Scientists find thriving fungi, a hopeful sign where 1.3 million Joshua trees were burned

An estimated 1.3 million Joshua trees burned as the 2020 Dome Fire swept through 43,000 acres of the Cima Dome in the Mojave Desert. Scientists feared the damage extended far beyond the trees, reaching into the underground networks of fungi that help sustain desert ecosystems.

Instead, fungi are thriving underground.

That finding — published in a peer-reviewed study in the journal Fire Ecology — is important because the fungi extend the reach of Joshua trees’ root systems, helping them survive harsh desert conditions. Without the fungi, the desert plants would struggle even more than they already are to recover from the fire.

“Even though things die, there are always plants and microbes that will take advantage of the fire and will really bloom after them,” said Sydney Glassman, a fungal ecologist at UC Riverside and the lead author of the study. “So it’s not all doom and gloom."

Two weeks after the Dome Fire was contained in August 2020, Glassman and a team of researchers collected samples from burned and unburned areas around the Cima Dome volcanic structure east of Baker. The area is home to one of the densest Joshua tree forests in the world. The team collected soil samples near Eastern Joshua trees to assess the fire’s effect on fungal communities. The samples were frozen, processed for DNA extraction, and later sequenced to identify which organisms were present.

Over the next three years, researchers returned to the sites five times, focusing on measuring the amount of the symbiotic fungi and bacteria that live within Joshua tree roots.

They found a fungal system that remained largely intact.

“In this case, other plants survived — like cacti, or different kinds of desert forbs, or other yuccas — so they were maintaining the soil microbial community,” Glassman said.

Sydney Glassman of UC Riverside collects samples of fungi in the Mojave National Preserve.

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Lynn Sweet

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UC Riverside

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These fungi help plants absorb water and nutrients from the soil, while also protecting against pathogens and environmental stressors such as drought.

Experts think that the fungal networks remained resilient partly due to the sparseness of the Mojave, where Joshua trees are spread far apart.

“There’s not really a lot of ground cover in between them, so the fire moves really fast,” Glassman said, meaning the heat did little damage to the soil.

But efforts to restore Joshua trees have seen little success so far. Seedlings face a multitude of threats, including pack rats and increasing temperatures, Glassman said.

“The seedling has to get growing and survive first,” Glassman said. “And then once it’s growing, then it definitely requires these fungi, and those can help them tolerate drought and survive.”

This image shows what's known as an arbuscule, a fungal structure, from an Eastern Joshua tree's root.

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Arik Joukhajian

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UC Riverside

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By 2100, Joshua trees are projected to lose up to 80% of their habitat if greenhouse gas emissions continue increasing. Amid concerns about climate change, experts said that the new study provided insight into how Joshua trees may fare in a hotter world.

Brendan Cummings, conservation director at the Center for Biological Diversity, said Joshua trees face increasing fire and drought risk as human-caused climate change accelerates.

“If we do everything necessary to save the Joshua tree, we will also be saving the broader desert ecosystem,” said Cummings, who has worked on Joshua tree conservation.

Glassman said her research will continue. She hopes to understand the traits of bacteria and fungi that survive fires, and how they're doing it.

Ohio State University evolutionary ecologist Alison Bennett said future research could investigate whether soil fungi play a role in improving the germination and growth of Joshua tree seedlings. However, Bennett noted that challenges in procuring Joshua tree seedlings and waiting for them to reach maturity over decades could make such research difficult.

“There are other aspects of restoration and looking at soil microbiology that need to be built more, and I feel like this paper lays a good foundation for a lot of that future work,” said Andrew Kaiser, an environmental scientist at the California Department of Fish and Wildlife who was not involved in the study.