plateau is the largest production base of grassland animal husbandry and an important ecological barrier in china. Severely constrained by the natural environment and social conditions, grassland resources are the material basis of survival and economic development for local people. As climate change sensitive and ecologically fragile areas, significant climate change of Tibetan Plateau has been and will continue to affect the plateau vegetation growth. Accordingly, the study of the plateau vegetation change process and its relationship with climate change is particularly important.In this study, the characteristics of climate change, dynamics of grassland vegetation and response of grassland vegetation to climate change were analyzed systematically on Tibetan Plateau from1981to2010. The results show that:1) The annual average temperature and annual precipitation of the Tibetan Plateau increased by0.7℃and12.4mm every10years during1981to2010, respectively. The distribution of temperature and precipitation were uneven within the year on Tibetan Plateau, precipitation mainly concentrated in the period from May to September. The annual average temperature of Tibetan Plateau was only-0.92℃, and the spatial distribution of temperature was significant difference, decreasing gradually from south to north. The average annual precipitation was404mm, and decreasing from southeast to northwest. The overall trend of Tibetan Plateau climate was warmmer and more humid, but presenting significant regional differences. The increased range of temperature was greater in higher altitude area than that of in lower altitude area, and precipitation increased significantly in areas with little precipitation.2) The spatial distribution of maximum NDVI of grassland in growing seasons was significant difference on Tibetan Plateau from1981to2010. The spatial distribution of NDVI had remarkable longitude zonal ity that presented a stairs type to continuously rise from west to east. The long time average value of growing season maximum NDVI for mountain meadow, hot herbosa and marsh were higher. Deterioration area of grassland was slightly larger than that of the recovery area, and most area of grassland remained stable on whole Tibetan Plateau during past30years. The deterioration area of marsh was largest in the all grassland types. The spatial distribution and area ratio of variation trend of grassland vegetation NDVI were significant differences in different periods of growing season.3) The biomass and coverage of grassland on Tibetan Plateau with a slight downward trend. The variation trends were diverse among the different grassland types, biomass and coverage of temperate meadow steppe, alpine meadow steppe and warm temperate herbosahad had an interannual increasing trend, while mountain meadow and warm temperate brush herbosa had a significant decreasing trend. There had no significant interannual variation trends in other grassland types. The grassland biomass and coverage increased gradually from May, and biomass peak appeared in July or August. Throughout the whole growing season, the biomass variation range of marsh was the greatest.4) Since1986, parts of the Tibetan Plateau grassland appeared varying degrees of degradation, the mainly degradation degrees were slight and moderate levels. The area ratio of degraded grassland was increased from44.43%during1986-1990to49.05%during2001-2010. The area of degraded grassland increased slightly over the past25years, but the proportion of severely degraded grassland was significant increased on Tibetan Plateau, it is indicated that the degradation degree of Tibetan Plateau grassland was increasingly serious. The overall degradation degree of grassland has been increasing, but the grassland also had a recovery trend in part of regions.5) The response of vegetation to temperature and precipitation changes showed different characteristics in different seasons. The correlation relationships between NDVI and temperature in winter and spring were better than that in summer and autumn, when correlation between NDVI and precipitation in summer and autumn were better than that in winter and spring. The response time of NDVI to precipitation was longer than that of to temperature for all seasons. The spring NDVI was mainly influenced by temperature and precipitation in the western part of Tibetan Plateau while summer NDVI was mainly affected by precipitation, the spring and summer NDVI were mainly affected by temperature in the eastern part of Plateau. In the northeast of the plateau, the major impact facotor of autumn NDVI was precipitation, in the rest area the major impact factor was temperature; winter NDVI was mainly affected by temperature and precipitation in the northern part and southwestern edge of the plateau, while it was mainly influenced by temperature in much of the rest area of the Tibetan Plateau. The response lag of seasonal NDVI to temperature and precipitation had no obvious spatial distribution regulation.