Species that have been introduced, or moved, by human activities to a location where they do not naturally occur are termed "exotic," "nonnative," "alien," and "nonindigenous." Conversely, "native" describes a species living in an area where it is found naturally. An exotic species is not necessarily harmful, in fact the majority have beneficial purposes. When a non-native species invades lands or waters " particularly natural communities " causing ecological or economic problems, it is termed "invasive." The terms "harmful exotic species," "plant pest," "pest plant," "nonindigenous aquatic nuisance species," and "non-native invasive species" are all groups of nonnative invasive species.
A number of invasive plants and animal species have been severe world-wide agents of habitat alteration and degradation, and competition for native species. They are the major cause of biological diversity loss throughout the world, and are considered "biological pollutants." Their populations can often rapidly increase allowing them to disrupt native plant communities and crowd out native species. By changing habitat, they can also affect species beyond those they may directly displace. They can cause problems for those who use natural resources, whether for recreational use of land or waters or industrial use of public waters. Once established, invasive species rarely can be eliminated.
There are many pathways of introduction that move species from their natural range to new, distant places. Most introductions are the result of human activities. Some introductions, such as common carp, buckthorn, and purple loosestrife, were intentional and have caused unexpected damage. Many exotic introductions are unintentional. Species are carried on barges, boats and trailers, animals, vehicles, commercial goods, packing materials, produce, footwear or clothing, and in ballast water of ships.
Ships take on ballast water in other countries for stability during the ocean crossing. This water is pumped out when the ships pick up their loads in Great Lakes ports. Many of the species, such as zebra mussel, ruffe, and spiny water flea arrived in the Great Lakes this way. But they are now being spread throughout the continent's interior in and on boats and through other recreational activities.
There are many characteristics of invasive species. The more a species may possess, the more it is likely to be widespread and troublesome. Here are a few:
Productivity: More seeds mean more seedlings. Purple loosestrife and white and yellow sweet clovers produce hundreds of thousands of seeds per plant. Invasive animals are often very prolific as well. The zebra mussel can produce up to one million eggs per year. Round goby, can spawn several times per summer.
Dispersal: Invasive plants often have seeds or other propagules that are easily spread by people, wind, water, or wildlife. They can establish in new locations far from their parent plants. Eurasian watermilfoil fragments can be carried on boats and trailers to new locations. Buckthorns and honeysuckle berries are eaten by birds, which later deposited where they fly. Tiny Siberian elm seeds are able to ride the wind far and wide. Purple loosestrife seeds can be carried by wind and water.
Growth period or seasonal advantages: Buckthorns, when planted in North America, leaf out early in the spring and stay green long after most deciduous trees an shrubs turn color and drop leaves. Buckthorn's longer growing season means faster growth to maturity, an advantage over native shrubs.
Lack of natural controls: When a species is transferred to a new location outside its natural range, the insects, diseases, or other pests that help control it may be left behind.
No, many of the worst invasive species are not known to be in Minnesota or are just invading near the state borders. The aquatic plant Hydrilla, the invasive fish black carp, and the terrestrial plants giant hogweed and yellow star thistle are not know to be in the state. Emerald ash borer has been found in a few locations near the border and a few bighead and silver carp have been found in the Mississippi River invading from the southern border of the state.
Invasive species costs landowners, resource management agencies, and others millions of dollars each year. Herbicides, labor, and research top the bill in fighting against plants which threaten to clog waterways, ruin fisheries, turn pasture to wasteland, compete with agricultural crops, shade out forest regeneration, and overrun natural areas. For many aquatic invasive species there is no known selective control, so the problems they cause continue indefinitely.
Get to know the common invasive threats. Inform friends and neighbors. If you see these offered for sale, explain the problem to your nursery, grower or supplier. If you find any on your property, consult information sources or contact a resource professional for control methods.