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U.S. cities will lose over 1.4 million street trees to insects by 2050

Some beloved species such as the ash are particularly at risk

The emerald ash borer’s larvae take up residence beneath ash bark, sapping the trees of their nutrients and killing them. (Minnesota Department of Natural Resources/AP)
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Invasive insects are a worldwide scourge.

Now, they could be coming to a tree near you — and that could have profound implications for urban areas.

An international group of researchers warns that by 2050, 1.4 million street trees will die because of the infestations, wiping out beloved species such as the ash.

How an uninvited pest doomed the ash tree

In research published in the Journal of Applied Ecology, the scientists drew on data from hundreds of U.S. communities to forecast invasive insects’ effects. Rather than focus on all urban trees, they homed in on the best-tracked trees: those planted alongside roads.

These street trees shape cities. But the researchers project that some will be more affected than others, with less than a quarter of the nation experiencing 95 percent of the losses. Milwaukee, Chicago and New York will be the urban areas most affected, in part because of their populations and their abundant ash trees.

Trees are very, very good for our health. But in many cities, they’re struggling.

That puts them in the path of the emerald ash borer, a beetle that originated in Asia and was first identified in the United States in Michigan in 2002. Their larvae take up residence beneath ash bark, sapping the trees of their nutrients and killing them. They spread with firewood and nursery trees, and they will make up 90 percent of the tree losses.

Maple and oak, the other most abundant street trees, are also at risk from pests such as San Jose scale and Japanese beetles.

Travel, trade and shortsighted planting all put street trees at risk. The more street trees are affected, the more urban trees will die, too: The researchers project an additional 100 million could go within the next three decades.

The cost will be tremendous, the researchers write; they project $30 million in management costs each year. And they note that even more risk could come from insects that aren’t here yet.

D.C. has become a leader in a movement to plant more diverse city trees

The researchers hope their findings help cities make wiser decisions. “These results can hopefully provide a cautionary tale against planting a single species of tree throughout entire cities,” said Emma Hudgins, a postdoctoral fellow at McGill University and the paper’s lead author, in a news release. “Increasing urban tree diversity provides resilience against pest infestations.”