Invasive plant species in North America is a growing concern of environmentalists and governments alike. Native species are endangered by invasive species that have no natural enemies and can harbor detrimental diseases such as wheat rust without being affected. The United States government has made provisions to prevent the introduction of new invasive species and try to control those non-native invasive species already present in the U.S., by Executive Order 13112 (64 Fed. Reg. 6183, Feb. 8, 1999) signed by President Clinton. This order makes provisions for a National Invasive Species Management Plan to be developed by a National Invasive Species Council. The Japanese barberry has already been blacklisted as a noxious weed and is considered to be illegal in Canada (USDA, ARS, et.al.2002). .
There are four criteria common to identified invasive plants. The first one is that the species is not indigenous to the biogeographical region in question. The second criteria is that the species has become naturalized and is becoming more abundant and/or more widely distributed. The third criteria is that there is a nuisance or pest value attached to the species in question and the last characteristic of an invasive species is that humans are normally responsible for the first introduction in the location in question (Tickner, Angold, et.al.). .
Invasive species can be successful for different reasons. One hypothesis is that they are allelopathic and inhibit the growth of other species in its immediate environment, usually through the use of chemicals (Rice 1984). Another hypothesis is that the invasive species out compete the native species because they are often quick growers, easily propagated, able to survive diverse conditions, and have no natural predators or diseases in the new environment (Davis, Grime, et. al. 2000). For example the Japanese Barberry is a successful invasive plant because potentially it is either allelopathic, out-competes the other plants for resources, or because people keep buying it for decorative uses making it more available for natural seed dispersal methods.
