What are Invasive Plant Species?
Invasive plants are non-native species that cause environmental damage and economic harm where they have been introduced (Definition). Plants are considered non-native if they did not occur in the U.S. prior to European settlement. Some native plant species can be aggressive and spread freely in certain environments or in response to human changes in the environment. Only non-native plants, however, should be considered invasive, since they have no evolutionary ties to the local plant assemblages and tend to have long-lasting, deleterious effects.
Not all non-native plants are invasive, but it’s important to understand that about 1% of all introduced non-native species have become invasive and damaging to the environment. Furthermore, all non-native plants will compete with native flora by taking up space, light, water, and nutrients; therefore, at times even relatively benign non-native plants, compete with native plants for resources. Although non-native species may not cause harm individually, the cumulative effects of non-native species may have a negative effect on native plants and weaken natural community integrity. Unlike our native flora, non-native plants provide little support for native wildlife.
The term “naturalized” is sometimes used to describe non-native plants that have escaped cultivation and established local populations. Used in this way, the term mistakenly implies that the escaped species has become part of the “native” flora. This use is a misapplication of the term. The use of “naturalized” therefore may be confused with “native” and should be avoided.
How do Invasive Plants Threaten Native Flora and Fauna?
Invasive plants cause environmental harm by spreading uncontrollably and replacing native plants, upon which native wildlife depend. Many of the non-native plants that become invasive here are native to Asia where the climate and other environmental conditions are similar to Louisiana. Plants that become invasive generally produce and disperse an abundance of seeds, grow rapidly, and tolerate a wide range of environmental conditions. Louisiana is more vulnerable than most other states to invasive-species infestations because of its favorable climate. High rates of precipitation; long, hot summers; and short, mild winters enhance the chances that once introduced into Louisiana, non-native species will become established here. These non-native plants also lack the predators and competitors found in their native habitat, so they thrive here in Louisiana and other parts of the U.S.
Attempting to control invasive plants once they become established is costly and time consuming. The annual costs of monitoring and controlling invasive species, and their damage to crops, fisheries, forests, and native wildlife has been estimated to exceed $130 billion in the U.S. alone (Pimentel et al. 2000). A more recent conservative analysis of the data reported that from 1960-2017, the U.S. incurred $1.21 trillion in economic costs from invasive species (Crystal-Ornelas et al. 2021). Preventing potentially invasive, non-native plant species from establishing here in the first place is more cost effective and less environmentally damaging. Once introduced, early detection and a rapid response offers the best chance to successfully eradicate an invasive species.
An effective method of managing invasive plants incorporates a three-pronged attack. First, recognize and remove non-native species. Employ a removal method that minimizes disturbance in the landscape as much as possible. Any disturbance tends to give the upper hand to invasive plants. Second, plant appropriate native species. Third, recognize native plant volunteers and consider keeping them. This approach will place non-native invasive plants under greater stress both by active removal and greater competition from native plants, resulting in a stronger, resilient, self-organizing landscape that may one day be able to hold its own against non-natives.
The Louisiana Wildlife Action Plan and Invasive Species
The Louisiana Wildlife Action Plan (WAP) is a good source for information about the most damaging invasive species in the state and the tools for managing them. The WAP, created by the Louisiana Department of Wildlife and Fisheries (LDWF), is essentially a blueprint for the LDWF and its conservation partners to develop and implement management actions to conserve fish and wildlife species and the habitats on which they depend. The current Louisiana WAP was published in 2015, and revisions to this document were published in 2019 (LA WAP 2015 and Revisions 2019).
Because invasive species are a major threat to native wildlife and their habitats, an entire chapter of the Louisiana WAP is devoted to this topic (LA WAP Chapter 6). The chapter provides sources of general information, laws and regulations, and the identification and control of invasive species. More specific to our state, Section C of Chapter 6 includes a list of invasive species known to occur in Louisiana that have, or are likely to have, impacts on native wildlife or their habitats. These species are classified into four different tiers defined by degree of invasiveness. Tier I species are defined as “currently causing severe or widespread negative impacts on wildlife or natural communities in Louisiana”. Tier II species are “currently causing moderately negative impacts on wildlife or natural communities in Louisiana”. Invasive plants classified as Tiers III or IV species are currently deemed to be having less impact on native species and their habitats. Tier III species may currently occur in the state, but have no known or anticipated significant or moderate impact on native wildlife or natural communities. Tier IV species are not known to occur in the state, but are deemed to have the potential to invade in the near future.
The next section of the chapter after the table is devoted to general management actions LDWF has identified to counter the threats from invasive species. More specific information for each of the Tier I species follows this section. A general description of each Tier I species’ native habitat, means of introduction, specific threats, and current distribution within Louisiana are given. The current range of distribution in Louisiana is presented in map form. Research needs and management actions are listed as well.
The Louisiana WAP is an important document for information about invasive species. The document must be updated every ten years beginning with approval of the original plan in 2005. Since the current WAP was published in 2015, look for the next update to appear in 2025.
HOW CAN YOU COMBAT INVASIVE SPECIES IN LOUISIANA?
As an Individual
Most (~89%) of the land in Louisiana is privately owned. Therefore, private landowners are key to managing invasive species here. Take your responsibility seriously to manage invasive species on your property.
First and foremost, before you purchase plants for your landscape or hire someone to landscape your property, do a little research on the species on your plant list. Never purchase invasive plant species. Sadly, even today, some of the many non-native plants available for sale at retail plant nurseries or online are invasive. Always check the scientific (botanical) name to ensure you are purchasing the correct plant. Using common names can be confusing; often the same name is used for different species or a species may go by several different common names. Purchase only native plant species or non-native species that are non-invasive to avoid contributing to the problem of invasive species infesting the natural areas of Louisiana.
Second, survey the plant species currently established on your property. Chances are the species list from this effort will contain at least some invasive species.
Third, develop and implement a plan to eliminate, or at least manage, the invasive species identified on your property. Manual, mechanical, chemical, or some combination of these methods can be used to deal with these species (Tu et al. 2001, Kissling 2022). The most cost-effective method for you to use will depend on the extent of infestation, target species, and plant form (e.g., grass, forb, shrub, or tree) and size. Choose the best approach given your particular situation.
Completely eliminating invasive species from your property may be possible if the area is relatively small, but becomes increasingly more difficult as property size increases. On large properties, managing invasive species may be all that is feasible.
Working toward eliminating invasive species from your property is a long-term process. After initially removing all visible signs of the species, the area must be periodically revisited to remove any seedlings that emerge from seeds already in the soil (seed bank) or that birds deposit in the area after having fed on fruit or seeds in nearby areas infested with invasive plants. If your property experiences a flooding event, look out for an increase in invasive plants after new seeds or plant parts are washed in with the floodwaters. Success may require years of work for large properties, but the amount of work required should gradually diminish each year as the invasive plant populations in the managed area are reduced. Gradually replacing invasive plants that are removed with native species may help to heal the damaged area and speed up the recovery process.
As a Plant Grower and Nursery Owner
- Become familiar with the list of known invasive Louisiana plants. See Section C, Chapter 6 of the Louisiana Wildlife Action Plan (LA WAP Chapter 6).
- Growers, ask your breeder whether a plant you plan to propagate has been evaluated for invasive potential. If a new cultivar of an invasive plant has been introduced with a claim of sterility, question whether this cultivar has been tested long enough for its sterility to be assured.
- Insist on the use of botanical plant names in your growing operation as well as common names. Retailers, be sure all of your plants are tagged with botanical names. It is only the botanical name that can correctly identify a plant and thus defend whether or not it is invasive.
- If you have current inventory of a known invasive plant, consider selling that remaining inventory and then discontinue propagating and purchasing this plant.
- Do any of your ads or public media posts encourage the planting of a known invasive plant, whether you carry that plant or not? If so, cancel them.
- Your customers are becoming more knowledgeable about the negative effects of invasive plants. Use the fact that you refuse to propagate or sell invasive plants as a marketing tool (we protect our customers’ landscapes – and the planet - from invasive overrun!).
- Promote the sale and use of native plants. It is fast becoming the most exciting, rewarding, and financially successful trend of the nursery industry!
As a Landscape Professional
- Learn which plants are classified as invasive in Louisiana from Section C, Chapter 6 of the Louisiana Wildlife Action Plan (Chapter 6).
- Learn the botanical names of the plants used in your business. Becoming familiar with botanical names will help you correctly distinguish between invasive and non-invasive species.
- Never use invasive plants in your work. Convince clients who request invasive species in their gardens to use a substitute species that is not invasive.
- When encouraging clients to go native make these points. Native plants will not only add beauty to your landscape, but native gardens are more resilient, sustainable, and diverse than traditional gardens composed of non-native plants. Gardening with natives also gives the homeowner a sense of place and teaches them about native plants in wild or natural areas.
- Check whether any of your business ads or public media posts feature or encourage the planting of a known invasive plant, whether you use that plant or not. If so, cancel these ads.
- Become certified to landscape with native plants. Certification will give you an advantage over your business competition.
- Your customers are becoming more knowledgeable about the negative effects of invasive plants. Use the fact that you refuse to landscape with invasive plants as a marketing tool.
- Ask your plant supplier to carry more natives to give you a wider selection from which to choose. Ask whether they would be willing to produce seed plugs or liners for you on a contract basis. If your supplier carries any invasive plant species, try to convince them to discontinue this practice.
- Promote landscaping with native plants. This is fast becoming an exciting, rewarding, and profitable trend of the landscaping profession.
Links to More Information About Invasive Plants
Barataria Terrebonne NEP (https://invasivespecies.btnep.org/invasive-species/)
Crystal-Ornelas, R., E.J. Hudgins, R.N. Cuthbert, P.J. Haubrock, J. Fantle-Lepczyk, E. Angulo, A.M. Kramer, L. Ballesteros-Mejia, B. Leroy, B. Leung, E. Lopez-Lopez, C. Diagne, and F. Courchamp. 2021. Economic costs of biological invasions within North America. NeoBiota 67: 4485-510. (https://neobiota.pensoft.net/artile/58038/)
EDDMapS - Invasive species distribution and mapping (https://www.eddmaps.org)
Kissling, F.R. 2022. Recommendations for Control and Eradication of Exotic Invasive Terrestrial Plants, 15 p. (https://scnps.org/wp-content/uploads/2023/06/Kissling-Invasives-Eradication-Guide.pdf)
Miller, J.H., E.B. Chambliss, and N.J. Loewenstein. 2015. A field guide for the identification of Invasive Plants in Southern Forests. U.S. Forest Service Southern Research Station. 126 p. (https://www.fs.usda.gov/research/treesearch/35292)
Pimental, D., L. Lach, R. Zuniga, and D. Morrison. 2000. Environmental and economic costs of nonindigenous species in the United States. BioScience 50:53-65. (https://academic.oup.com/bioscience/article/50/1/53/231855?login=false)
Reichard, S.H. and P. White. 2001. Horticulture as a pathway of invasive plant introductions in the United States. BioScience 51: 103-113. (https://academic.oup.com/bioscience/article/51/2/103/390610)
SE-EPPC – Southeast Exotic Pest Plant Council (https://www.se-eppc.org/index.cfm)
Tu, M., C. Hurd, and J.M. Randall. 2001. Weed Control Methods Handbook: Tools & Techniques for Use in Natural Areas (https://www.invasive.org/gist/handbook.html)
“Uninvited: The Spread of Invasive Species”; A Public Broadcasting Service documentary on invasive species and their impact on local ecosystems, the economy, and human health. This WMHT production is filmed mostly in New York and highlights the invasive Spotted Lanternfly, Emerald Ash Borer, Japanese Knotweed and other species that are damaging many ecosystems of the Northeast U.S. (Uninvited Documentary)
U.S. Geological Survey Aquatic Invasives Database (https://nas.er.usgs.gov/)
U.S. Department of Agriculture National Invasive Species Information Center (https://www.invasivespeciesinfo.gov)
U.S. Environmental Protection Agency. Invasive Non-Native Species (https://www.epa.gov/watershedacademy/invasive-non-native-species)