In a sense, fungi are a hidden earthly dimension we’re only now learning how to see.

They thrive in soil and grow edible stalks like plants, but many of their characteristics are distinctly unplantlike. Where plants have cell walls made of cellulose, fungi have chitin, a type of fiber also found in the exoskeletons of insects and crustaceans. And fungi are heterotrophs—capable of eating other organisms, often breaking down wood and dead plant matter by releasing and reabsorbing enzymes. Without fungi, dead plants and animals would pile up on forest floors, and most trees would struggle to find the nutrients they need to survive.

“They’re probably closer to animals than you think,” says Rabern Simmons, the curator of fungi at the Purdue University Herbaria.

For more than a billion years, fungi have evolved to live in specific environments, sometimes in partnership with just one other species. But when a fungus is moved anywhere from dozens to thousands of miles away, these complex relationships can go haywire. “It’s a perfect storm with fungal pathogens,” says Stephen Parnell, an epidemiologist at the University of Warwick who models the spread of plant disease.

Diverse strategies for reproduction help a fungus survive. Airborne spores from different species can intermingle in a new habitat, or the mushrooms might fuse together the threads that form their underground networks. But in a pinch, many can simply reproduce asexually.

With climates and landscapes changing at record pace, says Parnell, these reproductive traits make fungi uniquely—and worryingly—adaptable. In new environments, foreign fungi can spread voraciously and remake the topography around them.

American chestnut trees were once giants of Appalachia, growing a hundred feet tall and 10 feet wide. In the early 20th century, however, the fungus Cryphonectria parasitica landed on American soil. In Japan and China, the fungus was only a nuisance to Asian chestnut trees, but for the American chestnut it caused deep cankers that slowly choked it of water and nutrients. An estimated four billion trees died over the following century as a result.

As the last great American chestnut trees withered, frogs and other amphibians faced a similar peril with a fungal pathogen known as chytrid. Believed to have originated on the Korean Peninsula, the fungus lived in harmony with local amphibians. But over the past 150 years, chytrid has spread around the globe and is now associated with the decline of at least 500 amphibian species; it’s caused 90 species to disappear from their habitats. It’s been described as the worst wildlife disease in history.

“We’re moving biological material across the world in a matter of hours, across continents that were long separated,” says Ben Scheele, an ecologist at the Australian National University. “We essentially have re-created dysfunctional Pangaea.”

The aptly nicknamed coral spine fungus (Hericium clathroides) cascades from a tree in the Chalkidikí  Peninsula of Greece. 

Last autumn, Pringle and one of her students spent weeks collecting hundreds of death cap mushrooms from golden-hued forests in the United Kingdom, Hungary, France, and Poland. These samples could help scientists better understand why death caps thrive in some ecosystems and don’t in others.

Researchers are looking for a predator or pathogen they can replicate to stop the mushrooms from invading forest floors, a method called biocontrol. But Pringle says one of the most effective ways to keep fungi in the right environment is prevention: Monitor imports of foreign species, and test them for fungi.

When fungal diseases can’t be prevented in an environment, treating them can become an immense undertaking. To restore the American chestnut, several scientists have been working on decades-long breeding projects, one of which involves a controversial genetically modified tree. And while individual frogs can be cured of chytrid, eradicating the fungus in environments where it’s introduced is nearly impossible. Last year, new research on how death caps produce their powerful toxin opened the door to a possible antidote.

Some start-ups and nonprofits have promising solutions for helping fungi help us. Funga, a company in Austin, Texas, identifies native fungi that can assist trees in storing more carbon. SPUN, a scientific research organization, is mapping the world’s fungi to identify regional hot spots in need of conservation. At least 350 species are already at risk of going extinct, though the real figure is likely much higher.

For Simmons at Purdue’s Herbaria, winning the race against the biodiversity clock is critical—for humanity and fungi alike. “We’re finding things that are beneficial to humanity in some way, whether it be the production of compounds like biofuels or compounds that are understood to have medicinal purposes.”

What’s kept protected, he adds, may one day solve the next problem we might create.