西藏生态系统碳蓄积动态的土地利用/覆被变化归因分析

论文利用In VEST模拟了2001—2010年西藏生态系统碳蓄积动态变化,并从土地覆被类型转移和土地覆被碳密度变化两方面对碳蓄积动态进行归因分析。研究发现:1)2001—2010年西藏碳蓄积增加0.5×108t。藏西北、藏东南碳蓄积变化较大,藏中、藏北相对稳定。牧区碳蓄积增加,农区、半农半牧区减少。水源涵养区和防风固沙区碳蓄积增幅大,生物多样性保护区和特色产业区下降。草原碳蓄积持续增长,森林、稀疏植被碳蓄积稳中有降,灌丛碳蓄积下降。2)草地、林地等碳密度高的地类面积增加,灌丛、稀疏植被等碳密度低的地类面积减少,土地覆被类型转移增强了碳蓄积功能,对碳蓄积变化的贡献率为269%。3)森林等碳密度较高的地类碳密度下降明显,稀疏植被等碳密度较低的地类碳密度略有增加,碳密度变化对碳蓄积变化的贡献率为-169%。

Analysis on Dynamic of Carbon Storage in Tibet Attributable to Land Use and Land Cover Change

There is a prominent impact of land use/cover change (LUCC) on dynamic of carbon storage and sequestration in ecosystem. The LUCC influence carbon storage via two ways, one is land conversion, the other is land modification. Studies have focused on the former, while the exploring of the latter is scarce. Located in hinterland of the Qinghai-Tibet Plateau, Tibet is typical ecologically fragile and sensitive area. Dynamic of carbon storage in Tibet and the contribution from land conversion and land modification was analyzed in the period from 2001 to 2010 in this paper. With the land cover data from MODIS MCD12Q1, the biomass density from the Carbon Dioxide Information Analysis Center (CDIAC), the soil organic carbon density from the Joint Research Centre (JRC), the carbon storages and sequestrations of Tibet in four carbon pools including aboveground biomass, belowground biomass, dead wood, soil carbon were calculated by using the InVEST (Integrated valuation of ecosystem services and tradeoffs) toolset. With quadrats data such as aboveground biomass and soil organic carbon collected through field survey and analyzed in-lab subsequently, the output of the model was calibrated. The main conclusions are: 1) The carbon storage increased 50 million tons from 2001 to 2010 in Tibet. Southeast Tibet and northwest Tibet experienced large changes in carbon storage with increasing in some areas and decreasing in others, while the middle and northern Tibet have relatively stable carbon storage. The carbon storage in farming areas reduced 39 million tons, and that in farming-pastoral area reduced 26 million tons, while that in pastoral area increased 114 million tons. Carbon storage in water conservation area and that in wind break and sand fixation area increased remarkably. Seen from the perspective of land cover type, carbon storage in grassland was continuously growing, and those in forest and sparse vegetation decreased slightly, while in shrub decreased remarkably. Carbon storage in grassland accounted for 57.1% and 62.1%, that in forest accounted for 11.8% and 11.1%, and in sparse vegetation accounted for 20.1% and 19.2%, while that in shrub accounted for 7.1% and 3.9% in total carbon storage of Tibet in 2001, 2010, respectively. 2) The land covers characterized with high carbon density increased in area, such as grassland and forest; those with low carbon density decreased in area, for instance shrub and sparse vegetation. The land conversion improved the capacity of carbon storage. Assuming the carbon density in each type of land cover being constant, the increased carbon storage caused by land conversion was 126 million tons, accounting for 269% of the carbon storage dynamic. 3) The land covers characterized with high carbon density, such as forest, decreased remarkably in carbon density, while those with low carbon density increased slightly in carbon density, such as sparse vegetation. Assuming that there is no land conversion, the decreased carbon storage caused by carbon density change was 79 million tons, accounting for -169% of the carbon storage dyna-mic.