The history that made the Grasshopper Fire

THE DALLES — The Tree Ring Lab at Oregon State University (OSU) is using centuries of data held in the wood of old trees to understand fire on Mount Hood’s east slope.

Maddie Washburn’s film about the project, completed just as the Grasshopper Fire raged, showed at the Granada Theatre Sept. 24.

Scientists had thought the cool, high-elevation conifer forests on Mount Hood’s east flank burned little, while the dryer oak woodlands lower down burned a lot.

The truth is more complicated.

According to the film, the dry oak woodlands burn about every seven to 10 years, cleaning out dry fuels and young conifers. Those fires burned the neighboring conifer forests nearly as often, thinning out saplings and shade-tolerant undergrowth. Isolated areas of cool, moist conifers, high on the mountain, burned rarely — but did burn, once or twice a century.

The OSU team learned this by plotting and analyzing groves scattered across Mount Hood’s eastern forests. With long, slender tools, they sawed narrow cores from living trees. With chainsaws, they took samples of dead stumps. Cleaned and analyzed in the lab, burn scars in their annual growth rings revealed the exact dates of fires.

Odd as it seemed, they learned that fire actually helps old trees survive. By thinning out the new growth, removing “ladder fuels” — flammable material that reaches up into the canopy, letting fire climb — and dead limbs, the fires made open groves that burned less intensely. Flames moved more lightly over the forest floor, without rising and killing the large, thick-barked trees that anchored the forest.

Indigenous people took care of these forests by burning them regularly. Fire suppression and logging changed all that in the 1890s. Selective cutting removed the thick-barked ancients, letting shade-tolerant youngsters grow thickly. Meanwhile, thinking fire was bad, people kept it out of the forest. They forced the Indigenous residents to stop burning, too.

The Grasshopper Fire, ignited by lightning in August, burned much of the study area — which hadn’t burned like that in 130-plus years. Thick young forest had filled with fuels that fed high-intensity, tree-killing fire. Many of the old study trees, which had survived multiple fires, died.

That, and climate change, fuel hotter fires, said Andrew Spaeth, facilitator of the Wasco County Forest Collaborative, and USFS deputy ranger John Bowers. While historically fires could get this large, they burned with less severity.

After the film, panelists talked about what it may take to change these conditions.

For a very brief window after the Grasshopper Fire, before they rot, sawmills are willing to harvest fire-killed trees. The Forest Service is already working on a deal to have a logging company take out the standing dead, reducing roadside hazards, said Bowers.

After that, as young trees sprout up thickly in some accessible burned areas, there is another narrow window where prescribed fire could thin them out, keep dead wood from accumulating — again making open, fire-resistant groves that burn with low-intensity, safer fire.

If this isn’t done, the young trees may once again grow up into thick forest, laden with an understory of their scrawny shade-tolerant sisters, prone to hot, destructive fire. Fallen logs from previous hot fires make it worse.

Spaeth said this cycle of accumulation and torching could potentially resolve itself naturally, but it would take a long time, and involve major, blistering fires.

One bright spot, Bowers said: the Grasshopper Fire burned in a mosaic of different intensities. It appears Wasco County’s fuel reductions work in this area may have paid off, reducing the fire’s severity. But Bowers was careful to note that this is a first impression; the formal reports and surveys haven’t been completed, and until they are, this question can’t be answered with certainty.

“Fire is one of our neighbors in this place,” Washburn reminded the audience as the panel ended. “And so, living with fire, we have to have the understanding that it’s here too. We can’t live in a place that fire lives and expect it not to come back.”

She encouraged people to be curious and bring any questions to their local experts. “So if you’re curious, stay curious; ask more questions; and we can all continue to live in this place together with fire as our neighbor, not as our enemy.”