Exotic Plant Species

Numerous exotic plant species have been brought into Florida for various purposes. Most of these species have not become established, and do not threaten native vegetation communities. Some, however, have escaped cultivation and are spreading in the wild. Contributing factors include south Florida’s favorable climate and the virtual absence of natural population controls. Often these plants are characterized by a high reproductive rate that threatens to invade and displace native plants.

The Melaleuca or cajeput tree (Melaleuca quinquenervia) is native to Australia and was introduced to Florida in the early 1900’s as an ornamental tree and possibly as commercial sources of wood. This species tolerates both aquatic and terrestrial habitats, often out-competing native plant species for space and light. It develops most rapidly in sawgrass areas with peat soils; however it also occurs on marl and marly peat soils. Prolific seed production, high growth rates, resistance to fire, lack of insect parasites, and low competition from native plant species, further enhances melaleuca’s ability to compete with native vegetation.

Given the rapid growth of this species, Melaleuca has the ability to invade and alter vast areas of the Everglades by replacing native tree islands and wet prairies with dense Melaleuca stands. Mature stands (forests) of these trees often form dense monocultures that eliminate other species. These stands have limited wildlife value and are characterized by reduced species diversity. It should also be noted that Melaleuca has been identified as a potential threat to south Florida’s future water supply due to its extremely high evapotranspiration rates. These trees, when located in aquatic habitats, essentially suck water out of the wetlands, releasing this water as evaporated vapor. So, as dense Melaleuca forests replace the open sawgrass prairies, ET rates greatly increase, thus providing the potential for severe impacts on regional surface water supplies.

Australian pine (Casuarina equisetifolia) includes at least three species. It is a native of Australia and is used in Florida as windbreaks. Australian pine prefers dry areas. It is found most often in coastal areas, however, it can occur in spoil piles and in elevated areas such as canal banks and along road banks.

Australian pine forms dense monotypic stands with no understory. It is a brittle tree, which easily snaps in high wind conditions. It is not considered to be fire resistant; however, it is reported to resprout after fire. Australian pine spreads by wind blown and bird-distributed seeds. Occurrence of Australian pine is limited to coastal areas in the southwest region of the park and to various bayheads throughout the area where it replaces the native plant communities.

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