LAND USE/COVER CHANGE EFFECTS ON CARBON CYCLING IN TERRESTRIAL ECOSYSTEMS

Abstract

Land use/cover change (LUCC) is one of the most concerned environmental problems by scientists, land managers and policy makers. LUCC can affect energy flow, biogeochemical and hydrological cycling in terrestrial ecosystems through altering land surface and species composition. Ecosystem carbon cycling responds differently to various LUCC types, showing a pattern of CO2 release into the atmosphere when LUCC from a high-biomass forest to low-biomass grassland, cropland or urban area. Previous reports indicated that global terrestrial ecosystem released 2.21 Pg C (1 Pg C=1015 g C) per year induced by LUCC during the 1990s, which explains about 25% of the global C emission per year in the same period; and in the last two centuries, the released C from LUCC accounts for 50% of the C emission from fossil fuel combustion. The LUCC patterns are totally diversified for regions around the world, which cause obviously different C fluxes among them. The reports showed that LUCC in the tropics is a C source, while it is a C sink in the middle and high latitude regions in the northern hemisphere, which possibly explain a large part of the "missing carbon sink" in the terrestrial ecosystems. Currently, modelling is the most popular way to simulate LUCC-induced changes in ecosystem C cycling. The quantitative relationship between LUCC patterns and their related processes and ecosystem carbon cycling remains uncertain. This uncertainty causes great discrepancies in the estimation of terrestrial ecosystem CO2 fluxes from land use/cover changes. In the near future, except for carrying on long-term experiments to determine these quantitative relationships, model development by integrating LUCC with vegetation dynamic model and ecosystem process model will be essential for making an accurate estimation of C fluxes induced by LUCC. Sound land management can greatly increase C storage in the terrestrial ecosystems during LUCC processes. However, the quantification of land management effects is not well-established yet and land management is thus not included in most simulation models of LUCC impacts, which needs more researches in the future.