Fundamentals
Carbon fraction
The share of dry biomass that is carbon, used to convert biomass into carbon stock.
Biomass is roughly half carbon by dry mass, and a default fraction is applied when direct measurement is unavailable. The value varies by tissue and species but far less than biomass itself does.
Because the fraction is relatively stable, it is rarely the dominant uncertainty. It still must be stated, since confusion between biomass and carbon — a factor of about two — is one of the most consequential unit errors in reporting.
Frequently asked questions
Is the default always acceptable?
Usually, given its low variability, provided the value and source are documented.
What is the commonest error?
Reporting biomass tonnes as carbon tonnes, doubling the apparent result.