Think Like a Forest

 Photo by  Stephen Eginoire

A Legacy of Wildfires in the West

By Margaret Hedderman

The fading scars of the 2002 Missionary Ridge Fire were an ever-present reminder that it could happen again. All it would take was one long drought, one wayward spark. Sixteen years later, winter never came. Southwest Colorado suffered one of its driest winters on record and locals knew it wasn’t a matter of “if,” but rather “when” Durango’s next big fire would ignite. It happened on June 1st, 2018, approximately ten miles north of town in the bedroom community of Hermosa.

 The initial blaze raced up a steep hillside near the D&SNGRR tracks, quickly outpacing the efforts of local residents who battled the fire with homemade equipment. Within a week, the 416 Fire - as it became known - grew to 7,000-plus acres, forcing hundreds of Hermosa residents to evacuate, closing US Highway 550, and sending heavy plumes of smoke down the valley. Not long afterward, a second flame arose - the Burro Fire. Together, they affected over 50,000 acres in the San Juan National Forest and on private land.

The hot and dry conditions typical of June were exacerbated by the winter’s weak snowfall. The forest was ripe for wildfire. Marching through the tangled and overgrown Hermosa Creek drainage, the 416 Fire burned especially hot in areas loaded with fuel. It charred stands of pine on the steep, rocky terrain overlooking Highway 550 and quite possibly destroyed some of Colorado’s oldest Douglas firs and ponderosa pines. When the rains finally came in early July, flash floods ripped through the burn area, turning the Animas River black. Trout thrashed in the murky shallows, suffocating in the ash and heavy sediments.

It was a grim start to summer. The noxious smell of smoke seeping under the windowsills at night felt unhealthy, unnatural. And yet forests, at least in the American Southwest, have evolved with fire as a natural disturbance. Fire can help shape the character of forest ecosystems, affecting everything from its resilience to future fires to its quality of wildlife habitat.

“When we’re talking about the Western US, these are ecosystems that are very fire prone,” says Dr. Camille Stevens-Rumann, a former wildland firefighter and Assistant Professor of Forest and Rangeland Stewardship at Colorado State University. 

She describes the role fire plays in forest health as “resetting and restarting” and adds that “we need a certain proportion of that on the landscape.”

 Natural fires, which typically burn at a low to moderate severity level, creep through the forest understory, clearing brush and dense foliage. It’s almost like weeding the garden; by removing smaller, competing plants, the larger individuals have more room to grow. Sunlight freely filters through a more open canopy, shining on new seedlings and wildflowers. Fires create meadows, shrublands, and different types of forests, producing a wider variety of habitat for wildlife.

Oftentimes, a fire will burn in a patchwork pattern of severity levels, known as a “fire mosaic,” which provides a diverse range of wildlife habitats within a forest.

“Eagles are often hunting in those open meadow areas,” Stevens-Rumann says. “But then there are certain species that like those dense, closed forests - like the Mexican Spotted Owl.”

Fire mosaics also produce something known as an “ecotone” - or an edge between two different types of habitats. Imagine stepping out of a ponderosa forest into a mountain meadow; or the point where a piñon covered hillside unfolds into a rolling sageland. Species like the mountain lion thrive in ecotones, where they can prowl under the cover of trees, unseen by their prey in open areas.

More biodiverse ecosystems are typically better equipped to combat disease, pest infestations, and even future fire.

“Fire also creates more resilience to disturbances like wind storms or bark beetle infestation,” says Amanda Kuenzi, the Community Science Director at Mountain Studies Institute in Silverton, CO.

 Photo by  Stephen Eginoire

It’s difficult to talk about fire ecology without over-generalizing the subject. What is normal for one forest in one part of Colorado can be different for another forest in a different part of the state. The role fire plays within a forest ecosystem is extremely variable, depending on the region, climate, and type of trees present. But we can say (hopefully without too much generalization), where fire destroys it can also create. Certain species of trees, like the lodgepole pine, actually rely upon its presence in order to reproduce. Found throughout much of the Rocky Mountains, the serotinous cones of a lodgepole pine tree can only sprout when exposed to fire, typically after the parent tree has burned and died. A great example of this is the 1988 fire in Yellowstone where huge tracts of lodgepole pine forest burned. Today, much of the forest has regrown.

You can get a sense of how forests recover from fire simply by taking a hike. Most trails in the San Juan Mountains will likely meander through white stands of aspen bending in the breeze.

“Up around Vallecito Reservoir are some of the best examples of those huge patches created by these recent crown fires,” says Dr. Peter Brown, referring to the Missionary Ridge Fire. Brown is a dendrochronologist and fire ecologist at Colorado State University, who has studied fire history throughout Colorado.

Like gamble oak, aspen is one of the first tree species to come back after a fire. An entire aspen grove is often a single plant, with multiple trees sprouting from a single root system. The Pando aspen grove in Utah is possibly the largest living organism on earth, sharing a single root system that extends over 106 acres. After a forest fire, aspen roots are quick to re-sprout and cover the burn area with new growth.“It’s one thing to sit here and say everything will recover,” says Dr. Donald Falk from the University of Arizona School of Natural Resources and the Environment. “But we don’t know what that recovery projectory will be. There’s no question that the consequences can be very long lasting.”

Like Brown, Falk studies historic fire regimes, determining the nature and severity of forest fires across centuries. Using tree ring analysis to date fire scars, fire historians have been able to look at the presence of forest fires dating back to the 1500s. Of course, studying the size and perimeter of a fire that happened two or three hundred years ago has its challenges.

“Often the tree ring evidence has deteriorated, or the trees have been cut,” Falk says. “It’s really hard for us to draw a perimeter and say where this fire burned in this year.”

Where possible, fire ecologists will setup a grid across a forest and sample a selection of trees to determine the size of historic fires. Studies in the Rincon Mountains of southern Arizona and the Valles Caldera of New Mexico revealed surprising insights.

“We have a lot of evidence that fire area in the past was actually larger than it is today,” Falk says. “For example in the Rincon Mountains, you go back to the 19th Century and in the 1800s alone there were two years where fire was all over the landscape.”

With no one to put them out, these fires would burn for weeks, sometimes months at a time. Inching through a soft bed of pine needles, the fire would flare up when it found a load of fuel, then die back down. Some fire ecologists believe a particular fire in the Valles Caldera actually burned throughout the winter. While fires may have burned a larger swath of land historically, they were rarely the blazing walls of flames that we often see today.

“Everything we see suggests that historical fire was much more at that low severity end,” Falk says.

 Photo by Stephen Eginoire

Photo by Stephen Eginoire

Today’s forest fires burn hotter over a great percentage of land - sometimes tens of thousands of acres - than they ever have. What’s changed? Decades of fire suppression and climate change. Historically, a conifer, ponderosa pine forest would contain 80 to 120 trees per hectare (2.47 acres). Today’s forests are clogged with anywhere from 8,000 to 10,000 trees per hectare. We’ve essentially created a ladder for forest fires to climb from the ground through the understory and into the tree crowns.

Throughout much of the 20th Century, the US Forest Service enacted a total fire suppression regime. Fires were regarded as uncontrollable, destructive forces.

 “There was a policy we had nationally to put fires out by 10:00 am the following day,” Stevens-Rumann says. “We allowed for a lot of fuel buildup in these systems.”

It wasn’t until the 1960s that federal policies began to change. Part of that was due to the discovery that no new giant sequoias had sprouted and grown in the decades of fire suppression. The giant sequoia relies on fire for the germination of its seeds and reduction of competition from other tree species like the white fir. Although we no longer operate under a total fire suppression regime, forest fires are unable to burn as they once did in part because of how populous the landscape has become.

 "Land use is the biggest challenge to contemporary fire management. It’s as consequential as climate change,” Falk says. “It’s basically driving the entire equation right now. You can’t let a fire burn anywhere without hitting someone’s second home.”

 Photo by  Stephen Eginoire

The effects of fire suppression have been compounded by climate change. Historically fire season was limited by lingering snow pack in the spring and the onset of monsoonal rain in the late summer. Today, snow packs are not only weaker than they used to be, but are also melting earlier - sometimes four weeks earlier - allowing the fire season to begin sooner. Fires are also burning longer into the summer and fall. In Arizona, fire season was historically in May and June. Now, the state, which has been beleaguered by extreme forest fires in the last several years, experiences a year-round fire season.

Climate change isn’t just affecting the severity of forest fires; it’s also altering how forests recover. 

“A lot of us are still  in the mindset that climate change is perhaps real, but we’re going to see the changes later,” Stevens-Rumann says. “The truth is that our forests are feeling it right now.”

Stevens-Rumann recently authored a report linking climate change to slower forest regeneration after a fire. She found a significant decrease in the ability of forests to recover in the beginning of the 21st Century compared to the latter part of the 20th. The severity of forest fires is partially to blame. In 2002 the Hayman Fire near Colorado Springs torched thousands of acres, leaving nothing but a charred wasteland. Many of these high-severity fires are burning patches that are as big as the entire wildfire perimeter would have been twenty or thirty years ago.

“Hayman has a 60,000 acre hole where every acre was killed,” Brown says. “It’s still grass shrubland. There’s no recovery at all.”

To regenerate, there needs to be something to regrow from - like a seed or root system. When thousands of acres are destroyed, there is often nothing left to sprout. Ponderosa pine, for example, has a large, heavy seed that usually falls only a few feet from the tree. If an entire forest is destroyed, there may not be any seeds left to form a new forest.

The changing climate also makes it more difficult for seedlings to grow in a new set of conditions they’re not adapted to.

“Trees are most susceptible to mortality when they’re new. Just like humans, we’re more wary of babies getting hurt,” Stevens-Rumann says. “They’re going to be more susceptible to damage under extreme conditions.”

 Photo by  Stephen Eginoire

In places like Missionary Ridge that have been slow to recover in certain areas, seedlings have a difficult time taking hold. On the high, exposed slopes where tall pines once provided shade, new seedlings bake in the relentless sun. The changing climate could cause burn areas to transform into something other than a forest.

“The climate envelope is a big wild card,” Falk says. “It could push the forest into a new state like a shrubland or grassland. We could see a loss of forest habitat - a loss of sequestered carbon.”

 In Durango, there is cautious optimism that areas affected by the 416 Fire will have a natural recovery. An initial report released on July 3rd, estimated that less than 10% of the fire was high severity burn, with nearly 37% of that low severity.

“From what we’ve been able to see at this point, it burned in a mosaic,” says Gretchen Fitzgerald,   the Public Affairs Officer for the San Juan National Forest. “Where it burned low severity, that had an impact that doesn’t need a recovery.”

 It’s likely that the fire created patches of hydrophobic soil where it burned the hottest. Intense heat can cause plant material in the soil to form a waxy layer that repels water, which in turn can lead to severe erosion. When heavy rains swept over the mountains in July, several mudslides washed out roads and covered the train tracks near burned areas. Flash flooding is often a overlooked consequence of major forest fires, but frequently causes more property damage than the fire itself. Many cities have implemented wildfire mitigation programs as a result of extreme flooding.

 Unhealthy, overgrown forests paired with climate change have compounded the destructive effects of wildfires. And the problem isn’t going away. To restore our forests, fire ecologists are looking to the past to determine the best methods of land management.

“We use the historic understanding of disturbance regimes as a model to go into the future,” Brown says.

In Durango, the longterm effects of the 416 and Burro Fires are still continuing to unfold. It will likely be years before we have a good sense of how to the forest will recover. Which, of course, is perfectly natural.

“You have to think like a forest,” says Brown. “Humans have such short attention spans. Ten years for us is a long time, but it’s nothing in the life of a tree.”

 Photo by  Stephen Eginoire