Being conservative:
Carbon Sequestration Calculations
Carbon Sequestration Calculations
What makes the Forest Carbon model a conservative one is that it takes into account only the usable stem timber, measured by yield class. This means only 40% of the carbon sequestered by a tree is being traded, with the balance being held as a contingency reserve. Because that 60% balance will never be traded, the carbon sequestered in a forest will always be greater than, or equal to, the emissions being offset.
Our Carbon Calculator Model...
The rate of carbon sequestration in a forest is more or less proportional to the growth rate of the trees. Foresters call it 'yield class', i.e. the annual increment of stem timber in cubic metres per hectare, per year, over the growing life of the forest. Using a software system devised by Forestry Commission Research called ecological site classification (ESC) the forester can enter data (such as grid reference, altitude and soil type) and find out which tree and shrub species are best suited to that site. The expected yield class for each species is also given. A weighted average yield class may be estimated for a given species mix over a specific area. Foresters normally express yield class as whole even numbers (6', '8', etc.) but for greater accuracy Forest Carbon calculations show yield class to one decimal place. Conversion of yield class to mass of carbon dioxide sequestered is done arithmetically (see below).
...means a safe and sound basis for carbon credit trading
A calculation called 'the expansion factor' is used to estimate the additional carbon in non-stem components based on species, age, management and environmental conditions. Values published for mature trees ranges from 1.3-1.8. Taking a mid-range value of 1.5, the oakwood described below is sequestering 8.3 tonnes of CO2 /ha/yr over its growing lifetime. Over time a similar, or greater, quantity of carbon will be sequestered in the associated soil and this is accounted for accordingly.
How it works
1) Yield class (stem timber volume) is converted to dry weight by reference to tables of wood specific density generally in the range of 0.33-0.45 t/cu m for softwoods and 0.49-0.56 t/cu m for hardwoods.
2) The carbon content, typically 50%, is used to convert dry weight to carbon content.
3) Carbon content is converted to CO2 equivalent by a factor of 3.67.
Thus a stand of oak growing at YC6 is laying down 3 tonnes of stem dry matter, comprising 1.5 tonnes of carbon, equivalent to 5.5 tonnes of CO2 /ha/yr. Similarly a stand of spruce growing at YC18 is laying down 6 tonnes of stem dry matter, comprising 3 tonnes of carbon, equivalent to 11 tonnes of CO2.
2) The carbon content, typically 50%, is used to convert dry weight to carbon content.
3) Carbon content is converted to CO2 equivalent by a factor of 3.67.
Thus a stand of oak growing at YC6 is laying down 3 tonnes of stem dry matter, comprising 1.5 tonnes of carbon, equivalent to 5.5 tonnes of CO2 /ha/yr. Similarly a stand of spruce growing at YC18 is laying down 6 tonnes of stem dry matter, comprising 3 tonnes of carbon, equivalent to 11 tonnes of CO2.
