Going to extremes: field trials study biomass harvesting impact.

• Author: Ross, Ian
• Position: Green

Harvesting woody biomass in Northern Ontario for renewable fuels or value-added forest products hasn't quite reached Scandinavian-type proportions, but some forestry researchers want to "get ahead of the curve" in measuring the environmental impact of potentially large-scale operations.

Scientists at the Great Lakes Forestry Centre in Sault Ste. Marie teamed up with industry partner Tembec to conduct a range of ongoing field trials in the Martel Forest near Chapleau in northeastern Ontario.

On a 40-hectare block, researchers performed a broad spectrum of clear-cut harvesting methods on four experimental treatments.

They want to know whether intensive biomass harvesting can result in nutrient depletion in the boreal forest. Could removing nutrients from a cutting block, in the form of slash, which acts like garden compost, adversely impact the regeneration of a healthy forest?

"We've really barely started on it," said Paul Hazlett, a soil scientist with the Canadian Forest Service, of the trials which began in early 2011. "We've created these treatments on the site, but we want to monitor what happens to forest growth, soil nutrients, and biodiversity over the long term."

In one experiment, Tembec performed a stem-only "soft touch" harvest, where all the tree tops and branches were left behind, providing the most nutrients available for regrowth.

The next practice involved a full tree biomass harvest, bringing all the material to the roadside to be chipped for electrical generation.

The third approach involved the same previous treatment, but included plucking all the stumps from a plot where the biomass was removed. This practice is common in Finland and Sweden where it's used to produce bioenergy.

"It's about trade-offs of what is the environmental impact of leaving them or removing them," said Hazlett.

The most severe treatment involved removing all the aboveground material where a contractor bladed the top layer of the soil. The organic layer was plowed off to the side.

"What we've essentially done is create this gradient of nutrient retention--or removal--with our treatments. We come in and look at different measurements of the forest, soil and...