Not long after the sun rose over the Sonoran Desert in southern Arizona, a group of hikers set out on a mission in the Saguaro National Park.
The group marched up a rocky hillside armed with metal bars and pickaxes. The volunteer soldiers, most in their 60s and 70s, were going to war against a tuft of invasive grass.
Marci Shatz is a Sonoran Desert weedwhacker working hard to fight off the thick band of buffelgrass that's taken over one particular hillside. She bends over a tuft of brown-yellow grass, whacks the base of it with a pick and turns it over to show the individual root balls that comprise the base of the plant.
Shatz has been sweating under the desert sun pulling grass for 13 years.
“It's sort of almost like a life and death thing, I think, for the Sonoran Desert,” she says. “Random hiking has been ruined for me, because if I hike in an area that's never been cleared, then all I see is buffelgrass. And it's just so discouraging.”
That’s because the invasive buffelgrass is choking out native plants and animals — and turning the Sonoran Desert into a tinderbox.
Buffelgrass was brought from Africa to the U.S. in the 1930s to help deal with drought and overgrazing, says Julia Rowe, an expert on invasive species at Tucson’s Arizona-Sonora Desert Museum. The drought-resistant plants were placed in the desert’s lower grasslands, but in the 1990s, people started noticing buffelgrass in the wildlands too.
Now almost a century after the species came to the U.S., buffelgrass can be found throughout Arizona’s urban areas and in almost all of the state’s wildlands, she says. Without any natural predators, the buffelgrass is free to invade open spaces.
But here’s the problem: Buffelgrass is dry for at least two-thirds of the year.
“This plant is adapted to handle fire,” she says. “And so what happens is it burns down to the roots, but as soon as there's moisture again, it sprouts up green and lush. And so it's then able to take even more advantage of that opened up space.”
The expansive Sonoran Desert — home to majestic saguaros, palos verde trees, creosote bushes, barrel cacti — isn’t traditionally prone to fires. That’s why most of Rowe’s job focuses on dealing with the buffelgrass.
Without tortoises, bighorn sheep or Gila monsters to eat the vegetation, Rowe says the buffelgrass moves in and causes a chain reaction.
“You can see there's not much fuel for a fire. So if a fire does happen in one spot, it doesn't go very far,” she says. “[Buffelgrass] has such an ability to completely change an ecosystem from a Sonoran Desert ecosystem into an invaded grassland.”
Older saguaro can survive a fire but many younger ones die, killing off an entire generation of the beloved cacti, she says.
Last year's fire season in Arizona was the second-worst in state history. Nearly a million acres burned. Many of the fires took place in lower-elevation ecosystems that have been invaded by grasses, she says.
“These grasses are fueling an increase in fire frequency and spreading fire into new habitats, new ecosystems where fire hasn't been present before,” says Kim Franklin, another scientist at the Desert Museum who has witnessed stands of saguaro gutted by flames.
The threat is only growing. Climate change is making the Southwestern United States hotter and drier. In Saguaro National Park, minimum temperatures in the winter have risen up to 15 degrees in the past 100 years. And fires are getting more intense.
Franklin says invasive grasses — which don't do well in the cold — are spreading into higher elevations, which means every thwack matters.
Volunteer whacker Joe Ciaramitaro is 72 years old and still hard at work. He points out that the seeds he’s pulling from the ground now will still be viable for three to four years.
“If we get any kind of monsoon this year, if we come back here in August or September, there'll be hundreds of seedlings, so we'll have to hit it again,” he says. “It's persistent.”
But so are the volunteers. And that's a good thing because if they are going to win this battle against buffelgrass, they'll have to keep digging.
This segment aired on April 26, 2021.