Forest Carbon in Ontario

Estimates of forest carbon can vary depending on the researcher’s approach and assumptions. For example, in their calculations, researchers might:

• Treat climate as a constant over time or adjust climate to reflect potential future changes
• Treat rates of disturbance (such as fire) as a constant over time or adjust to reflect potential changes in disturbance regimes in the future
• Include wood products, which store carbon long after the trees are harvested, into their calculations or ignore carbon stored in wood products
• Assume that soil carbon is constant, since little is known about how forest management and climate change affect this pool or attempt to estimate how soil carbon could change over time
  

As a result of differing assumptions, carbon stock estimates can differ greatly. It is important to understand what approach and assumptions are used for each set of estimates.

To estimate carbon stocks accurately, researchers need to know about more than just the natural processes and how they are influenced by management. They also need to know how the carbon balance is affected by substituting wood for fossil fuels and carbon-intensive construction material, such as steel or concrete and burning fossil fuels during tree harvesting, log transporting, and processing wood products. In short, many factors affect estimates of carbon stocks associated with managed forests. Researchers have estimated the amount of carbon stored in Ontario’s managed forest (Figure 2). These estimates include the carbon in:

• Live tree biomass (all the living parts of the tree, above and below ground)
• Understory plants
• Standing and fallen dead trees
• Forest floor (layer of leaves and other organic material lying on top of the soil)
• Soil

Figure 2. The managed forest area used in carbon calculations excludes southern Ontario and most of the Far North, but includes the measured fire management zone (red line).

Carbon estimates for Ontario’s managed forests include the carbon stored in wood products as well as the carbon emitted during their manufacturing, use, and disposal. 

Ministry of Natural Resources researchers used the forest carbon modelling software FORCARBON, developed for Ontario, to estimate current and future forest carbon stocks based on approved forest management plans. Their results show when and to what extent Ontario’s managed forests will act as carbon sinks and contribute to mitigating climate change. Future work will examine how forests may respond to a changing climate. This will allow researchers to better estimate forest carbon stocks.

Over the 100-year period from 2001 to 2100, the managed forest (green bars) will likely be a carbon sink (Figure 3). This result does not include carbon emissions from non-forested wetlands and assumes that soil carbon will remain at current levels. For some decades (2031–2060), however, Ontario’s managed forest will likely be a carbon source.

When researchers included the carbon contained in wood products (dark red bars) in their estimates, they found that, after 100 years, five times more carbon will be added to carbon stored in wood products than will be added in forests. Overall, more carbon will be stored in Ontario’s managed forest area and in wood products than is released throughout the century (black bars).

Figure 3. Carbon change in Ontario for 2001 to 2100, estimated by decade for managed forests, for wood products, and overall.

Changes in climate can affect how much carbon forests store. For example, a longer growing season may increase the amount of carbon stored in forests. If conditions change such that the amount of rainfall is not sufficient to support tree growth, then less carbon will be stored. Fire and pest outbreaks resulting from drier conditions could also increase tree mortality rates and cause forests to emit more carbon.