Modeling Forest NPP Patterns On The Tibetan Plateau And Its Responses To Climate Change

NPP of ecosystem refers to the accumulated organic matter gross of green vegetation in unit time and unit area. NPP not only plays an important role in the global climate change, but also is susceptible to the climate change. Therefore, the study on the regional NPP would help to enhance the understanding of matter cycle and energy flowing of ecosystem and reveal the corresponding rules of ecosystem to the global climate change and impacts of global climate change to the ecosystem.In the support of Remote Sensing and Geographic Information System, based on the temperature and precipitation data measured at 139 stations and the DEM data of the Tibetan Plateau, the map of monthly temperature and precipitation on the plateau were drawn, which would be the elements of the carbon storage and NPP. MODIS data with 250m spatial resolution, climate data, 1km DEM, 1:2,500,000 forest map and 1086 plot data of National Forest Inventory (NFI) of the three test areas (Tibet, Yunnan and Sichuan) were used to estimate the above-ground forest carbon storage in Tibetan Plateau. Dummy variables,such as aspect and vegetation types derived from DEM, NFI and forest map of Tibetan Plateau, were used to the carbon model. To get a more accurate model of estimating forest carbon storage, the Plateau was divided into three separated sub-areas according to its physical geography characteristics and sub-area models were compared with the whole Plateau model. By the use of monthly NOAA\AVHRR data from August, 1991 to September, 2001 with spatial resolution of 8km, the spatial pattern and dynamics of annual NPP in recent 10 years were analyzed.The relationships of NPP and climate data were established to simulate the impacts of climate changes to the Plateau NPP. The results could be obtained as follows:1. In the dry seasons, the monthly precipitation is low no matter wet years or dry years, and the best results for dry monthly precipitation mapping were obtained using Kriging interpolation. In the wet seasons, the monthly precipitation was highly affected by the altitude, so the two mixed methods got better results than the corresponding other three methods. Furthermore, the mixed method II (the combination of Multiple Regression and Splines) got the best result. The spatio-temporal patterns of the Tibet Plateau in the precipitation maps were discussed. The precipitation in plateau's west and north is fairly low and Plateau's east and south is less low for the dry seasons. The wet monthly precipitation decreases as the spatial variation from southeast to northwest.2. The dummy variables improved the precision of the forest carbon storage models dramatically. When the forest carbon storage models included dummy variables, the determining coefficients (R2) of the linear models were increased from 0.20, 0.24, 0.16 to 0.48, 0.35, 0.33 in Tibet, Yunnan and Sichuan respectively. When the linear regression models were changed to logarithmic models, R2 of Tibet, Yunnan and Sichuan were increased from 0.23, 0.30, 0.14 to 0.60, 0.65 and 0.59, respectively.3. In Tibetan Plateau, the forest is mainly distributed on eastern part with forest cover-of about 11.3 % in 2002, and the mean above-ground forest carbon storage was about 19 t/hm². The carbon storage of shrub is fairly low, less than 10 t/hm², which is located in the Qaidam basin, the western Sichuan Plateau and the southernmost part of Tibet. The forest carbon storage in the easternmost and southeasternmost of Tibetan Plateau was mostly below 50 t/hm². In the Minjiang River watershed, the carbon storage is about between 100 t/hm² and 150 t/hm². In Tibet, the above-ground forest carbon storage was much higher, with more than 250 t/hm².4. The highest forest aboveground NPP was located in the closed coniferous forest in Linzhi of Tibet, the forest aboveground NPP is between 0.5 t/hm². m^-1 and 0.6 t/hm². m^-1. The next is the tropical and subtropical forest in Yunnan, the forest above-ground NPP is between 0.2 t/hm². m^-1 and 0.4 t/hm². m^-1. The forest above-ground NPP in the eastern Plateau is at the middling level, with the mean NPP of 0.3 t/hm². m^-1. The forest aboveground NPP in the northeastern Plateau is fairly low, which is no more than 0.3 t/hm². m^-1.5. The forest aboveground annual NPP of recent 10 years were in a fairly steady moving up state, which took change from 0.167PgC/a of 1991 to 0.185PgC/a of 2000. The annual NPP increased 0.002PgC/a of every year, and the annual increasing rate was about 1.1%. In recent 10 years, the forest aboveground average annual NPP was about 0.19PgC/a.6. In different forest vegetation types, coniferous forest NPP accounted for about 72.96% of the whole Plateau forest vegetation, and the total NPP of it was about 0.37TgC/m. The shrub forest accounted for about 21.62%, and the total NPP of it was about 0.11TgC/m. The total NPP of broad-leaf forest was fairly little, which was about 0.03TgC/m, which accounted for 5.42% of the whole Plateau.7. On the Plateau of Yunnan, the primary climate drive factor of forest aboveground NPP is precipitation, which is positive to NPP in certain precipitation scope. On the Plateau of Tibet, Sichuan and Qinghai, temperature and precipitation are both primary drive factors, and temperature is positive to NPP and precipitation is negative to NPP.