MELALEUCA The Everglades’ second-biggest threat OMNI Earth column, 1995 By Eddie Huffman Call it the tree that ate the Everglades. Melaleuca trees suck wetlands dry and bully out native plants, putting serious stress on an already overstressed ecosystem. It's not
melaleuca forests too dense to accomodate anything but the trees themselves. From an ill-advised airplane seed drop in the early part of the century to an ongoing,
as if the Everglades lacks enemies, since development, fire, and an unhealthy water supply already besiege it on all fronts. But the melaleuca ranks as one of the
tree-by-tree fight
The trees were introduced by a young scientist named
against the invader decades later, the melaleuca has made
John Gifford intent on
quite a name for itself
transforming the "mucky
trees were introduced
wasteland" of the
Everglades' most
Everglades.
serious threats,
in South Florida. The by a young scientist named John Gifford intent on transforming the
second only to humans altering the
"mucky wasteland" of the Everglades into a
ecosystem for development and farming.
more hospitable climate for the state's
The tree grows at a rate of 52 acres per day,
human inhabitants. Colleagues mailed
transforming diverse marshlands supporting
Gifford a packet of melaleuca seeds from its
native plants and animals into dried-up
native Australia, where natural enemies
keep the tree in check. No one seems to
many trees per acre. The tupelo gum, for
know the exact year Gifford tossed his
instance, which is a standard tree in the
seeds, though experts think it was in the
paper and pulp industry, will have about
early '20s. "From an airplane, he threw the
250 trees per acre. In a melaleuca forest,
trees out in two different epicenters in the
there are trees every 18 inches to 2 feet." In
eastern Everglades," says Mike Scott, a
other words, 2,000-4,000 trees per acre.
biologist who has studied melaleucas
That density helps explain why the
extensively and who heads the Jupiter-
melaleuca poses such a threat to the
based Florida Mitigation Trust. "It started
Everglades. A mature melaleuca forest dries
thriving, and it spreads when the trees are
up the groundwater; leaf growth and
agitated." Estimates of the land impacted by
transpiration require a lot of water, and
the melaleuca range from 300,000 to 1.5
melaleucas have a lot of leaves to suck up
million acres. University of Miami biology
water and release it into the atmosphere.
professor Ron Hofstetter, who has studied
Because of the tree's substantial leaf area,
melaleucas since 1970, ranks the tree as the
Hofstetter says, 10 square feet of melaleuca
Everglades' No. 2 threat.
pump four times as much water into the atmosphere as a comparable stand of saw
In a melaleuca forest, there are trees every 18 inches to 2 feet.
grass. With the melaleuca's dense canopy blocking sunlight to the ground below and a chemical in its leaves preventing the growth of other plants around the tree, the melaleuca excludes all other vegetation, in turn eliminating food sources and habitats
Melaleuca encroachments can range from a lone tree on an acre of land to
for wildlife. Traumatize a melaleuca by cutting or
thousands of times that number in a mature
burning it and the tree fights back hard,
forest. Scott has discovered the tree's shock
releasing seeds by the millions. Its papery
value: "I'll take people in the paper industry
bark is thick and heavy with water, making
out to a melaleuca stand and they'll say,
it hard to destroy by fire. When a melaleuca
`This is incredible.' They've never seen so
does burn it burns explosively, unleashing
chemicals that can cause painful allergic
similar work in the name of "wetlands
reactions in people downwind. "There
mitigation," using money that developers
probably isn't a plant that is better suited to
must pay into a fund when converting
the Everglades than the melaleuca,"
wetlands. To counterbalance the
Hofstetter says. The tree thrives in a
melaleuca's natural defense mechanisms,
subtropical climate, grows in organic or
Forestry Resources and other combatants
mineral soils, and can survive both frost and
haul the trees away before their seed pods
fire. A single melaleuca may hold millions
open, then go back to the cleared forest to
of tiny seeds in its seed pods, and any stress
curtail the growth of any new seedlings by
on a melaleuca -- from burning a tree to
burning or spraying herbicide on them. That
chopping one down -- causes those seed
kind of mechanical control is one of three
pods to open. While the tree won't take root
methods currently being employed or
in a wetland deeper than three feet or so,
studied to combat the tree. "It's not the total
once established it can survive constant
answer," says John Cauthen, president of
flooding. Unlike Australia, in Florida the
Forestry Resources. "Certainly it's a pretty
only thing keeping the melaleuca in check
healthy part of the total solution."
is man. The tree has a few negligible virtues: Melaleuca oil is used in some skin creams and tooth polishes, and the tree is used ornamentally in parts of Florida and Southern California. Forestry Resources of
Unlike Australia, in Florida the only thing keeping the melaleuca in check is man.
Ft. Myers, has found a positive use for the melaleuca that also helps control its spread. The company clears melaleuca forests, chips the trees into mulch (sold under such brand names as Enviromulch and Florimulch), and reintroduces native vegetation to the cleared ground. Scott's company, the Florida Mitigation Trust, does
The rest of the solution involves chemical control and biocontrol. Chemical control means spraying herbicides on the trees, done en masse from the air or ground in dry areas and on a tree-by-tree basis in areas of open water. Again, any effort to kill
melaleucas requires followup work in
from Australia, arriving nearly a century
which new seedlings are destroyed by
after John Gifford's initial packet of seeds.
flood, fire, or chemicals, or by simply
"If we can stop the spread of it, then that's a
pulling them up out of the ground.
major accomplishment," says Robert F.
Biocontrol is still in the research stages,
Doren, assistant research director for
with scientists studying the use of insects
Everglades National Park. "We will never
that will attack melaleuca seed pods and
get rid of the melaleuca completely. It's just
new seedlings. It is both ironic and fitting
not possible."
that the weevils and sawflies under consideration for biocontrol are imports