Confronting the Climate Impacts to Rocky Mountain Forests: From the Statistical to the Visceral

I was in Colorado a short time ago to release “Rocky Mountain Forests at Risk,” our latest report on the regional impacts of climate change. The report focuses on how climate change has amplified the effects of tree-killing insects, wildfires, and stress from heat and drought — what we called a “triple assault” — on forests. But my work on the report didn’t prepare me for the scene that confronted me on the ground. 

These three factors have probably been killing trees in the Rocky Mountains for millennia, and the forests have co-evolved in response to them. So what’s different now? In the past few decades, we’ve seen the rapid pace of climate change tip the balance in favor of these destructive elements, and as a result, trees in the Rockies have succumbed on a scale never seen before in our country’s history.

Fast-changing climate could transform the Rocky Mountain landscape

After months of research and work on the report, I had become a bit numb to the daunting statistics. More than 46 million acres of forest have been devastated by bark beetles, an outbreak nearly as large as the state of Colorado itself. The area burned by wildfires has increased nearly seven-fold in the past three decades—partly due to a policy change at the U.S. Forest Service, which allowed more fires to burn—but mainly due to warmer, drier conditions that have fueled larger, more frequent wildfires. And even in forests undisturbed by insects and wildfires, the tree mortality rate has more than doubled across the West, likely due to increased stress from heat and drought.

My co-authors and I also looked ahead at what is likely to happen to the forests if the globe fails to slow the pace of climate change. Working with U.S. Forest Service scientists, we examined projected areas of “climate suitability” for a few common tree species in the region. The projected areas of “climate suitability” show where future climate conditions would allow the species to persist.

When we dug into the data, what we found was staggering. If carbon emissions continue to increase at their current pace for the next 40 years, widespread species like ponderosa pine, lodgepole pine, Englemann spruce, and Douglas fir could die off in most of their current ranges. The losses of climatic suitability for these species ranged from 60 to 90 percent. The resulting change in the region’s character was hard for me to imagine.

Tree mortality may signal that the transformation is already underway

To get a better sense of what this massive die off would look like, I joined photographer Steven DeWitt on a hike near Vail, Colorado. Over the past 10 years, Steven has witnessed the effects of climate-driven tree mortality, as well as the forest management response. “You’ve got to see it with your own eyes,” Steven told me. “You can’t grasp everything that has happened just from reading the studies.”

I’m no stranger to forests in Colorado and the northern Rockies. Over the past several years, I have hiked in a number of them. I was accustomed to seeing red-needled trees that had been killed by bark beetles, and tiny holes in the sides of trees, often highlighted by popcorn-shaped clumps of resin, or “pitch-outs,” where the trees had tried to flush out the attacking beetles.

The scene that greeted Steven and me last week, however, was much more dramatic. We were in a landscape partway through an extraordinary transformation, and the attempts to manage this transformation seemed clumsy and piecemeal in comparison to the efficiency and extent of the impacts.

Entire valleys, once cloaked with vigorous, dark forest, now were drained of color, replaced by a bristly grey stubble of dead trees. As we drove deeper into the forest on a logging road, the skeletal trunks of lodgepole pines, devoid of needles, left an impression of what had been lost, reminding me of the rows upon rows of pale grave markers covering the sweeping hillsides of Arlington National Cemetery.

The few trees that were still alive were not faring well. We stopped alongside a sickly aspen tree.

“They bleed,” Steven pointed out. “When they are infected with cankers, a red fluid pours down the side of the white trunk, and it looks like blood.” I suspected this was some kind of fungus staining the sap, and the effect was indeed ghastly. Other aspens were riddled with black holes or patches of dead bark, encrusted like scabs over infected wounds.

Seeing these impacts first-hand put the projected losses of aspen into a new perspective.  Unabated climate change would mean an unsightly and disruptive change for the forests.

Forest management needs to improve, taking climate change into account

We reached a clearing with a wide-angle view of the phantom forest and distant mountain peaks. Nearby, logging equipment sat at the edge of a recent clear-cut, and we could hear the buzz of chainsaws over the next ridge. As we ate lunch, Steven explained that this was just the latest in a series of logging operations that had harvested areas of the forest to try to limit the spread of the beetles and reduce the risk of wildfire. The clear-cut looked raw and ugly, punctuated by stacks of beetle-ridden logs.

I know logging can be done sustainably to maintain forest health, but I was skeptical that this exercise would have much effect in slowing down the beetles, though it might reduce the risk of wildfire. Hitting the “reset” button on the forest might allow young trees to grow up in a few years, but it just might provide a smorgasbord for the next beetle outbreak. With each boom and bust cycle, the forest would gradually lose its regenerative capacity.

As we drove down the mountain, we passed a sparse stand of dead and dying trees. “They logged that area a few years ago, taking out the beetle-infested trees and leaving the living ones,” Steven said. “But in the next few years, the beetles killed the rest of the living ones.” Even the best attempts at management had been overwhelmed by this outbreak. “Look, those trees haven’t even made any pitch-outs,” he said. “The hillside must have dried out, and they just couldn’t produce enough resin. Their defenses were gone.”

Science is clear: we have a choice about the future of Rocky Mountain forests

To prepare our new report, my co-authors and I pored over more than 180 sources, all from peer-reviewed independent and government studies that document the links between climate change and the three agents of the “triple assault.” As comprehensive as we were, that scientific knowledge didn’t prepare me for the reality of what is happening on the ground.

Without rapid action to slow the pace of global warming, the scene I witnessed last week will only become more commonplace in the West. What used to be an unbroken landscape of trees will be replaced by gray sentinels, and the silence of the phantom forest will only be broken by the sound of chainsaws as crews salvage what remains of these once majestic forests.