Climate Change is Transforming Western Forests. And That Could Have Big Consequences Far Beyond Wildfires.

A VETA — From her family’s summer cabin north of Walsenburg, Camille Stevens-Rumann could see the glow of the Spring Creek Fireon the ridge to the south in the summer of 2018. “It was pretty spectacular, my 4-year-old was excited,” she said

This past June, Stevens-Rumann walked a burnt slope near the town of La Veta, a piece of the more than 100,000 acres ravaged by the fire that raged for more than two months. No tree survived on this hill, a vista of scarred black pillars that stretched in all directions.

Stevens-Rumann, a 33-year-old assistant forestry professor at Colorado State University, was there to measure and mark what comes next. In all likelihood, the ponderosa pine forest that had been there would not return.

Aspen and scrub oak have already sprouted, but all the pine trees and their cones were destroyed. No pine saplings poke through the charred soil.

Across the Rockies and even into the Sierra Nevada and the Pacific Northwest’s Cascades, forests are changing or simply vanishing. Wildfire has played a big role. Insect infestations have also had a hand, as has drought.

Behind it all is one driving force — climate change. Scientists charting the fate of forests see it, whether they are entomologists or botanists or wildfire ecologists like Stevens-Rumann. The heat of a warming planet, like an artist’s palette knife on a canvas, etches its way across Western forests, slowly altering ecosystems that have flourished for centuries.

“We are really moving out of a climate that is suitable for forests,” Stevens-Rumann said. “Old trees can persist, but when change comes in a disturbance like a wildfire and the ecosystem resets, the forests don’t come back.”

The transformation isn’t quite that simple. Lower elevation forests, like those along the Front Range, are most at risk, but as the forest rises into the mountains, the nature of the woods may change with spruce, fir and pine competing for survival even as new pests push into those higher, and now warmer and drier, mountain reaches.

“As ecosystems change, there are going to be winners and losers,” said Thomas Veblen, a biogeographer and distinguished professor at the University of Colorado. “The regulator function of the forest could diminish … leading to more runoff and flash floods. With a reduction of the forest canopy, we are going to see the potential for greater erosion. The question is how much of the forest will fail to regenerate.”

Fire changes the forest’s composition

Colorado’s Front Range has had five ecotones — shifts in plant and animal communities — from grasslands at 5,500 feet above sea level to alpine tundra at 11,300 feet.

“When we go to higher elevations under warming temperatures, we do expect the species from lower elevations to do better after a fire or other disturbance,” Veblen said.

After six years as a forest firefighter in an elite hotshot crew, Stevens-Rumann, curious about what happens after the fire is out, became a wildfire ecologist.

In a study of 1,485 sites that burned in 52 wildfires in forests from Colorado to northern Idaho, a team led by Stevens-Rumann found tree regeneration was significantly reduced at the sites that burned after 2000.

Fewer than half the spots had signs of growing back with a density of trees similar to the pre-fire forest, and nearly one-third of the sites had no trees at all.

These forests ranged from lower elevation dry conifer forests, containing ponderosa pine and Douglas fir, to moister conifer forests of Engelmann spruce and lodgepole pine. The highest elevation forests in the study were around 9,000 feet.

The researchers measured the site temperatures and moisture, and classified the areas by the severity of the burn.

It appeared that the hotter and drier the site, the less chance of a forest coming back. “There is an ecotone shift already underway,” Stevens-Rumann said. “We may see aspen and scrub oak replace pine and at higher elevations, maybe pine replace fir.”

This is happening across the Front Range. An analysis of five Front Range forest fires between 1996 and 2003 — Bobcat Gulch, Overland, High Meadow, Buffalo Creek and Hayman — found that 23% of the forest cover has been lost.

“Below 8,200 feet, we saw little generation; above 8,200 feet, where it tends to be cooler and moister, we saw more,” said Marin Chambers, a researcher at the Colorado Forest Restoration Institute and the study’s lead author.

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