Ask a project developer about deadwood and the usual answer is that it was excluded as conservative. In an ARR project on bare land, that is correct and uncontroversial. In an improved forest management or REDD+ project, the same move can be quietly anti-conservative, and it is one of the more common structural errors in forest carbon accounting.
Why Exclusion Is Conservative in ARR
Plant trees on degraded land and deadwood accumulates slowly from natural mortality and pruning. The pool grows from near zero.
Excluding it means not claiming that growth. You report less carbon than you have. Nobody objects to that.
Why Exclusion Can Be Anti-Conservative Elsewhere
Now consider a forest where the project intervention reduces harvesting.
| Scenario | Deadwood behaviour | Effect of excluding the pool |
|---|---|---|
| ARR on degraded land | Accumulates from ~0 | Conservative — unclaimed gain |
| IFM, reduced harvest | Baseline has harvest residues; project has fewer | Can overstate the project benefit |
| REDD+, avoided clearing | Baseline clearing creates a large deadwood pulse | Depends on decay treatment |
In reduced-impact logging, the baseline generates substantial logging slash. That slash is a carbon pool that decays over years. If you exclude deadwood entirely, you also exclude the baseline's decaying residue, and the comparison stops being like-for-like.
The general rule: exclusion is only automatically conservative when the pool is larger in the project scenario than the baseline. Reverse that and exclusion becomes a claim in the project's favour.
Measuring Them Is Genuinely Hard
There is a practical reason exclusion is popular: both pools are difficult and expensive to measure well.
Coarse woody debris is spatially clumped, meaning one large fallen stem in a plot swings the estimate enormously, and plot based sampling has very high variance. Line intersect sampling handles this better but requires its own protocol and density class assignments by decay stage.
Litter is easier to sample but highly seasonal, and a single measurement date can misrepresent the annual mean.
Neither problem is a reason to pretend the pools do not exist. They are a reason to decide deliberately, whether to measure with a design suited to the pool or exclude with a written argument showing the exclusion is conservative in this project's direction.
What to Write Down
For each excluded pool, the project file should state: the pool, the scenario in which it is larger, and therefore why exclusion understates rather than overstates the claim. Three sentences. Projects that provide them rarely get challenged; projects that simply say "excluded, conservative" frequently do.
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