Joshua trees are dying in California—scientists chase fungi

In the Mojave, only a small fraction of Joshua tree seedlings planted to replace those cut down along power lines are surviving. With wildfires, heat and drought accelerating losses, researchers are turning to an overlooked ally underground—mycorrhizal fungi—h

For the third straight morning in early spring, a scientist knelt where a Joshua tree should have been.

In the Mojave National Preserve, she parted creosote branches and revealed a shriveled seedling—just ankle-high, already doomed. The plant was one of nearly 200 “babies” grown for a National Park Service effort to replace dozens of Joshua trees that had been cut down by a Southern California Edison contractor tasked with protecting power lines. But of those 193 seedlings planted roughly five years ago, only 27—about 14%—are still alive, according to the Park Service.

The mortality has become urgent. If researchers can’t figure out why so few are surviving, an imperiled icon of the California desert could fade faster than anyone anticipated.

“Joshua trees are so resilient — they’ve been around for millions of years,” said Anne Polyakov of the Society for the Protection of Underground Networks, who led the expedition. “But now they’re facing too many stressors all at once.”

Joshua trees have long stood for more than survival in this landscape. Described by some as spiritual guides or even family members. they’ve inspired Indigenous people and pioneers. and also reached wider audiences through artists and writers—including U2 and the creators of “Euphoria.” Poet Ruth Nolan. the Mojave Desert literary laureate. called them unique and a bit weird. the kind of living landmark that feels both ancient and accessible. They look inviting from a distance, she said, but sharp up close.

“They kind of represent the whole spirit of the desert,” she said. “It’s beautiful and inviting, but it’s also really tough and acerbic.”

Those traits matter because Joshua trees are not just symbols. They are a linchpin of the Mojave Desert ecosystem, often the largest structures on the land where they grow. Dozens of animals rely on them for food and shelter.

But human development and wildfires have already destroyed swaths of habitat, and climate change is threatening to make much of what remains inhospitable. “If they all die and we can’t restore them properly, it’s going to be a big problem,” Polyakov said.

Her team believes part of the answer may be hiding below the surface.

Mycorrhizal fungi—microorganisms that form a vast underground network—can help plants reach nutrients and water. Research suggests these partnerships can play a crucial role in helping Joshua tree seedlings make it through their perilous early years and reach maturity.

Still, the plants need help on multiple fronts at once. By the end of the century. up to 80% of their range is expected to become too hot and dry to sustain them. said Drew Kaiser. senior environmental scientist at the California Department of Fish and Wildlife. Joshua trees are slow-growing, taking 50 to 70 years to start producing seeds. Those seeds are dispersed primarily by ground squirrels and wood rats, who do not travel far from their burrows.

That means the species has a slow-motion response to a rapidly shifting climate—one more reason losses can compound. “Climate change is pushing this habitat suitability window faster than the trees can be dispersed and start producing new individuals. ” Kaiser said. He added that Joshua trees are losing much more habitat than they’re able to gain by establishing in new. more favorable areas.

The desert’s mounting pressure shows up clearly in the preserve itself.

In the Mojave National Preserve—a 1.6-million-acre stretch of desert between Las Vegas and Los Angeles—wildfires have killed up to 2.3 million Joshua trees in the last six years alone. In 2020, the Dome fire decimated what was then known as the world’s densest Joshua tree forest. Three years later, the York fire scorched more than 145 square miles amid unprecedented heat and near-record dryness.

“We seem to be breaking records every other month. ” said Jim Andre. director of the University of California’s Sweeney Granite Mountains Desert Research Center. The center bordering the preserve recently recorded its hottest March, with a mean temperature of 11 degrees above average, Andre said. Though May is only halfway underway. he said the month is running about 4 degrees warmer than average after a slight cooldown in April. and conditions remain very dry.

Adult Joshua trees are more resilient than seedlings, but intense heat waves and drought can still overwhelm them. Extreme conditions can also drive wildlife behavior that turns deadly. Pocket gophers and antelope squirrels may strip off the outer layer of bark for sustenance. a process that can be fatal to the trees.

And then there are the power lines.

In 2017, a Southern California Edison contractor cut down more than 100 Joshua trees over fears they could come into contact with power lines and spark a fire. The utility later agreed to pay the Park Service $440,634 in damages, said spokesperson Jeff Monford.

“While vegetation work by a contractor was undertaken to address identified power line safety concerns, we worked with federal land managers to resolve the issue and support restoration efforts,” Monford said.

The National Park Service gathered seeds from the landscape, grew them in greenhouses, and planted them in the preserve in 2020 and 2021 when they were 2 to 3 years old, Polyakov said.

Some mortality was expected. Young Joshua trees can be nibbled to death by rabbits and rodents, or wither from drought, disease or fire. Of the 3,622 Joshua trees planted between 2021 and 2024 to replace those burned in the Dome fire, about 23% have survived, the Park Service said.

But Polyakov said the numbers don’t line up with what temperature and rainfall alone can explain in the power-line planting. “Since the aboveground variables aren’t telling us the reason why all these seedlings are dying, it’s likely something is going on below.”

That “below” is what this fieldwork is trying to capture.

In the soil. mycorrhizal fungi attach to plant roots and spread threadlike filaments in search of nutrients and water. supplying the plant in return for carbon. Polyakov called the relationship “an intimate symbiosis” that can help Joshua trees growing in dry desert soils reach pockets of nourishment their roots alone would struggle to access.

But she said the planted seedlings were grown in potting soil, which may mean they never formed partnerships with native fungi.

On an unseasonably warm March afternoon, Polyakov knelt beside a dead seedling and used a mallet to pound a metal tube into the rocky sand. After a few twists, she lifted the tube out and deposited the soil into a baggie.

“There’s a whole world inside this little bag, but it’s invisible,” she said.

Researcher Cameron Egan—an ecologist and professor at USC—will extract DNA from each soil sample and send it for sequencing to learn what species of mycorrhizal fungi are present. The team will compare results from dead Joshua seedlings with those that survived. and also with samples from older Joshua trees growing nearby.

Depending on what they find, Egan said, the fix for future planting projects could be as simple as mixing a bit of native earth into potting soil where Joshua tree seedlings are grown.

The Park Service is interested in exploring ways to improve restoration success and would be open to trying soil mycorrhizal treatment, a spokesperson wrote in an email.

This research fits the Society for the Protection of Underground Networks’ broader mission to map fungal networks across the globe. The Mojave Desert, the organization says, is under-explored, and its maps predict the region to be rich in fungal diversity.

The fieldwork is taking the team beyond the preserve, too. They also traveled to Joshua Tree National Park, where some research suggests the namesake plant will eventually become largely devoid of its trees.

On rocky trails, they sampled soils from the sweeping flatlands of Lost Horse Valley to the slopes of Eureka Peak, where massive Joshua trees grow alongside manzanita, juniper and pinyon pines.

The question running through every sample is whether the fungal communities that help Joshua trees endure hot. dry conditions are shifting along with the plants as habitat moves upslope. If the underground allies don’t migrate in step. seedlings could be planted into a world that looks right on top—but lacks what they need beneath.

Those findings could help California decide where to prioritize Joshua tree conservation as it implements a sweeping plan to protect the plants from climate threats. Egan also said the observations could open the door to the possibility that people could help Joshua trees migrate by inoculating certain areas with specific types of mycorrhizal fungi.

“Any time rapid environmental changes happen. evolution has to try to keep up. and if evolution doesn’t keep up. well. then the species goes away. ” Egan said as he looked out over a stretch of savanna-like grassland inside the national park. “Our hope is to give these populations a chance to keep up.”.

Behind him, a mature Joshua tree was dying, its graying limbs drooping sadly. In the shade beneath the fading giant, a seedling had sprouted.

Joshua tree Mojave National Preserve Joshua Tree National Park mycorrhizal fungi Southern California Edison restoration wildfires climate change California Department of Fish and Wildlife