Data Sources and Methodology
Data on woodland area in the UK presented in this release are derived from the following sources:
- Forestry Commission and Natural Resources Wales administrative records of FC/NRW land areas;
- National Forest Inventory (NFI) woodland map (GB);
- Statistics on new planting in Great Britain;
- Northern Ireland Woodland Register;
- Forest Service administrative records of FS woodland areas and
- Forest Service estimates of non-FS woodland area in Northern Ireland.
Estimates of woodland area in Great Britain are based on figures produced from forest inventories. Until recently, forest inventories in Great Britain were undertaken every 15 years or so. The current National Forest Inventory (NFI), unlike previous inventories, is planned to run on a continuous 5-year cycle.
As forest inventories are generally not designed to produce annual figures, a process is required for updating the results on an annual basis to take account of changes in woodland area. The methodology currently used to calculate annual woodland area estimates is described below.
The data processing takes place in Excel. The main outputs are aggregates from the source data, or breakdowns expressed as percentages, and do not require complex data analysis techniques.
- For Great Britain, woodland area estimates are based on the latest NFI woodland area map of Great Britain available. In this release, woodland area estimates at March 2017 and at March 2018 are both based on the provisional NFI woodland area map at March 2017.
- The map is overlaid with a map of Forestry Commission and Natural Resources Wales (ex Forestry Commission Wales only) land, to enable a breakdown by ownership to be estimated. This also enables FC/NRW "other land" areas to be derived (Table 1.5). For woodland area estimates at March 2017, FC/NRW legal boundaries at March 2017 are used, and for estimates at March 2018, FC/NRW legal boundaries at March 2018 are used.
- The woodland area breakdown by type of woodland (conifer or broadleaf) is estimated from the conifer/broadleaf breakdown of stockedwoodland area, with areas of felled and open space allocated to conifer or broadleaf pro-rata. Estimates for stocked areas at March 2012 derived from NFI interim field survey results are updated to take into account new planting since that date, for which the conifer/broadleaf breakdown is also known. As the area of new planting is much smaller than total woodland area, the effect of this update on the overall conifer/broadleaf breakdown is very small.
The steps above are sufficient to determine final woodland area estimates at March 2017, broken down by ownership and conifer/broadleaf.
To obtain estimates at March 2018, two more steps need to be performed, which are described below.
- Net ownership transfers of woodland between private sector and FC/NRW from March 2017 to March 2018, as inferred by the differences in FC/NRW legal boundaries between those two dates, are broken down by conifer/broadleaf. The breakdown is based on NFI Interpreted Forest Type (IFT) at those dates, derived from photographic interpretation of the NFI woodland map. The “Conifer” and “Mixed mainly conifer” (>80% conifer) IFT categories are assigned to conifers, and the “Broadleaves” and “Mixed mainly broadleaved” (>80% broadleaved) categories are assigned to broadleaves. For the other IFT categories, the conifer/broadleaf breakdown is allocated pro-rata based on the conifer/broadleaf breakdown of woodland area by ownership (private sector or FC/NRW) before transfer.
- The woodland area figures are then updated to March 2018 by adding areas of new planting in 2017-18, broken down by ownership and type.
Information on previous methodologies can be found in the Methodology Note: Annual Woodland Estimates produced in May 2012, on the Methodology and Outputs web page at www.forestresearch.gov.uk/tools-and-resources/statistics/about-our-statistics/methodology-and-outputs/.
The methodology and outputs relevant to UK woodland area, planting and restocking were reviewed in 2014. The review report is available at www.forestresearch.gov.uk/tools-and-resources/statistics/about-our-statistics/methodology-and-outputs/.
The provisional 2017 woodland map differs by around 23 thousand hectares (<1%) from the figures for woodland area provided in the NFI report "Tree cover outside woodland in Great Britain", that were based on the NFI 2013 map and the National Tree MapTM(NTMTM), the latter in combination with samples of visual aerial photograph interpretation and field sampling outside of areas on the NFI map. The estimates in the tree cover report are higher because they include estimates of woodland area outside the NFI map derived from the other sources. It is intended to publish revised woodland area estimates that will bring these two figures into line by reporting an updated, calibrated NFI woodland area that incorporates these additional areas and uses analysis of the main NFI fieldwork survey to exclude currently mapped areas that are not woodland. Further information on the methodology used by the National Forest Inventory and comparisons of results from the NFI and previous woodland area estimates is available at www.forestresearch.gov.uk/tools-and-resources/national-forest-inventory/.
Figures for Northern Ireland (Forest Service and private sector woodland) are provided by the Forest Service (http://www.daera-ni.gov.uk/topics/forestry). Woodland areas from 2012 provided in this release have been obtained from the NI woodland register.
The NI woodland register is based on a combined dataset derived from fourteen individual datasets from statutory bodies including Forest Service, Land and Property Services, and the Northern Ireland Environment Agency, and non statutory bodies which include Woodland Trust and National Trust. The minimum area of woodland that has been included in the register is 0.1 hectares.
The use of the NI woodland register has resulted in a step change in the non-Forest Service woodland areas reported for Northern Ireland. This should be interpreted as an improvement in the data reported, rather than an actual increase in woodland area.
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/.
Certified woodland area
Data on certified woodland areas are obtained from the Forest Stewardship Council (FSC), and contact with individual land owners and managers. Some of the certified woodland has dual certification, i.e. it is certified under both the FSC scheme and the Programme for the Endorsement of Forest Certification (PEFC) scheme.
The data collected from FSC are the areas that are certified for each certificate holder. Follow-up enquiries are then made with larger certificate holders to check the certified areas and to provide a country breakdown.
As all FC/NRW/FS woodlands are certified, the total woodland area (as derived above, from the NFI map and FC boundaries and from Forest Service administrative records) is used, rather than the area provided on the certificates.
The statistics on woodland area presented here refer to woodland as a land use rather than as a land cover, so felled areas and small areas (less than 0.5 ha) of open space are included within the definition of woodland. Some statistics on woodland area as a land cover are available from other sources (e.g. Countryside Survey 2007, www.countrysidesurvey.org.uk, and associated Land Cover Map; a more recent Land Cover Map 2015 is also available).
Detailed information on the quality of the woodland area statistics presented in this publication is available in the "Quality Report: Woodland Area, Planting and Restocking" at www.forestresearch.gov.uk/tools-and-resources/statistics/about-our-statistics/code-of-practice/quality-of-official-statistics/. Further quality information on FC Official Statistics is also available from this location.
Figures at March 2018 have not been revised since their previous release in "Woodland Area, Planting and Publicly Funded Restocking: 2018 Edition".
Information on revisions made since "Forestry Statistics 2017" are provided in "Woodland Area, Planting and Publicly Funded Restocking: 2018 Edition".
Information on significant revisions to published statistics is provided in the quality report on Woodland Area, Planting and Restocking, available from our Quality web page at www.forestresearch.gov.uk/tools-and-resources/statistics/about-our-statistics/code-of-practice/quality-of-official-statistics/.
The Forestry Commission's revisions policy sets out how revisions and errors are dealt with and can be found at www.forestresearch.gov.uk/documents/4355/FCrevisions.pdf.
Accompanying tables to this release, available at www.forestresearch.gov.uk/tools-and-resources/statistics/statistics-by-topic/woodland-statistics/, provide longer time series data by country for certified woodland.
Figures for woodland area in the UK are provided to international organisations every 4-5 years; to the Food and Agriculture Organisation of the United Nations (FAO) for the "Global Forest Resources Assessment" (www.fao.org/forest-resources-assessment/en/), and to Forest Europe for the "State of Europe's Forests" (https://foresteurope.org/).
Figures for woodland area are also used to compile the UK’s Greenhouse Gas Inventory for the Land Use, Land Use Change and Forestry (LULUCF) sector, submitted to the United Nations Framework Convention on Climate Change (UNFCCC, https://unfccc.int/process-and-meetings/transparency-and-reporting/reporting-and-review-under-the-convention/greenhouse-gas-inventories-annex-i-parties/national-inventory-submissions-2018). Summary factsheets, produced by the Department for Business, Energy and Industrial Strategy (previously the Department of Energy and Climate Change), are available at www.gov.uk/government/publications/uk-greenhouse-gas-inventory-summary-factsheets.
Woodland area and certified woodland area data are released twice a year. Provisional figures are published in Woodland Area, Planting and Publicly Funded Restocking (to be renamed Provisional Woodland Statistics from 2019) in early June. Final figures are released in Forestry Statistics at the end of September.
Provisional figures for woodland area and certified woodland area at March 2019 will be published on 13 June 2019 in "Provisional Woodland Statistics: 2019 Edition".
Final results for woodland area and certified woodland area at March 2019 will be published on 26 September 2019 in "Forestry Statistics 2019" and "Forestry Facts & Figures 2019".
Chapter 1: Woodland Areas and Planting