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How prescribed burns could help forests withstand disease and heat

Research in Montana shows that low intensity fires that frequently clear out overgrowth boost the trees’ immune systems against hotter, out-of-control wildfires, drought and bark beetle infestations.

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Firefighter Andrew Pettit walks among the flames during a prescribed fire in Cedar Grove at Kings Canyon National Park, Calif. on June 11, 2019. The prescribed burn, a low-intensity, closely managed fire, was intended to clear out undergrowth and protect the heart of Kings Canyon National Park from a future threatening wildfire.

Brian Melley, Associated Press

The weather is warming, the ground is drying and all across the West two things are becoming evident as summer nears: there is not enough water and fire season could be brutal. 

Out of control, high severity fires are becoming increasingly frequent and threaten forests in the West. Nearly 6% of forests in the Sierra Nevada are at risk of conversion — a process where grassland or invasive species take over previously forested land, and somewhere between 1.6%-15.1% are threatened in the Intermountain West according to a paper published in BioScience. Warming temperatures and the advent of “wildfire season” has meant transitioning landscapes and an uncertain future for the West’s forests.

But with the anxiety and days of smoke filled skies imminent, a signal of hope has emerged from research that’s been taking place over several decades in the Bitterroot National Forest of Montana. 

Research in the Lick Creek forest started in the 1980s after scientists started conducting prescribed burns and thinning. The area was not pristine — logging and decades of fire suppression had taken their toll. After the initial restoration work in the early 1980s, researchers continued monitoring the land and found that not only did the prescribed burns help prevent high severity fires, but had wide ranging benefits that increased the forest’s resilience to drought and bark beetles. 

Researchers with the U.S. Forest Service and the University of Montana wrote in the journal Frontiers in Forests and Global Change last summer that the Lick Creek forest supported previous research that found “fuel reduction and restoration treatments are most successful with a combination of cutting and burning strategies, but also show that fuel treatments in low-elevation dry forests will likely not remain effective for much longer.”

There was a time that fire wasn’t considered crucial to healthy forests in the West. In fact, preventing any type of forest fire in last half of the 20th century became the practice and policy of government land management.

With rapid settlement of the region came the end of the low severity fires that scientists now understand (and indigenous communities already knew) are crucial to the health of many types of forests — especially those like the low elevation ponderosa pine forests that are now threatened with hotter, bigger fires that destroy rather than fortify the trees. 

Ponderosa pine trees are naturally adapted to some fire, releasing seeds in temperatures between 113 to 122 degrees. These frequent, low severity fires spur growth by clearing out so-called ladder fuels of brush and saplings.

When a low severity fire goes through a ponderosa pine forest, it’s like the trees get a kind of “boost” to their immune systems, explained Sharon Hood, a co-author of the study and research ecologist with the Forest Service who has been working at Lick Creek Demonstration-Research Forest. 

The trees become stronger, better adapted to harsher environments — from warming temperatures to drought. Ponderosa pines even start producing more resin, which acts as a poison to pernicious bark beetles. “Plants are much more an active participant in their environment than we give them credit for,” Hood said. 

But when fire suppression lets ladder fuels build up, fires become larger, hotter and destroy well established trees.

Researchers found that forests that were cut and burned had a lower mortality rate from bark beetle invasions than those that did not receive the treatment. Clearing brush and thinning forests also meant less competition for water, making ponderosa pines better adapted to years of less rain. 

These findings are critically important as the West contends with a shifting climate and decades of poor forest management that have resulted in the loss of many forests that may not grow back

“It’s not a question of if the fires are going to occur, but when,” Hood said. And not just fire, but drought and bark beetle invasions as well. 

Prescribed burns must start sooner rather than later, she explained, and it must be consistent. 

In the Lick Creek forest, fire historically burned through the area every 3 to 30 years. Researchers are hoping to go back this spring and conduct another prescribed burn after a little more than 20 years — some Douglas Firs have already grown so tall though that there is some fear about controlling the fire. “Ideally these forests would have been burned 10 years ago,” Hood said. Prescribed burns are not a one time fix, but they are an important tool. 

Population density and development near forests make it unlikely that forest fires will be allowed to burn unchecked again, but allowing lower severity fires to burn in more controlled ways could hold the key to making forests healthy again. 

“It’s a shift to realizing that fire is part of our Western forests,” Hood said. “We’re learning how to better live with that reality so we can have fire more on our own terms.”