The Australian melaleuca tree was imported into South Florida in the early part of the century to dry out "worthless swampland" and transform it into lumber-producing forests. At the time, the tree was thought to have enormous water-absorbing qualities. Melaleucas were also brought in for their beauty and planted as ornamentals throughout South Florida, from Lake Okeechobee, south to the Gulf.
Although there is no scientific evidence that melaleucas draw more water than the native cypress, assumptions of early importers were not entirely incorrect. Large concentrations of the trees do dry up marshes. They also spread rapidly. Today the melaleuca is scattered over 2,000,000 acres of South Florida, with heavy concentrations in county, state and federal parks, including Big Cypress National Preserve (BCNP), a 720,000-acre watershed established by Congress in 1974 to protect Everglades National Park water. Fresh water from the preserve sustains the Everglades and acts as a natural barrier to the incursion of seawater from the gulf.
Dade County Biologist Sandra Wells described the potential impact of the tree on the county's 130-acre wetlands park, which is part of the historical Everglades. "What we have now is a grassy swamp, which we could lose. Leaf matter dropped from hundreds of melaleuca trees can raise the ground elevation, transforming marsh into forest and wiping out wildlife that live in the marsh."
Since marsh water percolates down through the earth to replenish natural underground acquifers, loss of wetlands also means loss of water resources. Amy Ferriter of the South Florida Water Management District (SFWMD) said the melaleuca is taking over water-conservation areas.
"Historically, Lake Okeechobee was largely marsh with many different plant species," she said. "There is a 100,000-acre marsh in that lake. In the 1940s, the Army Corps of Engineers planted melaleucas around the rim of the lake; now there are tree forests covering 12,000 acres of the marsh."
Tony Pernas, resource management specialist with the National Park Service (NPS) at BCNP, said several factors have contributed to the spread of melaleucas in the preserve -- offroad vehicles, ornamental plantings at home sites and hunting camps, fires, and a lack of natural enemies. "After a fire, a single melaleuca tree releases about 20 million seeds. The same fire kills off a lot of our native species, so the seeds have little or no competition for light and space. Native plants and trees have some sort of bugs that eat them and keep them in balance, but the melaleuca has no natural enemies here, no biological controls for checks and balances. The trees multiply and become so dense they eventually shade out a lot of the competition."
In 1984, NPS resource managers identified the melaleuca as a serious threat to the ecosystem of the preserve, and initiated an eradication program. Since the tree crosses many political boundaries, NPS efforts have been joined by other government and public agencies, and volunteer organizations. Eradication efforts involve systematic reconnaissance flights, aerial photography and ground crews. The driving technologies of the program are GIS and GPS, which are used to locate and provide map coverage of the trees and to maintain databases on treatment progress and follow-up programs.
According to SFWMD's Dan Thayer, the task of coordinating efforts and resources is the responsibility of an interagency steering committee made up of all the resource management people who have to deal with the melaleuca problem. "We function in a coordinated and systematic fashion," Thayer said, "so we know where everyone is working and which areas have been treated. We also share information, funding resources, and the research we all feel is needed."
Ferriter pointed out that the agencies involved in melaleuca eradication all use basically the same approach and share information on resources and procedures. "SFWMD, for example, flies periodic aerial surveys at 500 feet over