Invasive nonnative species are species that have been introduced by human activity into ecosystems and ecological communities where they did not previously exist. Nonnative species are common in today's world, with people intentionally and unintentionally transporting innumerable species across physical and ecological barriers that would otherwise restrict their movement and range. The behavior of nonnative species in new environments is widely variable, some fail to survive while others, without their traditional predators and competition, are able to rapidly reproduce and eventually dominate entire ecosystems. This leads to species homogeneity and the loss of diversity. It is almost always the case that ecosystems that are suffering from heavy disturbance, or are in transitional phases, are much more susceptible to invasion. These include forests that have recently been cut or, in the case of the Arboretum, former cropland that is being converted into prairie.
The following websites are useful resources for invasive nonnative plant species in Minnesota and the surrounding region:
Minnesota Department of Natural Resources Invasive Species Page
Wisconsin Department of Natural Resources Invasive Species Page
Invasive Plants Association of Wisconsin
Many of the current Cowling Arboretum management efforts are directed at the removal of invasive plant species. Because removing all invasive species is an impossibility the most aggressive invasive nonnative species are targeted first. For example, while the common dandelion is a nonnative species to Minnesota, it is not nearly as intrusive in the prairie ecosystem as the different species of nonnative thistle or wild parsnip and because of this, thistle and wild parsnip are the priority target of spring herbicide application. The most problematic invasive nonnative plant species found in the Arboretum are listed below.