By Andrew Stuart
In broad strokes, the impacts of climate change on West Texas are known. Average temperatures will rise at least 4 degrees by 2050 – and, if global emissions continue apace, 8 degrees by the end of the century. Annual rainfall will likely decline, and droughts become more frequent and intense.
The effects on animals and plants, on the landscape itself, are certain to be profound. But predicting those effects is no simple matter.
On Jan. 18, at Sul Ross State University’s Espino Conference Center, a coalition of conservation groups hosts a conference on the implications of climate change for West Texas. Texas Tech botanist Dylan Schwilk will be a featured speaker. His work highlights the complex interplay between human impacts and the non-human world.
Ramble the Trans-Pecos topography, and one is struck by shifting milieus: from sparse and barbed vegetation near the Rio Grande, to the grasslands of the plateaus, through oak and juniper savannahs in the foothills, to the pines, firs and aspens of the mountains. Generally, the higher the elevation, the cooler and wetter the conditions – and it shows.
As this harsh region becomes harsher still, the basic model projects vegetation moving “upslope,” following cooler and wetter conditions. There’s evidence that’s already happening. But the natural world is too complex to be captured by any generalization.
“One complication is that higher elevation is not always cooler in all senses,” Schwilk said. “Within an airshed, denser cold air flowing down that airshed at night can actually produce colder temperatures down low than up high.”
Schwilk and his colleagues placed temperature sensors in the Chisos, Davis and Guadalupe mountains. The phenomenon of “cold-air drainage” is well-established. But Schwilk was struck by how pervasive it is in the Texas mountains. In late winter, freezing events are much more common at lower elevations than higher ones.
“In some of these mountain ranges, the Davis or the Chisos especially, it’s freezing almost every night in March at 1,500 meters, where the junipers and gray oaks are,” Schwilk said, “and it’s freezing one or two nights in March at 2,200 meters, in the Southwestern white pine.”
The timing of freezing events is critical for plants. Warming temperatures could actually allow some plants – succulents among them – to move downslope.
Projections for how climate change will rewrite the landscape are also complicated by the sheer intricacy of our local flora.
The Texas mountains sustains a diversity of oaks, many unique to the “sky islands” of the Southwest and northern Mexico – Emory oak, Chisos red oak, silverleaf oak, and others. These related trees might be expected to respond similarly to the pressures of drought and wildfire. But Schwilk’s team found just how finely adapted they are to specific niches in the landscape.
Schwilk and a graduate student looked at the oaks’ “bark allometry” – how bark thickness develops during the trees’ lives. They found that some oaks, like the silverleaf and Chisos reds, favor relatively wet locations like canyons, while other oaks – including the Gambel’s and Emory – prefer drier settings.
Wildlfire is more frequent, but less intense, in dry, open slopes. Canyons are less likely to burn, but burn more intensely when they do. Bark development seems to reflect those realities. The oaks that favor dry areas invest early in thick bark, whereas the bark of canyon-dwelling oaks thickens more evenly over time.
“It showed that these trees which are often thought to be playing the same game, like oaks – we were showing that even within these oaks, on a small scale, in a single mountain range, a few miles distant from site to site, you were getting turnover in species and turnover in strategies,” Schwilk said.
It has implications not only for how and which trees will survive wildfires – which, in the short term, could intensify with climate change – but also how they will weather the hotter and drier conditions to come.
Preparing for the effects of climate change, and mitigating those effects, requires attending to details of the landscape, and its inhabitants, Schwilk said.
“To make predictions, it’s important to know the traits of the plants,”he said. “Fire is not the same thing everywhere it occurs, and even something as simple as temperature can be surprisingly complicated.”
The Jan. 18 conference is hosted by the Big Bend Native Plant Society, Sierra Club, Big Bend Conservation Alliance and Presidio County Underground Water Conservation District. Make reservations for this free event at firstname.lastname@example.org.