Non-native Invasive Plants – An Introduction
Non-native plants (“weeds” or “exotics”) have been introduced to an area from their native range, either purposefully or accidentally. The term non-native usually refers to plants from other countries, regions, or continents. Water hyacinth (Eichhornia crassipes) comes from South America. Melaluca (Melaleuca quinquenervia) comes from Australia. However, non-native can also mean plants from another region (within the same country). Smooth cordgrass (Spartina alterniflora), a desirable native plant on the U.S. Atlantic coast, is invasive on the Pacific coast, covering oyster beds and other vital habitat.
Approximately 1,400 of Florida’s plants are non-native plants. Many non-natives are not invasive and support human health and economic interests such as crop production and landscaping. These plants are well managed by those who grow them. Most other exotics present only minor problems in highly disturbed areas such as roadsides or along utility corridors. Based on the Florida Exotic Pest Plant Council's (FLEPPC) 2013 List of Invasive Plant Species, only about 11% of the nearly 1,400 exotic species introduced into Florida have become established outside of cultivation and are causing problems.
The term “invasive” describes exotic plants thriving outside cultivation, expanding into natural areas and disrupting native plant communities. The National Invasive Species Council defines invasive species as:
“. . .a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.”
The National Invasive Species Information Center says “. . .these plants are characteristically adaptable to new habitats, grow aggressively, and have a high reproductive capacity. They are often introduced to a new location without the environmental checks and balances such as seasonal weather, diseases, or insect pests that kept them under control in their native range. Their vigor combined with a lack of natural enemies often leads to outbreak populations.”
According to FLEPPC, “These population explosions can have catastrophic effects, out-competing and displacing the native plants and disrupting naturally-balanced native plant communities.” Destruction and replacement of our native plants by invasive species has several significant consequences. Wildlife that depends on native plants is often unable to adapt and may leave the area or die out. Invasive aquatic plants can completely fill the water, driving fish and wildlife from the area. FLEPPC says “This reduction in biodiversity can adversely impact wildlife and alter natural processes such as fire frequency or intensity and water flow.”
Aquatic invasive plants are especially troublesome in Florida where they can impede navigation and flood control, disrupt recreational water use, and create breeding grounds for mosquitoes. Control of invasive plants in Florida’s natural areas and waterways is expensive, costing millions of dollars each year.
The term “noxious weed” is used for state and federally regulated invasive plants. A noxious weed is defined in the Plant Protection Act of 2000 as
“. . .any plant or plant product that can directly or indirectly injure or cause damage to crops (including nursery stock or plant products), livestock, poultry, or other interests of agriculture, irrigation, navigation, the natural resources of the United States, the public health, or the environment.”
Plants on the Federal Noxious Weed List are designated by the Secretary of Agriculture or the Secretary of the Interior. Designated noxious weeds possess one or more invasive characteristics. They are difficult to manage; parasitic; a carrier or host of deleterious insects or disease; and being non-native, are new to, or not common to the U.S. or parts thereof. Listed plants are closely regulated and “prohibited or restricted from entering the United States” and “subject to restrictions on interstate movement within the United States.”
The Florida Department of Agriculture and Consumer Services, Division of Plant Industry, is the state regulatory agency responsible for implementing laws, rules, regulations, and various programs pertaining to plants and plant pests. (State of Florida Noxious Weed List)
Florida Statute 369.20, The Florida Aquatic Weed Control Act, says “The Fish and Wildlife Conservation Commission shall direct the control, eradication, and regulation of noxious aquatic weeds and direct the research and planning related to these activities, as provided in this section, so as to protect human health, safety, and recreation and, to the greatest degree practicable, prevent injury to plant and animal life and property."
FLEPPC's List of Invasive Plant Species is updated every two years by the FLEPPC Plant List Committee. The List is not a regulatory list. Only those plants listed as Federal Noxious Weeds, Florida Noxious Weeds or in local ordinances are regulated by law. FLEPPC encourages use of the List for prioritizing and implementing management efforts in natural areas, for educating lay audiences about environmental issues, and for supporting voluntary invasive plant removal programs.
For more information, see Florida's lists, laws, rules, regulations, and agencies regarding non-native plant species.
For more information on invasive species (including definitions, terminology, and guidance), visit the National Invasive Species Council (NISC) and read the White Paper created by the Invasive Species Advisory Committee (ISAC).
Non-native, invasive plants find their way here through a variety of pathways
- as seeds and weeds in imported nursery plants and soils
- as misidentified/unknown plants from aquarium keepers, water gardeners, landscapers and friends
- as whole plants or fragments in ballast water from foreign ships entering our ports
- as fruits and flowers brought home as souvenirs by travelers
- on boat trailers, propellers, and dive gear, or in bait wells.
In the past, some species were purposefully introduced to "improve" our natural areas. For example, melaleuca trees (Melaleuca quinquenervia) were introduced to Florida from Australia to dry up the Everglades for development. The plan resulted in millions of invasive melaleuca trees covering much of the Everglades. Melaleuca trees have been, and continue to be, removed at a huge expense to taxpayers.
The Chinese tallow tree (Sapium sebiferum), was sold widely as an ornamental before it was discovered to be invasive in some of Florida's wetlands. Thousands of Chinese tallow trees have spread on their own in Paynes Prairie Preserve State Park near Gainesville, and much money and labor are now spent controlling them.
Hydrilla (Hydrilla verticillata) was introduced as an aquarium plant and sold in pet stores. Hydrilla fluorishes here, now infesting tens of thousands of acres in Florida public waters. It has also spread to at least 30 states, as far away as Massachusetts and California. Hydrilla requires continuous management with herbicides and machines. Management costs in Florida public waters for this single plant species were approximately 12.4 million dollars state fiscal year 2011-2012.
Flowering plants produce seeds. Some aquatic plants even produce flowers and are pollinated under water. Ferns produce large numbers of tiny spores. Depending on the plant, its location, and other circumstances, plants may spread when
- their seeds are dispersed by wind, water, or birds and other animals
- the plant is fragmented (such as by a boat propeller or mechanical harvester) and the fragments grow into new plants
- yard waste or spoil material (from dredging or construction) is dumped elsewhere
- the root system or plant expands and gives rise to new plants
- prolific, tiny spores are spread by wind or water, or as a contaminant on clothing, mulch, or landscape material.
One of the most difficult things a management agency must do is predict which non-native plants might become invasive and which will not. Controversies exist among government agencies, environmental organizations, scientists, and those with an economic interest in new plants (ornamental plant growers or importers, and those seeking crops to produce biofuels).
To that end, the University of Florida/Institute of Food and Agricultural Sciences (IFAS) developed a working group of scientists who provide consistent recommendations concerning the use of non-native plants in Florida. The IFAS Assessment of Non-native Plants in Florida’s Natural Areas and the IFAS Invasive Plants Working Group were created in response to growing awareness of the threat posed by non-native invasive species.
The Florida Exotic Pest Plant Council (FLEPPC) is a non-regulatory organization of plant management professionals who assess the threat of Florida's non-native plants and categorize them according to their invasiveness. FLEPPC defines Category I plants as "invasive exotics that are altering native plant communities by displacing native species, changing community structures or ecological functions, or hybridizing with natives." In 2011 in Florida, 75 non-native invasive plants met these criteria.
The Aquatic Plant Management Society (APMS) defines aquatic plant control as “techniques used alone or in combination that result in a timely, consistent, and substantial reduction of a target plant population to levels that alleviate an existing or potential impairment to the uses and functions of the water body.” Levels of control can range from no attempt to control to an ongoing continuous effort of maintenance control, keeping the invasive plant population at the lowest possible level while conserving or enhancing native plants. Complete eradication is difficult, but can be achieved if invasives are detected early and treated aggressively before they proliferate throughout natural areas. See A Manager’s Definition of Aquatic Plant Control for a detailed discussion of level of control, desired outcomes, constraints and expectations. The Florida Aquatic Plant Management Society is the Florida chapter of the APMS.
Plant managers use several control methods depending on the plant and its habitat:
- Chemical control is the use of specially-formulated herbicides registered with the U.S. EPA and the Florida Department of Agriculture and Consumer Services to kill plants.
- Biological control is the use of imported insects, fish, and other organisms that eat or infect or otherwise keep specific invasive plants at low levels indefinitely. Before releasing such organisms, the United States Department of Agriculture and the Florida Department of Agriculture and Consumer Services must verify that insect biocontrols have proven to be host-specific.
- Mechanical control is the use of specially-made machines to "harvest" invasive plants by cutting and collecting them and transporting them to a place to decompose.
- Physical control includes hand-pulling, drawdowns (water removal), flooding, burning, dredging, and shading to control invasive plants.
- Integrated Pest Management (IPM) is a combination of the above methods. The integrated approach does not refer to a specific management technique, but rather a multi-strategy tactic that uses suitable and compatible techniques and methods to maintain pest populations below levels that will cause significant economic and environmental damage.
- When buying plants, choose a nursery aware of which species are restricted, both regionally and federally. Be sure to verify the plant identification. For aquatic plants, rinse them in tap water to remove unwanted plant material, sediments, and/or insects.
- If your community has native plant nurseries, support them (Florida Association of Native Nurseries). Native plants are best suited to the local microclimate and require minimal upkeep. They also help support native fish and wildlife.
- When disposing of plants with the potential of spreading into nearby woods or waterbodies, completely dry or freeze the plants to kill them, and then add them to household garbage that will not be composted. Do not dump aquatic plants into waterways.
- Learn to identify invasive non-native plants, as well as native plants. Contact your County Extension Office for advice and assistance.
- Stay informed about invasive species prevention through Best Management Practices.
The University of Florida has educational tools about aquatic plants, their identification, and their biology. This website has “Conservation Guidelines” to aid in aquatic plant management.