Land Use, Land-Use Change and Forestry

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5.4.2.1.4. Comparison of methods

Table 5-9 shows a comparison of the GHG benefits attributed to the sequestration project illustrated in Figure 5-3. The example assumes the following:

• The project is run for three rotations of 18 years each.
• At the end of each rotation, the carbon stock in the forest reaches 140 t C ha^-1.
• Harvesting reduces carbon stock to zero, and the baseline is zero.

Calculations were conducted assuming a minimum required project duration of 55 years [based on the Te of 55 years (Moura-Costa and Wilson, 2000)] and 100 years [based on the equivalence time of 100 years; see Chapter 2 (Fearnside et al., 2000)]. It is clear from this example that, depending on the accounting method used, different amounts of carbon benefits accrue to the project, as is shown by the following results:

• According to the stock change method, this project would receive 140 t C ha^-1 during the sequestration phase of each rotation and would need to return an equivalent amount after each harvest.
• The average storage calculated for the duration of this project is 84 t C ha^-1 (using the traditional average storage method, without a fixed minimum project duration), which is reached before the end of the first rotation and remains the same irrespective of the duration of the project. If a specified time frame is adopted for the calculation of the average storage (i.e., with a predetermined denominator in the average storage equation), the GHG benefits of a project would increase proportionally to the time frame under which the project is conducted.
• If a minimum project duration of 55 years were required, the equivalence-adjusted average storage of this project (which is conducted for 54 years) would be 83 t C ha^-1, whereas if the minimum time frame required were 100 years, the equivalence-adjusted average storage would be 45 t C ha^-1. Furthermore, if this project were conducted for only one rotation, the project's benefits would be lower (see values in parentheses in Table 5-9).
• Another accounting option (the stock change crediting with ton-year liability adjustment method) is to use the stock change method to calculate the benefits of the projects during the sequestration phase and to use ton-years to calculate the "loss" of benefits when emission takes place. Using this approach, the calculated GHG benefits of the project at the end of the first rotation would be 140 t C ha^-1 (the same as in the stock change method); when emissions take place after harvesting, however, the calculated GHG benefits "lost" are either 112 t C ha^-1 (if a ton-year equivalence factor Ef = 0.0182 is chosen, based on Te = 55) or 136 t C ha^-1 (if a ton-year equivalence factor Ef = 0.010 is chosen, based on Te = 100). The longer the project duration, the smaller the amount of GHG benefits "lost" after harvesting.
• If the GHG benefits of the project are calculated using the equivalence-factor yearly crediting method (ton-year accounting), the GHG benefit attributed to the project would increase gradually as the project is conducted for a longer time frame. Because this method assumes that the ton-year equivalence factor reflects the GHG benefit to the atmosphere derived from temporary storage, no loss of benefits is assumed when emissions take place.