The main culprit in this devastation is the emerald ash borer (Agrilus planipennis), which is believed to be responsible for 90 percent of those 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 replacing the trees and the associated damage could average as much as $30 million a year. If more invasive species were allowed to take hold in the U.S., that figure could quickly reach billions of dollars before 2050.
“These results can hopefully provide a warning against planting a single tree species in entire cities, as has been done with ash trees in North America,” says computational ecologist Emma Hudgins of McGill University in Canada.
The sobering estimates were made from data collected in about 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 City, Chicago and Milwaukee — were identified in the report because of their high numbers of ash trees and because they are in the recent or nearby path of the emerald ash borer. According to the study, less than a quarter of U.S. communities will take 95% of the invasive species affected by the trees.
Part of the problem is the lack of variety in terms of tree species in urban areas, as evidenced by the concentrations of ash trees. More species means greater resilience to threats such as EAB.
Emerald ash borer leaves behind a trail of windy destruction.
Emerald ash borer leaves 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 USDA Forest Service’s Southern Research Station.
“In addition to that, there are generally fewer natural predators and warmer temperatures compared to nearby natural forests, which can promote 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 longhorned beetle (Anoplophora chinensis), a creature known to kill many types of hardwood trees.
Despite the dire warning, the team behind the study hopes it can help urban tree managers plan ahead and prevent the same type of costly damage from happening in other countries.
We know that urban trees are important for keeping cities fresh, boosting biodiversity and even making people happier. With that in mind, it’s vital that these pockets of nature in our cities are allowed to flourish and stay healthy.
“Given that a number of European countries are already facing ash dieback, it is extremely important to prevent the spread of EAB in Europe,” says Koch. “Hopefully, the lessons learned from North America will be useful in Europe.”