Abstract

One of the environmental impacts of land-use change (LUC) is a change in the net exchange of the greenhouse gases (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O). Here we summarize data of changes in soil organic carbon (SOC) stocks and net soil CH₄ and N₂O emissions associated with LUC. We combine that with estimates of biomass carbon (C) stock changes and enteric CH₄ emissions following LUC. Data were expressed in common units by converting net CH₄ and N₂O fluxes to CO₂ equivalents (CO₂ eq) using established 100-year global warming potentials, and carbon-stock changes were converted to annual net fluxes by averaging stock changes over 100 years. Conversion from natural forest to cropland or grassland resulted in a change in net emissions of 7.3 ± 0.6 (mean ± 95% confidence intervals) or 5.9 ± 0.3 t CO₂ eq ha^-1 y^-1, respectively, while conversion of cropland or grassland to secondary forest reduced emissions by 5.3 ± 0.9 or 3.6 ± 0.7 t CO₂ eq ha^-1 y^-1, respectively. In all LUCs involving forests, changes in biomass C dominated the overall change in net GHG emissions. A retrospective analysis indicated that LUC from natural forests to agricultural lands contributed a cumulative 1569 ± 43 Gt CO₂ eq between 1765 and 2005, which is equivalent to average emissions of 6.5 ± 0.2 Gt CO₂ eq per year.

Keywords: Land use change; soil organic carbon; biomass carbon; enteric fermentation; carbon dioxide; methane; nitrous oxide.