BioControl DOI 10.1007/s10526-011-9390-6 Biological control of Melaleuca quinquenervia: an Everglades invader Ted D. Center • Matthew F. Purcell • Paul D. Pratt • Min B. Rayamajhi • Philip W. Tipping • Susan A. Wright • F. Allen Dray Jr. Received: 8 April 2011 / Accepted: 27 June 2011 Ó International Organization for Biological Control (outside the USA) 2011 Abstract A massive effort is underway to restore the the need to integrate biological control into conserva- Florida Everglades, mainly by re-engineering hydrol- tion biology. ogy to supply more water to the system at appropriate times of the year. However, correcting water flow Keywords Wetlands Á Weed biological control Á patterns alone will not restore the associated plant Ecosystem restoration Á Transformer species Á communities due to habitat-transforming effects of Herbivory Á Florida invasive species, in particular the Australian wetland tree Melaleuca quinquenervia (Cav.) S. T. Blake Description of the everglades, a threatened (Myrtales, Myrtaceae), which has invaded vast areas ecosystem and transformed sawgrass marshes into dense, bio- logically impoverished, structurally altered forest Located in a transition zone between temperate and habitats. To address this threat, an invasive species tropical ecosystems (Gunderson 1994), the Florida reduction program was launched that combined Everglades is a 500,000 ha subtropical freshwater mechanical removal and herbicidal control to remove wetland (Craft et al. 1995), unique in character and mature trees with the release of specialized insects to stunning in its beauty. With an average water depth of suppress seed production and lower seedling survival. only about 10 cm, it has been described as ‘‘a river of Melaleuca has now been removed from most public grass.’’ Its conservation and preservation has long lands while biological control has limited its ability to been a national conservation priority, yet paradoxi- regenerate and reinvade from nearby infestations cally it has been ditched, drained and extensively often located on unmanaged privately held lands. manipulated for water management to serve human This case illustrates how restoration of highly mod- needs. It has also been invaded by alien species that ified ecosystems may require both restoration of are highly damaging to the ecosystem. The Australia physical conditions (water flow), and suppression of tree Melaleuca quinquenervia (Cav.) S. T. Blake high impact or transformative invaders, showing well (Myrtales, Myrtaceae) is arguably the most important among these because of its power to physically Handling Editor: Roy van Driesche transform the nature of the habitat and adversely affect biodiversity (Austin 1978). Here we describe T. D. Center (&) Á M. F. Purcell Á P. D. Pratt Á an integrated control project targeting this tree, which M. B. Rayamajhi Á P. W. Tipping Á S. A. Wright Á has been conducted within the context of a larger re- F. A. Dray Jr. USDA-ARS, Fort Lauderdale, USA engineering project aimed at restoring more natural e-mail: [email protected] water flows to the region. 123 T. D. Center et al. The Everglades are part of a larger watershed that summer. Drainage and water conservation programs, originates near Orlando in central Florida, USA and however, have largely reversed this pattern by flows through Lake Okeechobee to the southern tip of retaining water during dry periods and discharging the peninsula. It now occupies a basin approximately water through drainage canals during high rainfall 170 km long by 65 km wide (Rader and Richardson events to meet urban and agricultural needs (Rader 1992) inclusive of most of the southern tip of Florida. and Richardson 1992). This has had profound neg- The topography is flat with a slight elevation change ative effects on the associated flora and fauna and has from the north to the south of only about 3–5 cm increased susceptibility to invasion by non-indige- km-1 creating a slowly southward flowing system nous species (Doren et al. 2009; Duever 2005). (ca. 0.8 km d-1) emanating from the southern end of Adjacent urban neighborhoods provide staging areas Lake Okeechobee and terminating in the mangrove for the invasion of numerous alien species, both plants estuaries of Florida Bay (George 2008;Kushlan1990). and animals, into Everglades systems (Bodle et al. It is geologically young with the oldest soils only 1994;Cox1999;Gordon1998). Over 400 introduced about 5000 years old (Gleason and Stone 1994). plant species have naturalized in south Florida. As a It encompasses one of the largest freshwater marshes result, 26% of the 840 plant species in Everglades on the North American continent and the largest National Park are not native (LaRosa et al. 1992). single body of organic soils in the world (Loveless While many of these invaders are seemingly benign 1959; Stephens 1956). It is composed of a variety of (see Williamson and Fitter 1996), some are truly habitats including marshes, sloughs, wet prairies, and transformer species capable of altering the structure tree islands. The global importance of the Everglades and functioning of the afflicted systems (Williamson is reflected in its designations as an International and Fitter 1996). The Australian tree M. quinquenervia Biosphere Reserve, a World Heritage Reserve, and is one such example due to its ability to alter ecosystem a Wetland of International Importance (Maltby and structure and functioning (Gordon 1998). Dugan 1994). Everglades plant communities contain elements of tropical (primarily Caribbean) and temperate floras, Melaleuca: the target invader and its ecological along with numerous endemic species (Gunderson impacts 1994). These communities are largely defined by their hydrology, i.e., the depth and duration of inundation Melaleuca quinquenervia is native to north-eastern (hydroperiod), which is governed by slight differ- Australia, parts of New Guinea, and New Caledonia. ences in elevation. Sawgrass (Cladium jamaicense It is a member of a larger group of 10–15 allied Crantz), the quintessential Everglades plant commu- broad-leaved species that show evidence of genetic nity, covers about 70% of the area either as mono- introgression among these species (Barlow 1988; cultures or intermixed with other emergent species Blake 1968; Brown et al. 2001; Cook et al. 2008). (Loveless 1959). The average hydroperiod for a These are often referred to as the ‘‘Melaleuca sawgrass marsh is about ten months, ranging from leucadendra’’ complex with a center of diversity in less than six months to continuous (Lodge 2004). northern Queensland. It has been present in south Shallow-water sloughs, which traverse sawgrass Florida since the late ninteenth century (Dray et al. marshes, are flooded year round and are dominated 2006), but exhibits substantial genetic heterozygosity by floating and emergent aquatic species. Tree islands and geographic population structuring (Dray et al. (bayheads, willow heads, and cypress heads) are 2009). Invasion of natural areas by this tree appar- interspersed within a matrix of shorter vegetation, ently began soon after the first trees attained seed- primarily sawgrass prairie (Rader and Richardson bearing size. Dispersal was assisted by nurserymen 1992). Upland, drier habitats include tropical hard- who are believed to have deliberately spread seeds into wood hammocks and pinelands (Gunderson 1994). natural areas as a cheap and easy means of propaga- The climate of the Everglades region is character- tion (Austin 1978;Drayetal.2006;Meskimen1962). ized by long, hot, wet summers and mild, dry winters The US Army Corps of Engineers planted trees in the (Rader and Richardson 1992). Historically, Ever- marshes of Lake Okeechobee during 1938–1941 to glades habitats were drier in winter and wetter in create offshore tree islands to protect the southern 123 Biological control of Melaleuca quinquenervia levee from erosion (Dray et al. 2006). Altered 2.3 yrs (Van et al. 2005) if conditions for germination hydrology from flood control and drainage projects are not immediately suitable. during the 1950s undoubtedly contributed to its Community transformation by melaleuca in long invasion. Stand coverage proceeds exponentially hydroperiod areas is driven by its ability to accelerate after initial colonization of suitable habitat (Laroche soil accretion. As mentioned above, slight elevation and Ferriter 1992) so by the late 1990s, it infested differences determine hydroperiod durations and lead about 400,000 ha and the Everglades was at risk of to large differences in plant communities. In contrast, being totally overwhelmed (Laroche 1998). M. quinquenervia, once established, is not much Although data are scant and some of the putative affected by hydroperiod (Woodall 1981a). Individual effects are dubious [e.g., increased transpiration M. quinquenervia trees growing in flooded environ- (Allen et al. 1997)], M. quinquenervia clearly alters ments produce adventitious ‘water’ roots surrounding fire regimes, soil elevations, water table depth, surface the base of the trunks up to the water line (Gomes flows, nutrient mineralization, disturbance regimes, and Kozlowski 1980; McJannet 2008; Myers 1983). vertical structure of plant communities, recruitment These directly add to the organic accumulation at the of native species, light availability, and nutrient base of the tree while also binding soil and trapping availability (Gordon 1998; Turner et al. 1998). One of sediments (McJannet 2008). In addition, litterfall the important impacts of melaleuca has