Melaleuca: Distribution and Ecological Associates

Melaleuca (Melaleuca quinquenervia), a native of Australia, has become well established and invasive in southern Florida, USA. It occurs in most counties south of Hernando, Lake and Brevard Counties (Wunderlin 2000). Melaleuca invades disturbed sites such as fallow farm land, urban areas, canal banks, and spoil piles, but the larger ecological problem is that it invades in-tact natural plant communities such as pine flatwoods, Everglades tree islands, cypress forest edges, freshwater marshes, sawgrass marshes, and the non-saline end of mangroves (references within Mazotti et al. 1997, and Laroche 1999). (See Everglades, and Slash Pine for a description of plant communities)

Melaleuca is well adapted to fire and flooding, both of which are driving processes in the ecosystems of south Florida (See Everglades and Slash Pine). Melaleuca was introduced into Florida in the early 1900’s (Laroche 1999) at two coastal locations, one in SE Florida (Broward County) and the other in SW Florida (Lee County). In the 1930’s it was planted along the south rim of Lake Okechobee and in the Big Cypress National Preserve (Laroche 1999). Since then its expansion has been rapid. Though melaleuca seeds don’t typically spread far, once it has gained a foothold, it can claim a site forming monospecific stands. For instance, a 1 square mile plot of sawgrass marsh 5% infested with melaleuca was observed to reach 95% melaleuca in 25 years. As of 1993 over 450,000 acres of south Florida were infested with melaleuca with the heaviest infestations around areas of original introductions (Laroche 1999). Large-scale coordinated efforts have gone into the control of melaleuca in south Florida because of the ecological threat melaleuca poses (See also Exotic Plants). These efforts have been successful on publicly owned conservation lands and as a result, the acreage of Melaleuca has decreased since 1993.

Melaleuca can establish and thrive in a variety of soil types and along a gradient of moisture regimes. Melaleuca tends to invade wet areas more than dry areas (Hofstetter 1991 in Myers and Belles 1995). Even exceptionally wet or dry sites may become invaded by melaleuca in dry or wet years as the soil moisture regime becomes favorable for melaleuca seedling establishment (Bodle et al.1994). Seedlings cannot withstand long periods of flooding or excessive soil drying. Once Melaleuca is established, however, it is able to withstand a variety of moisture conditions. Soil type does not seem to limit the establishment of melaleuca. It can become established on mineral soils, organic soils or marl soils, though it tends to do better on acid sands or organics rather than marl (Myers 1983).

Melaleuca infestations often start as scattered single outlier trees (Wade et al 1980) that become dense monocultures with closed canopies and little understory (Wade et al. 1980). Melaleuca is well known to displace native vegetation and reduce diversity of plant and animal communities (Laroche 1999). Plant species associated with Melaleuca are generally remnant plants that were representative species of the natural community melaleuca invaded. Melaleuca shades herbaceous vegetation, and tends to eliminate other woody vegetation (see Fire Regime). Shade tolerant ferns such as swamp fern (Blechnum serrulatum) are common associates of melaleuca (Sowder and Woodall 1985).

Animal communities associated with melaleuca tend to be less diverse and have lower abundance than those associated with native plant communities. Melaleuca heads (tree islands composed of tall, mature melaleuca trees at the center ringed with saplings and seedlings) are used by some rodents: cotton mice (Peromyscus gossypinus), short tailed shrews (Blarina carolinensis), and a few cotton rats (Sigmodon hispidus) (Mazotti et al. 1981, Ostrenko and Mazzotti 1981), Though Peromyscus were more abundant in melaleuca heads than in sawgrass prairies, the diversity of rodents in melaleuca heads was not representative of other native habitats (Mazotti et al. 1981 Ostrenko and Mazzotti 1981.). A few birds have been observed using melaleuca heads. Snail kites will use melaleuca trees as perches when other native vegetation is not available. Other birds will use melaleuca for nesting in the absence of other native vegetation (Schortermeyer et al. 1981).