Australian Weeds Overseas

Case Study - Florida, USA

The Florida Exotic Pest Plant Council (EPPC) was established in 1984. The Council studies the impact of exotic pest plants on biodiversity, on the integrity of native plant community composition and function, on habitat loss and on endangered species. It manages a programme to inform and educate resource managers about which species deserve to be monitored and about setting priorities for management.

The EPPC listes exotic plant pests under two categories:

Category 1: Exotic plant pest which invade and disrupt Florida native plant communities, without regard to the economic severity or geographic extent of the problem.

Category 2: Exotic pest plants which have the potential to invade and disrupt native plant communities as indicated by:

  • Aggressive weediness
  • A tendency to disrupt natural successional processes
  • A similar geographic origin and ecology to Category 1 species
  • A tendency to form large vegetative colonies, and/or
  • Sporadic, but persistant, occurrence in natural communities

Australian plant species currently listed by the EPPC are:

   Melaleuca quinquenervia
   Much appreciated in its homeland, Melaleuca quinquenervia has proved to be a particularly unpleasant guest in south Florida.
Photo: Brian Walters

Category 1

  • Acacia auriculiformis
  • Casuarina equisetifolia
  • Casuarina glauca
  • Cupaniopsis anacardioides
  • Ficus microcarpa
  • Melaleuca quinquenervia
  • Melia azedarach
  • Scaevola taccada var.sericea
  • Schefflera actinophylla

Category 2

  • Casuarina cunninghamiana
  • Eucalyptus "camaldulensis" (identity uncertain)
  • Ficus benjamina
  • Hibiscus tiliaceus
  • Murraya paniculata

Some of these listed species also occur naturally outside of Australia. The best known species for its invasive tendency is Melaleuca quinquenervia. This was introduced into Florida in the early 1900s and was soon widely planted as an ornamental and landscaping tree. It was also used as a means of drying up parts of the Everglades to decrease mosquitoes and allow development.

Since that time the tree has spread into almost every native ecosystem and is estimated to cover between 200,000 and 1 million hectares of south Florida. The plant is listed on the Federal Noxious Weed List and, as part of a campaign to educate the public about the problems posed by the tree, a brochure with the provocative title "Wanted: Dead not Alive" has been produced by the Florida EPPC.

The plant grows very densely and rapidly in the south Florida environment crowding out native vegetation and displacing cypress and sawgrass in the Everglades. The trees spread by both prolific seed production and adventitious root spread. Cut trees quickly resprout from trunks and roots.

The need to control the spread of the tree has been the subject of some debate over the years. The "Journal of Forestry", July 1981 commented:

"If you are interested in causing a stir in south Florida, just mention that melaleuca is a very fine tree. You will rouse the ire of wildlife biologists, some doctors, some hydrologists and most naturalists. Or, using another approach, say that you regard melaleuca as the worst pestilance ever to find its way into the south Florida ecosystem, but be ready to take on local beekeepers, nurserymen who use it as an ornamental, and even some foresters who see it as an energy source for the future."

Control of the plant is difficult but some progress is being achieved through the use of biological agents. In an article titled "It's Aussie v Aussie in the battle for Florida's wetlands", the Sydney Morning Herald (8 July 2006) reports that the melaleuca snout weevil (released in 1997) and a psyllid (released in 2002) "have helped Florida to reclaim 40,000 hectares". Physical removal, however, remains the principal means of preventing the spread of the species.

These notes were prepared (mainly) from material supplied by Amy Ferriter of the EPPC.

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