Does "direct human-induced" refer only to the ARD activities, or does it refer to stock changes that result from ARD activities as well? If it refers to stock changes, all indirect human-induced activities and natural impacts on stock changes would have to be excluded. For example, if a forest is growing at a rate of 3 t C ha-1 yr-1, 1 t C might be related to the effects of atmospheric nitrogen and CO2 fertilization. The DHI part would be 2 t C; only that amount would be credited. A converse case can be made for a forest growing at 2 t C ha-1 yr-1 that would grow at 3 t C in the absence of an adjacent pollution source. In other words, if "direct human-induced" refers to stock changes, the stock changes reported under Article 3.3 might be greater or smaller than the stock changes observed on the land. The exclusion of effects other than those that are DHI is technically difficult, if not impossible (see Section 2.3.3). Achieving this exclusion at a moderate uncertainty level will be costly and could create unbalanced accounting. For example, credits could be given for a growing stand, but subsequent emissions following a natural disturbance or local air pollution would not be counted. If the stand regrows after the disturbance, more credits could be gained even though there is no net GHG improvement for the atmosphere.
If "direct human-induced" refers only to the ARD activity, the technical problems involved in separating out parts of the stock changes disappear. In addition, only the afforestation and reforestation activity allows benefits from nitrogen or CO2 fertilization, for example. With this approach, stock changes are measured irrespective of their attribution as DHI (e.g., fertilization or thinning), indirect human-induced (e.g., CO2 fertilization), or entirely natural (e.g., wind-throw and avalanches) (see also Section 2.3.3).
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