EVERGLADES N.P., FLA.—On a recent flight over the Everglades, Tony Pernas looked down and saw the encroaching enemy, the deadly Old World climbing fern, smothering native species and appearing poised to destroy an ecosystem.
"It kind of looked like a lime-green cancer spreading across the vegetation," said Pernas, an exotic plant management specialist for the National Park Service (NPS). "This thing scares everyone to death."
South Florida has a long history of success with invasive plant species, but the Old World climbing fern (lygodium) is different—and deadlier, officials say. It casts an impenetrable blanket on vegetation, under which no native species can regenerate. Its stems, as long as 80 feet, wrap up and around native trees, building a ladder for fires.
"It starts at the base and climbs up the canopy, forming a dense mass up to two or three feet thick," said Pernas. "Once fire gets into the area, it climbs the canopy and goes high-intensity, killing a lot of native trees."
The climbing fern spreads easily and quickly on wind-blown spores that can travel up to 40 miles. Water managers in South Florida first began noticing the invasive species in the 1960s and 1970s, in areas such as Jupiter and West Palm Beach. The fern is an innocuous plant in its home countries of Asia, Africa, and Australia, but Florida lacks the natural enemies to fight its spread. The plant flourishes in nearly any habitat, from hardwood hammocks to swamps and roadside ditches.
According to aerial surveying done by the South Florida Water Management District, the fern covered about 30,000 acres of South Florida in 1993. Ten years later, it has crept across 150,000. At its current rate of spread, lygodium could entrench itself in every plant community south of Lake Okeechobee by 2009.
"We are concerned because of its spread into national parks," said Mary Munson, NPCA's Sun Coast regional director. "Everglades has some heavy concentrations, and it is bound to become a problem at Big Cypress.
"Invasive species compete with our native vegetation and often replace them," she added. "They can displace entire diverse plant communities."
Of serious concern to water managers is the effect the fern could have on the $8.4 billion Everglades restoration efforts, designed to improve water flow. One fear is that the area could become dotted with islands of lygodium, not the healthy hardwood hammocks birds rely on for habitat.
"We assume that when you restore the natural water flows you will get habitat back," said Munson. "But the introduction of this invasive species has brought a new factor into play. As you get the water back, you hope to get the birds back. But if their natural habitat is choked off by an invasive species, you aren't going to see them."
"The fern has the potential to derail the whole restoration," agreed Pernas. "While everyone worries about maintaining water levels to save tree islands, without anyone noticing, the climbing fern is sneaking up and eliminating plant communities. It has just been nasty."
Fighting the invasive fern will not be easy, particularly on a shoe-string budget already strapped by efforts to stop other invasive plants, including the melaleuca and Brazilian pepper. Removing the fern from Loxahatchee National Wildlife Refuge, where it is now most prevalent, "would cost millions," Pernas said, "and that's just one park."
Officials at Big Cypress recently celebrated the end of a 25-year battle with the melaleuca tree that dried thousands of acres of wetlands. The Park Service spent close to $3.5 million to eliminate the Australian native from the park. The annual exotic plant control budget provided by Everglades National Park, for comparison, is just $35,000.
"Because there has not been enough money directed to it, lygodium has continued to expand," said Pernas. "It will be incredibly difficult to control."
Scientists are studying the ecosystems of the fern's native countries to find its natural enemies. Sawflies and pyralid moths have shown promise, but the focus has been on an Australian moth (cataclysta camptozonale) that could be used in Florida once scientists determine whether it can control lygodium without harming native plants.
"We are trying to somehow get the [moth's introduction] expedited so that they get released and onto the vines," said Pernas. "That may not be the answer, but we certainly hope that we can attack [lygodium] with it."
Scientists believe that releasing another species to control the fern is probably the best long-term solution, because spraying herbicides can be costly, ineffective, and harmful to native plants.
The National Park Service, working with several other local agencies, has met with experts to discuss the invasive fern and how to best control it. They will do so again this spring in Gainesville.
"We know that lygodium is here already, but we must stop its spread," said Pernas. "This is a deadly problem for these ecosystems, and we will continue to search for the solution."
