The effect of geographical variation of planting rate on the uptake of carbon by new forests of Great Britain

Abstract

The planting rates from 1921 to 1996 of new coniferous and broadleaved forests for 11 regions of Great Britain were assembled for the state and private sectors. Over that period new planting totalled 231 kha of conifers and 132 kha of broadleaves in England, 141 kha of conifers and 16 kha of broadleaves in Wales and 881 kha of conifers and 52 kha of broadleaves in Scotland. These time series and regional values of Yield Class were used as input data for an accounting model of carbon in the trees, litter, soils and products to produce estimates of their net uptake of carbon by the forests from the atmosphere (i.e. increase in the carbon pools). On the assumption that conifer and broadleaf planting could be represented by Sitka spruce and beech trees respectively, litter and forest soil in Great Britain were accumulating carbon at 2.42 Mt a-1 in 1995-96. Coniferous forest accounted for 89 per cent of this uptake. Scottish conifer and broadleaf forests took up 68 per cent and mapping the uptake showed that the greatest rate occurred in western Scotland. The pool of carbon in wood products increased in 1995-96 by 0.31 Mt a-1. The estimated uptake rates were sensitive to the relative amounts of conifer and broadleaf forest planted (particularly in relation to increases in the pool of carbon in wood products) but not to regional differences in Yield Class. Use of any single Yield Class in the range 10-16 m3 ha-1 a-1 for all Sitka spruce planting produced estimates of uptake rate in Great Britain to trees, litter and soil within ±10 per cent of that, assuming yield varied across the country. Lack of precise knowledge on the parameters of the model was estimated to introduce an uncertainty of ±30-70 per cent into estimates of carbon uptake.