Any valid carbon mitigation project should meet the "additionality" criterion -- that a substantial portion of its full costs are met through carbon finance. If the carbon has already been locked up (say, in the case of a mature woodland) it is extremely difficult to demonstrate how further funding bestows any additionality.
It will usually be the case that there is a time lag between emissions having been made, a mitigation project being funded, and the carbon being drawn from the atmosphere. For woodland creation this delay is particularly pronounced.
To counter this problem, the size of the predicted carbon store is “discounted” – scaled down. In essence, more trees are planted than are required to neutralize the original emissions. These additional trees help mitigate the effect that the circulating CO2 has before it is eventually locked up.
It is important to note that although our figures are based over a 100 year period, the trees grow continuously – and therefore sequester carbon – throughout that time.
There is an initial lag in carbon sequestration as the woodland “recovers” from the forestry activities involved in its creation, but after just a few years the rapidly growing young trees begin absorbing a net quantity of carbon.
In any case, tree planting provides a positive action towards helping both wildlife and people adapt to future climate change. Locking atmospheric carbon away is just one of the many benefits that trees can bring to our denuded landscape.
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