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Thriving community. Tree-dwelling ferns are home to more critters than biologists thought.

Ferns Brimming With Life

Ferns perched in the treetops host a surprising amount of life. Scientists have discovered that a single one of these epiphytic ferns can hold the same weight of invertebrates as does the entire crown of the tree it rests in. The research suggests that epiphytes could contribute far more to the planet's biota than anyone imagined.

Bird's nest ferns (Asplenium nidus) and other plants that live suspended in trees are thought to play an important role in forest ecosystems by virtue of their ability to hold water and nutrients. But little is known about what animals live inside them. To find out, University of Cambridge ecologists Martin Ellwood and William Foster sampled bird's nest ferns growing on hardwoods in Borneo's lowland rainforest, where the ferns live up to 50 meters above the forest floor and can weigh as much as 200 kilograms.

The pair "fogged" 35 ferns and parts of the trees with insecticide and collected the invertebrates that fell into trays below. Comparing the fogging samples from the ferns and adjacent tree foliage, they found that each of the ferns in a tree held, on average, 120 times the invertebrate biomass of the crown. To take a more accurate count, they scaled the trees and brought down all 35 ferns. That was no mean feat, says Ellwood: "Nobody's been mad or stupid enough to attempt it before."

When they lowered the first fern to the ground, Ellwood and Foster realized they could be onto something big: Ants and termites were just “boiling out,” says Ellwood. This census revealed that fogging only sampled half of the invertebrates present in the ferns. Factoring that in, they calculated that bird's nest ferns alone contain up to half the invertebrate biomass within a hectare of rainforest canopy, they report in the 3 June issue of Nature.

Ecologist Owen Lewis of the University of Oxford applauds the pair's efforts to measure biomass in these epiphytes, but would also like to know what species live there. (Ellwood and Foster are currently working on a catalog.) If the epiphytes have a unique fauna, they could add to the planet's total species count, says Lewis. But there are only a few people in the world that can identify these things, and their ranks are dwindling, he adds.

Related sites
Kew Gardens information sheet on epiphytes
Martin Ellwood's home page