3.5.2.5. Landscape-Level Results
The numerical values selected for all aspects of carbon dynamics in the hypothetical
landscape are comparable to those of a temperate ecosystem. The actual values
are not important here, nor are the absolute numerical values of the results.
The purpose of these examples is to demonstrate qualitatively how, for each
definitional scenario, the reported carbon stock changes in the ARD land portion
of the landscape compare to the actual carbon stock changes in the simulated
landscape. Although the simulations extend over several commitment periods,
for clarity only the results of the first commitment period are reported here.
The area of ARD land in each commitment period is a function of the human activities
simulated in each of the nine cases, as well as the definitional scenarios that
specify which activities create ARD land (see Table
3-10). In all cases, the area of ARD land in the first commitment period
is much less than the total area in the landscape. For cases A through F, no
ARD land is created for the definitional scenarios that require a forest change
(Figure 3-5). For these scenarios, only cases G, H,
and I (i.e., those with a true forest/non-forest change) create ARD land at
the end of the first commitment period. The Degradation/ Aggradation definitional
scenario also reports ARD land for cases E and F, in which the potential forest
cover at maturity is changed for some areas.
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Figure 3-5: Area of ARD land (in kilo ha =
1000 ha) at the end of the first commitment period (2012) for each of
the nine cases (A-I) and for various definitional scenarios: FAO, Forest
Change [includes all scenarios requiring a forest/non-forest conversion
(i.e., IPCC, Land Use, Flexible, and Biome)], Land Cover, and Degradation/Aggradation
(Deg/Agg). Missing bars indicate zero area. FAO options 1, 2, 3 refers
to the three approaches for accounting carbon stock changes.
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The definitional scenarios in which a harvest/regeneration cycle creates ARD
land (i.e., FAO and Land Cover) report large areas of ARD land. In case A, the
area of ARD land is 23 kha for both the FAO and the Land Cover scenarios. In
case B, the area naturally regenerated in the FAO scenario does not create ARD
land. In cases H and I, the afforested area is not included in the Land Cover
scenario because the planted areas have not grown past the forest cover threshold
at the end of the first commitment period. In case I, all deforested and afforested
area contributes 9.2 kha of ARD land at the end of the first commitment period-except
in the Land Cover scenario, in which the afforested area again has not yet grown
past the forest cover threshold.
Figure 3-6 summarizes the results for the nine cases
defined in Table 3-10 for the first commitment
period and for three carbon pools: aboveground biomass; dead organic matter,
including soil carbon; and total ecosystem carbon, which is the sum of aboveground
and below-ground biomass and dead organic matter. Below-ground biomass is not
shown separately because it is proportional to aboveground biomass. All carbon
stock changes are reported in kilo tons over the 5-year commitment period. The
actual stock change is that observed in the hypothetical landscape.
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Figure 3-6: Changes in carbon stock during
the first commitment period for each of the nine simulated cases of
human activities for aboveground (top), dead organic matter including
soil (middle), and total ecosystem (bottom) carbon.
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In most combinations of definitional scenarios and simulated cases, Figure
3-6 shows large discrepancies between the actual carbon stock change in
the landscape and that reported for the ARD land. In cases A and B, the actual
carbon stock change in the landscape is zero. The scenarios that limit the creation
of ARD land to only forest change activities report no ARD land, therefore no
carbon stock changes for cases A-F. These definitional scenarios fail to account
for increases (case D) or decreases (case C) in actual carbon stocks resulting
from accelerated or decelerated harvesting rates and from changes in forest
productivity (cases E and F). These scenarios do capture the land-use change
activities of cases G, H, and I and represent the correct carbon stock increase
in case H, as well as the decrease in cases G and I.
Definitional scenarios in which the harvest/regeneration cycle creates ARD
land (FAO, Land Cover) report a large decrease in carbon stock in the ARD land,
except with an activity-based accounting approach in the FAO scenario. In cases
in which the actual landscape carbon stock increases (cases D, F, and H) or
decreases (cases C, E, G, and I), the reported stock change becomes somewhat
larger or smaller relative to case A, respectively. Despite these small differences
between cases, the reported change is always negative, even if the actual carbon
stock increases in the landscape (e.g., cases D and F).
The choice between the three carbon accounting approaches (land-based I and
II and activity-based) for the FAO definitional scenario does not affect the
area of ARD land. The approaches do report different carbon stock changes for
the ARD land, however. The stock change in land-based approach I is reported
for the 5-year commitment period. For land-based approach II, the stock change
on the land is reported from the time of the activity to the end of the commitment
period. In the activity-based approach, stock changes that do not result from
the reforestation activity but happen on the land after reforestation has taken
place are excluded from the accounting.
The impacts of the three accounting approaches differ between carbon pools.
For aboveground biomass, the FAO definitional scenario with land-based approach
I (FAO opt 1 in Figure 3-6) always yields a large negative
carbon stock change because this option indirectly accounts for harvesting during
the commitment period. Land-based approach II (FAO opt 2) reports a small positive
carbon stock change in aboveground biomass, resulting from the growth of reforested
seedlings. This increase in aboveground biomass is more than offset by decreases
in dead organic matter carbon stocks. Land-based approach II does not account
for the increase in dead organic matter from the input of logging slash and
root biomass during harvest. It does account for the decay of all dead organic
matter from the reforestation activity to the end of the commitment period.
Thus, land-based approach II reports a large negative carbon stock change for
the dead organic matter pools. Total ecosystem carbon stock change under land-based
approach II is negative-albeit only about one-third of the values reported for
land-based approach I. The results for the activity-based approach are the same
as for land-based approach II, except that the negative stock change from decaying
slash between reforestation and 2012 is excluded from the accounting because
it does not result from the reforestation activity. Therefore, the FAO scenario
with activity-based accounting results in carbon credits in the first commitment
period; that is, only the aboveground biomass increase under FAO (option 2)
would be reported.
The definitional scenario that is designed to capture degrading or aggrading
carbon stocks (the Degradation/Aggradation scenario) correctly reports no change
in carbon stocks in cases A and B. By design, it does not capture carbon stock
changes associated with altered harvest rates (cases C and D) because they do
not change the potential cover of carbon density at maturity. This scenario
fails to accurately report the actual carbon stock changes in cases E and F,
which represent degrading and aggrading forest conditions. As before, the changes
at the landscape level are different from those reported for the ARD land. Moreover,
even when the carbon stock at the landscape level is increasing (case F), the
reported carbon stock change is still negative.
The decision about which pools to include will also affect the differences
between the actual carbon stock changes in the landscape and those reported
for the ARD land. For aboveground biomass, below-ground biomass (not shown),
and total ecosystem carbon, the differences are in the same direction but of
different magnitude (Figure 3-6). The differences can
be of opposite direction for the dead organic matter pool alone, but it is not
likely that carbon stock changes for only this pool will be reported. For definitional
scenarios in which the harvest/regeneration cycle creates ARD land, the dead
organic matter pool can increase when biomass pools are decreasing because logging
slash-including stumps and root biomass-is added to the dead organic matter
pool following harvesting.
We have conducted additional simulation experiments as sensitivity analyses.
We systematically altered the rates of land-use change and harvest to cause
landscape-level carbon stocks to either increase, remain approximately unchanged,
or decrease. It can be demonstrated that combining one rate of land-use change
with three different rates of harvesting, or vice versa, creates very different
reported carbon stock changes for the three groups of definitional scenarios.
We drew the following conclusions from the analyses of the simulations:
- The area of ARD land in the first commitment period is much less than the
total area in the landscape. The area is greater in definitional scenarios
in which forest harvesting creates ARD land.
- Definitional scenarios that limit ARD land to areas with forest/non-forest
change and scenarios in which the harvest/regeneration cycle does not create
ARD land (IPCC, Land Use, Flexible, and Biome) report very similar amounts
of carbon stock changes for the same amount of deforestation. These definitional
scenarios are insensitive, however, to actual changes in the landscape-level
carbon stock. Thus, although the same carbon stock change is reported for
the ARD land area, the actual carbon stock change in the landscape could be
positive, unchanged, or negative.
- Definitional scenarios in which a harvest/regeneration cycle creates ARD
land (FAO and Land Cover) report changes in the ARD land in the early commitment
periods that are much more negative than the actual changes in the landscape
because regrowth on lands harvested prior to 1990 is not counted. This conclusion
holds for land-based accounting approaches I and II but not for the activity-based
approach: In some cases the activity-based approach does report an increase
in aboveground biomass even if the actual carbon stock change is zero or negative.
In the FAO and Land Cover scenarios, the rates of harvest and deforestation
affect the reported carbon stock change. Thus, with the same deforestation
rate, the reported change in carbon stocks becomes more negative with increasing
harvest rate.
- If the intent is to report carbon stock changes that are similar to the
actual carbon stock changes in a landscape, only full carbon accounting can
achieve this objective. If the intent is to best account for carbon stock
changes in the ARD land area, a definitional scenario that only includes forest/non-forest
transitions is best suited.
- Differences between actual and reported carbon stock changes can be reduced
further if forest management activities that alter landscape-level carbon
stock are included using the mechanisms defined in Article 3.4.
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