Invasive species are plants, animals and micro-organisms that are not native to a particular area. They are also species that are capable of causing severe damage in areas outside their normal range; harming the economy, the environment, or human health once they become established.
Not all non-native species are harmful. Corn is a non-native whose introduction has been very beneficial. The term "invasive" is reserved for the most aggressive non-native species capable of changing site or living conditions for the worse where they establish.
Invasive species are found in water and on land. In fact, invasive species can occur in just about every habitat type you can imagine: lakes and streams, cities, fields and farms, all of the native areas of the state. A few of the common species found on land include Canadian thistle, common buckthorn, wild parsnip, and the two fungal species that cause Dutch elm disease and oak wilt. Another one that folks are becoming aware of is the emerald ash borer.