Sources: UK Forests and Climate Change
Forests can help address climate change by reducing the amount of greenhouse gases in the atmosphere. They do this by absorbing carbon dioxide, using the carbon to produce sugars for tree growth and releasing the oxygen back into the air. As trees grow, they store carbon in their leaves, twigs and trunk, and in the soil around them.
Globally, deforestation caused by the unsustainable harvesting of timber and the conversion of forests to other land uses accounts for almost 20 per cent of global carbon dioxide emissions. The amount of carbon stored can be increased by actions to reduce the amount of deforestation and to convert non-forested areas to forest.
Although they cover a small part of the global area, the forests and woodlands in Britain have a role to play too. They can be managed as a sustainable source of wood – an alternative energy source to fossil fuels, and a low-energy construction material.
Woodlands can also help society adapt to a changing climate. The right trees planted in the right places can reduce the risk of flooding, provide shade for wildlife, reduce soil erosion and help to cool down towns and cities.
The diagram showing the carbon cycle is adapted from Figure 3 of the Forestry Commission Information Note on Forests, Carbon and Climate Change: the UK Contribution (M Broadmeadow and R Matthews, 2003).
Forest carbon stock
Table 4.1 is updated from Table T8 in the final draft UK report for Global Forest Resources Assessment (FRA) 2010.
Units: This table is now shown in million tonnes carbon dioxide equivalent (MtCO2e) rather than million tonnes carbon (MtC). To convert from CO2e to C multiply by 12/44.
Timescales: Carbon stock is estimated for 1990, 2000, 2005 and 2010, as in FRA 2010.
Growing stock is taken from calculations for Table T7 of the FRA 2010. These estimations of growing stock are based on data from the 1995-99 National Inventory of Woodland and Trees and data for the FC estate.
Total biomass: These figures are updated from Table T7 of the FRA 2010, using a new 'biomass expansion factor' for conifers to account for branches, foliage and other above ground biomass (Levy et al (2004)). Average densities of 0.4 ODT/m3 (oven-dry tonnes per cubic metre) for conifers and 0.5 ODT/m3 for broadleaves are taken from Jenkins et al (2011). In addition, a new 'root to shoot ratio' (below ground biomass = 0.36 x above ground biomass) accounts for the below ground biomass (Levy et al (2004)).
Deadwood: Consistent with Table T8 of the FRA 2010 and Morison et al (in press), estimates of deadwood volume per hectare are taken from Gilbert (2007). These are rated up by woodland area estimates from FRA 2010 (for 1990 and 2000) and Forestry Statistics (2005 and 2010) and assuming a density of 0.45 ODT/m3.
Litter: New estimates of the carbon content of the litter layer are available from Morison et al (in press). These are rated up by woodland area estimates from FRA 2010 (for 1990 and 2000) and Forestry Statistics (2005 and 2010).
Soil carbon: New estimates of the carbon content of soil 0-100 cm for England, Wales and Scotland are available from Morison et al (in press). An estimate of the carbon content of soil for Northern Ireland is taken from Bradley et al (2005) and rated downward to reflect the generally lower carbon content found in Morison et al (in press). These are rated up by woodland area estimates from FRA 2010 (for 1990 and 2000) and Forestry Statistics (2005 and 2010). This soil estimate does not take account of soil carbon accumulation. This was previously included from estimates made by the Centre for Ecology and Hydrology in 'Land Use, Land Use Change and Forestry' (LULUCF) modelling. It also assumes that the soil carbon content of afforested (and previously unwooded) land has the same soil carbon content as woodland soils, whereas in practice this may vary.
Comparison with other data sources: Figures in this updated table are now similar to the estimates made in Morison et al (in press) and MacKay (2003).
Future updates: This table will be updated once further information is available from the National Forest Inventory.
Bradley, RI, Milne, R, Bell, J, Lilly, A, Jordan, C, Higgins, A (2005) A soil carbon and landuse database for the UK, Soil Use and Management 21 (363-369)
Forestry Commission (2005) Forestry Statistics 2005, Forestry Commission, Edinburgh
Forestry Commission (2010) Forestry Statistics 2010, Forestry Commission, Edinburgh
Gilbert, J. (2007) National Inventory of Woodland and Trees 1995-1999, Analysis of Management and Biodiversity Data, Forestry Commission, Edinburgh
Jenkins, T.A.R., Mackie, E.D., Matthews, R.W., Miller, G., Randle, T.J., White, M.E., FC (2011) Woodland Carbon Code: Carbon Assessment Protocol, Forest Research
Levy, P.E., Hale, S.E., Nicoll, B.C. (2004) Biomass expansion factors and root: shoot ratios for coniferous tree species in Great Britain, Forestry, Vol 77, No 5
McKay (2003) Woodfuel resource in Britain, Final report B/W3/00787/Rep
Morrison et al (in press) Understanding the Carbon and GHG balance of UK Forests, Forest Research
Food and Agriculture Organisation of the United Nations (2010) Global Forest Resources Assessment 2010 – UK Report, FRA2010/221, Forestry Department, UNFAO, Rome.
The information in Table 4.2 is taken from inventory and projections of UK emissions by sources and removal by sinks due to land use, land use change and forestry, produced by CEH for input to 2009 final UK Greenhouse Gas Emissions (DECC, March 2011). They exclude the pool of carbon in timber products.
Figure 4.2 shows annual estimates of carbon accumulation by country, taken from the same source but shows carbon in living forest biomass only; it excludes carbon in litter, soils and forest products. Future predictions of carbon uptake assume that commercial conifer plantations will be replanted when felled, and that planting of new woodland will continue at the same rate as in 2009 (mid projection).
Emissions and sequestration can be presented as tonnes carbon or tonnes carbon dioxide (CO2). To convert from tonnes CO2 to tonnes carbon multiply by 12/44.