3.1 Carbon baseline


Projects shall describe the original condition of the project site including details of the vegetation cover and soil type. 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 ‘net carbon sequestration’ (Section 3.4). Otherwise, the carbon baseline is assumed to be ‘No change over time’.

Means of Validation

For site description:

  • Appropriate maps, photographs or remotely sensed images to indicate previous land cover
  • Results of field survey for vegetation or soil depth

For baseline calculations:

  • Carbon baseline calculations in Project Design Document

Means of Verification

  • Not required


A carbon baseline is the reference sequestration over time from which the impact of the project can be measured. It is based on a continuation of the current land use in the absence of the project. Changes to baseline are significant if they are ≥5% of the project carbon sequestration over the duration of the project.

Carbon pools included:

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


Baseline according to cover type

1. General introduction

The term baseline refers to two things: on the one hand, the amount of carbon (carbon stock) in the ecosystem before forestry begins, and on the other hand, what the development of that carbon stock is likely to be if there were no afforestation. Questions about the initial state of carbon stocks are of a technical nature and can be answered by measuring soil samples and vegetation. This creates information about the status at one point in time, which can then be compared with the status at some later time.

More important for certification are forecasts of the development of the carbon stock. If it is likely to increase without afforestation, it may be necessary to subtract the expected increase from the carbon capture due to the forest. If it is likely to remain the same or decrease without afforestation, all carbon sequestration in the area can be attributed to forestry.

Decomposition of organic compounds always takes place in the soil, releasing CO2 into the atmosphere ("exhalation"). Plants add organic carbon compounds to the soil mainly by their roots growing and then dying and by litter accumulation (leaves, twigs etc.) ("inhalation"). The baseline status of an area with respect to carbon stocks before afforestation is shaped by these processes and the dominant land use, especially livestock grazing. It is also shaped by the likely future land use if afforestation did not take place. There are many measurements of forest carbon stocks, but relatively few measurements of treeless land, and their results are very mixed. Ecosystem carbon flow measurements are also expensive to implement. For now, it is not possible to give average figures on the basic state of carbon stocks on different cover types before afforestation, only the probability of a positive, negative og neutral development.

2. Vegetated land protected from grazing (grasslands, flower fields (e.g. lupine meadows) and heathland with willow and/or dwarf birch)

In well vegetated land protected for grazing, it can be assumed that vegetation biomass changes are slow, often none on land that has been protected for a long time, but possibly increasing slightly on land that has recently been protected. Plant growth and the breakdown of carbon compounds generally go hand in hand. It can be assumed that carbon stock changes of such areas are neither significantly positive (increase in carbon stocks in vegetation and soil, inhalation>exhalation) nor negative (decrease in carbon stocks, exhalation>inhalation). The baseline status is therefore assumed to be neutral (zero) with respect to of CO2 emissions. If land use is not likely to change in the future, vegetation changes will continue to be slow. It is unlikely that natural birch regeneration will take place to a significant extent due to the dense vegetation cover. Therefore, a neutral status remains for a long time. Afforestation on such land increases the carbon stock by that sequestered by the trees (both above and below ground). In the shade of the trees, the carbon stock of the ground vegetation layer may decrease compared to the vegetation on the land without forest, but the growth of the trees compensates for this and much more.

3. Vegetated land used for grazing (degraded grass-, ericaceous- and moss heathland)

On land used for grazing, it can be assumed that the carbon balance is generally somewhat more negative than in protected land due to the biomass that grazing takes from the area. Depending on grazing intensity, it can therefore be assumed that the basic situation is slightly negative (exhalation>inhalation) and the carbon reserve is decreasing, although it does not have to be much every year. The baseline status is therefore neutral to negative with respect to CO2 emissions and will continue to be so if there are no changes in land use. Afforestation on such land increases the carbon stock by that sequestered by the trees (both above and below ground). Due to the necessary exclusion of grazing, depletion of the carbon stock is also reversed, as removal og biomass from the area by grazing is halted. Carbon stock benefits are therefore likely to be greater than the growth of the forest.

4. Eroded land (glacial till, sand and alluvium)

Eroded land varies in properties but is characterized by a discontinuous vegetation cover. Loamy till contains organic compounds in the soil, but sands and alluvium almost none. The vegetation cover is not sufficient to add a significant amount of carbon to the soil, and therefore the soil carbon stock is usually depleting (exhalation>inhalation). Sometimes the stock is so small that the shrinkage is also small or non-existent. There is often active soil erosion in such areas, and as a result, the carbon stocks are further depleted. Unchanged land use rarely leads to an improving situation, but often to a worsening situation. Afforestation on such land increases the carbon stock by that sequestered by the trees (both above and below ground). Other vegetation also increases over time, and with that, the depletion of carbon stocks in the soil reverses, increasing both soil and undergrowth carbon stocks. Benefits are therefore very likely to be greater than the growth of the forest, in many cases significantly greater.

Carbon contents of Icelandic soils (chart)

Table 1. Carbon contents of Icelandic soils showing the percentage C per total volume of dry matter in the top 15-35 cm of the profile.

Wetland soils/mires

Dryland soils

Histosols >20% C

Brown Andosols <12% C – vegetated areas

Histic Andosols 12%-20% C

Vitrisols <1,5% C – sparsely vegetated /barren areas

Gleyic Andosols <12% C


For further information see: Icelandic soils and Íslenskt jarðvegskort [1]

The carbon content of Icelandic soils varies greatly. The organic soils of the mires contain the most carbon (C), where partly decayed wetland plant remains have accumulated over the past few millennia. The wetland soils furthest away from the volcanically active zone, where aeolian volcanic glass deposition is minimal, contain over 20% C and are classified as Histosols1. Closer to the eroded areas of the volcanically active zone, the organic content of mires is lower, commonly between 12%-20% C. These soils are classified as Histic Andosols1. Mires receiving the highest amount of aeolian volcanic glass deposition, tend to be rich in clay and amorphous plant remains, contain less than 12% C. These soils are classified as Gleyic Andosols1.

The highest carbon content of dryland soils is found among Brown Andosols1. These are the soils of well vegetated heathland and forests and can contain up to 12% C. The Vitrisols of eroded and poorly vegetated drylands, however, have a carbon content lower than 1.5%1.

The total amount of soil carbon at any site is a function of the C content of different soil horizons and the total soil depth. The soil depth varies greatly from one place to another and is influenced by the soil age and the history of local soil formation. This further increases the variability of the total carbon content. The carbon content usually decreases with increasing soil depth. However, the top-soil C content is not necessarily a good predictor of total soil C, because in some cases deeper horizons, buried under younger material, can store a considerable amount of soil C.


[1] Ólafur Arnalds og Hlynur Óskarsson 2009. Íslenskt jarðvegskort. Náttúrufræðingurinn 78 (3-4) 141-153