NOT FAR BEHIND the ranger station, the forest ends. Sunlight floods over grasses, wildflowers, and burnt trunks still standing after the most recent wildfire. The 2013 Thompson Ridge Fire charred the ridgeline by the Cabin District, charging toward the old ranch buildings and one of the last remaining stands of old growth in the Valles Caldera National Preserve.
It’s hard to miss the blackened trees and bare slopes, so Ranger Adam Dean often gets asked, “When was the fire?” To which he replies, “Which one?”
The Cerro Grande Fire started near the preserve’s eastern boundary in 2000. Las Conchas Fire swept through in 2011 on its way to becoming what was then the largest fire in state history. Two years later, the Thompson Ridge Fire left more of a mosaic pattern but damaged a site sacred to the Jemez Pueblo. In total, more than half the 88,900-acre preserve has burned in the last two decades.
Wildfires have always been a part of the Jemez Mountains. But recent blazes, fueled by changes to the forest and the climate, have been more extreme and more devastating. Dean and other rangers lead fire ecology hikes, talking through these changes and what the National Park Service is doing to create more fire-resilient forests.
In a healthy Southwestern ponderosa pine forest, wildfires browse through every decade or so, thinning trees and clearing the understory. The resulting forest sees loosely scattered trees over wildflowers. A mature ponderosa pine’s thick bark insulates it from burning and drops lower branches to keep fire from climbing into the tree canopy, where it more easily spreads tree to tree. Thousands of acres could burn, but leave the trees looking lightly toasted, while the soil and grasses underneath enjoy a reset.
Wet mixed conifer forests, as are found at higher elevations and on some north-facing slopes in the preserve, also burned, but in smaller footprints that left a patchwork of meadows and aspen behind.
Now, both types of forest are seeing wildfires that wipe out every tree for thousands of acres, a shift driven by a few factors. Perhaps learning from the positive effects of lightning-induced fires, Indigenous residents of what’s now New Mexico set fires to drive wildlife toward hunters and clear soil that often then sprouted with edible plants.
When colonists arrived, that practice stopped. Overgrazing left no grass to fuel fast-moving, cooler fires that big trees can survive. Clear-cut logging took out most of the preserve’s forest, and what’s since regrown came in thick, branches tangling together over a knotted understory. When a forest like that burns, the whole thing goes up in smoke.
“When you change the age structure and the species composition of forests by logging, by grazing, by keeping fire out of forests, you change the entire relationship of this complicated system,” says Rachel Loehman, a fire ecologist with the U.S. Geological Survey. Anthropogenic warming—a faster and unprecedented change in the climate—also contributes.
The Park Service is trying to restore the forest to what it might have looked like before the Spanish arrived in the 1600s by thinning and burning piles of cut trees and brush and, potentially, returning fire to the ground through prescribed burns.
“If you think about it from the standpoint of a ponderosa pine tree, which is about 400 years old, human-driven climate change is only a very short part of that tree’s life,” Dean says. “This whole period will actually be pretty short in the life of a tree, which gives me hope.”
Read more: National Park Service staff has stocked the calendar with events that offer gateways for visitors to connect with the caldera.
