Invasive Organisms

Invasive organisms are alien, exotic or non-indigenous species that originally evolved somewhere else in the world then were transported for a reason or accidentally to a habitat that is not their own. Though many species have already done this on their own through natural processes it is the great expanse of human exploration along with human colonization that has caused great increases in the scale of invasions by non-indigenous organisms. (10) The most widely accepted answer to the reasons why these exotic creatures thrive and spread is due to the fact that these organisms do not have natural predators and enemies that would feed specifically on that organism. When this happens the expenses are that of our native wildlife, plants, or in some cases an entire ecosystem. Some of these species also carry human diseases, which is concern for a completely different kind of epidemic.(11)

Invasive organisms ranging from microbes to mammals are second only to forceful removal of habitat for being the leading causes of extinction to native plants and animals during the 21st century in America. At this point more then 30 percent of the acreage in the United States National Park System is infected with one or more form of exotic organisms. Varying estimates explain that these species contribute to the decline of 35 to 46 percent of U.S. endangered and threatened species. Not only do these non-native organisms cause problems within niches of specific ecosystems they are also the cause of more than one hundred billion dollars a year in lost resources. When there is a loss of resources there is a loss jobs that would have gone towards these lost resources and along with the loss of resources there is also the threat of losing the biological heritage of this country. (15)

With the threat of invasive species becoming a larger problem to the nation's environment and economy the President declared an executive order on invasive species that it was imperative that federal agencies began to coordinate their power and man power to address this threat. The President expressed how the public needs to be educated on the threats, how developments need to be made in fighting against these invaders and that as much information needs to be documented as possible to better help the chances of defeating the exotic organism.(15)

According to the Brooklyn Botanic Garden's Handbook of Invasives about half of the worst invasive plant species that are taking over natural areas across North America were brought here for horticultural use. Many of these plants are available commercially across the United States such as the Japanese barberry and the Norway maple, which is one of the most popular tree to be planted across the country.(16)

One invasive plant that is reported to be of exceptional intrusion is Lythrum salicaria or better known as purple loosestrife, which is native to Eurasia. L. salicaria was first discovered in North America off the northeastern coast in 1814 and now has rooted itself in just about every corner of the US. (1) The northeast part of the country where the wetlands are located remains the location where L. salicaria can be found in the highest quantities. The plant is non-sensitive to a wide array of soil types including clay, sand, silt and muck. As of now the only ways to control this invasion is by keeping the plants under observation and minimize seed production until a form of biological control can be found or herbicide is found that is selective. L. salicaria germinates in high densities often causing native seedlings to be pushed out of their own

habitat. The buildup of debris around the roots enable loosestrife to invade deeper water and to form dense stands that shade out other emergent species and push out floating vegetation by closing open water spaces. L. salicaria is an extremely successful invader of wetlands that have been subjected to some type of disturbance: drawdown, siltation, drainage, ditching. Expansion in a wetland can be extensive and sudden due to the abundance of seeds produced and the rapid growth of seedlings. High seed viability and prolific seed production can build up a seed bank of massive proportions. (2)

An invasive plant that has covered over 100,000 acres of the Hawaiian Islands, Morella faya, also know as the fire tree, can adhere to many types of habitats and soil types. Since the roots of this plant possess the ability to manufacture nitrogen it is able to spring up in recent, nutrient-poor volcanic sites long before the native plants. When the fire tree is able to do this the native plants are not able become part of the natural plant community. The plants native origin is Portugal where it was brought to Hawaii in the late 1800s for ornamental use along with its ability to produce edible fruit, which was used to make wine. The fire tree was not introduced accidentally though because during the early 1900s it was used in reforestation projects on Kauai, Oahu and Hawaii. It was not until after the tree had been planted that its invasive potential was discovered in 1937 and seven years later was the first attempt at cutting back the tree's spread. Since birds and pigs are the organisms that help disperse the seeds from this tree then need to be controlled. (3) There is no specific biological control agent recorded that could be used in controlling the fire tree, but the two-spotted leafhopper, Sophonia rufostachia, has been noted for killing the tree on Hawaii.(4)

Pueraria Montana or the Kudzu vine is a native perennial vine of Asia that was introduced in 1876 at the Philadelphia Centennial Exposition and promoted by Franklin D. Roosevelt's Civilian Conservation Corps from 1935 to the 1950s where it was planted for many years by farmers in the south to help reduce soil erosion. It was not until 1953 that it was recognized as an invasive organism by the U.S. Department of Agriculture and taken off the list of allowed cover plants. The exotic plant is described as a climbing, semi-woody, perennial vine in the pea family. The threat this organism carries is that of growing over other plants and trees and smothering them with a solid blanket of leaves. (12) This leaves the native plants with no way of getting sunlight along with being pushed to the ground. The vine is also known to uproot trees merely by its weights. The Kudzu is capable of growing 32 to 100 feet in length in a very short time possessing stems that are half of an inch to four inches thick and can weigh up to 400 pounds. For the Kudzu to be controlled the root system must be completely eradicated. This is done by either mechanical sources of through the use of herbicides. Because of the great threat this