Invasive species are those which are so opportunistic that they quickly displace native plants. Often they trigger cascade effects by eliminating a key food source for herbivores and in turn the native predators that depend upon them. They can carry plant diseases, pathogens and destructive insects. They can have negative effects on agriculture, livestock, natural ecoystems and even the appearance of a cherished area. One invasive plant species can seriously cripple a natural resource, local economy or the general health of people, plants, forests, prairies and more.
In the United States Midwest they are routinely studied with an idea toward control and eradication if necessary by the Upper Midwest Environmental Sciences Center (UMESC) and the Midwest invasive Species Information Network (MISIN). MISIN is assisted greatly by Michigan State University, but they rely heavily upon citizen report and awareness. Some of the plants they continue to control are kudzu, Japanese knotweed, buckthorn, loosestrife and several types of pond-weed and grasses.
There are almost as many reasons for the accidental or deliberate introduction to invasive plant species as there are people arriving in any new area. They may have been introduced as ornamental, livestock fodder, hitchhiking on vehicles, carried by unplanned animals and birds or even arrived by the event of an unplanned weather event. A drought or flood can weaken existing species, favoring hardier and aggressive invasives no matter which way they arrived.
Researchers prefer to use non-toxic controls such as insects or other plants that will eliminate the invasive species. These are called bio-controls, and there are many yet to be discovered to restore a natural balance. Until bio-controls are effectively implemented, much vegetation is still eradicated by use of toxic chemicals, herbicides and controlled burns. In natural systems, the plants which evolved in an area are kept in balance by co-evolved natural predators and competitors. Before the advent of industrialization, even individual people were better able to live closer to nature and even mechanically keep aggressive species in check.
Two tree species that are also categorized as Midwest invasive are the autumn and Russian olive and the alilanthus tree. The alilanthus is much larger than the olive species. It can grow to over 80 feet tall. These trees will opportunistically set seed in cleared areas, secondary forests and even empty, unattended lots.
Also, it must be considered that some of the most invasive species of plants are neither trees nor grasses, but vines. Kudzu vine is notorious for smothering almost everything in its path. It can strangle upright plants by girdling them around the trunk. It can choke whole areas blocking natural pathways and even streams and waterways. Like some kind of gruesome but slow creature from an old Japanese mutation monster movie, Kudzu can even crush other species by its sheer weight.
The three greatest challenges of trying to maintain invasive plants begin with the real-time speed of commerce and trade. Trade always entails some risk of uninvited plant “guests” either in cargo, ballast or even by design. The second factor of the three challenges is increased population. And the third (due to all that commerce being done by greater numbers of people, animals and other plants) is altered environments which are vulnerable to invasives. For example, a place with degraded or even flood- or fire-eroded soil will be prime real estate for invasives to quickly colonize and spread their seeds.
The general public does not always know when a harmless looking ornamental, valued in another region, such as a nice honeysuckle or rose variety, might be aggressive and problematic when unintentionally spread beyond the familiar house garden. This is why education programs are extremely critical for everyone to learn the importance of what usually appears to be just a “harmless plant.”
