The West Texas sky islands are hidden worlds, zones of mystery amidst the desert expanse. Charismatic creatures haunt the shaded canyons of the Chisos, Davis and Guadalupe mountains — bears and mountain lions, deer and elk, foxes and ringtail cats. In summer, you glimpse whirring hummingbirds, and colorful songbirds up from the tropics.
But there's one particularly graceful being concealed in these heights: Populus tremuloides, the trembling or quaking aspen. New research into West Texas aspens could shed light on their history, and on the continent-wide story of this iconic species.
Dr. Chen Ding is a forestry professor at Auburn University.
“These populations are very important,” Ding said of the West Texas aspens. “We can learn the species history, the evolutionary history. I hope we can find something new this time.”
An aspen specialist, Ding recently collected hundreds of West Texas leaves for analysis.
It wasn't easy. Aspens in Guadalupe Mountains National Park are far from a trail. A Big Bend National Park stand grows on a rocky slope below Emory Peak. The most robust stands are in The Nature Conservancy's Davis Mountains Preserve, Ding said.
“There are multiple stands preserved beautifully there in the Davis Mountains,” he said. “That's kind of a treasure you have in that area.”
Aspens thrive today in Canada's boreal forest, and in the Rockies. According to statistical models, West Texas aspens shouldn't exist at all. They're likely Ice Age relicts. In that cooler, wetter time, aspens may have flourished widely here. Now, the sky islands are their final sanctuary.
Aspens can grow from seedlings. But often a stand shares a common root system. A 108-acre stand in Utah, known as “Pando,” is thought to be the world's largest land organism. Genetic analysis could reveal whether each West Texas grove is in fact a single being.
“If the stand is one genotype,” Ding said, “it's really likely they could be a single organism, all of them developed from one huge root system of a tree.”
Ding and his colleagues are reconstructing aspen's continental “colonization.” As ice sheets receded millennia ago, aspens advanced north, into Canada and Alaska. Some came from what's now the eastern U.S. But others spread from the south. The research could show that our aspens are the “grandmother” trees of those that adorn northern forests today.
“You could consider Texas would be a source or founder for some of these populations, potentially,” Ding said.
The West Texas aspens, like stands in Mexico's Sierra Madre and Baja California, are at the limits of their endurance. Their future would be tenuous even without human-driven climate change. But as heat and drought intensify, the trees become more vulnerable to pathogens. And their clonal reproduction means they're still “wired” for the Ice Age.
“They adapted to the climate thousands of years ago, when it was much cooler,” Ding said, “with higher moisture, and you had more space to grow. But right now, it's a totally different climate. You have a maladaptation, and the trees may die.”
Indeed, there have been “die-backs” here. But Ding said there are also opportunities. While they're hard to reach, aspens can be seen from South Rim trails in Big Bend. Visitors could be encouraged to appreciate these trees, whose leaves ripple and shine like a mountain stream, and flare up each fall in golden splendor. Appreciation would drive conservation.
“We could try to let people know that, 'Here are these trees. Some of them may live happily here, but some of them are dying,'” Ding said. “And maybe year after year there will be more attention to the aspen in this little area.”
In addition to Ding, the team of scientists studying West Texas aspens include Dr. Fred Raley and Mickey Merritt of the Texas A&M Forest Service; Jerritt Nunneley of the Southwest Research Institute; Dr. Ilga Porth of Lavar University; and Dr. Benjamin Blonder of the University of California, Berkeley.
