What is an invasive plant and how do managers and law-makers determine which plants are invasive? Let's start with the definition. MIPN and most state governments and other stakeholders have adopted the two-part definition that was established through Federal Executive Order 13112 in 1999. The first part says that an invasive plant is one that is not native to the location being considered. The majority of plants that are invasive in the Midwest are not native to North America. However, there are some species that have spread to the Midwest from elsewhere on the continent and can be considered invasive. The second part of the definition is that the species, once it spreads, has to cause or be likely to cause some type of harm. This harm can be environmental, economic, to human health, or a combination of those things. The majority of non-native plants do not cause any harm, and thus are not invasive.
Managers often determine which plants are invasive and which pose the highest risk for their area by conducting risk assessments. Risk assessments are generally conducted by a formalized group using an agreed-upon method. The groups are usually either non-profit invasive plant councils or advisory committees assembled by state agencies to help guide invasive plant policy. Both types of group usually include members from different stakeholder sectors including scientists, representatives of the nursery and horticulture industries, and representatives of conservation groups.
Risk assessment methods vary considerably between groups, but most call for research and documentation of the current distribution of the species in the state or area being considered, the species’ biology and behavior related to population growth and competitive advantage, and the ecological impacts caused by the species. Some also call for investigation of economic and cultural impacts, and of management techniques that can be used to stop the spread and/or reduce populations of the species. Several MIPN participants and partners conducted a formal comparison of risk assessment methodologies in use across the Midwest, which was published in 2016.* This analysis found that although risk assessment methods vary between each state, often the outcomes and policy recommendations for the same species are very similar.
MIPN uses the results of risk assessments done in the Midwest (and the subsequent placement of assessed species on regulatory and non-regulatory lists) to create our regional invasive plant list. In addition, we aim to help stakeholders across the region continually improve their risk assessments by sharing important sources of invasive species information and by improving communication between states on risk assessment methods and outcomes.
*Buerger A, Howe K, Jacquart E, Chandler M, Culley T, Evans C, Kearns K, Schutziki R, Van Riper L (2016) Risk assessments for invasive plants: a Midwestern U.S. comparison. Invasive Plant Science and Mangement 9: 41-54.
