3.1 Carbon baseline

What is a baseline scenario?
Which carbon pools do I include?
Calculating the carbon stock onsite at the start of the project
Calculating changes to the baseline scenario over the project duration

Requirement

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'.

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 This email address is being protected from spambots. You need JavaScript enabled to view it. 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.

Future Developments

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.