Land use effects on terrestrial carbon sources and sinks

Abstract Current and past land use practices are critical in determining the distribution and size of global terrestrial carbon (C) sources and sinks. Although fossil fuel emissions dominate the an-thropogenic perturbation of the global C cycle, land use still drives the largest portion of anthropo-genic emissions in a number of tropical regions of Asia. The size of the emission flux owing to land use change is still the biggest uncertainty in the global C budget. The Intergovernmental Panel on Climate Change (IPCC) reported a flux term of 1.7 PgCa−1 for 19901995 but more recent es-timates suggest the magnitude of this source may be only of 0.96 PgCa −1 for the 1990s. In addi-tion, current and past land use practices are now thought to contribute to a large degree to the northern hemisphere terrestrial sink, and are the dominant driver for some regional sinks. However, mechanisms other than land use change need to be invoked in order to explain the inferred C sink in the tropics. Potential candidates are the carbon dioxide (CO2) fertilization and climate change; fertilization due to nitrogen (N) deposition is believed to be small or nil. Although the potential for managing C sinks is limited, improved land use management and new land uses such as refores-tation and biomass fuel cropping, can further enhance current terrestrial C sinks. Best manage-ment practices in agriculture alone could sequester 0.40.8 PgC per year in soils if implemented globally. New methodologies to ensure verification and permanency of C sequestration need to be developed