Model

Overyield’s carbon model is based on an allometric equation, which provides biomass estimates from anticipated tree measurements across a 30 year timeline:

• Wood Density
  • The amount of wood material in a unit volume of wood, calculated by finding the ratio between the mass of dried wood vs green wood.
  • Although slight variation in wood density across time and species morphology may occur, Overyield assumes this value is consistent across 30 years.
• Trunk Height
  • Trunk height is species-dependent, but may be management dependent as well, as certain practices such as pollarding may cease upward growth.
• Branch Mass as a % of Trunk
  • This factor will depend on management practices, such as the intensity of pruning.
• Diameter at breast height (DBH)
  • Many factors influence DBH, not limited to species growth rate and growth habit, tree age, environment, and management factors.
  • DBH is typically measured at 4.5ft.
• Root Mass as % of Above
  • Below-ground biomass varies across species, though on average root biomass constitutes 27% of a tree’s above-ground biomass.
• Soil Carbon % of Above
  • Carbon from leaf litter, stems, branches and root exudates may contribute to soil carbon.
  • This value is again species and management dependent, but may average around 7%.

Calculation

• Your design decisions (e.g. sections drawn, start year selected) and crop template data (e.g. loss events, mortality) influence your farm’s total tree count and tree age, which in turn impacts per-tree carbon sequestered.
• Per-tree carbon sequestered per year is determined by the numbers entered in the Carbon tab of your crop template. Years 1-30 in the life cycle of a tree are represented by the fields labeled 1 - 30, which can be adjusted for each value (DBH, Trunk Height, etc.).

Assumptions

• When a tree dies, Overyield assumes that that carbon remains stored