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Lovely, Dark and Deep: “Good Burns” in the West Texas Sky Islands

guadalupes-bowl-for-web
photograph by Andrew Stuart. Along with the Chisos and Davis, the Guadalupe Mountains are one of West Texas' three “sky islands” – isolated pockets of forested terrain rising above desert “seas.” In the Guadalupes' highlands, agaves and chollas grow beneath pines and firs.

Catastrophic wildfires have become numbingly familiar in the 21st Century American West. Smoke often obscures the summer sky. Air quality becomes dangerous. Homes are threatened or destroyed. Lives are lost. The causes are likewise familiar – climate change is making a dry region even drier, and hotter. And after a century of suppressing wildfires, forests have become tinderboxes, loaded with fuel. 

Does this story apply to West Texas? Certainly we've tasted fire. Since 2011, all three of our “sky islands” – the Chisos, Davis and Guadalupe mountains – have burned. And for local communities, the drought-driven fires of 2011 were painful indeed. Dozens of homes and businesses, along with livestock and ranching infrastructure, were destroyed, from Fort Davis to Midland County.

But our region is unique. Dr. Helen Poulos is a plant ecologist at Wesleyan University, who's spent 20 years studying forests and fire in the Chihuahuan Desert borderlands. These mountain woodlands, she's found, have a distinctive ecology and history. And in many ways, Poulos said, recent forest fires have been “good burns,” offering hope for the future of these special places.

The Guadalupes, Davis and Chisos mountains – as well as the Maderas del Carmen, opposite Big Bend National Park in Mexico – are classic “sky islands” – isolated pockets of forested terrain rising above desert “seas.” But when Poulos began her work here in 2003, as a PhD student, they'd received relatively little scientific attention. 

“These are all sky islands out here,” Poulos said. “It's just that nobody in Arizona cares about them. And that actually was one of my entry points into my research in West Texas. The main thing is nobody really had studied this area much. It's sort of forgotten – because it takes six hours to get there from the airport.”

Poulos partnered with The Nature Conservancy's Davis Mountains Preserve, with Big Bend National Park and with Mexico's Maderas del Carmen Protected Area – and set out to unlock the secrets of these forest redoubts. Reconstructing their wildfire history was an important thread.

Scientists have a general narrative of wildfire in western North America. Periodic fire is a natural feature of mountain forests here. Many plants are adapted to low-intensity fire – some even require it. But in much of the Southwest, wildfires ended in the 1880s, with the introduction of cattle. 

As cattle filled the highlands of Arizona and New Mexico, they grazed away the grasses that allow fires to ignite and spread. Then, aggressive fire suppression became government policy. Fuels accumulated, setting the stage for the devastating, high-intensity fires we see today.

To test that story here, Poulos headed into the mountains, to sample “fire-scarred” trees.

Fires can leave their mark on a tree's growth tissue, without killing the tree. And a tree that's scarred once tends to be scarred again in subsequent burns – preserving a record of multiple fires. By matching the scars to tree ring data, Poulos dated more than 500 fire scars in the Davis, Chisos and Carmen mountains – and traced the history of fire here since the 1700s.

She found that wildfire in the Chihuahuan Desert borderlands has a character of its own.

Historically, fires occurred in these ranges every five to nine years – any one location burned every 15 to 25 years. And historic patterns continued here much later than in points farther west. In the Chisos and Davis mountains, regular fires continued until the 1920s – after that, the time between fires doubled. A similar pattern applies in the Guadalupes. In the Carmens, the historic pattern continued up to the 1950s.

The explanation is found at the intersection of topography and history, Poulos said. 

“History is very important,” she said. “There's this ecological memory in these systems. What we see out on the landscape today – people don't realize that that's actually a legacy of historical climate patterns, human land use, fire regimes, and all those things.”

Cattle ranching boomed here as early, and as intensely, as anywhere in the Southwest. But grazing in the mountains was apparently limited – perhaps because the ranges are so rugged, and largely dry. It seems to have been a different class of livestock that changed fire patterns here: the end of periodic wildfires corresponded with a boom in sheep and goats.

And the Maderas del Carmen have their own distinctive history. There was no 19th Century ranching boom there. And in the early 20th century, Pancho Villa's insurgency was an effective barrier to development. It was until after the Mexican Revolution, when land was redistributed to create communal “ejidos,” that people came to the Carmens to graze livestock in numbers. 

There's another way our sky islands differ from those elsewhere: the seasonality of fire. Most Southwestern forest fires occur in summer, triggered by monsoon lightning. But in the fire scars, Poulos found that historically 75 percent of wildfires here occurred in spring. It's perhaps no surprise – recent forest fires have come in April and May.

“So that's been one of the most interesting things in all the work I've done,” Poulos said. “These systems are similar, but they're not exactly the same. They're somewhat unique in some ways – and that's pretty cool.”

A hiker in the West Texas mountains is struck by the blending of Chihuahuan Desert and Rocky Mountain flora – agaves and chollas grow beneath pines and firs. But the true “mainland” for our sky islands is the Sierra Madre Oriental – the great range that runs for 800 miles through eastern Mexico.

The Chisos and Davis include the northernmost populations of an important Sierra Madre species: Pinus cembroides – Mexican pinyon pine. Pinyons elsewhere in the western U.S. are typically wiped out in large fires, but pinyons here have evolved to thrive with regular, low-intensity fire. 

Since 2011, natural forces and human choices have collaborated to bring fire back to the West Texas mountains. That year's record-breaking drought drove multiple fires through the Davis Mountains. In 2016, the Coyote Fire burned the Guadalupes' densely wooded uplands. And the Chisos burned in 2021, in the South Rim Fire.

But these fires weren't forest-devastating events. They mostly burned at low- to moderate-intensity. Dense thickets that had developed during decades of fire suppression were cleared, freeing up water resources for the trees that remain.

“There's not very much good news about wildfires,” Poulos said. “But these fires may have very well increased the health and resilience of these forests to future disturbances.”

There are areas of concern for our sky-island forests – especially with the biggest trees, the Ponderosa or Arizona pines. These trees are “climate relics” to begin with – the old trees date to a wetter, cooler past. Sustaining them here will take focused conservation efforts, and foresters are working to grow drought-resistant pines for planting. 

But with a natural and human history that sets them apart, there's reason to think our region's sky islands have a distinctive future as well. 

Drew Stuart is the producer for the Marfa Public Radio series Nature Notes.
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