- Soil and the Woodland Carbon Code
- What are Organic, Organo-mineral and Mineral soils?
- Which soils are eligible for woodland creation under the Code?
- How do I confirm the soil type on my site?
- Future Developments
The Woodland Carbon Code recognises that the carbon benefits associated with woodland creation are generally greatest on soils with lower organic matter content (such as mineral soils) and where establishment and management techniques disturb the soil as little as possible. As such, it advocates ground preparation techniques with the minimum soil disturbance necessary for successful establishment. Research is still ongoing to fully understand the changes to soil carbon as a result of landuse change and land management activities. As such, we are adopting a conservative approach to soil carbon. It ensures that soil carbon emissions associated with the woodland creation project are not under-estimated and that any soil carbon sequestration associated with the woodland creation project is not over-estimated. This approach has been developed with the support of a group of soil experts from across the UK. See Soil Carbon and the Woodland Carbon Code.
A comparison of the soil classifications used in the soil surveys of England & Wales, Scotland and the Forestry Commission classification is given here. It identifies which soils are considered organic, organo-mineral and mineral.
Organic Soils: In Scotland and Northern Ireland, organic soils are those with an organic layer of at least 50cm. In England and Wales they are recognised as having an organic layer of at least 40cm. According to the Forestry Commission’s own classification, organic soils are classified as having an organic layer of > 45cm. These organic soils can also be known as peats in Scotland and Northern Ireland and deep peats in England and Wales.
Organo-mineral Soils: Thus in Scotland and Northern Ireland, organo-mineral soils have an organic layer of 50cm or less, and in England and Wales 40cm or less. According to the Forestry Commission’s own classification, organo-mineral soils are classified as having organic layer of < 45cm. These can include humus-iron podzols, peaty podzols, surface and ground water peaty gleys, peaty rankers and podzolic rankers.
Mineral soils In soil surveys across the UK, mineral soils are not defined as having an organic layer (primarily composed of decaying plant material) although they do contain an organic horizon (with higher organic content than underlying horizons). The Forestry Commission classifies mineral soils as having an organic layer of less than 5cm. These can include brown earths, brown rankers and rendzinas, cultivated podzols, surface water and ground water mineral gleys.
Organic soils: On some soils with a deep organic layer the magnitude of soil carbon losses due to disturbance and oxidation can be greater than carbon uptake by tree growth over the long term. For this reason, in addition to habitat and biodiversity value, the Woodland Carbon Code does not allow any woodland creation to occur on soils with an organic (peat) layer of more than 50 cm*.
Organo-mineral soils: On soils with an organic layer of 50 cm or less, there are still likely to be some soil carbon losses due to disturbance for establishment and management purposes, but these are likely to be smaller. The conservative approach here means projects on organo-mineral soils need to account for the loss of carbon due to establishment activities.
In future, in the case where there is minimal ongoing intervention planned (e.g. no thinning or clearfelling) the project will be able to claim some carbon sequestration over the project duration. Projects with more intensive management (e.g. thinning or clearfelling) may be able to account for soil carbon gains but will also have to account for soil carbon losses during ongoing management.
Mineral soils: On mineral soils where no organic layer is present, we can be fairly confident that any losses of soil carbon due to disturbance for management are likely to be minimal. Here the conservative approach only requires projects with higher impact establishment techniques to account for an initial loss of soil carbon; for low impact methods it is assumed that there is no initial loss. On arable soils where there is minimal ongoing intervention planned (i.e. no thinning or clearfelling) the project can claim some carbon sequestration over the project duration.
In future, projects on arable land proposing more intensive woodland management (thinning or clearfelling) may be able to account for soil carbon gains but will also have to account for soil carbon losses during ongoing management. Projects on grassland/pasture will likewise have to account for losses as well as gains to soil carbon.
*Note definitions across UK. For the purposes of the Woodland Carbon Code, the decision not to allow projects on soils with an organic layer exceeding 50cm is applied consistently across the UK. Soils in England and Wales with an organic layer depth of 40-50cm will be considered alongside the organo-mineral soils for the purposes of the Woodland Carbon Code.
Projects should assess the soil type onsite using one of the following methods:
- Using the following maps to check for areas of peat;
- The British Geological Survey 1:250,000 or 1:50,000 scale data for mapped areas of peat exceeding 100cm in depth.
- Soil Survey of Scotland, Soil Survey of England and Wales and Soil Survey of Northern Ireland 1:250,000, 1:63,360, 1:50,000 and 1:25,000 data for mapped areas of peat.
- FC soil maps for mapped 'deep peat' soil types.
- Ascertain soil type using one of the following tools;
- Independent assessment of soil type by relevant expert who has undertaken a field survey
- If mapped evidence suggests that the site could contain peat, then use a peat probe to assess depth (contact us if further information required):
- Use GPS to set out a regular 50mx50m sampling grid across the site
- Use a peat probe measure and record the depth at each point
- If you need to show where the 50cm depth boundary falls, 3D Modelling packages can then estimate the '50cm depth' peat boundary if necessary. This can be affirmed or refined by probing on a 10mx10m grid as above.
- We will add a comparison to the Soil Classification in Northern Ireland
- We will develop a soil assessment protocol which, through field survey, will aid the identification of soil type as well as soil carbon content