Clearcut carbon calculator explainer
HOW ARE WE CALCULATING the emissions associated with logging and milling of logs? First off, we are not including any of the hydrocarbon emissions associated with industrial forestry machinery or transportation of logs and products. The magnitude of these emissions are small in comparison to the carbon released prematurely to the atmosphere by the felling of forests.
Looking at the province as a whole, or the ministry of forest's administrative divisions of "the Coast," "the South" and "the North," we apply a common multiplier to volumes of merchantable timber harvested as recorded in the ministry's Harvest Billing System. That common multiplier is explained below.
For calculating carbon released by smaller areas, such as a series of clearcuts in the same general area, we use site specific accounts of species and measured values of merchantable volume per hectare that are derived from the Harvest Billing System. We then use the National Forest Inventory Biomass Calculator to determine above-ground biomass. To that we add estimates for below-ground live biomass (roots), breakage and rejects, and release of forest floor carbon.
The example below outlines in slightly more detail our method of estimating carbon released as a result of clearcut logging.
Estimating for large areas, for example, the whole province
(1) First, we calculate the emissions associated with an average cubic metre of wood harvested in BC:
• About one-half (.5) the dry weight of a tree is carbon.
• The decay of one tonne of tree carbon will result in the release of 3.667 tonnes of carbon-dioxide-equivalent emissions.
• The average density of timber felled in BC (based on 2018 MoF numbers for relative volumes of tree species cut, and their known dry-weight densities) was about .447 tonnes/cubic metre.
So, carbon-dioxide-equivalent emissions released by decay of one tonne of average wood = 1/2 x 3.667 x .447 = .82 tonnes/cubic metre.
If we multiply that number by the total volume recorded by the Harvest billing system, we would have an estimate for the amount of carbon that will be released (most of it within 100 years) by the logs that passed through the ministry's harvest billing system. But that would not account for the portion of the live forest biomass that was left in the clearcut.
(2) Second, we estimate the volume of forest biomass that was left in the clearcut. This consists of several categories of biomass:
• Non-merchantable tree tops
• Non-merchantable trees
• Dead standing trees
• Breakage and rejects
• Forest floor carbon that will be released after logging
The National Forest Inventory Above-ground Biomass Calculator allows us to estimate the weight of several of these categories: stumps, branches, foliage, non-merchantable trees, and dead standing trees. Roots are estimated as 20 percent of above ground biomass, as per Simard et al. Breakage and rejects are estimated as per a US Forest Service manual. Forest floor carbon released is estimated as ???? In practice, all these additional sources of emissions are slightly larger than the emissions associated with just the merchantable volume. Multiplying emissions associated with the merchantable volume by a factor of 2.1423 accounts for these additional sources.
So, for the province as a whole, emissions associated with industrial forestry on public land as a whole = 2.1423 x .82 tonnes/cubic metres multiplied by the total volume harvested in any given year.