Trevor Lewis tries to mimic lightning but, lacking the ability to generate a couple hundred million volts as he strolls through the forest, he relies on a mixture of diesel and gasoline.

Which when ignited produces flames.

But no thunder.

Lewis is an assistant fire management officer for fuels for the Wallowa-Whitman National Forest.

Along with his colleagues on the two other national forests in the Blue Mountains — the Umatilla and Malheur — Lewis plans each spring to light “prescribed” fires on several thousand acres of public land.

Much as medications are prescribed to yield particular effects for people, these controlled blazes are intended to achieve specific goals, Lewis said.

At the most basic level, he said, these fires are designed to reduce the amount of “fuel” in the forest — the logs, limbs, twigs, needles, dried grass and cones that also burn during wildfires.

Prescribed burning is done during the spring (and, some years, during the fall), because flames don’t spread as rapidly as they would during the summer, when fuels can be as dry as kiln-dried lumber.

The idea, Lewis said, is to scorch the fuel in a controlled way rather than waiting for lightning to ignite a wildfire in July or August that costs millions of dollars and takes weeks or months to extinguish.

“It’s critical work we try to get done,” said Brian Anderson, district ranger for the Wallowa Mountains Office in Joseph. “It helps us reduce fuels before fires later in the summer. It helps us out when it’s hot and dry during fire season.”

Prescribed fires can benefit the land in other ways, Lewis said, such as spurring the growth of shrubs and grasses that are palatable to wildlife such as deer and elk, as well as cattle that graze on each of the national forests each summer.

But reducing fuel loads is the main goal, he said.

Often, prescribed burning is the last part of a long-term project that begins with cutting trees, either through a commercial timber sale or what’s known as noncommercial thinning — cutting trees too small to be processed in mills.

Parts of the Blue Mountains are “overstocked” with trees, Lewis said, meaning there are more trees per acre than was the case in centuries past.

Human activities have contributed to this unnatural situation, including past logging that favored the biggest, most valuable trees such as ponderosa pines and western larches, as well as decades of mostly successful firefighting.

Both logging and fire exclusion have allowed other trees, primarily firs, to proliferate in some places, particularly lower elevation, drier areas where ponderosa pines predominated in the past. Firs are in general more vulnerable to insects, disease and wildfire, however, compared with ponderosa pines and larches.

Lewis said prescribed fires are designed to mimic historic, lightning-sparked blazes that helped maintain the less-dense forests by burning fuel before it could accumulate, and by burning young trees before they could become thickets.

“We’re trying to get forests back to a healthy stocking situation that we used to see around here when fire was doing its natural thinning on its own,” Lewis said.

Different types of fuels

Prescribed fires that follow logging, whether commercial or not, are designed to burn the fuel that remains from the tree cutting, Lewis said.

In some cases workers pile this slash, which reduces the amount of fuel left on the forest floor.

(The piles are burned during the late fall and winter, usually after snow has fallen, rather than in the spring, because fires aren’t likely to spread during the winter.)

Other prescribed fires, though, are “natural fuels burns,” Lewis said.

In those places there hasn’t been any recent logging, so there’s no slash.

The fuel burned is the natural stuff that falls to the forest floor — needles and limbs and cones, as well as grass and shrubs.

Waiting for the ‘window’ to open

During the spring, Lewis said, fire managers wait for specific conditions conducive to prescribed fires— not so dry that flames will spread too rapidly or burn too hot, but not so damp that blazes will quickly flicker out.

Fire bosses call it a “burn window,” and some years it’s not open for long.

In the spring of 2022, for instance, a series of soggy spring storms largely squelched the prescribed burning season in the Blues.

Last spring, lingering snow kept the burn window closed longer than usual in some parts of Northeast Oregon.

This year the ground is still too wet for successful prescribed burning in many areas, Anderson said.

If conditions improve, fire managers would like to burn as much as 1,500 acres in Wallowa County — about 1,000 acres near Big Sheep Creek Summit, and about 500 acres near Upper Chesnimus Creek.

Moisture isn’t the only potential challenge, Lewis said.

A proliferation of green grass can also stifle prescribed fire plans, since flames won’t spread much across a forest floor with lush grass even when other fuel is abundant.

Besides waiting for proper burning conditions, fire managers work wth the Oregon Department of Forestry to ensure prescribed fires comply with the state’s smoke management plans.

Where are fires planned, and when?

The three national forests maintain an online map that shows places where prescribed fires could happen this spring.

The map is available at tinyurl.com/prescribedburnmap.

Other sources of information include each forest’s Facebook page and X account, as well as the Blue Mountains Prescribed FIre Council blog, bluemtnprescribedfire.blogspot.com/.

Each fire typically takes two to five days, including post-fire monitoring.

Travelers should expect extra traffic, as well as the potential for low-lying smoke, near prescribed fires. The Forest Service sometimes sets up signs along highways when blazes are burning.