THE CARBON SINK PROVIDED BY PLANTATION FORESTS AND THEIR PRODUCTS IN BRITAIN

The rate of accumulation of carbon in forest plantations in Britain is estimated using the record of forest planting since 1925 and a model that calculates the flow of carbon from the atmosphere to trees, litter, soil, wood products and back to the atmosphere. It is assumed that all trees planted so far have the carbon accumulation characteristics of P. sitchensis, Yield Class 14 m(3) ha(-1) a(-1), but that future planting could include F. sylvantica Yield Class 6 and Populus Yield Class 12. It is further assumed that conifer plantings increase surface litter, but not soil organic matter, whereas broadleaved tree plantings (on mineral soils) increase both. Because the current forest estate is relatively young, it is estimated to be accumulating about 2.5 million tonnes of carbon per year (1990), and to be still increasing in carbon density (tonnes C ha(-1)). In order to maintain this rate of carbon removal from the atmosphere, planting would need to continue at a rate of 25-30 thousand ha of conifers or (theoretically) 10 thousand ha of poplars per year (on good mineral soils). It is noted that 2.5 million tonnes C is about 1.5 per cent of the UK carbon emission, and may be similar to the natural carbon sink in Britain represented by wetlands and rivers.