3. Carbon sequestration

• Projects shall describe the original condition of the project site including details of the vegetation cover, soil type and their carbon content.

   

• Project developers shall estimate the baseline, or changes in the carbon stock at the site for the duration of the project in the absence of the project activities (i.e. business as usual).

   

• Where the carbon baseline shows significant sequestration, it shall be accounted for in 3.4 net carbon sequestration. Otherwise, the carbon baseline is assumed to be 'No change over time'.

What is a baseline scenario?

A baseline scenario is a projection of the changes to carbon on the site, over the project duration, in the absence of the project (e.g. woodland creation) going ahead. It is the reference scenario from which the impact of the project can be measured.  

Small projects (5 ha net planting area or less): We assume that the baseline is 'no change in carbon stocks over time'. No assessment is necessary

Standard projects (over 5 ha net planting area): It is often the case with standard projects that the baseline will be 'no change in carbon stocks over time' if the project was previously grazed pasture or arable land. It would be unlikely there was any carbon sequestration in these cases and we do not allow projects to claim for the 'reduction in emissions' from stopping the previous land-use. However, standard projects should consider whether there would have been significant sequestration in the 'baseline' scenario.

Which carbon pools do I include?

The Woodland Carbon Code is adopting a conservative approach to the construction of the baseline scenario, meaning greenhouse gas emissions from the land use prior to woodland creation (e.g. from livestock, fertiliser or burning) cannot be included in the baseline.

The following carbon pools shall be included in the baseline scenario:

• Tree biomass (above and below ground)
• Litter and deadwood
• Non-tree biomass (above and below ground)
• Soil

Calculating the carbon stock at the start of the project

Reference can be made to any maps, photographs, remotely sensed images or field survey results which confirm the condition of vegetation and soil previous to woodland creation. This will allow an estimate of the carbon stock onsite prior to the project taking place.

• For tree biomass - The Carbon Assessment Protocol should be used to survey the trees already existing onsite and estimate the carbon they contain.
• For litter and deadwood - It is unlikely that this carbon pool, or changes to it, will be significant.
• For non-tree biomass - Reference Natural England's Carbon Storage and Sequestration by Habitat 2021 (NERR094) or contact the Woodland Carbon Code Secretariat for further information on estimates of carbon stock of other shrubs and vegetation.
• For soil carbon - Unless the project has undertaken specific soil carbon assessment prior to tree planting, then we will assume that the soil carbon content at the site at the start of the project can be derived from looking at the closest land use type in the table Soil Carbon Estimate Prior to Planting. Note we recognise these figures are the mean mass of soil carbon across each land use and country, and in reality there is a large variation. 

Calculating changes to the baseline scenario over the project duration

If likely to be significant (i.e. ≥ 5% of the project carbon sequestration over the duration of the project), projects need to calculate how carbon stocks on the site would have changed over the project duration had the project not gone ahead (the 'baseline' or 'business as usual' scenario). The baseline scenario is conservative by accounting for sequestration but not emissions. This means the net carbon sequestration (project sequestration minus baseline) will not be more than the actual sequestration of the ecosystem.  

If the change to the carbon pools is not significant (i.e. < 5% of the project carbon sequestration over the duration of the project) then it can be assumed that the baseline scenario is 'no change of carbon stocks over time'. However, projects should clearly lay out in the project design document how they came to this conclusion.

For tree biomass In the baseline scenario, any trees already present on the site will continue to accumulate carbon without the project going ahead and this should be accounted for. This can be done by:

• assessing the density of trees present and their current age
• converting this to an equivalent area of woodland of a given age at a given planting spacing
• using the Carbon Lookup Tables to estimate the likely changes to that stock over time

For litter and deadwood  It is unlikely that this carbon pool, or changes to it, will be significant. Projects can assume that in the baseline scenario there is no change over time to this carbon pool.

For non-tree biomass  In the baseline scenario, non-tree biomass could accumulate or it could be in equilibrium over the project duration (in which case no changes over time will be accountable). This depends largely on the type of vegetation present. Crops and established grass can be assumed to be in equilibrium and therefore there will be no change over the project duration in the carbon stock of non-tree biomass. However, other biomass may still be growing and sequestering carbon and projects should account for the change to the carbon stock over the duration of the project. Projects should refer to the IPCC 2003 Good Practice Guide for LULUCF.

For soil carbon It is hard to predict what soil carbon changes would have occurred in a given baseline scenario, however, given that gains to soil carbon in the non-wooded baseline scenario are unlikely to be significant (≥ 5% of the project carbon sequestration over the duration of the project) for sites with an organic/peat layer 50 cm or less, projects can assume that there is no change over time to soil carbon in the baseline scenario.

• We will publish estimates of the carbon stock of other types of non-tree vegetation.
• We will update the table Soil Carbon Estimate Prior to Planting with information by soil grouping (organic, organo-mineral and mineral) or, where possible, by soil type to increase the accuracy of these predictions.
• In future for Scotland more soil type-specific carbon stock information may be available from the Soil Information for Scottish Soils website.
• We will publish a Soil Carbon Assessment Protocol to allow projects to undertake a field assessment to estimate the soil carbon stock at the site.

• The land manager shall confirm any intention to change or intensify the use of land elsewhere on the holding as a consequence of the woodland creation.

   

• If leakage (land use change/intensification outside the project boundary but within the UK) is proposed, then projects shall carry out an assessment to determine whether this will result in greenhouse gas emissions.

   

• If significant greenhouse gas emissions occur, they shall be quantified for the duration of the project and accounted for in 3.4 net carbon sequestration. Otherwise leakage is assumed to be 'no change over time'.

What is 'leakage'?

Many international carbon standards involve assessments of leakage or changes to carbon stocks outside of the project boundary as a result of the project going ahead.  International carbon standards describe two main types of leakage and their relevance in terms of a woodland creation project is described below:

• Activity-shifting leakage: When the activity (agriculture or other) which was taking place on the project site is moved and causes land-use change elsewhere. In some countries there is concern that this might cause deforestation away from the project site or degradation of other semi-natural habitats. These emissions from deforestation or intensification of use of non-wooded land are normally accounted for.
• Market leakage: If the presence of the project causes production of a product to be stopped on the project site, forcing additional production elsewhere to ensure the market demand is met. This tends to be used where a project involves accounting for changes to woodland management and timber production on the project site is stopped or postponed. In the case of new woodlands, this is not likely to occur since there is no woodland product produced at the site prior to planting.     

Likelihood of leakage of emissions in the UK

Given that the Woodland Carbon Code only deals with woodland creation, only activity-shifting leakage would appear to be relevant. However, there are a number of laws governing the protection of semi-natural habitats and existing woodlands so that any activity-shifting leakage within the UK (in terms of intensification of use of land outside the project boundary) is highly unlikely. 
 
For deforestation:

• Environmental Impact Assessment (Forestry) (England and Wales) Regulations 1999 and the Environmental Impact Assessment (Forestry) (Scotland) Regulations 1999.  Requires an Environmental Impact assessment for any deforestation over 1ha (0.5ha in sensitive areas).
• Forestry Act 1967.  Requires a felling licence for deforestation. Unconditional (i.e. no restocking required) felling licences are rare. There are some exceptions including:
  • Very small volumes of timber felled annually by the woodland owner
  • Development granted under the Town and Country Planning Act 1990 or the Town and Country Planning (Scotland) Act 1997
  • Electricity operator

For protection of biodiversity and other semi-natural habitats:

• Wildlife and Countryside Act 1981 and amendments
• Countryside and Rights of Way Act (England and Wales) 2000, Nature Conservation (Scotland) Act 2004, The Conservation Regulations (Northern Ireland) 1995

Approach to leakage in the Woodland Carbon Code

Due to the existing legislation in the UK which protects semi-natural habitats, biodiversity and also protects against deforestation, the Woodland Carbon Code assumes that in most cases there will be NO LEAKAGE (i.e. leakage = 0, no change over time) in woodland creation projects. 

Small projects (5 ha net planting area or less): Can assume that there is no leakage.

Standard projects (over 5 ha net planting area): Should consider whether the project will result in more intensive use of another area of land under the same ownership or lessee. If so, then any significant greenhouse gas emissions through changes in land use or management of the area of land should be accounted for over the project duration (significant is more than 5% of the project carbon sequestration over the duration of the project). Leakage assessments are likely to be project-specific. The following guidance should help define the scope of the assessment.

1.  The following carbon pools shall be included:

• Tree above and below ground biomass
• Litter and deadwood
• Non-tree above and below ground biomass
• Soil
• Increased emissions from management of the land

2.  Any land use change or intensification within the UK which can be attributed to the project going ahead should be accounted for.

3.  Only significant greenhouse gas emissions need to be accounted for in the project's net carbon sequestration. Emissions are considered significant if they amount to more than 5% of the project carbon sequestration over the duration of the project.

4.  Projects can refer to the IPCC 2003 Good Practice Guide for Land Use, Land-Use change and Forestry and the IPCC 2006 Guidelines for national GHG inventories for guidance.

• Project developers shall use the relevant template Carbon Calculation Spreadsheet (Standard or Small Project tab) to predict the project carbon sequestration.

   

• Emissions resulting from the preparation of a site prior to planting shall be calculated and subtracted from the project carbon sequestration at year 1. This includes losses of carbon through removal of vegetation (trees or other biomass) or disturbance of the soil.

   

• Carbon sequestration in woodland biomass shall be restricted to the long-term average carbon stock that is projected to accumulate on the site.

What is 'project carbon sequestration'?

Project carbon sequestration is the changes in carbon stocks due to woodland creation over the project duration as a direct result of the project.

This page outlines how to predict changes to carbon stocks that will occur over the duration of the project. The monitoring section explains how to assess actual carbon stocks later on in the project once the trees are growing and carbon has been sequestered.

Project developers should bear in mind when agreeing to sell Pending Issuance Units that the tools here provide a prediction of the carbon that is likely to be sequestered and not a guarantee that a particular woodland will sequester a certain amount.

Accounting for project carbon sequestration

Projects should account for project carbon sequestration using the Carbon Calculation Spreadsheet version 2.4.1 April 2024 following the associated guidance. The calculator includes the following:

• Emissions from establishment activities, ongoing management and clearfell.
• Emissions from soil disturbance
• Sequestration in tree biomass, litter and deadwood (and in a limited number of scenarios, soil)

Small projects (5 hectares net planting or less): Can use the 'Small Project Carbon Calculator' which is simpler to complete and conservative. Projects using this prediction tool can use the less intensive 'basic monitoring' from year 15 onwards.

Standard projects: Should use the 'Standard Project Carbon Calculator'.

Vegetation removed at start of project

If any vegetation is removed prior to the start of the project, this should be accounted for (both tree and non-tree biomass). Projects can use Natural England's Carbon Storage and Sequestration by Habitat or contact us for further information on estimates of the carbon stocks of non-tree biomass. They can also refer to the IPCC 2003 Good Practice Guide for Land Use, Land-Use change and Forestry and the IPCC 2006 Guidelines for national GHG inventories for guidance on estimating the carbon stock of existing vegetation.

Carbon in the soil

Soil Carbon and the Woodland Carbon Code (see left) sets out the methodology for organomineral and mineral soils. The Carbon Calculator includes assumptions about the likely soil disturbance and soil greenhouse gas emissions. Alternatively, projects can make a soil carbon assessment prior to tree planting with repeat assessments as the project progresses.

Soil carbon accumulation can currently only be claimed for projects on a mineral soil where the previous land use was arable or rotational grass and the woodland will be managed as minimum intervention. This is included within the Carbon Calculator.

• Tree biomass: Data behind the Carbon Calculator is being reviewed and revised to incorporate new growth and yield models and to refine estimates of contributions from root and branch biomass. The revised estimates for some tree species may be more conservative than current predictions, particularly for the early growth period of broadleaved species. The Carbon Calculator already subtracts 20% from modelled predictions and it is anticipated that these revisions will fall within this threshold.
• Tree biomass: We will develop our Carbon Calculator to include a wider selection of spacings and to account for the carbon stored in roots and stumps when clearfelling.
• Non-tree biomass: We will publish estimates of the carbon stock of other types of non-tree vegetation.
• Soil. There will be a number of developments:
  • We will update the soil carbon methodology using results of ongoing research. This will allow us to say with more certainty both the amount of soil carbon lost on woodland establishment as well as the rate of accumulation of soil carbon as the woodland grows and matures.
  • We will establish a soil carbon assessment protocol to enable projects to consistently assess the soil carbon content of their soil.
  • Ongoing research will help us better understand the changes to soil carbon due to woodland creation and management.

Carbon prediction tools

Carbon calculation guidance version 2.4 March 2021 (pdf)

Carbon calculation spreadsheet version 2.4.1 April 2024 (xlsx)

Example carbon calculations March 2021 (xlsx)

Ecological Site Classification version 4

• Net project carbon sequestration shall be calculated within the relevant worksheet (standard or small project) of the Woodland Carbon Code Carbon Calculation Spreadsheet (includes 3.3 total project carbon sequestration adjusted for 3.2 leakage minus 3.1 baseline).

   

• The predicted number of carbon units by vintage shall be identified according to the project's verification schedule. These shall be divided into the contribution to the Woodland Carbon Code buffer and the claimable carbon sequestration.

   

• The net carbon sequestered to date and carbon sequestered in the current vintage/ monitoring period shall be confirmed in the monitoring report. At year five, this is based on the projected carbon sequestration. From year 15 onwards, this is based on field survey measurements.

   

• If the ‘self-assessment’ option has been used, then there is no update to the actual carbon sequestration of a project at verification; this section will not be completed.

Net carbon sequestration is the total amount of carbon sequestered by the project which can be converted into carbon units. These are divided between the proportion that will contribute to the shared Woodland Carbon Code buffer and the claimable carbon sequestration which is the amount the project can sell or claim. The number of units will be set out by vintage or monitoring period in the project design document.

Net carbon sequestration =  project carbon + leakage - baseline.

The Woodland Carbon Code Carbon Calculation Spreadsheet helps project developers to calculate their net carbon sequestration. See 3.3 Project carbon sequestration.