The Tree Carbon Calculator

Assumptions and calculations used in the tree carbon calculator

The tree carbon calculator uses general allometric relationships to estimate above-ground biomass of the tree. The biomass of the tree roots is then estimated using a root:shoot ratio. These two values are then summed to give the total tree biomass and converted to carbon assuming that 50% of the tree biomass is comprised of carbon (Gifford 2000).

ABOVE-GROUND BIOMASS
Softwoods
A general allometric equation for Pinus radiata is used to calculate above-ground biomass (Snowdon et al., 2002).

Above-ground biomass (kg) = 1.019^a x e ^{(ln dbh x 2.391 - 2.413)}

ln dbh is the natural log of tree diameter at breast height (cm).
NB the tree carbon calculator uses tree circumference at breast height(cm) as its input. To convert to diameter the circumference is divided by pi (3.14).
^a Bias correct factor based on Baskerville (1965)

Hardwoods
An allometric equation developed by the CRC for Greenhouse Accounting and State Forests of NSW for Eucalyptus pilularis is used to calculate above-ground biomass(Montagu et al., 2002)

Above-ground biomass (kg) = 1.021^a x e ^{(ln dbh x 2.589 - 2.733)}

This equation has been tested against a data set of above-ground biomass of 611 trees (20 eucalypt species from 20 locations in Eastern Australia, South Africa and Hawaii).

ln dbh is the natural log of tree diameter at breast height (cm).
NB the tree carbon calculator uses tree circumference at breast height(cm) as its input. To convert to diameter the circumference is divided by pi (3.14).
^aBias correct factor based on Baskerville (1965)

ROOT BIOMASS
The Intergovernmental Panel on Climate Change (IPCC) has default values for estimating root biomass when the above-ground biomass is known (IPCC, 1996). These values were used in the carbon calculator to estimate the below-ground component of the total tree biomass.
For conifers (pines) root:shoot is 0.2.
For hardwoods (eucalypts) root:shoot is 0.25.
See their website at http://www.ipcc.ch

Limitations

This equation however can only reliably estimate carbon for softwood trees up to a circumference of 157cm (diameter of 50 cm) and hardwood trees up to a circumference of 408 cm (diameter of 130 cm).

This calculator does not reliably estimate carbon for trees that have more than one stem at a height of 1.3 m from the ground either (however, watch this space as this will soon be included).

References

Baskerville, GL. (1965). Estimation of dry weight of tree components and total standing crop in conifer stands. Ecology. 46(6):867-9.

Gifford, R. (2000). Carbon Content of Woody Roots: Revised Analysis and a Comparison with Woody Shoot Components. National Carbon Accounting System Technical Report No. 7 (Revision 1). Australian Greenhouse Office, Canberra.

(IPCC) Intergovernmental Panel on Climate Change, 1996. Revised 1996 IPCC Guidelines for National Greenhouse Gas Inventories: Reference Manual.

Montagu, K., Duttmer, K., Barton, C. and Cowie, A. (2002). Estimating above-ground biomass carbon of Eucalyptus pilularis across eight contrasting sites - what works best? International Conference on Eucalypt Productivity 2002, 10-15 November. Hobart, Tasmania, pp 49-50.

Snowdon, P., Eamus, D., Gibbons, P., Khanna, P., Keith, H., Raison, J., and Kirschbaum, M. (2000). “Synthesis of allometrics, review of root biomass and design of future woody biomass sampling strategies”. National Carbon Accounting System Technical Report No. 17, September 2000. Australian Greenhouse Office. http://www.greenhouse.gov.au/ncas

Snowdon, P., Raison, J., Keith, H., Ritson, P., Grierson, P., Adams, M., Montagu, K., Bi, H., Burrows, W., and Eamus, D. (2002). “Protocol for sampling tree and stand biomass”. National Carbon Accounting System Technical Report No. 31, March 2002. Australian Greenhouse Office.
http://www.greenhouse.gov.au/ncas