Invasive Weeds Pose Major Threat To American Landscape

April 28, 1998

Wrong time, wrong place. Accidentally and on purpose, America is sowing seeds -- literal seeds -- of destruction. These are the conclusions of a soon-to-be-published book examining weeds in the United States.

"The invasion of noxious weeds has created a level of destruction to America?s environment and economy that is matched only by the damage caused by floods, earthquakes, wildfire, hurricanes and mudslides, Secretary of the Interior Bruce Babbitt said. This is truly an explosion in slow motion by opportunistic alien species with few if any natural enemies.

A multi-agency committee on invasive weeds found that the march of non-native plants across the American landscape is so pervasive that the unique differences of regional plant communities are blurring. Their report, "Invasive Plants: Changing the Landscape of America," is a systematic attempt, involving 17 partner agencies, to define the seriousness of the problem. The report will be available for public distribution this summer.

Invasive non-native plants, the book says, are now considered by some experts to be the second-most important threat to native species, behind habitat destruction.

"This fact book will help readers understand the scope and magnitude of the problem. We hope it will encourage them to act, to help us control the invaders that are already here and prevent future invasions,? Babbitt continued. ?People are carrying plants or their seeds from the far reaches of the globe into every corner of our nation to compete with -- often to destroy-- the wonderful variety that nature once gave us.?

Over the past decade, the report says, devastating impacts from invasive species have been reported on every continent except Antarctica. In the United States, introduced invasive plants comprise from 8 to 47 percent of the total flora of most states, a figure especially alarming considering a recent report from the International Union for the Conservation of Nature documenting that 1 in 8 plant species is globally threatened with extinction.

Invasive plants are those that have been introduced into an environment in which they did not evolve. Consequently, the invaders usually have no natural enemies to limit their reproduction, and thus easily spread, often unchecked. In addition, aggressive non-native species often deal a harsh blow to rare species -- about two-thirds of all endangered species are threatened by non-native species, the report said. As the native plant species decline, the animals that depend on them for food and habitat may also be jeopardized.

The book was developed by many of the federal agencies and others with weed management responsibilities. These agencies are part of the Federal Interagency Committee for the Management of Noxious and Exotic Weeds. In 1994, in response to the economic and biological threats posed by invasive plants, these agencies began working together to develop biologically sound techniques for managing invasive plants on federal and private lands. After noting the lack of adequate surveys and reliable monitoring data for many of these invaders, the interagency committee worked with more than 100 outside authorities to publish a national strategy on the management of invasive plants.

Secretary Babbitt called for the implementation of a national strategy for invasive plant species. "Invasive non-native weeds," he said, "are changing the landscape of the United States ... coming in as a result of globalization of transportation and trade, and putting U.S. ecosystems and lands at an increasingly greater risk of damage due to invaders."

USDA Deputy Secretary Richard Rominger likewise called for a "greater awareness of the impact of non-native invasive plants on all ecosystems, be they agricultural or natural areas."

The report calls the threat of invasive weeds "biological pollution" and "a silent green invasion." Thomas Casadevall, acting director of the U.S. Geological Survey, which is responsible for helping develop better methods of dealing with invasive species, explained that on a plant-by-plant scale the effects of these plant invaders are often subtle. "It's like metastatic cancer," he said. "It starts with a single individual or seed and then is carried to other places by people or nature where nodes get established and proliferate, eventually affecting entire ecosystems."

"The human-induced migrations of invasive species now underway around the world is unprecedented," the report states. Unchecked, it adds, the impact "will be a devastating decline in biodiversity and ever-increasing threats to food and fiber production." In wild landscapes, the book concludes, invasive plants alter plant and animal communities, water-flow regimes and are especially threatening to native plants and animals.

According to a recent Department of the Interior survey, noxious weeds are invading western wildlands at a rate conservatively estimated to be nearly 5,000 acres a day. Pat Shea, director of the Bureau of Land Management, says that, "Western wildlands and deserts are an important part of our biological heritage and need to be protected from invasive non-native species."

But the invasive species problem is not just in the West, as the book emphasizes. It affects most states and most public lands throughout the country.

National Park Service Director Robert G. Stanton called invasive species one of the most significant threats facing the natural and cultural resources of the National Park System. At least 1.5 million acres of national park lands are severely infested and need immediate treatment, the book reports. Says Stanton: "Although vast fields of flowering plants may look attractive to the visitor, many of these plants are actually silent, green invaders, slowly destroying the native, living natural heritage the parks are supposed to preserve."

USDA Forest Service Chief Michael Dombeck said that Forest Service lands are in a similar situation, with non-native invasive plants affecting every habitat type found on National Forest lands. "We need to be paying particular attention to the east where non-native invasive plants such as kudzu, Japanese honeysuckle and mile-a-minute weed are completely draping forested areas and affecting forest ecosystem health," Dombeck said.

The report's authors blame the increase and spread of invasive plants on an increasing human population that has led to greater disturbance of the land, increased demand for food and fiber, overuse of public land for recreation and commercial purposes, increased international travel and globalization of world trade. The problem is compounded, the report adds, because "many introduced plants appear innocuous when first introduced; these plants then adapt, and, in the absence of their co-evolved predators, explode in their new environment."

The committee's partners are:

NOTE TO EDITORS: Reproducible figures showing a) Weed Losses and Costs in the United States, b) Native and Non-native Plants in the United States by State/Region, and c)Weed Losses and Control Costs in Agricultural and Nonagricultural Areas in 1994, can be obtained at the USGS Biological Resources Division website at

US Geological Survey

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