What It Would Take to Stop Invasive Pests From Destroying Millions of U.S. Trees

When cheap consumer goods arrive on American shores, they sometimes bring invasive parasites that go on to decimate forests and urban trees. A new study, out Tuesday in the journal Ecological Applications, synthesizes the information available on the true costs of these species and lays out the best available policy responses.

Tree-killing insects have been hitching rides across the oceans for years, but the rate of imports to the U.S. has risen dramatically over the past three decades and now totals 25 million shipping containers a year. As trade expands, so too do the opportunities for parasites to cross over in wooden shipping material or nestled into imported plants. (Their increase is tracked in the chart below.) A hundred years ago, it was chestnut blight and Dutch Elm disease; today, leading pests include emerald ash borer, the Asian longhorned beetle, and hemlock woolly adelgid. When these insects arrive and find trees that lack evolved defenses to them, they can wipe out entire species within a few decades. A startling 63 percent of U.S. forests are now at risk of losing trees to invasive species.