In the 20th century, chestnut blight and Dutch elm disease decimated billions of U.S. trees, in forests and along urban and suburban streets. The tree diseases, caused by invasive pests, effectively changed the face of one American city landscape after another—chestnut trees were virtually wiped out and elms diminished to but a few locations—and cost local governments and homeowners a fortune.
A paper published May 10 in the journal Ecological Applications illustrates how American homeowners today bear the brunt of the burden posed by current invasive forest pests. The emerald ash borer, hemlock woolly adelgid and others are costing Americans well over $2 billion dollars a year. Gary Lovett, a forest ecologist at the Cary Institute of Ecosystem Studies, based in Millbrook, New York, was inspired to pursue the study after realizing that in his field work he was coming across more and more hemlock and other Eastern U.S. trees that were dead or destroyed by forest pests.
Sixty-three percent of U.S. forestland, or 825 million acres, is at risk of increased damage from established pests, according to the U.S. Forest Service. Urban and suburban trees are the costliest casualties. Removal and replanting are expensive, and loss of trees from streets, yards and parks affects property values and robs communities of the benefits trees provide such as cooling and improved air quality. And those costs are not evenly distributed: Local governments tasked with tree removal and treatment pay 10 times more than the federal government does in responding to pest invasions. Homeowners who have to remove dead trees from their properties are stuck with $1 billion of the costs, compared with the federal government's $216 million and the timber industry's $150 million burdens. That's apart from the effect on homeowner property values, estimated at $1.5 billion per year.
Lovett calls forest pests, present in all 50 states, the most pressing and underappreciated forest health issue today. Working with 15 other scientists to synthesize information found in previous scientific studies of invasive pests, Lovett found that, on average, 25 new pests become established in the country every decade. The scientists say efforts that exist to prevent new forest pests from entering the country are far too weak to keep up with escalating trade and an increased reliance on shipping containers—25 million enter the U.S. each year.
More than 90 percent of wood boring insects that have recently invaded the U.S. entered on wood packaging materials, mostly within shipping containers. And while the federal government does require that wood packaging material be treated to prevent pest importation and that plants are inspected upon entry to the U.S., there are simply too many shipments coming in each day to inspect everything. Lovett's team is calling for new trade practices that are more conscientious of the harm that non-native invasive pests can inflict.
"Current policies are helpful but not sufficient in face of this burgeoning global trade," says Lovett. "What we need to do is shut down these pathways that allow pests to enter, phase out the use of solid wood packing material. We need to restrict the import of live, woody plants that can carry diseases and insects that can infect trees."
Lovett says we've been lucky not to have yet encountered an imported pest destructive to the Southeast's loblolly pine or the Northwest's Douglas fir, two of the country's most commercially important trees. He estimates the economic damages would then be far greater than they already are.
However, the stakes are already higher than most people realize. Forest pests are the only threat that can decimate an entire tree species within just decades, as they did the American elm and chestnut. Much evidence exists of the benefits of trees to human health, and a 2015 study even showed that rates of cardiovascular disease among women living in areas that used to have ash trees claimed by the emerald ash borer increased after the trees were wiped out. In 2013, another paper showed increased death among both men and women due to cardiovascular and respiratory illness in areas affected by emerald ash borer.
Alternatives do exist to the solid wood packaging vulnerable to pests present in most shipping today. Packaging made of manufactured wood, for example, is a safer choice because pests are killed during the manufacturing process. Non-wood packaging, such as paper-based products, is already in use by some companies for economic reasons.
"I think the public has a tendency to see non-native forest pests as something that only affect national or state forests," says Stanley Burgiel, assistant director with the National Invasive Species Council Secretariat, an independent council established by presidential executive order in 1999. "They don't think these are the trees that line their streets or exist in their yards. And they probably don't know they are now footing more of the bill for dealing with the pests that destroy them than the federal government and timber industry combined."
