Nonindigenous Aquatic and Semi-Aquatic Plants in Freshwater Systems

Nonindigenous Semi-Aquatic Plants

Australian Pine, Beefwood, Swamp She-Oak (Casuarina equisetifolia) L. ex J.R. and G. Forst., (C. gluaca) Sieb. exk Spreng, (C. cunninghamiana) Miq.

Several species of Australian pine were introduced into Florida before 1920 (Morton 1980). The three species of Australian pine in Florida are Casuarina equisetifolia, C. glauca, and C. cunninghamiana. Hybridization of these species is extensive and complicates identification (Schardt and Schmitz 1990). The tree is an emersed hardwood, native to Australia and Malaysia, and occurs along rocky coasts, dunes, sand bars, and islands.

The Australian pine was primarily planted to form windbreaks along coastal areas. The trees can reach 35-m heights. Published surveys or estimates of area in Florida that were invaded by Australian pine were not available; however, the species is abundant in southern Florida and extends as far north as Gainesville. Australian pine occurs in 30 of Florida's state parks (Schardt and Schmitz 1990).

Australian pines grow at a rate of 1.0 to 1.5 m a year. This fast growth rate has created problems for utility companies in southern Florida because of interference with power and telephone transmission lines. In southern and central Florida, Australian pines typically produce dense stands and form thick carpets of needles on the ground that prohibit the growth of native vegetation. In dune communities, Australian pine's dense shade and leaf litter retard the growth of native coastal vegetation (Schardt and Schmitz 1990).

Dense monospecific stands of Australian pine crowd out native vegetation in coastal areas and affect the cotton rat (Sigmodon hispidus), marsh rabbit (Sylvilagus palustris), and gopher turtle (Gopherus polyphemus; (Morton 1980). The trees also usurp the nesting places of loggerhead turtles (Caretta caretta caretta) and green sea turtles (Chelonia mydas mydas) and American crocodiles (Crocodylus acutus) on sandy beaches above the high-tide line (Schardt and Schmitz 1990).

The herbicides tebuthioron or hexazinone are used for control in nonaquatic sites. Imazapyr applied to girdled trees provides some control of mature trees. Small trees can be controlled with the herbicide tryclopyr or with a combination of 2,4-D and dicamba. Cutting does not provide acceptable control because regrowth from root sprouts is quick (Schardt and Schmitz 1990).