8 AUSTRALIAN PAPERBARK TREE (MELALEUCA) M. B. Rayamajhi,1 M. F. Purcell,2 T. K. Van,3 T. D. Center,3 P. D. Pratt,3 and G. R. Buckingham4 1Fort Lauderdale Research and Education Center, University of Florida, Fort Lauderdale, Florida, USA 2U.S. Department of Agriculture Australian Biological Control Laboratory, Indooroopilly, Queensland, Australia 3U.S. Department of Agriculture, Agricultural Research Service, Invasive Plant Research Laboratory, Fort Lauderdale, Florida, USA 4U.S. Department of Agriculture, Agricultural Research Service, Florida Biocontrol Laboratory, Gainesville, Florida, USA fested areas and causing local municipalities to incur PEST STATUS OF WEED additional fire fighting costs (Diamond et al., 1991). The exotic tree Melaleuca quinquenervia (Cav.) Blake Melaleuca quinquenervia infested areas become (commonly referred to as melaleuca or paperbark less attractive and monocultures become impen- tree) aggressively invades many south Florida eco- etrable to tourists, hikers, boaters, and other recre- systems (Fig. 1), including the Everglades (Hofstetter, ational users. Such impacts result in decreased rev- 1991; Bodle et al., 1994). It was introduced during enues for parks and harm the economies of surround- the early 1900s or late 1800s (Gifford, 1937; ing communities that rely on tourism associated with Meskimen, 1962; Dray, pers. comm.). Melaleuca wilderness areas (Diamond et al., 1991). quinquenervia displaces native vegetation, degrades Ecological damage. Prolific seed production, wildlife habitat, creates fire hazards, and causes hu- tolerance of brackish water, flooding, and fire enable man health problems (Morton, 1962; Diamond et al., M. quinquenervia to aggressively invade various wet- 1991). Florida state laws enacted in 1990 and 1993 land habitats and diminish the value of these habitats prohibit the sale, cultivation, and transportation of for native plant communities and associated wildlife M. quinquenervia. It was placed on the United States (Meskimen, 1962; Crowder, 1974; Myers, 1975; Department of Agriculture’s Federal Noxious Weed Hofstetter, 1991). Melaleuca quinquenervia may ac- List in 1992 (Bodle et al., 1994; Laroche, 1994). celerate loss of groundwater due to increased evapo- Although M. quinquenervia is a major pest in transpiration (Alexander et al., 1977), although this south Florida, it is considered threatened in its na- view has been challenged (Allen et al., 1997). Trees tive Australia. Therefore, conservation groups in produce allelopathic chemicals (Di Stefano and Australia advocate its protection. Melaleuca Fisher, 1983), which may enhance their ability to dis- quinquenervia habitat in Australia comprises low- place native flora. Melaleuca quinquenervia invasion lying, high-rainfall areas, primarily in coastal regions has resulted in significant (60 to 80%) losses of (Resource Assessment Commission, 1992). Most of biodiversity in freshwater herbaceous marsh commu- the remaining and remnant M. quinquenervia wood- nities in south Florida (Austin, 1978). lands in Australia are located on private land, where Extent of losses. The extent of the M. clearing for commercial development continues. quinquenervia infestation in southern Florida (the area south of Lake Okeechobee) has been estimated Nature of Damage at 0.20 to 0.61 million ha of the total 3.04 million ha (7 to 20% of the total) in the region (Bodle et al., Economic damage. Melaleuca quinquenervia flow- 1994). It has been suggested that many of the remain- ers several times a year producing large amounts of ing natural areas within this region will be overtaken pollen, allegedly a mild respiratory allergen (Morton, by uncontrolled growth of M. quinquenervia within 1962; Lockey et al., 1981; Stanaland et al., 1986), from 30 years (Bodle et al., 1994). which as much as 20% of the population may suffer The National Park Service, the U.S. Fish and allergic reactions (Diamond et al., 1991). In addition, Wildlife Service, the U.S. Army Corps of Engineers, M. quinquenervia trees burn with extremely hot and the South Florida Water Management District crown fires due to high foliar concentrations of es- repeatedly conduct costly and labor-intensive opera- sential oils. These fires are difficult to extinguish, of- tions to control M. quinquenervia. Mechanical re- ten threatening buildings near M. quinquenervia-in- moval of a moderately thick stand (about 988 trees/ 117 Biological Control of Invasive Plants in the Eastern United States ha) cost $2,080/ha (McGehee, 1984), whereas ground herbicide treatment using tree injection techniques cost $1,330/ha (Laroche et al., 1992). Aerial treat- ments are less expensive but less effective and cause more damage to non-target plant species. Addition- ally, seed release is accelerated among trees stressed by herbicides and new infestations are created by dis- persal of these seeds (Laroche and Ferriter, 1992). This regeneration of treated stands necessitates repeated herbicidal applications, which compromises environ- mental preservation. According to a recent estimate, Figure 1a. the South Florida Water Management district alone spent more than $13 million from 1991 to 1998 for M. quinquenervia control in water conservation ar- eas, Lake Okeechobee, and Loxahatchee Wildlife Refuge (Laroche, 1999). Millions of dollars also have been spent by other agencies such as Loxahatchee National Wildlife Refuge, Big Cypress National Pre- serve, Everglades National Park, Lee County, Mi- ami-Dade County, and Palm Beach County. Melaleuca quinquenervia trees benefit Florida’s beekeeping, chip, mulch, lumber, and pulp industries. However, M. quinquenervia honey is less valuable than that from fruit tree sources. Furthermore, ac- Figure 1b. cess to M. quinquenervia infestations limits commer- cial utilization. Failure to control expanding M. quinquenervia infestations would result in an esti- mated loss of $168.6 million/year in revenue from reduced ecotourism of the Florida Everglades (Schmitz and Hofstetter, 1999). Geographical Distribution Native range. Melaleuca quinquenervia is the south- ern-most member of the M. leucadendra complex. It is distributed within a 40-km-wide zone along Australia’s northeastern coast from Sydney in New South Wales to the tip of Cape York peninsula in Figure 1c. northern Queensland; in New Guinea; and in New Figure 1. Melaleuca quinquenervia in Florida: (a) Caledonia (Fig. 2) within the range of 11 to 34o S lati- Flowering sapling representing early invasion tude (Boland et al., 1987). Its altitudinal range is from stage in seasonally flooded habitat; (b) A well- sea level to about 100 m, sometimes up to 165 m established mature stand in a permanently (Boland et al., 1987). It occurs in coastal wetlands that flooded sawgrass habitat in the Everglades, note are at least seasonally inundated, such as freshwater the tree stand is surrounded by sawgrass; (c) Vertical section of a stand in seasonally flooded swamps, stream banks, and in brackish water behind site in the Everglades. (Photographs by M. mangrove swamps. The center of diversity for the M. Rayamajhi and W. Durden.) leucadendra complex is on the Cape York Peninsula in northern Queensland (Turner et al., 1998). Barlow 118 Australian Paperbark Tree (Melaleuca) 1989). The genus contains at least 219 and perhaps more than 250 species (Craven and Lepschi, 1999) and is the third largest angiosperm genus in Austra- lia (Barlow, 1986). Melaleuca quinquenervia is a mem- ber of the M. leucadendra (L.) L. group, 15 species that are mostly large shrubs or trees and occur pri- marily in northern and northeastern Australia (Boland et al., 1987; Craven, 1999). Biology Holliday (1989) and Bodle et al. (1994) describe M. quinquenervia as being erect trees up to 25 m tall with multi-layered, thick white or grayish papery bark that insulates the trunk and branches. Leaves are lan- ceolate-elliptical to oblanceolate with five prominent longitudinal veins; up to 3 cm broad and 10 cm long; and flat, stiff, and leathery when mature. In general, woody biomass constitutes a major portion (83 to Figure 2. Melaleuca quinquenervia distribution in 96%) of dry weight across habitats (non-flooded, Australia and neighboring islands. Solid black seasonally flooded, and permanently flooded), with colors and stars represent continuous and the remaining portion (4 to 17%) being comprised relatively isolated M. quinquenervia forests, of foliage and seed capsules (Rayachhetry et al., 2001). respectively. (Map by D. Johnston.) (1988) noted the genus Melaleuca to be of northern Australian (tropical) origin, with the high diversity in temperate areas representing a secondary area of species radiation. Florida. The main infestations of M. quinquenervia exist along both coasts of southern Florida with scattered infestations in between (Fig. 3). The northernmost records (ca. 30o N latitude) are in Gainesville (Turner et al., 1998). BACKGROUND INFORMATION ON PEST PLANT Taxonomy The taxonomic position of M. quinquenervia accord- ing to Cronquist (1988) is as follows: class Magnoliopsida (Dicot), subclass Rosidae, order Myrtales, family Myrtaceae, subfamily Myrtoidea, tribe Leptospermae, genus Melaleuca, species quinquenervia (Cav.) Blake. Synonyms include M. leucadendra L., M. viridiflora var. angustifolia (L.f.) Byrnes, M. viridiflora var. rubiflora Brong. and Gris., Figure 3. Melaleuca quinquenervia distribution in and Metrosideros quinquenervia Cav. Florida. Note stand concentrations along east Linnaeus coined the genus name Melaleuca and west cost of central