Melaleuca, Melaleuca quinquenervia, is a fast-growing and hardy tree with a
slender crown and a layered, peeling paper-like white bark somewhat resembling
that of a birch tree. Branches occur at irreglar intervals off of the main
Melaleuca leaves are 10-15 cm long, evergreen, lanceolate, simple and
short-stalked, parallel-veined, alternate in arrangement, and aromatic when
crushed. The flowers are small and white, with multiple stamens, arranged in
botllebrush-shaped clusters at the branch tips. The fruits are small, round
woody capsules containing 200-300 seeds (Langeland and Burks 1998, FLEPPC 1999,
Potentially Misidentified Species
Melaleuca are unlikely to be mistaken for any other species where it
grows in Florida. The river birch (Betula nigra), whose papery bark is
somewhat similar to that of melaleuca, is restricted to north Florida
counties in which M. quinquenervia does not occur (University of Florida
HABITAT AND DISTRIBUTION
Melaleuca quinquenervia is a non-indigenous species whose native range includes Australia,
New Guinea and the Solomon Islands (Langland and Burks 1998).
In Florida, melaleuca is restricted to the southern half of the state, and
counties at the southern end of the state are most vulnerable. The northern
limit of its potential range is commonly cited as Indian River County on the east coast and Pinellas County on the Gulf
coast. However, melaleuca has been found naturalized as far north
as Hernando, Lake, and Brevard counties, and even up into Volusia County on the
east coast (Wunderlin et al. 1995, FLEPPC 2005).
Melaleuca quinquenervia is established in all six counties in the IRL watershed.
LIFE HISTORY AND POPULATION BIOLOGY
Age, Size, Lifespan
Melaleuca quinquenervia can grow to around 33 m in Florida at a rate of approximately 1-2 m/year (Langeland ad Burks 1998).
Melaleuca quinquenervia is considered the most prominent of 60 non-native plant species
presently invading the natural areas of south Florida. The species has invaded had
invaded more than 200,000 hectares (nearly a half-million acres) in South
Florida by 1994, including significant acreage within the Everglades (Langland
and Burks 1998, Mazzotti et all 2002).
Melaleuca quinquenervia primarily propagates by sexual seed production. The
species matures rapidly, and is capable of flowering within three
(and as little as two) years of germination and as frequently as
five times each year (Meskimen 1962, Laroche 1994b). In South
Florida, the species blooms primarily during the winter months
(November-January), although it is capable of some flowering
throughout the year. Flowering is asynchronous both among trees
and among the flowers of a single specimen (FLEPPC 1999).
Large M. quinquenervia specimens have a very high reproductive
potential and up to 20 million seeds per year are stored in the
seed capsules of a single tree. Seed capsules must be dried out
before they can release seeds to the environment. Seeds can
remain viable within seed capsules for several (at least ten) years
(Meskimen 1962, Langland and Burks 1998).
Physical damage such as broken or cut branches will trigger the rapid
release of seeds from capsules on the injured branch. If a tree is
felled or experiences a hot-burning fire this will trigger the
shedding of all seeds within a few days (Woodall 1983).
Percent seed viability is reported to be fairly low at 10-20%, although the
seeds that are viable may remain so in their seed capsules for years (Meskimen
1962). Because trees can harbor several million seeds, the viable seedstock on
each tree can reach a level of several hundred thousand seeds.
Manipulitive studies suggest that the viability of released seeds is reduced by
50% after 8 months in the ground (FLEPPC 1999). Germination occurs in moist
soils within several days of wetting and inundated seeds can germinate or
can remain viable for up to six months (Myers 1975, Lockhart 1996).
Frost appears to limit northward expansion in Florida, although young trees may
be the most susceptible to freezing; mature melaleuca have been observed to
survive record-breaking freeze events. Freezing is yet another environmental
stress factor known to trigger mass seed release (Woodall 1981).
Melaleuca quinquenervia responds optimally in seasonally wet sites, but is also able to
flourish in standing water as well as in well-drained upland soils (Laroche
1994b). Wetter communities are usually more susceptible than drier sites to
initial invasion and unusually wet years extend the flowering and growing
season in M. quinquenervia (FLEPPC 1999).
Salinity is believed to be a limiting factor, although melaleuca is capable of
growing in mangrove and backmangrove areas in both its natural and introduced
range (Myers 1975, Center and Dray 1986).
Young seedlings are usually killed by fire, but older individuals withstand
fire well (Meskimen 1962, Myers 1975, 1983). Frequent fires facilitate the
establishment of Melaleuca quinquenervia by triggering seed release, killing back
competitors, and preparing the site for germination of seedlings (Myers, 1983,
FLEPPC 1999). Melaleuca invasion alters community fire regimes, as when it
displaces herbaceous species such as sawgrass, Cladium jamaicense (Flowers 1991).
Within its native range Melaleuca quinquenervia thrives in low-lying wet areas that
experience periodic fires. These are conditions similar to those found in a
number of south Florida habitats. Florida habitats that have been invaded by
melaleuca include natural systems such as lake margins, pastures, pine
flatwoods, mesic prairies, sawgrass marshes, and cypress stands, as well as
marginal habitats like roadsides, rights-of-way, and ditch banks. Habitat
disturbance may facilitate invasion by this pioneering species but it is not a
prerequisite condition (FLEPPC 1999).
In general, melaleuca stands in South Florida are reported to be little-used by
native wildlife. Schortemeyer et al. (1981) reported an exception in a number
of bird species (including anhingas, egrets, and herons) who were observed to
utilize melaleuca stands where artificially deep water and extended
hydroperiods had killed or damaged a significant number of native trees.
Melaleuca was brought to Florida through multiple introduction
events in the early 20th century, originally for use as a landscape
ornamental tree and also as a source of wood. The first two
introduction sites were in Broward and Lee counties, where M.
quinquenervia seeds transported from Australia were planted. In the
1930s, M. quinquenervia trees were planted as soil stabilizers on
canal levees bordering the southern end of Lake Okeechobee and also
in Big Cypress National Preserve. Seeds were also intentionally
scattered from airplanes over the Everglades in the 1930s to
facilitate the rapid establishment of melaleuca forests (Austin
The popularity of melaleuca as an ornamental species, as a
windbreak, and for fence rows further facilitated spread of the
species in Florida. Environmentally-mediated spread of melaleuca
through South Florida and deep into the interior of the Everglades
was also greatly facilitated by propagule transport via wind and
water (FLEPPC 1999). Even decades later, the general South Florida
distribution of melaleuca centers around those areas where the tree
was originally introduced (Mazzotti et al. 2002).
As recently as 1970, M. quinquenervia continued to be recommended as
"one of Florida's best landscape trees" (Langland and
The speed at which melaleuca spreads and comes to dominate new areas
has been described as explosive (Cost and Carver 1981, Hofstetter
1991). As little as 25 years is required for a one square-mile
area to progress from 5% to 95% M. quinquenervia infestation
(Laroche and Ferriter 1992). It poses a serious threat to ongoing
Everglades restoration and preservation efforts, and a threat to
South Florida's other natural areas as well (FLEPPC 1999).
Potential to Compete With Natives
Melaleuca is principally an invader of disturbed sites, but undisturbed native
Florida habitats may exhibit a degree of resistance to invasion and
establishment (Ewel et al. 1976). Canal banks, pine savanna, managed pineland
margins, prairie and cypress marshes and sawgrass prairies are among the
disturbed and undisturbed habitats susceptible to M. quinquenervia
(Myers, 1975, Richardson 1977, DiStefano and Fisher 1983, Duever et al. 1986,
Laroche and Ferriter 1992). Where it does become established, M.
quinquenervia can form dense monotypic stands capable of sisplacing native
plants (Richardson 1977).
Langland and Burks (1998) note that melaleuca is now recognized
internationally as a threat to the Florida Everglades, a World Heritage Site
and International Biosphere Reserve.
Possible Economic Consequences of Invasion
Although melaleuca appears to have minor positive economic benefit in Florida as a
plant utilized by commercially managed honeybees, the negative impacts of
invasion by this species are of far greater consequence.
Diamond et al. (1991) published a cost-benefit analysis for south Florida in
which they contrasted a modest estimated annual benefit to the beekeeping and
pollination service industry of around $15 million with an estimated $168.6
million a year gained through Eco-tourism and other industries that would be
lost in the event of complete infestation by melaleuca of the Everglades and other south Florida wetlands.
The World Conservation Union's Invasive Species Specialist Group (ISSG) lists
melaleuca as among "100 of the world's worst invasive alien species" and
recognizes them as potentially major drivers of ecosystem change.
Austin D.F. 1978. Exotic plants and their effects in southeastern Florida.
Environmental Conservation 5:25-34.
CenterT.D., and F.A. Dray, Jr. 1986. Melaleuca quinquenervia, a serious
threat to South Florida wetlands, report of the U.S. Department of Agriculture.
Agricultural Research Service (ARS), Aquatic Plant Laboratories, Ft.
Diamond C., Davis D., and D.C. Schmitz. 1991. Impact Statement: The addition of
Melaleuca quinquenervia to the Florida Prohibited Aquatic Plant list.
In: Proceedings of the Symposium on Exotic Pest Plants, November 2-4, 1988,
Doren, R.L. Hofstetter, R.L. Myers, and L.D. Whiteaker, eds), pp. 87-110.
NPS/NREVER/NRTR-91/06 Tech. Report, U.S. Department of the Interior, National
Park Service, Denver, Colorado.
DiStefano J.F., and R.F. Fisher. 1983. Invasion potential of Melaleuca
quinquenerviain southern Florida, U.S.A. Forestry Ecological Management
Duever M.J., Carlson J.,. Meeder J, Duever L., Gunderson L., Riopell L.,
Alexander T., Myers R., and D. Spangler. 1986. The Big Cypress National
Preserve. The National Audubon Society Research Center Report No. 8. New York.
Ewel J., Meador R., Myers R., Conde L., and B. Sedlik. 1976. Studies of
vegetation changes on South Florida. Report to U.S. Forest Service on Research
Agreement 18-492, University of Florida, Gainesville, Florida.
FLEPPC. 1999. Melaleuca management plan: Ten years of successful melaleuca
management in Florida 1988-1998. Recommendations from the Melaleuca Task Force,
Florida Exotic Pest Plant Council (3rd edition). Laroche F.B. (Ed.). 128 p.
FLEPPC. 2005. List of Florida's Invasive Species. Florida Exotic Pest Plant
Council. Available online.
Flowers J.D. 1991. Subtropical fire suppression in Melaleuca
quinquenervia. In: Proceedings of the Symposium on Exotic Pest Plants,
November 2-4, 1988, Miami.
Hofstetter R.H. 1991. The current status of Melaleuca quinquenervia in
southern Florida. In: Proceedings of the Symposium on Exotic Pest Plants,
November 2-4, 1988, Miami.
Langeland K.A. and K.C. Burks (Eds.). 1998. Identification and biology of
non-native plants in Florida's natural areas. UF/IFAS. 165 p.
Laroche F.B., and A.P. Ferriter. 1992. Estimating expansion rates of melaleuca
in south Florida. Journal of Aquatic Plant Management 30:62-65.
Lockhart C.S. 1996. Aquatic heterophylly as a survival strategy in Melaleuca
quinquenervia (Myrtaceae). Canadian Journal of Botany. 74:243-246
Mazzotti F.J., Ostrenko W., and A.T. Smith. 1981. Effects of the exotic plants
Melaleuca quinquenervia and Casuarina equisetifolia on small mammal
populations in the eastern Florida Everglades. Florida Scientist 44:65-71.
Meskimen G F. 1962. A silvical study of the Melaleuca quinquenervia tree
in south Florida. Unpublished MS Thesis. University of Florida, Gainesville,
Florida 177 p.
Myers R.L. 1975. The relationship of site conditions to the invading capability
of melaleuca in southern Florida. Unpublished MS Thesis. University of Florida,
Gainesville, 151 p.
Myers R.L. 1983. Site susceptibility to invasion by the exotic tree
Melaleuca quinquenervia in southern Florida. Journal of Applied Ecology
Richardson D.R. 1977. Vegetation of the Atlantic Coastal Ridge of Palm Beach
County, Florida. Flaorida Scientist. 40:281-330.
Schortemeyer J.L., Johnson R.E., and J.D. West. 1981. A preliminary report on
wildlife occurrence in melaleuca heads in the Everglades Wildlife Management
Area. p. 81-89 in: Proceedings of the Melaleuca Symposium, Sept. 23-24, 1980.
Florida Division of Forestry, Tallahassee.
University of Florida 2006. Florida Forest Stewardship Trees Of Florida online
database. Available online.
Woodall S.L. 1981. Site requirements for melaleuca seedling establishment. Pp
9-15 In: Geiger R.K. (Ed). Proceedings of the Melaleuca Symposium, Sept. 23-24,
1980. Division of Forestry, Florida Department of Agriculture and Consumer
Woodall S.L. 1983. Establishment of Melaleuca quinquenervia seedlings in the
pinecypress cotone of southwest Florida. Fla. Scientist. 46:65-71.
Wunderlin R.P., Hansen B.F., and B.L. Bridges. 1995. Atlas of Florida vascular
plants. Available online.