Amur Honeysuckle – Lonicera maackii

Trends and rising threats from invasive species
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 (Pimentel and others 1999).

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 (Mitchell 2000).

Invasive Species on National Forests / Invasive Plants
The United States has about 2,000 non-native invasive plant species, which are concentrated in California, Florida, and Hawaii (Mitchell 2000). On non-croplands in the midwestern states, one Forest Service researcher estimates that 14 percent of the plant species are non-native invasive plants. Trend data from the 19th century to the present indicates a significant escalation in the percentages of non-native invasive plants in the last half of the 20th century (Mitchell 2000). An estimated 3.5 million acres of National Forest System lands are infested with invasive weeds, according to the 2000 RPA assessment, which summarized local estimates from individual national forests (USDA Forest Service 2001). However, local estimates vary widely, and the agency lacks a comprehensive inventory for either terrestrial (land) or aquatic areas infested with invasive species. The Framework for Invasive Species calls for expanding inventory and monitoring activities to identify more invasive insects, pathogens and plants (Forest Service 2003).
Some species of particular concern to Forest Service managers are leafy spurge, knapweeds and star thistles, saltcedar, non-indigenous thistles, purple loosestrife, and cheatgrass in the West and garlic mustard, kudzu, Japanese knotweed, Tree-of-heaven, and purple loosestrife and hydrilla in the East (Mitchell 2000).

Insect Damage and Disease
Insect damage and plant disease are natural disturbances that are part of a healthy, functioning ecosystem, along with fire and wind damage. However, both native and non-native insects and diseases have caused above normal mortality rates on forested lands in the United States. Some 58 million acres or 8 percent of forested land are at risk for mortality rates that exceed the norm by 25 percent or more (USDA Forest Service 2001). High mortality rates can accelerate the development of high fuel-loading in fire-dependent forests, effectively remove important ecosystem elements, and reduce private property values. The highest profile exotic insects and diseases include Asian Longhorn Beetle, Emerald ash borer, Dutch elm disease, chestnut blight, white pine blister rust, Port-Orford cedar root disease, European gypsy moth, hemlock wooly adelgid, and beech bark disease. Aside from the potential economic loss from timber volume, many wildlife and fish species are dependent on the ecosystems affected by these invasive insects and diseases (USDA Forest Service, 2001).