Harvesting Our Forest Biomass in a Sustainable Way

By Emmanuelle Brière
February 2011

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Cut branches, tree crowns, roots and leaves are currently the major source of forest biomass in Canada.

These days, the forest industry isn’t restricted only to the production of lumber and newspaper. Forests and their components are now being used as sources of renewable energy, thanks to forest biomass consisting of tree crowns, branches, leaves and roots. However, some of the material collected to create this type of energy plays an important ecological role within forest ecosystems, and removing it could have a negative impact. So, in order to ensure the sustainable production of bioenergy, the Canadian Forest Service (CFS) of Natural Resources Canada (NRCan) monitors the effects that the intensive harvesting of forest biomass may have on the health of our forests.

Forecasting the Ecological Impacts of Intensive Harvesting

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Leaving forest biomass on the ground plays an important role in maintaining the productivity and health of forest ecosystems.

Forest biomass can be regarded as something like the fertilizer of our forests. It contains, among other things, the nutrients that allow a forest to regenerate itself after cutting, fire, insect infestation or other disturbances. The decomposition of this biomass fertilizes the soil and maintains a balance in acidity levels and chemical composition. Removing the forest biomass could therefore have a significant impact on forest renewal.

However, the intensive harvesting of forest residues is not harmful to all forest sites. In fact, most soils are unaffected by intensive harvesting, although some are particularly sensitive to it.

For instance, in some boreal forest stands of Quebec, particularly of jack pine growing on coarse and poor sand, the harvesting of the whole tree — trunk, branches, crown and foliage — reduces the reserves of soil nutrients and thus affects regrowth, while harvesting only the trunk doesn’t seem to create a problem. That’s why it’s crucial to determine the sensitivity of different types of soil in order to conduct harvests without harming the forest.

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The CFS is putting in place a network to monitor the long-term effects of forest-biomass harvesting practices.

Soil Indicators

The impacts of harvesting forest residues are not yet known for all soil types and tree species. Consequently, the CFS is developing a set of indicators to rate the sensitivity of sites and avoid negative repercussions on soil fertility.

Long-term field studies and environmental monitoring are the best tools for evaluating the effects of harvesting. Working in partnership with organizations such as Chantiers Chibougamau, an international lumber exporter located in northern Quebec, the CFS is developing a monitoring method to assess the impact of residue harvesting on site productivity. With this method, it’s now possible to monitor the soil composition over time and determine the extent that harvesting affects site productivity.

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With the development of the bioenergy chain from the forest biomass, the residue from felled trees becomes as much a forest product as wood used for pulp, lumber or panelling.

For “Greener” Harvests

Science can’t provide a perfect answer on the question of site sensitivity. “Using the current body of knowledge with caution, it’s possible to harvest the biomass without threatening the health of ecosystems,” says Evelyne Thiffault, an NRCan research scientist at the Laurentian Forestry Centre, located in Quebec City. “However, a good monitoring system needs to be put in place, and our practices need to be constantly reviewed in light of all the new data being collected.”

Combining past and current results with monitoring provides the ecological data that helps improve forest management decisions and establish standards for residue harvesting and appropriate site selection.

For more information on forest biomass, visit the Canadian Forest Service.

To read about related articles, see Renewable Energy

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