Can planting more saguaros help reverse climate change impact?
Heat, drought & invasive grass are driving wildfires killing Arizona's cactus giants
This article originally appeared on Inside Climate News, a nonprofit, independent news organization that covers climate, energy and the environment. It is republished with permission. Sign up for their newsletter here.
Jerry McHale dug a small hole with a shovel near the base of a palo verde and placed a cactus a few inches tall in it. The saguaro was just old enough to sprout the needles it needs to keep desert rats and jackrabbits from devouring it. One by one, McHale and a small group of volunteers planted the young cacti under "nursing plants" that will help them grow, some to nearly 40 feet tall, over the coming centuries at the Tucson Audubon Society's Mason Center.
Each saguaro planted was a small part of a big project from the conservation and birding group, which is planting 14,000 saguaros over the next two years to help restore the dwindling population of the cacti. At the same time, they are removing 1,000 acres of an invasive grass that has helped fuel wildfires that have been more destructive across the Sonoran Desert in recent years, particularly to the cactus giants.
"Saguaros aren't regenerating and establishing populations in the wild anymore in the last 24 years," Aya Pickett, a restoration project manager with the Tucson Audubon Society, told the group of volunteers before they set off to plant cacti. "They really require specific weather conditions. A really good monsoon season. One really good winter. And then another really good monsoon season after that."
Because of changing weather patterns due to climate change, she said, that hasn't happened for over two decades. That means when a saguaro dies in the wild, there's frequently no new one to replace it. With hotter temperatures, dryer landscapes and bigger and hotter wildfires, thousands of saguaros have died in recent years. Without human intervention, desert ecologists said, their ability to recover in some areas is unlikely.
The Tucson Audubon Society has received just over $500,000 in grant money from the Wildlife Conservation Society and the U.S. Forest Service, making its saguaro project one of the biggest restoration efforts in the Sonoran Desert. The money will help fund planting thousands of saguaros, mostly in areas recovering from wildfires in the Tonto and Coronado national forests, and developing bird nesting boxes to help replace the habitat once provided by saguaros that have died.
Most of the money, though, will go not toward planting cacti, but ripping out buffelgrass, an invasive species from West Africa brought into the region as cattle forage. The National Park Service has named it the "archenemy of the Sonoran Desert."
Saguaros planted by the Tucson Audubon Society are just a few inches tall but old enough to develop spines to protect themselves from feasting rodents. Once mature, they are the largest cactus in the Americas, growing up to 40 feet tall with dozens of elbowed arms, but it takes decades to get there. Saguaros take around 35 years to even begin flowering, decades longer to grow out their iconic arms, and more than a century to reach adulthood.
Icon of the American Southwest, they are integral to the region's culture. For the Tohono O'odham Nation, it's a sacred plant and its fruit has been harvested for generations as a staple food source during the desert's hot summers. The cactus even has its own national park.
The saguaro is also a keystone species of the Sonoran Desert. More than 100 other species rely on it for their survival. Gilded flickers and Gila woodpeckers make nests within the cactus, which other birds take over once they leave.
Various insects subsist on its nectar during the summer "when the rest of the desert is brown and crispy," said Jonathan Horst, director of conservation and research at the Tucson Audubon Society, who is leading the project. "It's like the worst of the worst of times," Horst said. "And then suddenly you've got this amazing crop of flowers with nectar and pollen."
While the saguaro isn't in danger of going extinct, "they're definitely in danger of disappearing in large sections of the landscape, especially after wildfires," he said, "and having incredibly long periods before they can re-establish." Without the giant cacti, other species that depend on them will struggle. And the landscape of the Sonoran Desert will change.
Invasive grass drives change in the desert
The Mercer Spring Fire didn't draw much notice when it broke out in the Catalina Mountains near Tucson in 2019. But the images of saguaros burning caught Horst's attention.
"It was the first fire that was predominantly fueled by buffelgrass," he said, which thrives on wildfire, which it is spreading to habitats with species like saguaros that haven't evolved to endure the blazes.
Around the same time as the Mercer Spring Fire, the Tucson Audubon Society had been monitoring the desert purple martin, a swallow that nests only in cavities they find in the oldest saguaros, which are typically around 150 years old.
Horst realized that if buffelgrass wasn't contained and restoration efforts made to establish lost saguaros, the Sonoran Desert ecosystem could see serious change and desert purple martin populations would likely plummet.
For the growth of saguaro populations, it's a numbers game, said Ben Wilder, a desert ecologist and the director of Next Generation Sonoran Desert Researchers. As a succulent, it pulls in resources when it can—particularly during monsoon seasons—and then stores them for months or even years. It flowers each year and its fruits each have a couple of hundred seeds, he said.
That means that across the landscape, you have billions of seeds. But the Southwestern drought of the past 20 years has led few of those seeds to grow into new saguaros, something Wilder said isn't unexpected.
This could currently be a saguaro establishment period thanks to recent rainy seasons, Wilder said, but another wildfire could very well take out what has been gained. Wildfires are "novel" to the Sonoran Desert, Wilder said, but species like buffelgrass are driving more of them, fueling bigger and hotter fires and then quickly growing back to serve as tinder for more fires.
Saguaros, especially the young ones, are poorly adapted to fires, he said. One blaze can wipe out a saguaro recruitment event that occurs only every few decades, which "could be catastrophic to their ability to produce and to maintain populations," Wilder said.
That has complications for other species as well. After a bad fire, Horst said, there could be a 150-year gap before new saguaros can replace what was lost and support the desert purple martin.
"We're looking at a future that will be more and more difficult for saguaros to get established," Horst said.
The buffelgrass does more than just fuel fires. It changes the landscape, too. Peter Breslin, a postdoctoral researcher at the Desert Laboratory on Tumamoc Hill at the University of Arizona and editor of The Cactus and Succulent Journal, said the lab has begun researching the effect the invasive grass is having on saguaros. They've yet to fully analyze their data, but Breslin said when buffelgrass proliferates, other native species seem to struggle.
Saguaros often rely on other plant species to provide shade and shelter that helps the cactus flourish when they are young, he said. That's why the Tucson Audubon Society plans to plant them as often as they can under nursing trees.
But the buffelgrass is changing that by allowing fires to burn away some of the larger plants that the cacti depend on. Parts of Tumamoc Hill, Breslin said, are "shifting from Sonora upland to desert grassland. That's a massive ecological change."
Desert grasslands, which typically occur in valleys and basins, can spread invasive, fire-dependent grass species that fuel bigger and hotter blazes in a landscape known for its long-living vegetation that has lived for centuries without frequent wildfire.
"You just stand there and you can see it," he said. "There's no denying it."
The radically different life cycles and time frames of the grass and the cactus are speeding change.
Things happen slowly in the desert, Breslin said. It's not unheard of for saguaros to not regenerate for decades and then recover their population once the right weather conditions return. But the invasive grasses are bringing rapid change to the slow-moving ecosystem.
"That's the general doom of the Southwest," he said.
That makes the Tucson Audubon Society's project a crucial restoration project for the Sonoran Desert.
But recovery for the cacti with raised arms will be tough. In the burn scars that need to be replanted, other vegetation the saguaros depend on may have also died in the flames, Breslin said, while buffelgrass that could bring more blazes is challenging to remove.
But there are few other options for saving the cactus ecosystem.
"Unless there's human intervention, I don't see a path forward based on soil biology for (saguaros) to reestablish themselves back in those areas that have turned into what has regressed to savanna grassland," Horst said.
Over the course of two hours, the volunteers and staff at the Tucson Audubon Society's Mason Center planted a few dozen young saguaros and logged their locations to monitor them over the coming years, a small step toward planting thousands of the iconic cacti across Arizona.