Soil Fungi Prove Central To Native Forest Recovery On Remote Pacific Atoll

by Simon Mansfield
Sydney, Australia (SPX) Apr 29, 2026
New research conducted on Palmyra Atoll, one of the most remote and ecologically intact islands on Earth, has found that native soil fungi are essential to the regeneration of indigenous rainforest following the removal of invasive coconut palm plantations.

The study, published in the journal Current Biology, shows that restoring native Pisonia grandis trees - the backbone of Palmyra and hundreds of other atolls worldwide - requires more than clearing introduced palms. The right underground fungal partners must also be present for forest recovery to succeed.

Palmyra Atoll sits roughly halfway between Hawaii and American Samoa. Native forests were cleared and replanted with coconut palms as early as the 1850s, and U.S. military activity during World War II further transformed the landscape and likely introduced black rats, which devastated seedlings, bird hatchlings, and crab populations. After The Nature Conservancy and partners eradicated the rodents in 2011, Pisonia seedlings and land crabs returned across the atoll in large numbers. By the time fungal researchers arrived in 2022, crews had removed approximately 1.5 million coconut palms and the atoll was undergoing a visible recovery.

"It reveals a hidden dependency at the heart of an entire ecosystem," said lead author Charlie Cornwallis, an ecology professor at Lund University in Sweden. "The health of Palmyra's coral reefs ultimately depends on seabirds, which depend on Pisonia trees for nesting, which depend on fungi. Remove any link in that chain and the whole system could unravel."

Cornwallis worked on the study alongside the Society for the Protection of Underground Networks (SPUN), the University of Oxford, The Nature Conservancy, and other institutions. The research team was led by evolutionary biologist and SPUN co-founder Toby Kiers, who traveled to the central Pacific to map the atoll's underground fungal networks.

In every soil sample taken beneath Pisonia trees across 27 of Palmyra's islands, the scientists found rare fungi. Several species had not been documented anywhere else on Earth. Fungal diversity declined with distance from Pisonia trees, and fungi were even detected on tree roots suspended several feet above the ground - suggesting that soil contact is not a requirement for the fungi to associate with their hosts.

Around the world, mycorrhizal fungi form complex subterranean networks that partner with approximately 80 percent of vegetation, supplying water, phosphorus, and nitrogen to plant roots in exchange for carbon. Before this study, no one had documented the role that fungi on Palmyra might play in moving nutrients between the forest and the surrounding ocean.

The ecological chain on Palmyra is unusually direct and traceable. Pisonia produces dense canopies that provide nesting sites for millions of seabirds, including red-footed boobies and great frigatebirds. The birds' guano drains through the thin sandy soil into the ocean, feeding plankton that supports coral reef ecosystems. Those reefs in turn sustain large populations of reef sharks and other marine life. Guano on land also fertilizes vegetation consumed by land crabs, which dig burrows that aerate and mix the soil. Comparing fungal diversity inside and outside crab burrows, the team found that burrowing activity appears to increase the density of Pisonia's fungal partners.

"It's not that other ecosystems aren't interconnected," said co-author Stuart West, professor of evolutionary biology at the University of Oxford. But on Palmyra "it's rammed in your face and amplified because it's all squashed onto a small, simple island with fewer things."

Alex Wegmann, lead scientist for The Nature Conservancy's Island Resilience Strategy, described it as "one of the few places you can literally say, with science backing you up, 'That tree right there is important to that coral out there.'"

Based on their findings, the scientists identified fungal hotspots where soil transplants could accelerate Pisonia seedling establishment in areas cleared of coconut palms. Kiers, whose work documenting fungal networks earned her the Tyler Prize and a MacArthur Fellowship, said the study signals a broader shift in restoration science. "Until now, restoration has almost exclusively focused on native plants. That is changing. Research is showing how successful restoration involves introducing native plants together with native fungi."

Since Pisonia is the dominant tree across Palmyra and many of the world's other 598 atolls, the findings carry implications well beyond this single location. On remote island systems, the loss of symbiotic partners can be difficult or impossible to reverse, and documenting underground fungal networks may be critical to preventing ecosystem collapse on such fragile islands.

TNC's Palmyra Preserve lies within the U.S. Fish and Wildlife Service's Palmyra Atoll National Wildlife Refuge and within the Pacific Islands Heritage Marine National Monument, one of the largest protected ocean and island areas in the world.

Research Report:Symbiotic fungi underlie the regeneration potential of island rainforests