Invasive exotic plant species have collectively disrupted thousands of acres of natural ecosystems throughout Florida (Langeland and Burks, 1998). Out of the 21 United States ecosystems ranked as the nation's most endangered, the South Florida landscape is ranked #1 (Peters and Noss, 1995), partly due to invasive species. Invasive species damage natural areas, alter ecosystem processes, displace native species, hybridize with natives, and support other potentially damaging plants, animals, and pathogens (Randall and Marinelli, 1996).

 

Control and management of many invasive species is very expensive since it often requires many labor hours, herbicides, and specialized transportation such as helicopters in remote areas (Langeland and Burks, 1998). Measures used for the control of invasive species may also be disruptive to surrounding ecosystems. Many of the problematic, invasive plant species found in North America were originally introduced into the landscape as ornamentals (Schmitz et al., 1997). For example, Melaleuca quinquenervia, which is disrupting many parts of the Florida Everglades ecosystem, was recommended as late as 1970 as "one of Florida's best landscape trees" (Watkins, 1970). Schinus terebinthifolius was imported as an ornamental in the 1840's (Barkley, 1944) and is now estimated to occur over 283,400 ha (700,000 acres) in central and south Florida (Ferriter, 1997). In fact, over 20% of the species listed as Category I invaders by the Florida Exotic pest Plant Council are currently used as ornamentals in urban landscapes, or were originally introduced into the Florida landscape as ornamentals. Category I plant species are those that are currently invading and disrupting native plant communities in Florida. Randall and Marinelli (1996) have described other ornamental species that are invasive throughout regions of North America. Most of these plants characteristically (list from FLEPPC,1999):

• grow and mature rapidly

• produce large numbers of seed

• have highly successful seed dispersal, germination, and colonization strategies

• spread rampantly by vegetative means

• have the ability to out-compete native species

• have high costs associated with removal or control

Previous models have demonstrated that it is possible to predict invasive success based on plant traits and habitat range (Panetta, 1993; Tucker and Richardson, 1995; Rejmanek and Richardson, 1996). Reichard and Hamilton (1997) developed and evaluated several other models for predicting the invasiveness of woody plant species in North America. Their models were fairly predictive (76-86%) when evaluated with known invasive or noninvasive species (Reichard and Hamilton, 1997). The same authors also developed a decision tree for woody North American invasive species. This tree gives three options when deciding whether to allow a new species into the landscape - namely, accept, reject, or further analysis/monitoring needed. However, no standardized framework is in place for screening new ornamental species for their potential invasiveness in Florida. The United States Federal Noxious Weed Act passed in 1974, currently prohibits the import of 94 listed species (U.S. Congress, 1993) but does not require evaluation for invasive potential of "new," intentionally introduced species at the time of introduction. Because there are very few restrictions limiting what can be introduced, botanical gardens, nurseries, agricultural organizations, and individuals can import plants and exchange seeds at will (Reichard and Hamilton, 1997). As a direct consequence of invasive introductions, the Florida Nurserymen and Growers Association (FNGA) and the Florida Exotic Pest Plant Council (FLEPPC) are currently asking growers to stop production of 11 species that are invasive in Florida (Ornamental Outlook, 1999). However, new plant species are still being introduced into Florida everyday, and by the time we recognize them as seriously invasive, it may be too late for effective control measures. Screening protocols must be developed to allow the evaluation of species invasive potential prior to introduction.

 

Literature cited

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Ferriter, A. 1997. Brazilian pepper management plant for Florida. West Palm Beach: Florida EPPC. 38.
FLEPPC. 1999. List of Florida's Most Invasive Species. Florida Exotic Pest Plant Council. http://www.fleppc.org
Langeland, K.A. and K.C. Burks, eds. 1998. Identification and biology of non-native plants in Florida's natural areas. University of Florida, Gainesville, FL.
Ornamental Outlook. 1999. Industry Update: Invasive Plants. 8:6.
Panetta, F.D. 1993. A system of assessing proposed plant introduction for weed potential. Plant Protection Quarterly. 8:10-14.
Peters, R.L. and R.F. Noss. 1995. America's endangered ecosystems. Defenders Magazine.
Randall, J.M. and J. Marinelli, eds. 1996. Invasive Plants, Weeds of the Global Garden. Brooklyn Botanic Garden, Inc. Brooklyn, NY.
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Rejmanek, M. and D.M. Richardson. 1996. What attributes make some plant species more invasive? Ecology. 77:1655-1661.
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Tucker, K.C. and D.M. Richardson. 1995. An expert system for screening potentially invasive alien plants in South African Fynbos. Journal of Environmental Management. 44:309-338.
United States Congress, Office of Technology Assessment. 1993. Harmful non-indigenous species in the United States. OTA-F-565. U.S. Government Printing Office, Washington, D.C.