William Melhado
Highly burned soils don’t absorb precipitation well, experts say, and the resulting movement of water across the landscape strips the land of earth and nutrients necessary for the forest’s recovery.
In the aftermath of a forest fire, the public’s eye is drawn to blackened hills and charred structures. But the story of a wildfire’s severity—and the forest’s future—is often buried beneath the soil.
The dirt plays a vital role in a forest. Analyzing it offers insights into what will happen to a landscape following a wildfire.
In the already-burned areas of the Hermits Peak/Calf Canyon Fire, scientists have begun the work.
April Ulery, a professor of soil and environmental sciences at New Mexico State University, tells SFR that soils have an outsized impact on a forest’s ecosystem, more than most would imagine.
“It provides a home for microbes and nutrients and life as we know it really wouldn’t be possible without soil,” Ulery says.
The extent to which soils have burned tells scientists about a fire’s intensity and whether the earth will absorb rain, or lead to the kind of flooding and erosion so commonly seen after devastating blazes. With monsoon season around the corner, many have concerns about post-fire effects.
Ulery says soil is not technically flammable, but organic material and microbes living in the earth can burn or be lost.
“One of the biggest issues with forest fires and their effect on soil is that if you denude the landscape, if you remove all of the plants above the soil, then you expose it to more heat or temperature variations, and erosion becomes a huge problem,” Ulery says.
Without vegetation to hold it in place, wind and water can move the soil. Additionally, soil exposed to rain and heat can prevent regrowth of vegetation. In places like New Mexico, an arid environment, “We’ve seen that those consequences can last for years,” Ulery says.
Todd Ellsworth, the Burned Area Emergency Response team interagency coordinator, has been working with partners from several agencies to evaluate what those consequences will be for the Hermits Peak/Calf Canyon Fire.
The group is developing post-fire preparation plans to protect assets downstream of the fire, from bridges and buildings to the City of Las Vegas’ water supply.
“Fires have this one-two punch, a lot of people forget about this. The first punch obviously being the fire, you know, devastating effects that can burn homes, obviously forests,” explains Owen Burney, the director of NMSU’s John T. Harrington Forestry Research Center, based in Mora.
“The second punch is massive amounts of erosion and flooding,” Burney says. He adds that flooding complicates the restoration process, because it’s difficult to know “where we can plant trees where we won’t lose them due to those erosive forces.”
Burney notes it’s still too early to make generalizations about the severity of the fire. It’s still active and much of the initial assessment resulting in the soil burn severity map for the southern portion of the Hermits Peak/Calf Canyon Fire was completed with remote sensing.
“Boots on the ground are critical” to verify the maps that are already available, Burney tells SFR.
But based on those maps, Ellsworth says, the severity of the fire is similar to other large blazes such as the 2011 Las Conchas Fire and the 2000 Cerro Grande Fire.
“It’s bigger, for sure,” Ellsworth says, “but then in terms of severe burn, we’ve seen other types of severe burn in New Mexico before.”
Compared to the Cerro Pelado Fire, the percentage of highly burned soil in the southern part of the Hermits Peak/Calf Canyon Fire is larger: 21% of the acreage analyzed was burned to a high severity, while only 1% of the 45,605-acre fire 7 miles southwest of Los Alamos was burned to that same degree.
Those figures include just the Phase 1 assessment area, the headwaters of the Gallinas River and Tecolote Creek. Phase 2 will cover the northern area of the fire, including the Sapello River Watershed, Upper Mora Watershed and portions of Embudo Creek Watershed. It began June 6.
Nearly 20% of the acreage impacted in the 2011 Las Conchas Fire burned at a high severity.
Amidst the blotches of red on the burn maps, a mosaic of yellow and green indicates that parts of the forest burned at moderate or low levels. Experts note that high-severity burns aren’t unnatural, but the scale of those intense fires is increasing in frequency and size.
“As you increase in burn severity, the ability of the landscape to soak up water is reduced,” Adam Atchley tells SFR. He notes this is a generalization, and there are many factors that impact soil’s ability to absorb water, but in his research as a hydrologist with the Los Alamos National Laboratory, this relationship is broadly true.
Soils burned to a high severity are especially water resistant, due to several complex and “super dynamic” factors, Atchley says. A loss of vegetation and a post-fire property of soil known as hydrophobicity, which Atchley likens to waxing a car, are two reasons soils remain dry during significant periods of rain and result in “flashy runoff events.”
Those events can be significant. He points to the 2017 Thomas Fire in Southern California that resulted in mudslides that killed 21 people.
Atchley notes the upcoming monsoon season presents the greatest risk to communities in the Hermits Peak/Calf Canyon Fire footprint, but flooding events could continue for three to seven years.
In areas not so significantly burned, the fire can help soils absorb water and maintain the forest’s health. Given the increasing severity and frequency of fire events—due to climate change and decades of fire suppression—Atchley acknowledges the need to minimize the bad effects of wildfires.
“We also need to recognize that fire can help water resources,” he counters.
Restoration will require unprecedented resources, says Burney, who drove the perimeter of the Hermits Peak/Calf Canyon fire last week. At last report, the fire measured 318,172 acres and was 65% contained.
“Now it’s time to step up to the plate and play the game of scale and urgency,” he says. “We need to do things at a scale that we’ve never seen, and we need to do it today.”
