Pile Burning 101

This Article contains information from DCFP experts and Deschutes Land Trust write up By Amanda Egertson and Jana Hemphill

Here in Central Oregon, we often hear about pile burning in our forests. Get a step-by-step account of what goes into planning this type of forest restoration.

Why does forest thinning happen?

The forest ecosystems of the east Cascades of Central Oregon are complex. All of them are forests that are historically adapted to fire.

And our mid- and lower elevation forests (think forests of ponderosa pine and mixed conifer species around Sisters, Bend and Sunriver) in particular evolved with frequent fires that burned on average every 10 to 25 years – regularly enough to “clean up” and maintain healthy, resilient forests for millennia.

But a history of unsustainable forest management practices has created unnatural forest conditions: overly dense forests, full of young trees…fewer of the older, larger fire-tolerant species…overgrown, shrubby understories.

All of this contributes to a lack of resilience in the face of natural fire, insects, diseases and climate change. It’s negatively impacting the plant, fish and wildlife communities that rely on and thrive in these fire-adapted forest conditions. And it means we now face a greater likelihood of high magnitude and high severity wildfires, which threaten the values we care about—and the forest itself.

The process of reducing the thickness of trees and brush in the forest. This is done in two stages:

  • Stage One: Mowing cuts the top off the brush like a lawn mower. Mastication chops the brush into the soil like a tiller.
    • Historically, the fires that moved through our forest would do this, so we are mimicking this action. 
    • When wildfire next moves though our forest, this act will help keep the fire on the forest floor vs. moving up into the trees and killing them. 
  • Stage Two: Removal of some of the trees. The DCFP usually recommends a technique called thin from below in which the smallest trees are prioritized for removal. The larger, more fire-resilient trees are left is the goal for most restoration projects.  Of course, a few small trees are always left to grow into the big trees of the future.

Why burn slash piles instead of hauling them out?

Sometimes these piles are located in hard-to-reach areas or the woody debris is unusable for commercial products. Slash piles of vegetation are created during thinning or other types of fuel reduction work, and when ignited, burn hotter and produce less smoke. Prescribed burns are also ignited by hand, but the goal is to burn green vegetation across a broad area. Both pile and prescribed burning are important tools that reduce hazardous fuels and restore forests to healthier conditions!

The process of pile burning:

The first step in pile burning is to develop a plan for thinning and burning, then submit the plan to the Oregon Department of Forestry (ODF) for review. Once thinning is complete, the cut material is carefully piled, making sure to construct the piles properly so they burned well. Because the piles are often comprised of both juniper and pine, restoration work has to wait a year for the pine to dry out sufficiently so that it burns well.

Next, a safe burn window must be determined by taking into account temperature, relative humidity and wind as well as soil moisture and surrounding vegetation. The public must be made aware of the burn so everyone knows why there is smoke in the air!

It’s time to burn!
Because of the intense heat at the center of the burn pile, the material in the center burns most quickly and breaks away from the material at the perimeter of the pile. Once this occurs, we “chunk” the piles, meaning we toss the material from the perimeter of the burn piles into the center, so it burns as well. The goal is to ensure as much of the material is burned as possible.

Once all of the piles are lit, usually by late morning, the piles burn and management stays on site for the entire day until all of the fires are completely out.

Thanks for learning about pile burning!

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(c) 2023 Deschutes Collaborative Forest Project