Island rainforest regeneration depends on specialized fungal symbioses
spun authors
summary
On remote tropical islands, giant rainforest trees called Pisonia support entire ecosystems by providing nesting sites for seabirds. The birds bring nutrients from the ocean onto land through their droppings, helping forests grow and indirectly supporting nearby coral reefs. But this study shows that the trees cannot thrive alone — they depend on special underground fungi called Tomentella.
Researchers mapped fungi across Palmyra Atoll and discovered that every Pisonia tree was connected to Tomentella fungi. These fungi were most common near healthy Pisonia forests and may help trees survive in the harsh, nutrient-heavy conditions created by seabird guano. The team also found that land crabs increase fungal diversity by digging through soils, and that the atoll contains rare or possibly unique fungal species found nowhere else on Earth.
The study highlights that restoring island forests requires more than planting trees — it also means protecting the hidden fungal networks beneath them.
Remote island rainforests rely on hidden fungal partnerships to survive and regenerate. Every Pisonia tree on Palmyra Atoll depended on Tomentella fungi, showing that restoring tropical islands requires protecting both trees and their underground microbial allies.
The regeneration of remote island rainforests depends on invisible fungal partnerships beneath the soil. Protecting and restoring these underground symbioses is essential for rebuilding resilient island ecosystems.
Island ecosystems often depend on a small number of tightly linked species interactions. On remote tropical atolls, the rainforest tree Pisonia grandis plays a central ecological role by providing nesting habitat for seabirds, whose nutrient-rich guano supports forest growth and nearby coral reef ecosystems. Scientists have long suspected that mycorrhizal fungi are essential for helping Pisonia survive in these nutrient-poor sandy soils, but little was known about how these fungi are distributed across islands or how they influence forest restoration.
The study revealed several striking findings:
- Pisonia grandis showed a 100% association with a specific ectomycorrhizal fungal genus, Tomentella. Every sampled Pisonia tree contained these fungi in its roots.
- Tomentella fungi were most abundant near Pisonia forests, and their abundance declined sharply beyond ~250 m from these stands, suggesting limited natural dispersal.
- Some Tomentella fungi appeared specially adapted to the extreme phosphorus-rich conditions created by seabird guano.
- Areas with active land crab burrowing had significantly higher fungal diversity overall, indicating that crabs act as ecosystem engineers that help maintain soil biodiversity.
- The atoll also contained potentially new or globally rare fungal species, highlighting the uniqueness of island microbiomes.
