中国西部地区植被净初级生产力的时空格局

Terrestrial net primary productivity and its spatial-temporal variability in western China

利用基于Monteith光能利用率理论的碳通量估算模型C- FIX,1km分辨率逐旬SPOT/ VEGETATION遥感数据和全球1.5°×1.5°格网化逐日气象数据,估算了2 0 0 2年中国西部地区植被净初级生产力(NPP)。对西部地区植被NPP的空间分布格局、季节变化及不同土地利用类型植被的NPP总量和平均生产力水平进行了初步研究。结果表明:2 0 0 2年我国西部地区植被年NPP总量约为0 .96 Pg C(1Pg=10 1 5g)。西部地区年NPP空间分布基本格局是东南和西北两区域高,然后以东南西北方向为轴心逐渐向内陆中心迅速递减,该分布格局与各区域的水热条件差异和植被类型的地带性分异规律紧密相关。西部地区陆地生态系统NPP具有显著的季相变化规律,这与温度、降水的季节变化以及人为生产活动安排有很高的相关性。西部地区尽管土地面积广阔,由于区域气候和自然条件相对恶劣,导致土地资源可利用率差,生态系统整体生产力水平相对低下,区域内各种土地利用类型植被的生产力水平差异大且空间分布十分不均衡,是我国生态环境相对脆弱的区域。

Net Primary Productivity (NPP) is an important variable in the studies of the carbon cycle and in natural resource managements at regional and global scales. The Monteith type parametric model, C-FIX is used to estimate the NPP of the terrestrial ecosystems in western China (73°～112°E, 26°～50°N) in 2002. The principal driven variables in the C-FIX model are temperature, radiation and the fraction of Absorbed Photosynthetically Active Radiation (fAPAR). The mean daily air temperatures and daily incoming global radiation in western China in 2002 are obtained from the global meteorological data with a grid size of 1.5°, provided by Meteo France. The ten-day fAPAR data set in the same region in 2002 are extracted from the SPOT4/VEGETATION NDVI remote sensing data with a pixel resolution of 1 km. In addition, a land use for the western China is mapped for further evaluation of the NPP values of different ecosystems. Validations by comparing the estimated NPP with some in situ NPP observations in the same region indicated a satisfactory accuracy for simulated results. The results show that the annual total NPP of the western China in 2002 is estimated about 0.96P (=10^(15))g C, which is an equivalent of 168g C/m^2 per year over the study area of 4.5 million km^2. The fundamental spatial pattern of annual NPP in western China is characterized by high NPP levels distributed in the southeast and northwest corners probably due to relatively richer precipitation. Then the NPP levels rapidly decrease from the two corners into the arid inland regions. In addition, the terrestrial NPP in western China has pronounced seasonal variations in the year. For most ecosystems, maximum NPP growth rates are observed in summer, whereas minima are obtained in winter. Furthermore, the NPP seasonality vary geographically in western China, probably due to the influences of strong zonation in climate, vegetation and farming practices. Different land use types and their corresponding NPP values also are compared using the latest 1:1M land-use map of western China. Grasslands contribute the most to the annual total NPP of western China due to their large area extends. Forests have the highest mean unit NPP values. On the other hand, large expanses of western China such as desert, glaciers and permanent snow have very sparse vegetation or even no vegetation. Although Western China has a large area of land, mean unit NPP level was very low due to the very limited availability to water resource over large arid inland regions and other harsh ecological environments.