How much carbon does a tree store?

The calculations for determining the amount of carbon stored within a tree are fraught with assumptions, estimates, margins of uncertainty, generalisations …. But hey, this is a tree blog so let’s have a go!

All plants absorb carbon dioxide but trees do it best.

Mountain Ash in Glen Nayook - columns of carbon

Trees take in carbon dioxide and release oxygen while cleaning the air we breathe and they do this, day in, day out. The process in which they do this is called photosynthesis –

           carbon dioxide + water (and sunlight) = glucose (carbohydrate) + oxygen + water(vapour).

Trees store carbon in their leaves, branches, trunks, bark and roots.

If the wood in a tree is used for making timber products – furniture, house frames, railway sleepers, etc – the carbon remains in the wood for the life of the product.

If a tree or wood product is burnt or allowed to rot and decay, the carbon is returned to the atmosphere.

Fast growing and long-lived tree species store the most carbon but usually these two factors are mutually exclusive. In Australia, the best species for carbon sequestration are the eucalypts and the acacias.

Blackwood in Mt Worth State Park

Australian forests sequester about 57 million tonnes of carbon dioxide each year, which sounds a lot but this accounts for barely 10% of the greenhouse gasses released into the atmosphere – we need to plant many, many more trees and even then it would only be part of the solution to global warming.

So here goes – let’s try and work out how much carbon is stored in the Bill Kraft Giant, a Mountain Grey Gum in Albert Rd Drouin. We can then do a simple conversion to determine the quantity of carbon dioxide that has been extracted from the atmosphere by this single tree.

Bill Kraft Mountain Grey Gum Albert Rd Drouin

(The method used here has been taken from the website forest learning which aims to serve school teachers and educators, children, and the public with information on Australian forests and forest-based products, and provision and access to forestry teaching resources.)

Circumference c from BBS tree register (note 1 below)   c = 7m

Radius r                                                                              r = c ÷ 2π = 1.11m

Height h from BBS tree register                                        h = 35m

Volume v from forest learning website (note 2 below)     v = πr²h x 0.7854 = 106.4m³

Estimated green density ρ                                                  ρ ~ 1000kg/m³

Mass of green tree above ground Mgreen                         Mgreen = vρ = 106400kg
                                                                                                                 = 106t

Plus estimated 20% for root system                                   Mgreen = 106 +
                                                                                             (0.2 x 106) = 127t

Dry mass of tree (approx. 65% of green mass)                  Mdry = 0.65 x 127 = 82.6t

Estimated mass of C (50% 0f dry mass)                            Cmass = 0.5 x 82.6
                                                                                                        = 41.3t

Estimate mass of carbon dioxide CO₂ (note 3 below)        CO₂mass = 41.3 x 3.67
                                                                                                            = 151.6t

Notes

1 The Baw Baw Shire tree register is now available on-line.

2 The coefficient 0.7854 in the volume formula is provided to allow for trees not being exactly cylindrical, spaces between branches, etc.

3 The coefficient 3.67 in the carbon dioxide calculation is to account for the ratio of the molecular weights of carbon dioxide to carbon.

Conservatively then, The Bill Kraft Giant in Albert Rd Drouin has sequestered about 41 tonnes of carbon in its lifetime.

So valuable!

These 41 tonnes of carbon represent 151 tonne of the greenhouse gas, carbon dioxide, that has been removed from the atmosphere.