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 pre-determined, east-west flight lines laid out in a grid across the state," she said. "An observer on each side of the plane has a Trimble Differential GPS (DGPS) receiver, with built-in datalogger. Every eight seconds the system beeps, and observers enter attribute codes relating to density and species seen in about a half-acre area. The data are given to the Forest Service, and they generate the estimated acreage for us."
Data from the aerial surveys are used to set up sectors to be treated. Ground crews go to the sectors by airboat or helicopter, depending on the distance. When crews spot a tree, they cut it down, treat the stump with herbicide, and pull up any seedlings in the area. A crew member enters the latitude and longitude of the stump into the GPS and fills out a report, noting treatment methods, number and size of trees treated and other related data.
Field data are entered into a GIS, which is used to manage information relating to tree location, size and concentration, type of treatment, date and scheduled follow-up. SFWMD Geographer Teresa Bennett first puts the GPS latitude and longitude coordinates into Florida State Plane Coordinates so they can be overlaid with databases on county lines, roads, water canals, trails and camps. "Then I make a plot that shows which sectors the field crews treated, what was done, when, and what eradication methods were used. For a basemap, we use digitized USGS 1:24,000 quad sheets. Sector treatment dates are indicated on the map by color dots. All of '94 might be in red; '93 in green; '96 in another color. We can display all the years on one map so we can tell what year a particular sector was treated."
Dade County GIS Specialist Cathy Black said, "I do a lot of the work in ArcInfo, then take it into ArcView because it makes map display and printing easier, and allows us to query management data in Paradox. For example, the data groups are assigned a plot ID number. From ArcView, I can pull up that ID number and find out the percentage of herbicide used, or the number of saplings killed -- whatever is in that database. I can also do complicated queries by taking the coverage back into ArcInfo, along with the Paradox table."
SFWMD project manager for the melaleuca program, Francois Laroche, said that after a sector has been treated, systematic follow-up treatments are scheduled over a period of several years, with field work eventually tapering off to inspections and monitoring. "For example, we have an area we've been working in for five years, and we've been back in there twice to treat those trees a year and a half apart. When we kill a tree, it's dead. But if it drops seeds, we have to go back periodically to pull up the seedlings and ensure there is no regrowth." Laroche expects that it will take five years or more of going back to sites and doing labor-intensive work. After that, it will be a matter of inspecting and monitoring scattered seedlings, which can be easily pulled.
Pernas said NPS has a similar follow-up program. "We started on the southern boundary to protect the Everglades first, then moved our way north. Every three years we go back to an area we've treated and re-treat it. We allow the seedlings to get up high enough so we can spot them and pull them up easily before they produce seeds. We've been going back to some sites for eight years, and we're still finding stuff at the original site, but each time it gets less and less. We hope eventually we will get all of it."