The effect of land-use change on the net exchange rates of greenhouse gases: A compilation of estimates

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 +/- 03 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. (C) 2015 Elsevier B.V. All rights reserved.