Forest carbon in Ontario

Ontario’s managed forests have the potential to remove carbon dioxide, a greenhouse gas, from the atmosphere and thereby slow global warming.

What is forest carbon?

Carbon is a chemical element that is a key building block of life on Earth. It is the basis for all life forms, from microbes to plants to animals to people. The carbon cycle describes how carbon moves through land, water, and air as plants and animals live, die, and decompose.

Carbon exists naturally in the atmosphere in the form of carbon dioxide and other compounds. Carbon dioxide is one of many greenhouse gases that trap heat in the atmosphere and make life on Earth possible. Human activities such as burning fossil fuels increase the amount of carbon dioxide in the atmosphere and contribute to global warming.

Forests take up carbon dioxide through photosynthesis and convert it to wood and other plant parts. Forests therefore have the potential to help remove carbon dioxide from the atmosphere and to slow global warming. If more carbon can be stored in forests and wood products (e.g., lumber, furniture, and paper), then less carbon dioxide will remain in the atmosphere. To understand how best to manage the carbon in Ontario’s forests, forestry professionals need to know how much carbon is contained in forests and wood products and how that amount changes over time.

Researchers around the world are working to estimate the amount of carbon stored in trees, soil, and harvested wood products. Their methods vary, but they agree that accurate accounting is needed. Ontario is focussing on determining the potential for carbon storage in the managed forest.

Figure 1: The forest carbon cycle

Background

The forest carbon cycle is defined as the combined processes—including photosynthesis, decomposition, and plant respiration—by which carbon moves between the atmosphere, soils, water, and living organisms. The forest carbon cycle can be extended to include forest harvesting and wood manufacturing, as well as the use and disposal of wood products (Figure 1).

Photosynthesis is the process by which plants use sunlight and carbon dioxide to grow. Carbon dioxide is absorbed from the atmosphere and combined with water to create wood, stems, roots, and leaves. At night, leaf cell nutrients are consumed to provide energy for the plant, and carbon dioxide is released back to the atmosphere through plant respiration.

Fallen leaves and branches, dead trees, and decaying root systems are broken down by insects, fungi, and other soil organisms. Some of the carbon in this decaying material attaches to soil particles and remains in the soil, some is emitted to the atmosphere as carbon dioxide, and the rest dissolves in water and is carried into rivers, streams, and lakes. Forests also release carbon dioxide when there is a natural disturbance, such as a forest fire.

In short, forests take up carbon dioxide from the atmosphere through photosynthesis, and release it through respiration, decomposition, and forest fires. Forests are considered ‘carbon sinks’ when their trees and plants absorb and store more carbon dioxide from air than the forest emits by fire, decomposition, and respiration in a given time period. Conversely, forests are considered ‘carbon sources’ when more carbon dioxide is emitted than removed.

The most accurate estimates available are for above ground tree carbon (trunks, stems, and leaves). Estimates of root carbon and soil carbon are less certain because they are more difficult and costly to measure.