Land Use, Land-Use Change and Forestry

Other reports in this collection Average storage method

To account for dynamic systems-such as afforestation projects, in which planting, harvesting, and replanting operations take place-an alternative approach has been used (e.g., Dixon et al., 1991, 1994; Masera, 1995): the average storage method (Schroeder, 1992). This method entails averaging the amount of carbon stored in a site over the long term according to the following equation:

where t is time, n is the project time frame (years), and measurements are expressed in tons of carbon per hectare. The advantage of this method is that it accounts for the dynamics of carbon storage over the whole project duration, not only at the times chosen for accounting. This method is also useful for comparing different projects with different growth patterns. As Figure 5-3 shows, the average storage over three rotations of Project 1 is higher than that of Project 2. A weakness of this method, however, relates to the still subjective time frame, n, chosen for running the analysis. In the case of Figure 5-3, for example, the average net carbon storage in either project would be equal whether the calculation was performed for one, two, or an infinite number of rotations, as long as the denominator chosen for the foregoing equation coincided with the last year of a rotation.

Figure 5-3: Projection of carbon stored in two tree plantation projects over three rotations. For simplicity, it is assumed that the baseline is zero, that harvesting leads to an immediate release of all carbon stored, and that equilibrium of carbon pools is reached in the first rotation cycle. The curves illustrate carbon storage over time; the straight horizontal lines show the average storage calculated for the two projects.

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