When a tree brushed against a power line in the Jemez Mountains two months ago and sparked a wildfire, officials at the Valles Caldera National Preserve were immediately worried that the blaze could destroy the historic lodges, biodiversity and compelling landscape that draws tourists and scientists year round.
After all, officials worried, the fire was ignited roughly in the same unhealthy forest, due to the same cause and under the same parched conditions as the Las Conchas Fire, which, in 2011, left more than 150,000 acres charred to a crisp, creating a blackened “moonscape” that will take centuries to recover.
But the Thompson Ridge Fire surprised firefighters and others when it slowly crept along the forest floor, only occasionally torching trees or burning at the high intensity that New Mexico forests have seen over the last several years – fires attributed in part to drought conditions and higher average temperatures.
“If you’re going to have a wildfire, this is not a bad fire,” said Valles Caldera executive director Dennis Trujillo. “When you look at the low to moderate (burning), there’s still enough organics in that soil to hold moisture, to allow plants to grow.”
Just 640 acres of the almost 24,000 acres that burned in the Thompson Ridge Fire burned at high intensity, which means that the flames leapt from treetop to treetop and destroyed everything in their path from the needles on trees to the organic matter in soils.
Those acres were part of a section of the Valles Caldera slated to be thinned in 2015.
More than 18,000 acres at the fire burned at low intensity, and the rest of the fire burned at moderate, meaning the flames aren’t just crawling along the ground but they aren’t leaping from treetop to treetop, either.
The low intensity came as a huge relief to Robert Parmenter, the preserve’s chief scientist, especially because fire officials decided early on to step back and allow the fire to burn wherever it wanted inside the 24,000-acre perimeter.
In the last decade or so, fire managers have begun treating wildfires differently, focusing on the big picture and forest health over the immediate suppression of fires that don’t threaten structures. The historic lodges at the preserve got special protection, but the fire had free rein everywhere else.
“The surprising part is that because the firefighters did not try and put anything out in the middle, we thought it would turn out worse than it did,” Parmenter said.
Doing some good
A low-intensity fire can be beneficial for a forest because it allows a cleansing of some of the unhealthy vegetation built up over the last century while still retaining older, healthier trees that provide cover for the new wave of plants.
High-intensity fires char and blacken everything in their path. Such fires not only devastate the forest, but they leave soils prone to erosion by floods from rains that typically hit New Mexico after peak fire season.
The low-intensity Thompson Ridge fire leaves the Valles Caldera well equipped to recharge its forests and promote biodiversity, Parmenter said.
Just a month after the blaze was fully contained, patches of aspen trees are already 6 to 8 inches, he said. They’ll be a foot tall by September.
When the aspens grow, they’ll provide shade for an undergrowth, which will thrive and ultimately surpass the aspens, creating a healthy mixed-conifer forest.
Still, the Thompson Ridge burn scar will be prone to flash flooding in the next few years. After the blaze stopped smoldering July 1, the Thompson Ridge Burned Area Emergency Response team swooped in to prepare the area for flash floods and help it recover.
But the older Las Conchas burn scar on the preserve still poses the biggest flooding risk, Trujillo said. Trujillo went out into the forest recently to look at flood damage and to monitor erosion.
“We went out and looked at it, and the flooding was from the Las Conchas Fire,” he said. We’re still seeing a lot of runoff and ash flow from the Las Conchas Fire.”
Temps and topography
The Thompson Ridge Fire burned at such low intensity thanks in part to luck and also to the environment.
Parmenter said the two fires were in similarly unhealthy forests, meaning both areas were not logged and thinned recently enough to avoid the buildup of fuels that allows fires to burn quickly, destructively and at high intensity.
Wind speeds and relative humidity were “very comparable” during the early days of both fires, Parmenter said. The major differences between the two fires had to do with initial temperatures and topography.
The area where Thompson Ridge ignited was about 15 degrees cooler on the day it started than in the early days of the Las Conchas Fire. In fact, that part of the Jemez Mountains got below freezing the night of the blaze.
The Thompson Ridge Fire burned in a month what the Las Conchas Fire burned in half a day.
Also, topographic features like ridges kept the Thompson Ridge Fire from gaining too much momentum. Once it crested the Redondo Border northwest of Redondo Peak, it slowed down immediately.
From that point on, firefighters, who also worked quickly to establish fire lines, largely had to worry only about spot fires. They didn’t have to worry about the massive head fires that propelled the Las Conchas Fire into the record books at what was then the largest fire in recorded state history.
“Las Conchas was an inferno compared to Thompson Ridge,” Parmenter said.