Dominant control of climate variations over land-use change on net primary productivity under different urbanization intensities in Beijing, China

Abstract

Climate variations and land-use change induced by rapid urbanization can lead to crucial impacts on ecosystem Net Primary Productivity (NPP), especially in regions with intensive human activity. However, the relative contributions of land-use change and climate variations to NPP changes under different urbanization intensities are still a topic of debate. This study reports on a case study in Beijing, which is undergoing rapid urbanization, to estimate the effects of land-use change and climate variations on NPP in regions with diverse urbanization intensities in recent decades using remote-sensing data and the Carnegie-Ames-Stanford Approach (CASA) model. The results reveal obvious land-use changes in Beijing, showing an increase in both built-up and forested areas in the two inner, highly urbanized regions and a dramatic conversion from built-up area and grassy bush to forest in the two outer, less urbanized regions. Factorial experiments were performed to estimate the contributions of land-use change and climate variations to NPP changes for different regions and land-use types. An increasing trend in regional NPP was observed with decreasing urbanization intensity in all experiments. However, the increment in NPP between 2002 and 2009 tended to decrease with decreasing urbanization intensity in most experiments. Climate variation was the dominant factor in increasing NPP in the study region during 2002e2009, with a mean contribution of ~89.5% over different regions and land-use types. However, land-use change contributed to a certain extent to NPP changes for specific land-use types (e.g., ~28.1% for forests) in regions of intensive urbanization. Eco-engineering approaches such as increasing vegetation cover, especially forest, in built-up areas and reforestation and afforestation in non-built-up areas may be useful in mitigating the impacts of urbanization on NPP, especially in intensively urbanized regions.