Why an invasive insect species could kill 1.26 million trees in the United States by 2050

A terrible ecological disaster is on the way, researchers warn: invasive insects are expected to kill somewhere in the region of 1.4 million trees across the United States over the next three decades.

The main culprit of this devastation is the emerald ash borer (Agrilus planipennis), should be responsible for 90% of these 1.4 million dead trees. The beetle could wipe out ash trees in more than 6,000 urban areas, according to a new study.

The cost of tree replacement and associated damage could average up to $30 million per year. If more invasive species could take hold in the United States, this figure could quickly reach billions of dollars before 2050.

(Sam Droege/USGS)

“These findings can hopefully provide a cautionary tale against planting entire cities with a single species of tree, as has been done with ash trees in North America,” says computational ecologist Emma Hudgins, from McGill University in Canada.

The sobering estimates were made using data collected from approximately 30,000 urban areas in the United States. Tree population models were then combined with predictions of the spread of 57 different invasive species.

Hotspots – including New York, Chicago and Milwaukee – were identified in the report because of their high numbers of ash trees and because they are on or near the recent trajectory of the emerald ash borer. According to the study, less than a quarter of American communities will take 95% of invasive species struck on trees.

Part of the problem is the lack of variety in terms of tree species in urban areas, as shown by concentrations of ash trees. More species means greater resilience to threats like the emerald ash borer.

Emerald ash borers leave behind a trail of windy destruction.Emerald ash borers leave behind a trail of windy destruction. (corfoto/E+/Getty Images)

“Many urban areas are dominated by a single species or genus of tree, which means that a newly arrived insect for which these trees are a host can spread easily,” says ecologist Frank Koch of the station. USDA Forest Service Southern Research Center.

“In addition to this, there are generally fewer natural predators and warmer temperatures compared to nearby natural forests, which can encourage the development of invasive insects.”

The researchers also considered the potential effect of insect species that have not yet arrived in the United States, including the citrus longhorn beetle (Anoplophore chinensis), a creature known to kill many types of leafy trees.

Despite the dire warning, the team behind the study hopes they can help urban tree managers plan ahead and prevent the same kind of costly damage from happening in other countries.

We know that urban trees are important for keeping cities cool, boosting biodiversity, and even making people happier. With this in mind, it is vital that these pockets of nature in our cities can thrive and stay healthy.

“As a number of European countries are already dealing with ash dieback, it is extremely important to prevent the spread of the emerald ash borer in Europe,” says Koch. “Hopefully the lessons learned from North America will be useful in Europe.”

The research was published in the Journal of Applied Ecology.