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Field trials study biomass harvesting impact

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 o
Island-L-stumping_Cropped
A stump is removed at a test plot in the Martel Forest near Chapleau for forestry researchers to study the after-effects of what happens to the soil during harvesting biomass.

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 above-ground 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 organisms across these treatments over time, measuring the immediate and long-term impacts.”

Ontario forest policy dictates that it’s unacceptable to remove all the woody debris and the rich organic layer on top of the soil.

But in Scandinavian countries there is a stronger culture, backed by government directives, to use renewable energy sources.

“That’s driving the push to utilize the biomass,” said Hazlett. “The reason we conducted these experiments is we want to look at the extremes.”

After the treatments the harvest sites were replanted with black spruce and jack pine seedlings, said Hazlett.

“We really have to look at this experiment for up to 30 or 35 years as the trees get really large to see the long-lasting effects of moving different amounts of
biomass.”

For an added wrinkle, wood ash from Tembec’s co-generation plant in Chapleau was spread on the plots, similar to a homeowner using wood stove ash on their garden, as a method of replacing nutrients removed by the full-tree biomass harvest.

Since it’s a long-term study, Hazlett said it’s too premature to arrive at any definite conclusions or identify any best practices that can be shared with industry and government, much less put into use right away.

Usually forest management plans operate in five-year cycles and companies like Tembec wouldn’t be legally allowed to change their practices.

“The hope is that over the longer time period this kind of work will have an impact on the forest management policies in the province and beyond.”

For more information, visit nrcan.gc.ca.