ROBERT SIEGEL, HOST:
Florida has a long list of invasive species it's battling - Burmese pythons, lizards from Argentina, Cuban tree frogs. The Old World climbing fern is a new addition to that list. The fern is toppling trees as it spreads across the state. And as Amy Green of member station WMFE reports, it is posing a particular threat to a national wildlife refuge.
AMY GREEN, BYLINE: LeRoy Rodgers spends plenty of time in the Florida Everglades, mainly in airboats.
(SOUNDBITE OF ENGINE IGNITION)
GREEN: He eases the boat alongside a tree island and doesn't like some of the changes he's seen. He pulls a pair of clippers from a bag and hops over the side. Rodgers will need the clippers to cut a path through the Old World climbing fern that's almost swallowed the island.
LEROY RODGERS: A white-tailed deer trying to make your way through this - you can see how difficult it would be.
GREEN: The florescent green fern is everywhere. It cascades from trees, its vines weaving a thick mat near the ground, obstructing every step. Rodgers works for the South Florida Water Management District. He says the tree islands dotting the sawgrass prairie here in the Arthur R. Marshall Loxahatchee National Wildlife Refuge are where birds and other wildlife forage and nest. He takes the fern in his hand.
RODGERS: That's where the spores are produced, and if you - now that you know what you're looking for, if you look out, you see they're everywhere. So there are spores by the billions all around us right now. And that's the other part that makes this plant so invasive.
GREEN: The Old World climbing fern first appeared in Florida as an ornamental plant and is native to Africa, Asia and Australia. With no natural predators here, it grew unchecked. The fern stands to take down more than tree islands.
Its grip on Loxahatchee has prompted the state to threaten to kick the U.S. Fish and Wildlife Service off the land because it's been unable to stop the weed. That's strenuously opposed by environmental groups in a region where a multibillion-dollar environmental restoration is underway, the nation's largest ever.
CHERYL MILLETT: I think it is the worst invasive species that Florida has faced in a very long time.
GREEN: Cheryl Millett of the Nature Conservancy considers herself on the front line of the fern's march north. She's part of a team of government agencies and private landowners monitoring its spread in central Florida. She steps among the pine trees of an eight-acre conservation area in a residential neighborhood near Orlando. The fern flows from trees like a waterfall.
Crews control the fern by spraying it with herbicide and hacking at it with machetes, leaving the vines overhead to die. It's exhausting work.
MILLETT: They've got their big boots on. They're coming through. And before they treated all this, this was all covering up here. And so they have to hack through all of that, cut it with machetes, climb through. You saw the blackberries that are growing in here, the thorny vines. They have to go through. It's really hard work.
GREEN: Back in Loxahatchee, Rodgers motors over to a tree island where the Old World climbing fern is just beginning to grow.
RODGERS: Here you can actually make out individual trees in the canopy. First of all, you can see that there is at least, you know, 40 trees here, probably about five different species of trees. And in some areas, you can actually see a little bit of an understory - shrubs and ferns.
GREEN: Rodgers says biologists are trying other ways to corral the fern, including experimenting with a moth and mite found where the fern originates and that feed only on the plant.
RODGERS: These tree islands are something that took centuries and millennia in some cases to form, so it's worth the battle and try to win.
GREEN: Otherwise, they too will succumb to the stranglehold of the Old World climbing fern. For NPR News, I'm Amy Green in Orlando.