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         General Impact

    For a detailed account of the impacts of M. quinquenervia please read: Melaleuca quinquenervia (Broad-Leaved Paperbark) Impacts Information. The information in this document is summarised below.

    Melaleuca is the most problematic invasive plant species in Florida because of its wide distribution range, prolific seed production and potential impact on human health (Fuller 2005). Melaleuca threatens the preservation of critical wildlife habitat in southern Florida including in the Florida Everglades National Park. Despite control efforts melaleuca still occurred in around 170 000 hectares of southern Florida in 1997, representing 6% of the total region (Bodle & Van 1999, in Rayamajhi et al. 2007; Laroche 1999).
    Ecosystem Change: Melaleuca threatens the integrity of subtropical freshwater ecosystem processes in Florida (Dray & Center 1994, in Lopez-Zamora Comerford & Muchovej 2004) by altering soil chemistry, reducing de-composition rates and modifying hydrology and fire regime. Melaleuca also reduces species biodiversity and alters species composition.
    Reduction in Native Biodiversity: Melaleuca forests provide limited food and habitat value for native wildlife and can reduce indices of native species in Florida wetlands by as much as 80% (Dray et al 2006; Bodle et al., 1994, O’Hare & Dalrymple, 1997, in Dray et al. 2009; Porazinska Pratt & Giblin-Davis 2007). Decreases in diversity of native plant biodiversity have also been linked with melaleuca in the Bahamas.
    Habitat Alteration: Melaleuca is contributing to significant habitat loss in the Everglades National Park by converting fire-maintained sawgrass communities into Melaleuca forest (Turner et al. 1998, in Munger 2005).
    Displacement: Melaleuca displaces pond cypress (Taxodium ascendens) (Myers 1975 1983, Ewel 1986, in Rayamajhi et al. 2008b), slash pine (Pinus elliottii) and sawgrass (Cladium jamaicensis) (Bodle et al., 1994, in Tipping et al. 2008).
    Competition: Melaleuca is competitively superior to most native vegetation occurring in the Florida Everglades (Turner et al. 1998, in Pratt et al. 2005b). It is fire-adapted, herbivore-adapted and produces seeds and roots prolifically.
    Inhibits the Growth of Other Species: Allelochemicals present in roots can have a detrimental effect on the soil biota (Porazinska Pratt & Giblin-Davis 2007).
    Economic:Balciunas and Center (1991, in Serbesoff-King 2003) reported that by the year 2010, close to $2 billion would be lost due to the melaleuca invasion in southern Florida. Financial losses included $1 billion in tourism to the Everglades NP, $250 million in tourism to the rest of south Florida, $250 million in recreation, $250 million due to fires, $1 million in control efforts, $10 million due to loss of endangered species and $1 million to nursery growers.
    Agricultural: In one study 18 economic arthropod pests were collected from M. quinquenervia (Costello et al. 2008).
    Human Health: As melaleuca populations expand in southern Florida and the human population increases the risk of fire and loss of human life and property increases (Laroche 1999).
    Modification of Hydrology: A stand of melaleuca may transpire more water than the sawgrass communities it replaces (Hofstetter 1991a, in Laroche 1999).
    Modification of Fire Regime: Ground fires, high temperatures, rapid spread rates and abundant smoke, all present in burning melaleuca stands, present new risks for wildlife in the Everglades wetlands (Flowers 1991, in Laroche 1999).
    Modification of Nutrient Regime: The rate of decomposition of melaleuca litter is slower than that of native plants (Van & Rayamajhi, Unpub. Data, in Rayamajhi et al. 2006b).




         Location Specific Impacts:
    Florida Everglades (United States (USA)) English 
    Habitat alteration: Melaleuca has altered thousands of areas of the Everglades by replacing native tree islands, sawgrass marshes, mesic prairies and aquatic sloughs (Laroche 1999). For example, the presence of melaleuca in fire-maintained sawgrass communities can promote conversion of these habitats to melaleuca forest. Everglades marshlands are comprised of fire-maintained communities of mostly sawgrass prairies. Natural fires periodically eliminate the native, fire-intolerant hardwoods that would otherwise colonise this habitat. However, because melaleuca is so well-adapted to fire it can persist and even thrive in this environment, eventually shading out the herbaceous community and transforming the site into a melaleuca forest (Turner et al. 1998, in Munger 2005).

    Threat to endangered species: This unique area has produced approximately 65 endemic plant taxa, many of which are threatened due to habitat diminishment (Turner et al. 1998, in Munger 2005).
    Florida (USA) (United States (USA)) English 
    Competition: Melalueca quinquenervia has proven to be a superior competitor to most native vegetation occurring in the organically rich soils of forested and sawgrass dominated wetlands that characterize the Florida Everglades (Pratt et al. 2005).

    Economic/Livelihoods: Diamond et al. (1991, in Buckingham 2000) prepared a state economic impact statement in support of adding melaleuca to the Florida Prohibited Aquatic Plant List. It was consequently added to the list.

    Habitat alteration: Dense monospecific stands of melaleuca displace vast areas of native plant species (Pratt et al. 2005).

    Modification of fire regime: Massive seed dehiscence and release follows disturbances such as fire events. Once established, melaleuca is likely to attain and retain dominance on sites visited by frequent fire. March to June is typically considered wildfire season in southern Florida (Robbins & Myers 1992, in Munger 2005).

    Reduction in native biodiversity: Melaleuca-dominated landscapes result in drastically reduced biodiversity. Infestations have been found to reduce above- and below-ground biodiversity by as much as 80% (Poraziska et al. 2007). Density declines of melaleuca, due to control techniques, coincided with two to four fold increases in plant species diversity in some areas (Rayamajhi et al. 2008b). Bancroft et al. (1992, in Laroche 1999) claims that the trend of increasing Melaleuca forest, along with formerly rare cattail (Typha dominguensis) populations in the water conservation areas of the Everglades, can be expected to degrade native wood stork (Mycteria americana) habitat.

    Threat to endangered species: South Florida encompasses the only region of the continental United States where temperate, subtropical and tropical floral elements coexist. This unique interface has produced about 65 endemic plant taxa, many of which are threatened due to habitat diminishment (Turner et al. 1998). There are concerns that M. quinquenervia invasions could further reduce populations of such endangered species as the Wood Stork (Mycteria americana) (Bancroft et al. 1992, in Turner et al. 1998) and the Florida Panther (Felis concolor coryi) (Grow 1984, in Turner et al. 1998).



ISSG Landcare Research NBII IUCN University of Auckland