Estimating forest carbon emissions and removals
The greenhouse gas (GHG) inventory methodologies used to monitor and report on Canada’s forest carbon balance reflect state-of-the-art science and the best available data. The models used to produce annual estimates of forest GHG emissions and removals are anchored in extensive peer-reviewed science, quality assurance, and quality control consistent with the guidelines of the Intergovernmental Panel on Climate Change (IPCC).
Specifically, the Government of Canada uses its internationally accepted forest Carbon Budget Model Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3), which includes carbon in:
- living trees
- dead organic
- mineral soils
Developed by scientists at the Canadian Forest Service over 30 years ago and continuously improved since then, the CBM-CFS3 is fully documented in peer-reviewed scientific literature. Many countries use it to estimate as well as understand forest emissions and removals.
Each year, scientists from Natural Resources Canada and Environment and Climate Change Canada identify and agree on multi-year priorities for improvements in Canada’s forest carbon estimates based on the maturity of scientific understanding and the availability of data.
A science-based approach is crucial
The annual GHG emissions and removals for any large, forested area cannot be measured directly. Instead, models integrate data from millions of measurements to scale up tree, stand and landscape-level characteristics to provincial / territorial and national estimates.
Using information obtained from forest inventories, the CBM-CFS3 represents Canada’s managed forest as approximately 3 million forest stands. The CBM-CFS3 estimates forest growth rates using over 100,000 growth curves developed from millions of tree measurements and tens of thousands of plot measurements. Some of these data are based on decades of observations of stand dynamics.
These growth curves indicate the full range of observed forest growth rates in Canada and the age-dependent decline in growth rates of older stands. The CBM-CFS3 integrates this information with observations from remote sensing (for example, area annually burned) to estimate forest carbon stocks and changes over time.
Benefits of forest protection
Estimates using the CBM-CFS3 fully capture the forest carbon implications of forest protection.
The climate benefits of protecting old forests vary depending on:
- forest types
- age-class distributions
- risk of natural disturbances
In some cases, live biomass declines in old forests, as documented by scientific studies.
Another variable is whether forest protection causes harvesting to shift elsewhere or results in increased use of more emission-intensive products. Not all protection efforts will produce significant climate benefits. The assessment of any potential actions involving forests should consider all factors.
Impacts of human activities on forest carbon
Having a clear understanding of direct human impacts on forests is important to inform how we develop approaches to reduce carbon emissions and increase the carbon sequestered by forests.
For this reason, Canada’s GHG inventories separate forest emissions and removals in the managed forest due to human activities from emissions and removals due to wildland fire, forest insect outbreaks and other natural disturbances.
If such an approach was not used, it would be impossible to assess how forest management activities affect estimates. This is because natural disturbances would dominate emissions and removals estimates.
For example, natural disturbance emissions can vary by over 200 million tonnes of carbon dioxide equivalent (Mt CO2e) from year to year, depending on large inter-annual variations in the area burned by wildfire.
Calculating the impact of harvested wood products
A fundamental scientific principle of GHG inventories is to reflect emissions and removals as they actually occur.
Consistent with IPCC guidance, this principle also applies to harvested wood product GHG estimation and provides the clearest indication of human impacts. Canada and other countries use this principle in reporting to the United Nations Framework Convention on Climate Change.
Wood harvested in Canada is used worldwide for a variety of products such as paper, panels and lumber. Different types of products store carbon for varying periods of time depending on how long the product remains in use. For example, carbon in wood used for bioenergy is assumed to be emitted in the year of harvest, while carbon in recycled packaging can be stored for several years. Much of Canadian lumber is used in housing, where carbon can be stored for decades.
As in other parts of forest-related emission and removal estimates, there are large uncertainties in the emissions estimates of harvested wood products. These uncertainties apply in both directions.
Canada’s wood products could be either larger or smaller GHG sources of emissions than currently estimated. For example, the assumptions about the period over which Canada’s different wood products remain in use, after which carbon is emitted, (half-life assumptions), are highly uncertain. Canada bases these assumptions on IPCC default values that may not accurately represent how our wood products are used.
Complexity and uncertainties
Currently, numerous processes that may affect forest carbon estimates cannot be included in calculations due to a lack of data or scientific understanding to capture the complex processes involved. For example, the impacts of narrow strips or patches of disturbances, such as seismic lines and tertiary logging roads, are not included because of uncertainty about the net carbon impact of such practices.
There is a range of factors not well reflected in the estimates, including those whose exclusion could result in overestimation of emissions associated with forest management. Some of these factors include efforts to improve forest growth through management or better estimates of how long wood products remain in use.
Well-established scientific techniques consistent with the guidance of the IPCC are used to quantify uncertainties in estimates produced using the CBM-CFS3. While uncertainties in complex estimates such as national-level forest GHG emissions and removals are high and apply in both directions, the goal is to prepare estimates that neither overestimate nor underestimate emissions and removals.
A continuous improvement process is in place for GHG inventory estimates based on the maturity of scientific understanding and the availability of data. Some improvements can be implemented relatively quickly, while others require substantial time to improve scientific understanding and develop the necessary data.
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