Behind the Scenes: Uncovering the Secret Lives of Cacti and Fungi in the Sonoran Desert

With sizzling temperatures and a parched climate, it can be hard to survive in the Sonoran Desert of Arizona. But some species have evolved to thrive in this extreme environment, including the iconic saguaro cactus. Part of the reason for this prickly plant’s success is its intimate relationship with a smaller—but similarly mighty—desert player: fungi. 

A team of researchers is working to uncover the mysterious symbiotic relationship that mycorrhizal fungi have formed with the cacti, which are increasingly threatened by climate change and urban development. My colleague Wyatt Myskow, ICN’s Southwest reporter, recently joined a few of these researchers on a trip to the Sonoran Desert to see this effort firsthand. I asked Wyatt to tell me more about his experience covering the secret lives of cacti and fungi—and the compounding risks they face.

How did you learn about this story? 

The researchers actually reached out to me first. I’ve been covering public lands and wildlife in Arizona and the Southwest for years and have written about the struggles the saguaro cactus faces because of climate change in the past. They had seen my coverage and reached out to see if I was interested in joining them in the field—which I can never say no to. 

You say that the arid deserts like that in Saguaro National Park can be unforgiving. Can you describe this type of ecosystem more and how the fungi and cacti interact to survive it? 

Saguaro National Park is found just outside of Tucson, Arizona, which is in the heart of the Sonoran Desert. Unsurprisingly, it’s a hot and dry place, getting around 12 inches of rain a year and summer temperatures exceeding 100 degrees Fahrenheit. But unlike some other deserts, like, say, the Mojave where I grew up, it’s much greener in large part due to it being wetter. In the Sonoran Desert, creosote bushes, an assortment of cacti and palo verde and mesquite trees dominate the landscape, and the saguaro cactus towers above them all. 

We know lots of things about the Sonoran Desert and saguaros: The cactus is a keystone species, meaning it’s vital to the ecosystem; they can live for centuries and don’t mature until they are around 100 years old; their fruits and flowers have helped sustain life in the region during the hottest time of the year, when the rest of the desert is brown and crispy. 

We know mycorrhizal fungi live in the soil—and we know those fungal systems help create highways of nutrients to plants they support, trading water and nutrients like nitrogen and phosphorus in exchange for carbon. But we don’t know much about the exact mycorrhizal fungi found living in the soil with saguaros and how they support the iconic cactus species. 

What was your reporting trip like? Is there anything that didn’t make it into the story that you can share? 

I drove down from Phoenix early to meet with the researchers on the east side of the park, which borders the Rincons, one of the mountain ranges that surround Tucson. On the other side is perhaps my favorite place on Earth, my beloved San Pedro Valley. The researchers were—and I hope the story conveys this—just a blast to spend the day with. 

We tasted the dirt to see if we could taste the fungi (in this case, it just tasted like dirt) and hiked beautiful desert hillsides that look like a forest made out of saguaros. The process itself was fairly simple: They collected soil samples to test at the lab and took measurements of the saguaros. That night I camped, and the next morning I headed out to Mammoth to cover a copper mine coming into the region that’s threatening the area’s scarce water supply.

It’ll be some time before we have results from the researchers’ expedition. But not long after the story came out, the group they are with, the Society for the Protection of Underground Networks (SPUN), published a study that for the first time mapped global mycorrhizal fungal networks. The study found that more than 90 percent of fungal communities are unprotected, threatening their ability to draw down carbon and support ecosystems across the globe.

What threats do the saguaros face? 

Saguaros, like most desert species, are incredibly resilient, able to withstand years of drought and extreme temperatures. But climate change is pushing even them to their limits, and often past it. 

Higher temperatures, drier landscapes, human development, bigger and hotter wildfires and invasive species—which can outcompete saguaros by growing quickly and fueling fires that kill native vegetation—are all major threats the species is facing. In recent years, thousands have died. 

In Phoenix, where I live, recent summers have left saguaros in people’s yards falling over dead from the extreme heat. Ecologists who study saguaros have told me the species in many areas will not recover, though they aren’t at threat of becoming endangered yet. 

One of the more recent threats, and a big theme of the story, is that protected areas that serve as refuges for saguaros and other species are under threat from the Trump administration. National parks across the country have less funding and staff, slashed by the current administration. 

The administration is also looking to downsize and eliminate some national monuments, which are basically the little siblings of national parks. Many of those targeted are found in Arizona, like nearby Ironwood Forest National Monument, which is threatened for downsizing to allow a nearby copper mine to expand. Protected areas like these are increasingly uncommon around the world as habitat is disrupted to make way for human developments.

How can this effort to increase studies on fungi help? 

Right now, how fungi help saguaros is just a black box. We don’t know how exactly they interact and how beneficial they might be in the species’ survival, something that will only become more important as the Sonoran Desert is continually affected by climate change. This study can help change that. As one of the researchers told me, “Once it’s gone and deleted, it’s gone. The thing that upsets me is, if they’re gone before we actually know what’s there, we have no idea what we’ve lost. That’s an immeasurable loss to humanity.”

Note: There’s no “More Top Climate News” this week because I am on vacation! See you next week. 

Postcard From … Arizona

Obviously, I had to ask Wyatt to send us some photos from his adventures with the researchers studying the cacti and fungi. Here’s what he said:

“I spent the day in the field with Jinsu Elhance and Justin Stewart (as seen left to right in the top photo), researchers with the Society for the Protection of Underground Networks. Though the science to understand the fungi’s connection to saguaros is complicated, getting the samples in the field is not. All they needed was a cylinder and a mallet to get soil samples and test tubes to put them in. 

“As the two collected samples, they also collected data on the saguaros themselves. Mature saguaros can get pretty tall, so they used ladders to get to the top. From there, they used their phone’s LiDAR (who knew phones could be so technologically advanced?) to create a 3D image showing how tall the cactus is and how many limbs it features, allowing the researchers to estimate its age.”