1.4 Million Urban Trees Will Be Dead By 2050 Due to Infestation of Invasive Species

A new study shows that an invasive infestation will kill over a million trees in urban areas across the United States. The forecast shows that nearly all ash trees in more than 6,000 communities will be infested by the emerald ash borer.

Emma Hudgins Ph.D. authored the study as part of her doctoral research at McGill University in Montreal.

Hudgins' goal was to translate predictions of the spread of invasive insects into predictions of ecological and economic impacts.

The research focuses on the insects' impact on urban trees since 82% of the U.S. population lives in urban areas. This rate continues to increase.

The models Hudgins created to estimate the impact of invasive insects on urban trees in the United States from 2020 to 2050 in 30,000 communities.

She also developed a simulation model that predicts insect dispersal and population growth, a distributional model that shows the location of susceptible trees, a probabilistic model that shows the impact of each insect species on each tree species, and a basic model of the cost of removing and replacing trees of different sizes.

Hudgins and her team were able to identify cities that are considered "hot spots," cities that are expected to have the most dead street trees in the next 30 years.

Hudgins explains that the emerald ash borer, a highly lethal wood-boring pest, has recently appeared or is expected to appear soon in cities such as New York and Chicago, where a lot of ash trees have been planted along the streets.

Although small cities and towns in the U.S. have not been identified as hotspots, most of their street trees will be infested because ash trees make up the majority of the urban landscape.

The study shows that about 1.4 million street trees will die from infestation over the next three decades. The projected cost of maintenance and replacement is $30 million per year and $900 million in total.

Emerald Ash Borer

In 2002, the emerald ash borer (EAB) accidentally entered the U.S. when a shipment from Asia was infested with the insect.

Trees infested with EAB lose most of their canopy within two years, decay, and die in the third or fourth year.

Hudgins explains that wood-boring species feed on the parts of trees responsible for supplying nutrients. The insects often cut off the circulation of a tree - known as girdling.

EAB is a threat to traditional livelihoods as well as urban landscaping.

Black ash basket-making, for example, is a long-standing tradition and livelihood for indigenous peoples in the Great Lakes region. The main material is harvested from the trunks of black ash trees. However, the current spread of infestations and lack of viable ash trees have led basket weavers to use other tree species.

Conservation and Motivation

Simulation models can be used to identify trees at risk and thus determine the starting point for conservation. The researchers hope to use this to both change urban tree planting strategies and increase participation in campaigns to limit the transport of firewood, which can carry many pests.