Various methods have been used to account for GHG mitigation effectiveness of LULUCF projects. Some of these methods are based on absolute measurements at a point in time; others take into account the time dimension of carbon sequestration and storage. These methods are discussed below.
The method most commonly used to express carbon storage is based on calculating the difference in carbon stocks between a project and its baseline at a given point in time. This method is referred to as the stock change method [previously the flow summation method (Richards and Stokes, 1994)]; measurements are usually expressed in tons of carbon per hectare. This method is limited, however, insofar as it provides only a "snapshot" of the carbon fixed: The values will vary depending on the often arbitrary decision of when to account for the project's benefits. Furthermore, this method does not differentiate between projects that earn credits earlier rather than later. For these reasons, this method does not provide a useful tool for comparison between projects.
For example, Figure 5-2 illustrates a projection of carbon stored in two hypothetical tree plantation projects with different growth rates. The arrows illustrate that stock change measurements carried out at time t1 would provide different results between the two projects, whereas the same result would be reached if measurements were carried out at time t2. If measurements were carried out at time t3-after harvesting-an entirely different result would be reached for both projects in relation to measurements at t2.
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Figure 5-2: Projection of carbon stored in
two tree plantation projects with different growth rates. For simplicity,
it is assumed that the baseline is zero and that harvesting leads to
an immediate release of all carbon stored. Arrows illustrate the net
carbon storage of the projects at different points in time, calculated
by the stock change method.
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