The General Features Of Vegetation Activities Over China And Its Numerical Simulation

The general features of terrestrial vegetation distribution and its variations over China have been investigated by using the GIMMS-NDVI data during 1982-2002, togehther with the model simulation results with a dynamic vegetation model - VEgetation-Global Atmosphere-Soil model (VEGAS).The analysis results show that NDVI in China is higher for the east and lower for the west. The highest NDVI covers both southeast and southwest parts of China, and the desert in northwest China demonstrates the lowest NDVI. The inter-annual variability is higher in some arid and semi-arid areas; and lower in the region where the vegetation coverage is well. For seasonal cycle, vegetation coverage is the best in summer and worse in other seasons, especially for autumn. Generally speaking, vegetation activity is increasing over most parts of China, although there are remarkable differences among various regions. For example, the vegetation activity shows a relatively sharp decrease over South China, which may be ascribed to the rapid urbanization over this region. The response of vegetation to temperature and precipitation for the corresponding period has been studied, and it shows that the dominate factor for vegetation activity is different from area to area.The numerical simulation results show that the spatial and temporal changes of vegetation and carbon flux simulated by VEGAS are consistent with observations. Even though VEGAS, a dynamic vegetation model, considers not many types of vegetation, it is still able to recapture main characteristics for vegetation distribution in China. The variability of Leaf Area Index (LAI) simulated by VEGAS also agrees quite well with that from the remote sensing retrieval data. The simulations for various parts of China are also consistent with observations. For the reason that model is forced by natural condition instead of human activity such as land use, vegetation coverage in Southern China decreases for observations but increases for simulations, which further proves the idea that urbanization might be the main reason for vegetation decrease in Southern China. Furthermore, the patterns of distribution for Net Primary Production (NPP) and Net Ecosystem Production (NEP) simulated by VEGAS are also consistent with other model simulation results. All these may suggest that the VEGAS is capable in simulating the dynamical vegetation processes over China, and can be further applied for the study on the climate-vegetation interaction.