|Invasive Species of North America|
An invasive species is defined as a species that is non-native to the ecosystem under consideration and whose introduction causes or is likely to cause economic or environmental harm or harm to human health.
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European White Birch is a medium-sized deciduous tree in the birch family (Betulaceae). It is reported invasive in KY, MD, WA, and WI. Ecological Impacts: Escaped populations of European white birch tend to be relatively uncommon, and little is known about the ecological impacts of the species in North America. At one Long Island site the species has become a co-dominant forest tree, and is reproducing via seed. In southeastern Massachusetts the tree has colonized forest openings where it may be competing with its native congener, gray birch. In eastern Kentucky it has been planted on strip mines and in some cases become invasive. It can compete with native plant species for available resources.
Thousands of invasive exotic plants, insects, fish, mollusks, crustaceans, diseases, mammals, birds, reptiles, and amphibians have infested hundreds of millions of acres of lands and waters across the nation, causing massive disruption in ecosystem function, reducing biodiversity, and degrading ecosystem health. Forests, prairies, mountains, wetlands, rivers and oceans have been infested by these 'aggressive' exotic species.
Aesculus hippocastanum L.
Ox Eye Daisy
European White Birch
Humans intentionally and unintentionally spread invasive species. The foundations of agriculture and animal husbandry are based on ancient habits of selectively favoring some plant and animal species and their habitats over others for food, fiber, and medicine (Flannery 1973). According to Pimentel and others (1999), about 50,000 non-native species have been introduced in the United States. Many nonnative species have been deliberately introduced for erosion control (kudzu), food animals and fish (brown trout), agricultural crops (Johnson grass), and ornamental trees and landscape plants (purple loosestrife).
Some insects and diseases have been introduced in ignorance, as was the Gypsy Moth, or as the unintentional result of a global economy, as with the West Nile virus and Zebra mussels (Pimental and others 1999). Many invasive plants in the United States were originally introduced for food, fiber or erosion control, or as ornamentals. For example, purple loosestrife was introduced as an ornamental in the early 19th century. Loosestrife is present in riparian areas throughout the continental United States and control costs are an estimated $45 million per year. Riparian areas are extremely valuable to native plants and animals, and the wholesale invasion by Loosestrife poses a serious threat of eventual extinction to numerous riparian-dependent species.
Poster child invasive "Multicolored Asian" lady beetle, Harmonia axyridis
Other plant species, such as European Cheatgrass, have almost entirely displaced sagebrush-grassland plants and associated animals. Cheatgrass has also seriously altered the fire regime from an average return interval of 60-110 years to 0-3 years. Cheatgrass is an example of the adverse impacts an introduced species can have on the environment. Some scientists estimate that Cheatgrass is present on 100 million acres of grassland-steppe in the western United States. Cheatgrass forms a dense, uniform carpet that out-competes native grasses and shrubs. It greens quickly, dries quickly and produces a very flammable cover that often burns completely, without allowing native plants to reestablish. In pinyon-juniper woodlands, the combination of Cheatgrass and fire may effectively prevent the re-establishment of the original woodlands.
Invasive species cost the public approximately $137 billion per year in damage, loss, and control. The economic losses are significant but the ecological and cultural losses of native flora and fauna are equally important. For example, the bullfrog, a nonnative species in California, has almost completely replaced the native California red-legged frog--the famed jumping frog of Calaveras County. Another introduced plant, the Giant Reed, eliminates native streamside vegetation and dries up creeks that provide habitat for four endangered species: least bell’s vireo, southwestern willow flycatcher, California red-legged frog, and unarmored three-spine stickleback (USDA Forest Service 2003a).
Approximately 46% of the plants and animals federally listed as endangered species have been negatively impacted by invasive species. Introduced insects and disease have also taken their toll on the environment. Chestnut Blight and Dutch elm disease are two well-known examples. Gypsy moth was intentionally introduced in the 1800s as a possible source of silk production. As a result of these well-known pests, the American chestnut and American elm have virtually disappeared from the US landscape and numerous other eastern trees are at risk from Gypsy moth (USDA Forest Service 2001).
Law and policy governing invasive species
Forest Service responsibilities and management direction for the control of insects and disease are listed in the Cooperative Forestry Assistance Act of 1978 (92 Stat. 356; 16 U.S.C. 2101) and Forest Service Manual 3400." - (USDA Forest Service, 2003)
1. USDA Forest Service, Forest Health Staff, Newtown Square, PA. Invasive Plants European White Birch
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The birches have long been popular ornamental trees in North America, chiefly in the northern United States and Canada. Several are native Americans, but many species have been introduced from Europe and Asia. Our specimens include river birch, Dahurian birch, paper birch, Arctic birch, Manchurian birch, Manchurian alder, downy birch, Japanese white birch, and 10 other species. --Tree Index--