Article 3.3 of the Kyoto Protocol is specific in that the allowable offsets from ARD activities must be "measured as verifiable changes in carbon stocks in each commitment period." Once a piece of land falls under the definitions of Article 3.3 during one commitment period, can it subsequently be removed from the accounting? It is logical to assume that land could change from the deforestation category to reforestation or vice versa. If a piece of land can be removed from the ARD lands category at later times (e.g., when the activity ends in an activity-based approach), large carbon stocks that were credited previously could be released without debits (Schlamadinger and Marland, 1998). The words "in each commitment period" in Article 3.3 suggest a reporting requirement for future commitment periods. Over time, the area of ARD land would increase because no land can be removed from this classification.
The inclusion of afforestation and reforestation since 1990 provides countries with an additional tool for achieving their assigned carbon emission targets during the first commitment period because most forests established since 1990 would still be growing rapidly in 2012. If the Kyoto Protocol were applied to future, contiguous commitment periods and if more and more post-1990 forests were harvested during these periods, credits would be followed by debits on the stand level (see also Section 18.104.22.168 on ways to limit such debits). On the national level, however, credits would only decrease over time as the forest estate approaches a biomass equilibrium. Carbon trends in these future commitment periods will partly depend on the definitions of stocks (see Section 2.3.6). On-site carbon stocks in post-1990 forests are likely to increase for decades (provided the total area of eligible forests does not decrease over time and forests are logged on a sustainable-yield basis). However, the rate of increase-hence the amount of allowable offsets-is likely to diminish over time.
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