Root-to-shoot ratio
The proportion of below-ground to above-ground biomass, used to estimate root carbon that is difficult to measure directly.
Root systems hold a substantial share of forest carbon but are expensive and destructive to measure. The root-to-shoot ratio lets an above-ground estimate be extended into the soil volume beneath it.
The ratio is not constant. It tends to rise where water and nutrients are scarce, because plants invest more in acquisition, and it varies strongly between ecosystems — grasslands, temperate forest and tropical peat each behave differently. Disturbance also shifts allocation, at least temporarily.
Because roots turn over and contribute to soil organic carbon, the ratio feeds both biomass accounting and soil carbon models. Treating it as a fixed global constant is one of the more common sources of overstatement in rapid assessments.
Frequently asked questions
Can roots be measured directly?
Yes, through excavation or coring, but the work is destructive, slow and usually limited to a small number of calibration pits.
Does the ratio apply to removed biomass?
It applies to living biomass pools. Harvest removes above-ground material, and the fate of roots must be handled separately in the accounting.