Behind the noisy cafeteria at Illinois Valley High School stands a small silver silo that looks like it ought to hold a grain crop. This public school in southern Oregon is one of about a dozen in the Northwest heated almost entirely by wood pellets.
Twice a month, a truck stops by and fills the silo. The pellets sound like Rice Crispies popping as they slide through a system of PVC pipes into the firebox of a biomass boiler. A computer program connected to the school’s thermostats controls the entire process.
Jim Bunge oversees maintenance and energy for the schools in Cave Junction, an old timber town west of Grants Pass. He realizes burning wood products might strike some as backward.
“It’s not backward at all. It’s pretty high tech, with the computer system. It’s just switching from a fossil fuel to a renewable energy source,” Bunge says.
In 2011 the Three Rivers School District got rid of an aging diesel heat system at the high school. It installed this $650,000 biomass boiler with the help of stimulus funding, an Oregon renewable energy tax credit, and a low-interest loan.
The boiler at Illinois Valley High is part of a broader initiative to replace fossil fuel use in rural Oregon with a literally homegrown source of energy. The group Sustainable Northwest calls it the “forest to boiler” movement.
Sawmills across the region have used bark, sawdust, and their own wood waste to generate heat and electricity for years. Now Oregon Gov. John Kizhaber is encouraging rural schools and hospitals to install high efficiency biomass boilers, making a renewable energy tax credit available. Policymakers in Washington state have also identified forest biomass as a vast, underused energy resource.
Proponents of forest biomass talk about a triple benefit: social, economic, and environmental.
Jim Bunge estimates that burning wood pellets at llinois Valley High saved the school district $30,000 in heating costs last year and replaced about 20,000 gallons of diesel. Those dollar savings will increase if the price of fossil fuel continues to rise. The district says the system will pay for itself in four more years.
The change has made the school more energy independent and kept dollars in the state: the boiler was built by a Portland company, and the pellets come from a company in Cascade Locks.
“The concept here is that we can be taking the byproducts of forest management and turning it into a sustainable homegrown fuel which competes really well with fossil fuels,” says Marcus Kauffman, Oregon’s state’s biomass specialist.
As for environmental benefits, proponents say a market for pellets and wood chips could help drive tree thinning and restoration east of the Cascades, where a history of overzealous firefighting has left many dry forests unnaturally crowded with small trees.
“Those trees have very little value; it’s hard to get a two by four out of them,” Kauffman says. “That means we have a significant amount of material leftover, all the biomass. Tops, limbs, branches. That’s the part we need to find markets for.”
Kauffman and others want to scale up the demand for pellets and chips by encouraging communities to install cogeneration facilities that could heat and power a neighborhood block or a university instead of just a high school.
As Oregon and Washington work to develop new energy markets for pellets and wood chips, some scientists have pushed back and raised concerns that replacing fossil fuels like diesel and coal with forest biomass may actually increase greenhouse gas emissions in the near term.
After all, wood, like fossil fuels, emits carbon dioxide when it burns.
And calculating the greenhouse gas impact of swapping a wood pellet for fossil fuel is complicated. Scientists say the carbon dioxide balance sheet for forest biomass hinges on a series of questions that do not always have precise answers:
“Biomass burning from wood pellets releases a large amount of carbon dioxide in the atmosphere, a carbon debt that can last for decades,” says Beverly Law, a professor of global change biology at Oregon State University.
Law is the coauthor of a study, published in Nature Climate Change, that found that large-scale bio-energy harvest in Northwest forests could increase regional carbon emissions over a 20 year time frame.
Many previous studies have assumed that all wood in a sustainably managed forest will eventually decay or burn and be replaced by new growth that soaks up more carbon dioxide, so burning biomass in a boiler or power plant doesn’t add any new carbon into the atmosphere.
Law says that often, it takes decades or longer for new forest growth to recapture the burst of carbon that’s released when pellets or wood chips burn. Meaning it takes years before the use of woody biomass for energy actually decreases carbon emissions, even if it takes the place of a fossil fuel.
“If you look at (the forest) as a bank, it takes a long time for the stock to build up. And the carbon stays there as long as its not being cut. You’ve built up assets very slowly, but its very quickly emitted to the atmosphere when you combust it.”
Law contends that if policymakers want to cut carbon emissions as quickly as possible to limit the impact of climate change, burning biomass isn’t an effective strategy.
Some are critical about studies by Law and others, which assume that whole trees will be harvested to produce pellets or chips. Oregon’s Kauffman says that assumption is wrong: in the Northwest, biomass products like pellets are made out of branches and treetops left behind after a harvest or thinning, or from log milling waste, like sawdust.
Biomass proponents say studies like Law’s likely overestimate how much CO2 would enter the atmosphere immediately and underestimated how much could remain locked up in conventional wood products like two-by-fours that are relatively long lasting.
Research suggests that using slash or harvest residuals instead of whole trees would shorten the time lag before biomass burning reduces greenhouse gas emissions, but not eliminate it.
A Canadian study, for example, found that burning wood pellets to generate electricity in place of of coal increased CO2 emissions for 16 to 38 years, depending on whether the pellets were made of harvest residuals (branches) or standing trees. After that time lag, biomass reduced CO2 emissions.
John Mckechnie, one of the study’s authors, cautioned that the calculations were based on forests in Ontario and that the CO2 emissions could be significantly different for biomass from a Northwest forest. McKechnie’s study didn’t consider wood pellets made from sawdust, but he says those could be considered carbon neutral, as long as that sawdust wasn’t diverted from some other use like producing particle board.
Finally, there’s the question of removing trees to reduce wildfire risk and how that impacts carbon emissions.
And that is the state’s vision for biomass production.
Jeremy Fried, with the Forest Service’s Pacific Northwest Research Station, has conducted extensive research on forest stocks and fire treatments.
Fried says tree thinning treatments can be an effective way to reduce overall carbon emissions, in forests where the fire risk is high.
“If you do it on the Olympic Peninsula where fires happen every 200 years, it would be pretty difficult to justify the benefit. If you do it on the east side of Oregon, where fires happen every 20 to 50 years, it does make sense,” he says.
Fried says the most effective thinning strategy involves removing a combination of large trees, which can be milled, and smaller material, suitable for turning into pellets or chips.
There is a caveat, though. Based on his research, Fried says thinning only reduces emissions if the treatments are effective and actually prevent trees from torching or spreading a crown fire. In some parts of the forest landscape, preventing that kind of a fire is nearly impossible. Fried has estimated that thinning for fire prevention is effective - and therefore reduces CO2 emissions - on about a third of dry forest acres in the region.
Fried cautions against putting too much stock in any one analysis of how forest thinning or biomass harvest will affect forest carbon emissions.
Much of the science is based on modeling, he says, and even the simplest models — say, a model that predicts how much carbon is in a single Douglas fir tree — produce results with a great deal of uncertainty attached.
“It’s really hard to say definitively whether something is [carbon neutral] or not, because it’s an ‘all depends’ kind of thing,” he says.
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