US cities will lose more than 1.4 million street trees to insects by 2050

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In research published in the Journal of Applied Ecology, scientists drew on data from hundreds of American communities to predict the effects of invasive insects. Rather than focusing on all urban trees, they focused on the best-tracked trees: those planted along roads.

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

This puts them in the path of the emerald ash borer, a beetle native to Asia and first identified in the United States in Michigan in 2002. Their larvae take up residence under the bark of ash trees, undermining trees of their nutrients and killing them. They are propagated with firewood and nursery trees, and they will account for 90% of tree losses.

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

Short-sighted travel, trade, and planting all put street trees at risk. The more street trees are affected, the more urban trees will also die: the researchers predict that another 100 million could disappear over the next three decades.

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

The researchers hope their findings will help cities make smarter decisions. “These findings can hopefully serve as a warning against planting entire cities with a single species of tree,” said Emma Hudgins, postdoctoral fellow at McGill University and lead author of the paper, in A press release. “Increasing the diversity of urban trees provides resilience against pest infestations.”

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