Introduction

Forests can help mitigate 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 surrounding soil.

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. Forests 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, by reducing the risk of flooding, providing shade for wildlife, reducing soil erosion and helping to cool down towns and cities.

Data sources and methodology

Carbon cycle

The diagram showing the carbon cycle is adapted from Figure 3 of Broadmeadow and Matthews (2003).

Forest carbon stock

Table 4.1 is adapted from Table 3e in the final UK report submitted in August 2014 to FAO for the Global Forest Resources Assessment (FRA) 2015 (www.fao.org/forest-resources-assessment/en/).

Units: This table is 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, 2010 and 2015.

Living biomass: Carbon in living biomass is based on data from “NFI report: Carbon in live woodland trees in Britain” (Forestry Commission, May 2014), uprated from GB to UK estimates based on estimated volumes of growing stock. A “root to shoot ratio” (below ground biomass = 0.36 x above ground biomass) is used to estimate the breakdown between above- and below- ground biomass (Levy et al., 2004).

Deadwood: Consistent with Morison et al. (2012), estimates of deadwood volume per hectare are taken from Gilbert (2007). These are rated up by woodland area estimates for FRA 2015, assuming a density of 0.45 ODT/m³, and an average carbon content of 50% is applied.

Litter: Estimates of the carbon content of the litter layer are available from Morison et al. (2012). These are rated up by woodland area estimates for FRA 2015 to provide a consistent time series.

Soil carbon: Estimates of the carbon content of soil 0-100 cm for England, Wales and Scotland are available from Morison et al. (2012). 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. (2012). The soil carbon estimates are then rated up by woodland area estimates for FRA 2015 to provide a consistent time series. 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 broadly similar to the estimates made in Morison et al. (2012).

Future updates: This table will be updated once further information is available from the National Forest Inventory.

Carbon sequestration

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 2013 UK Greenhouse Gas emissions final figures (DECC, February 2015) and the National Atmospheric Emissions Inventory (NAEI, http://naei.defra.gov.uk) which incorporates all air pollutants including greenhouse gases. 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 follow a mid-projection whereby planting will increase slightly from current levels until 2022, when it will decrease to just below current levels up to 2050.

For more information, please refer to the CEH “Greenhouse Gas Inventories for England, Scotland, Wales and Northern Ireland: 1990 to 2013” (http://naei.defra.gov.uk/reports/reports?report_id=810) and “Projections to 2050 of emissions and removals from the LULUCF sector in Scotland, England, Wales and Northern Ireland” (http://naei.defra.gov.uk/reports/reports?report_id=767).

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.

Woodland Carbon Code

The Woodland Carbon Code is a voluntary standard, initiated in July 2011, for woodland creation projects that make claims about the carbon they sequester (take out of the atmosphere). All projects must be placed on the UK Woodland Carbon Registry. Their claims about potential carbon sequestration are validated by an independent certification body. Validated projects are then verified on a regular basis to confirm the progress of carbon sequestration.

Information about Woodland Carbon Code projects comes from the UK Woodland Carbon Registry, housed on the S&P Global Environmental Registry (Environmental Registry | S&P Global (spglobal.com)). The register is a live database and summary data are extracted on a quarterly basis.

Further information on the Woodland Carbon Code is available on the Woodland Carbon Code website.

Further information on administrative sources can be found at: www.forestresearch.gov.uk/tools-and-resources/statistics/about-our-statistics/code-of-practice/administrative-sources/.

Public opinion on climate change

Public Opinion of Forestry Surveys have been run every 2 years by the Forestry Commission. The surveys cover public attitudes to forestry and forestry-related issues. The surveys included 2 questions on climate change: one asking about ways in which forests and woodlands can impact on climate change (Figure 4.4) and one asking about how UK forests should be managed in response to the threat of climate change. Further information on the surveys is available in the Sources: Public Opinion of Forestry page.

References

Bradley, R.I., Milne, R., Bell, J., Lilly, A., Jordan, C., Higgins, A. (2005) “A soil carbon and land use database for the UK”, Soil Use and Management 21 (363-369), DOI: 10.1079/SUM2005351 (http://onlinelibrary.wiley.com/doi/10.1079/SUM2005351/abstract).

Broadmeadow, M., Matthews, R. (2003) “Forests, Carbon and Climate Change: the UK Contribution”, Forestry Commission, Edinburgh (fcin048.pdf).

Department of Energy and Climate Change (2015) “2014 provisional UK greenhouse gas emissions and final emissions by fuel type and end-user 1990 to 2013: statistical release” (https://www.gov.uk/government/collections/provisional-uk-greenhouse-gas-emissions-national-statistics).

Gilbert, J. (2007) “National Inventory of Woodland and Trees 1995-1999, Analysis of Management and Biodiversity Data”, Forestry Commission, Edinburgh (/fr/INFD-86XC6C).

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 (www.forestry.gov.uk/forestry/infd-8juhc7).

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, DOI: 10.1093/forestry/77.5.421 (forestry.oxfordjournals.org/content/77/5/421.abstract).

Morison, J. et al. (2012) “Understanding the Carbon and GHG balance of UK Forests”, Forest Research (FCRP018.pdf).

Quality

All of the statistics in this chapter are outside the scope of National Statistics, but are included here to give a broad indication of the role of UK forests in climate change.

Revisions

Statistics on UK forests and climate change obtained from others are subject to revision whenever the source data are revised.

The Forestry Commission’s revisions policy sets out how revisions and errors to these statistics are dealt with, and can be found at: FCrevisions.pdf.

Release schedule

For information on the release schedules of statistics produced by others, see relevant websites (above).

“Woodland Carbon Code Statistics: data to September 2016” will be released on 13 October 2016

“Woodland Carbon Code Statistics: data to December 2016” will be released on 19 January 2017.

“Woodland Carbon Code Statistics: data to March 2017” will be released on 13 April 2017.

“Woodland Carbon Code Statistics: data to June 2017” will be released on 20 July 2017.

“Forestry Statistics 2017” and “Forestry Facts & Figures 2017” will be released on 28 September 2017.

The next Public Opinion of Forestry Survey is expected to run in early 2017, with results available in summer 2017.