Impacts Of Climate And Land-use/Cover Change On Southern China's Grassland NPP

Climate change and Land-use/cover change(LUCC) in the world are two important themes in the study of global environmental change. Research of the effects by the two factors to net primary production(NPP) is a key research content on terrestrial ecosystem carbon cycle. Both climate change and LUCC would lead to different effects on net primary production on different spatial-temporal scales, and they have a complex relation and feedback mechanism each other. So there is significance on quantitating the effects of climate change and LUCC to net primary production. As a carbon dioxide absorber that is only second to forest in the world, grasslands play an important part of the terrestrial ecosystem. To date, the approach of estimating net primary production tends to be mature, and significant research attention has focused on grasslands in northern China because of their regional and global importance. However, far fewer studies have focused on grasslands in southern China, especially for the impacts of climate change and LUCC on net primary productivity.Combining meteorological data and remote sensing data, this thesis explores the spatial and temporal pattern of the grassland NPP and the impacts of climate change and LUCC on the grassland NPP in southern China. In particular, the Carnegie-AmesStanford-Approach(CASA) model was employed to simulate NPP from 2001 to 2013, and to differentiate the individual impact of climate change and LUCC on NPP given the 13 possible scenarios. The main conclusions are as follows:(1) During 2001-2013, great fluctuation on NPP in the southern China's grasslands caused by climate changes and LUCC was presented. The average annual NPP for the whole region is 283.25 gCm-2yr-1, with the highest value of 600 gCm-2yr-1 in some area. The results indicate that grasslands in southern China were a relatively productive ecosystem over the study period. NPP is highest in the southwestern region, lowest in the northeastern region, and moderate in the central region.(2) During 2001-2013, A negative effect of climate change on NPP was found, resulting a reducing trend of NPP with the rate of 0.065 TgCyr-1(p=0.43). The LUCC exhibited a positive relationship with NPP, with a mean annual increasing rate of 0.151 TgCyr-1(p <0.01). The transformation for grassland to shrubs and forests are the main reasons. From 2001 to 2013, climate changes and LUCC resulted in an overall small positive effect on NPP in the southern China's grasslands. The total NPP for the southern China's grassland increased at the speed of 0.081 TgCyr-1(p=0.37).(3) The average annual carbon sequestration for the whole southern grasslands in China was 30.26 TgC, with a relatively large annual variation of 27.81-32.4 TgC. Overall, LUCC contribute 37.59% for the whole grassland NPP changes, and the climate change and other factors accounting for 33.49% and 28.9%, respectively.