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Plastic sheeting keeps burn piles dry

Could you please explain the function of the plastic sheeting in burn piles? I imagine they serve to keep materials from blowing away, but isn’t it toxic to burn the plastic?

— Dale

When crews thin brush and small-diameter trees in the forests to reduce wildfire danger, they move the material that can’t be sold and trucked out for timber or biomass production into piles, according to Lomakatsi Restoration Project, a local nonprofit organization that restores forests and watersheds.

Because freshly cut woody debris doesn’t burn well, workers cover about two-thirds of the pile with polyethylene sheeting, then pile on the remaining third to hold it down. Workers return to burn the piles after six months to a year when the material has dried out, Lomakatsi says.

Removing the polyethylene would require workers to unstack the top third of every pile, then put the woody debris back. They would also have to make sure water trapped by the tarp doesn’t wet the wood below, Lomakatsi says.

Dry piles are easier to ignite and take much less diesel, which is used as an ignition fuel. Dry wood burns with less smoke, decreasing emissions, the organizations says.

Burning polyethylene does release insignificant amounts of pyrene and fluoranthene. Polyethylene sheeting doesn’t contain chlorinated compounds and other toxic chemicals associated with burning regular plastic. The use of polyethylene sheeting is standard in the industry, Lomakatsi says.

When requested, Lomakatsi does use slash paper instead of polyethylene on municipal and private land projects. Slash paper works well on small projects when the burning of piles can occur in a timely manner. Slash paper keeps piles dry for a limited time before breaking down, and burn piles covered with paper need three times as much diesel fuel to light effectively, which increases emissions, Lomakatsi says.

The organization can treat 16,000 acres a year with ecological thinning — creating 40 to 160 piles per acre. Because of the scope and magnitude of the work, some piles may sit for a few years through rain and snow, especially since burning is limited to short seasonal burn windows. The weather must also be right to clear out smoke.

This spring, pile burning and prescribed burning was stopped over concerns the smoke could worsen COVID-19 symptoms.

Lomakatsi says it wishes there were good alternatives to using diesel fuel and polyethylene sheeting. But given the warming climate, wildfire risk to communities and millions of acres of forest in need of treatment across Oregon and Northern California, where the organization works, Lomakatsi says it needs to maximize the number of acres it can treat.

In the Rogue Basin alone, Lomakatsi estimates there are 1.2 million acres of forest in need of restoration.

Send questions to “Since You Asked,” Mail Tribune Newsroom, P.O. Box 1108, Medford, OR 97501; by fax to 541-776-4376; or by email to youasked@rosebudmedia.com. We’re sorry, but the volume of questions received prevents us from answering all of them.