Thinning forests may not prevent fires study shows

September 5, 2018

By: The Working Forest Staff

The polluted air that hung over a vast stretch of the West Coast — from San Francisco to Vancouver, B.C. — has generated a fresh wave of support for more logging and cool-season burns to thin the forests and reduce the potential fuel.

These tactics are standard practice, but according to a report in the Olympian News,  a peer-reviewed paper published this year by a research team of University of Washington, state Department of Natural Resources and U.S. Forest Service scientists caution that such tactics won’t do much to tame or head off west-side fires, which are forecast to happen more often

“We can think of the Norse Peak fire as a kind of tip of the iceberg of what these fires have been in the past and will be in the future,” said Brian Harvey, a University of Washington forestry scientist and one of six co-authors of the fire-science article “Nature of the Beast” that appeared in the March 2018 edition of the journal Ecosphere.

Harvey is working with graduate students and some of his colleagues to set up research sites within the boundaries of the Norse Peak fire zone to assess what happened to the forest. This is part of a larger effort to survey burn zones across the Northwest, and involves laying out circular plots, each 30 meters in diameter, and taking all kinds of measurements ranging from how much the fire charred the trees to the impact on soils.

Harvey is a recent arrival at the UW, a 37-year-old assistant professor whose earlier research focused on tree regrowth after fires in more arid forests in Montana and Wyoming.

The findings, detailed in a study that he led, show that trees had yet to return to some of the driest edges of burn zones, which were dominated by shrubs and grasses. In other areas, trees did take root, but there were fewer of them than in moister, cooler times.

On the east side, in forests dominated by thick-barked ponderosa pine, low-intensity fires in centuries past often came every five to 30 years, clearing out brush and small trees. In the 20th century, decades of human intervention, in the form of fire suppression, sometimes squelched that natural fire cycle, allowing big buildups of fuel. In recent years, restoration efforts are aimed at bringing those forests back to a more natural balance.

But wetter forests, such as the stand torched in the Norse Peak blaze, have a very different relationship with fire. They burn infrequently but the toll on the trees often is severe. Trying to head off these fires would require thinning these public lands every decade or so, and that would change the natural character of these lands in what Franklin calls a “fool’s exercise.”

There also are benefits to these west-side fires, which Franklin says can act as powerful sources of forest renewal.

Within the Norse Peak burn zone, some of the dead trees eventually will topple. Many more will gradually drop off pieces of their trunks until only short snags remain. More sunlight will reach the forest floor. That will usher in a spectacularly productive few decades of the forest cycle, when a profusion of plants and shrubs such as huckleberries will provide nourishment for mammals, reptiles and amphibians.

It remains unclear just how the west-side forests will be reshaped by this warming world. Harvey hopes that the Norse Peak study sites can be used to launch a decades-long monitoring effort to help answer the question.

“I’m still early in my career,” Harvey said. “This is a really unique opportunity to look one, 10 and 30 years down the road and track this system as it’s changing.”

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