Estimating forest and other terrestrial carbon fluxes at a national scale: the U.K. experience

For the U.K. the best understood terrestrial carbon flux is that associated with the expansion of forest area over the past 80 years. Modelling methods are described that have been used to estimate this uptake of carbon for the Land-Use Change and Forestry sector in the Greenhouse Gas Inventory of the UNFCCC. Measurements of losses of carbon from afforested organic soils are also presented and the consequent effect on the net national carbon sink for forests is discussed. These calculations show that the expansion of forests is currently causing about 2.8-4.0 Tg (C) per year to be removed from the atmosphere, the uncertainty depending on assessment of the situation for plantations on organic soils. Within these totals about 1.9 Tg (C) per year is being added to living trees, about 0.4 Tg (C) per year to the stock of wood products and the rest to soils. A preliminary estimate for emissions of greenhouse gases resulting from removal of forests for residential development is also presented. Methods to map the variation in the net flux across Great Britain are discussed. The methods used, and the values estimated, for other UK terrestrial carbon fluxes are summarized. A comparison with emissions of CO2 from energy generation, etc. is made.