They come in many forms, from delicate blue butterflies to microorganisms unseen by the naked eye. And they are deadly.

More than 400 non-native insects and plant diseases are now permanently established and wrecking havoc in North American forests, which are defenseless against the attacks.

These invaders — which often hitched a ride on imported plants distributed by nurseries — are taking a disastrous toll on ecosystems from dying oak trees in California's woodlands to the standing ghosts of dead Fraser fir on North Carolina mountain peaks.

And these infestations damage not just ecosystem health. Private landowners, state governments and timber- and horticulture-related businesses stand to lose billions of dollars in lost revenues and eradication efforts.

An Ounce of Prevention

But a new report issued by The Nature Conservancy (PDF, 560 KB, new window) calls for regulatory changes to enable the U.S. government to more effectively deal with the threat invasive species pose to forests. The idea is time-tested: An ounce of prevention is worth a pound of cure.

“Once the pests are established, getting ridding of them is difficult and costly,” says Faith Campbell, senior policy representative at The Nature Conservancy and a co-author of the report. “Often it is simply impossible, which is why we need better regulations in place to prevent invasive insects and diseases from entering the country.”

Getting a Free Ride

About 2.5 billion live plants are imported into the country each year, and many arrive with unintended hitchhikers. Plants, cuttings and seeds, imported by nurseries for sale to the public, have repeatedly served as a pathway for devastating pests to reach U.S. forests.

Of the 25 most damaging forest pests introduced since the mid-1800s, 18 are believed to have arrived on nursery stock — including sudden oak death, the citrus longhorned beetle, chestnut blight and the cycad blue butterfly.

Because the pests and diseases arrive on live hosts, they can survive a relatively long time. In many cases, they live long enough to arrive at a nursery, where they can spread to other plants and even develop new characteristics by breeding with related diseases or insects already present.

And since nursery stock is distributed all over the United States,  many plants end up planted in places where it is a short hop to local forests.

Preventing New Invasions

 The U.S. Department of Agriculture’s Animal and Plant Health Inspection Service (APHIS) is the primary agency tasked with preventing the entry of potentially invasive pests and pathogens though nursery plant imports and other pathways.

But existing APHIS regulations are outdated and do not afford adequate protection against non-native insects and diseases. As international trade continues to expand,  Conservancy experts believe that stronger federal regulations are needed to prevent invasive insects and diseases from spreading into forests.

“The USDA’s regulations need to prevent the unreasonable burdens falling on our cities, towns, and private landowners by doing more to prevent pests and pathogens from entering the country,” says Frank Lowenstein, director of the Conservancy’s Forest Health Program.

“At a time when the threat of invasive species is at an all-time high," he adds, "we need a more effective and efficient program addressing this significant risk to our economy and environment.”

In the Conservancy's report, Campbell and Lowenstein call for regulatory changes that will enable APHIS to prevent risky imports. They commend APHIS for moving in the right direction, but recommend a five-point plan of action, cautioning that current proposals and funding is inadequate. 

“A few regulatory modifications will enable APHIS to take account of risks before damage occurs, rather than after the invasion is under way. The agency can make these modifications without violating international trade agreements or unfairly restricting the sale of nursery plants,” says Lowenstein.

“The United States should not continue to suffer economic or ecological damages because of imported insects and diseases.”

What You Can Do

• Until stronger federal regulations are in place for plant imports, consider buying seeds or locally grown plants from nurseries. 
• Write to your representative and voice your concern about insects and plant diseases traveling on plant imports.
• Discover how you can help stop the spread of invasive species.
• Learn more about forest pests and diseases.
• Find out more about the Conservancy’s approach to forest health and invasive species.

Nature picture credits (top to bottom, left to right): Photo © Oregon State Department of Forestry (damaged forests); Photo © Oregon State Department of Forestry (clearing infected forests); © Washington State Department of Agriculture (Seattle neighborhood before and after infestation).