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3.2 Carbon Baseline

What is a baseline scenario?

A baseline scenario is a projection of the changes to carbon on the site 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.   

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Which carbon pools do I include?

The Woodland Carbon Code is adopting a conservative approach to the construction of the baseline scenario.  As such, greenhouse gas emissions from the current landuse (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

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Calculating the carbon stock at the start of the project

Projects shall describe the original condition of the site including details of the vegetation cover and soil type.  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 to be made.

Where it is necessary to calculate a project baseline, projects shall estimate the carbon content of the site (in pools indicated above) prior to the start of the project. 

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 Please contact us for futher 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 landuse type in the table Soil Carbon Estimate Prior to Planting.  Note we recognise these figures are the mean mass of soil carbon across each landuse and country, and in reality there is a large variation.  At present, this is the only dataset sourced that has been developed using consistent protocols for the UK as a whole. 

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Calculating changes to the baseline scenario over the project duration

Having calculated the carbon stock of the site at the start of the project, projects shall calculate how the stocks 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 ensures 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 significant (ie ≥ 5% of the project carbon sequestration over the duration of the project) then it should be accounted for in 'net carbon sequestration' (Section 3.5 of the Project Design Document). 
  • If the change to the carbon pools is not significant (ie < 5% of the project carbon sequestration over the duration of the project) then it does not need to be accounted for (and it can be assumed that the baseline scenario is 'no change of carbon stocks over time' or '0'.   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.

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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 Indicators 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.

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