People are killing California Joshua trees. Can the fungus save them?

MOJAVE NATIONAL PRESERVE — In the heart of the Mojave National Preserve, a scientist hunted a baby Joshua tree that would never reach adulthood.

He split the creosote branches to reveal a gnarled, ankle-high tree. The doomed sapling was part of a National Park Service planting effort to replace dozens of Joshua trees cut down by a Southern California Edison contractor tasked with protecting the company’s power lines.

But of the 193 children planted here nearly five years ago, only 27, or 14%, are still alive, according to the Park Service. If researchers don’t understand why there are so few survivors, an endangered icon of the California desert could disappear very quickly.

“Joshua trees are 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 are facing many pressures at the same time.”

Described by some as spiritual guides or family members, Joshua trees have inspired a variety of artists and writers, from Native people and pioneers to U2 and the creators of “Euphoria.”

The spiky succulents are symbols of what makes the desert special to people, says poet Ruth Nolan, winner of the Mojave Desert Literature Award. They are different and strange, they speak to something deep and ancient. And although their branches are colored like teddy bears, they are sharp when you get too close.

“They symbolize the whole spirit of the desert,” he said. “It’s beautiful and inviting, but also tough and acerbic.”

Joshua trees also play an important role as the linchpin of the Mojave Desert ecosystem. They are often the largest structures in their habitats, and many animals rely on them for food and shelter.

But human development and the wildfires we create have destroyed their habitats, and climate change threatens to make much of what remains unacceptable. “If they all die and we can’t restore them properly, it will be a big problem,” said Polyakov.

He believes the clues to the problem may lie deep beneath the sun-baked sand, where bacteria known as mycorrhizal fungi form a vast network that can help plants access nutrients and water. Research suggests that this interaction may play an important role in helping Joshua tree seedlings reach their critical early years and reach maturity.

And Joshua trees need all the help they can get.

By the end of the century, up to 80% of their range is expected to become too hot and dry to survive — a pace plants are ill-equipped to handle, said Drew Kaiser, senior environmental scientist at the California Department of Fish and Wildlife.

They are slow growing and take 50 to 70 years to start producing seeds, which are dispersed mainly by squirrels and wood mice that do not venture far from their burrows. That means it takes longer for Joshua trees to transition to cooler, higher elevations.

“Climate change is compressing this window of habitat suitability faster than trees can disperse and start producing new populations,” Kaiser said. Because of this, he said, Joshua trees are losing more habitat than they are gaining by establishing new, more favorable habitats.

In the Mojave National Preserve – a 1.6 million acre desert between Las Vegas and Los Angeles – the challenges facing the iconic plant are evident.

Here, two wildfires have killed up to 2.3 million Joshua trees in the past six years alone. In 2020, the Dome fire wiped out what was then known as the world’s densest Joshua tree forest. Three years later, the York fire burned more than 145 square kilometers amid unprecedented heat and near-record dryness.

“It seems like we’re breaking records every other month,” said Jim Andre, director of the University of California’s Sweeney Granite Mountains Desert Research Center. The border storage facility just recorded its hottest March — so far — with temperatures 11 degrees above average, he said. Although we’re only in the middle of May, the month is about 4 degrees warmer than average after a slight cooldown in April, and conditions remain very dry, he said.

Mature Joshua trees are hardier than seedlings, but they can still succumb to strong heat waves and drought. Such excesses can also cause squirrels and antelope squirrels to strip their outer bark to survive, which can kill trees.

Then there are the high voltage transmission lines that thunder above the terminal.

In 2017, a Southern California Edison contractor cut down more than 100 Joshua trees out of fear that they might come in contact with power lines and start a fire. The company later agreed to pay the Park Service $440,634 in damages, said department spokesman Jeff Monford.

“While the contractor’s plant work is being done to address the identified electrical safety issues, we have worked with federal land managers to resolve the issue and support restoration efforts,” he said.

The Park Service collected seeds from the area, planted them in greenhouses and planted them in the reserve in 2020 and 2021 when they were 2 to 3 years old, Polyakov said.

Of course, certain deaths were expected. Young Joshua trees can be eaten by hungry rabbits and rats, or withered by drought, disease or fire. Of the 3,622 Joshua trees planted between 2021 and 2024 to replace those that burned in the Dome fire, about 23% survived, the Park Service said.

But in the case of planting power lines, temperature and rainfall data failed to fully explain why many seedlings were not established, Polyakov said. “Since the variables above don’t tell us why all these seedlings are dying, it’s possible that something is going on below.”

Egan and Elhance walk past a seedling sitting among mature Joshua trees while taking soil samples from the tree floor at Upper Covington Flat in March in Joshua Tree National Park.

(Gary Coronado / For The Times)

There, mycorrhizal fungi attach themselves to the cells of the plant’s roots and spread out filaments, looking for nutrients and water to provide the plant with carbon. The result is what Polyakov calls an “intimate symbiosis” that can help Joshua trees growing in the dry desert access pockets of nutrients that their roots alone can’t find, he said.

But the 193 “Joshies” planted, as Polyakov calls them, were planted in clay soil, so they may not have formed this relationship with native fungi, he said, kneeling next to a dead seedling on an unseasonably warm afternoon in March.

He used a hammer to pound the steel tube into the rocky sand. After twisting it a few times, he lifted it up and put the soil in the bag.

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

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

Depending on what they learn, preparing future planting projects may be as simple as mixing a little native soil into potting soil where Joshua tree seedlings are planted.

Soil samples were collected by scientists with the Association for the Protection of Underground Networks on the Upper Covington Flat.

(Gary Coronado / For The Times)

The Park Service is interested in exploring ways to improve the success of its restoration projects and could be open to experimenting with soil mycorrhizal treatments, a spokesperson wrote in an email.

The research is part of the Society for the Protection of Underground Networks’ mission to map global networks of fungi. The Mojave Desert is underexplored, and federal maps predict it to be rich in fungal diversity.

The mission also took the team to Joshua Tree National Park, which some research suggests will end up without its namesake plant.

They wind down rocky roads in a rented Kia, sampling soil from the sweeping plains of Lost Horse Valley to the slopes of Eureka Peak, where giant Joshua trees grow alongside manzanita, juniper and pine.

They hope to gain an understanding of whether, as Joshua trees move to higher elevations, the fungal communities that help them withstand the hot and dry conditions in their understory go with them.

Such observations could help California decide where to prioritize Joshua tree conservation as it implements a sweeping program to protect the plants from climate hazards. They could also open the door for people to help plants migrate by injecting certain areas with certain types of mycorrhizal fungi, Egan said.

“Whenever there are rapid changes in the environment, evolution must try to keep up, and if evolution doesn’t keep up, then species become extinct,” he said as he looked out over the savannah-like plains inside the national park. “Our hope is to give these people a chance to move on.”

Behind him, a mature Joshua tree was dying, its gray limbs sadly withered. In the shade under the withering giant, a seedling sprouted.