Chicago Botanic Garden Invasive Plant Policy

Introduction:

Invasive plants and animals are threatening our nation’s environment and economy.  Invasive species pose an enormous threat to our native plants, animals and ecosystems.  In fact, their toll on the environment is second only to habitat destruction.  Nearly half of the species listed as threatened or endangered under the Endangered Species Act are at risk due to competition with or predation by non-native species.  Invasive species can also alter communities by changing the hydrology or soil chemistry.  Invasive species are costing the United States nearly $125 billion per year (www.invasivespecies.gov).  Some of the worst weeds in natural areas in Illinois include purple loosestrife (Lythrum salicaria), Japanese and bush honeysuckles (Lonicera japonica, L. maackii, L. tatarica, L. morrowii), garlic mustard (Alliaria petiolata) and buckthorns (Rhamnus cathartica and R. frangula).

Although invasive plants are almost always not native to a region, it is important to note that most non-native species are not invasive.  In addition, some native species can become invasive.  For the purposes of this document, the following definitions will be used:

  • Native (indigenous) – a species that was present in North America prior to European settlement or has arrived since through natural means of dispersal.
  • Non-native (exotic, alien, introduced) – a species that was brought to North America by humans, either deliberately or accidentally.
  • Naturalized – a non-native species, or native species from another region of the country, that has become established in disturbed areas and/or native communities.
  • Weedy – a species that readily spreads, especially in disturbed areas, but generally does not pose a threat to the integrity of native plant communities.
  • Invasive – a species, usually non-native, that is able to establish itself within existing native plant communities and is posing a threat to the integrity of the community.

When plants are introduced to a new location, either intentionally or accidentally, they can spread prolifically, out-compete native species for resources, and eventually even dominate the landscape.  Biologists are studying the mechanisms underlying a taxon’s ability to become invasive, but for now it is still difficult to predict whether or not a species will become invasive in a new habitat.  Some factors common to many invasive plants include:

  • Escape from natural enemies
  • Rapid growth and early maturity
  • Production of many seeds
  • Ability to reproduce vegetatively
  • Seeds that are dispersed widely (such as by birds or wind) and seeds that germinate quickly (do not have long dormancies)
  • Apomictic seed production (production of seed asexually)

People have introduced the vast majority of invasive species, either accidentally or deliberately.  For example, kudzu was introduced to control soil erosion.  Many non-native species came to the United States with the colonists who wanted familiar food and garden plants.  Some invasive species were, or still are, popular ornamental plants used in landscaping.  The rapid expansion of global trade and human mobility has led to many species arriving accidentally.  Seeds can hitch rides to new locations in cargo or even stuck to the bottom of hiking boots.

The federal government has responded to the invasive species crisis in several ways.  President Clinton issued an Executive Order (13112) on invasive species in February 1999.  The order established the National Invasive Species Council to provide national leadership on invasive species; see that Federal efforts are coordinated and effective; promote action at local, state, tribal and ecosystem levels; identify recommendations for international cooperation; facilitate a coordinated network to document and monitor invasive species; develop a Web-based information network; provide guidance on invasive species for Federal agencies to use in implementing the National Environmental Policy Act; and prepare a management plan.  The plan, “Meeting the Invasive Species Challenge Management Plan” was completed by the Council and signed by President Clinton on January 18, 2001.  Of relevance to botanic gardens, the plan calls for the development of a screening and evaluation process by 2006 for the introduction of non-native plants to the United States.  The USDA and Department of the Interior will have oversight for plant importation processes.