The study was conducted by researchers from McGill University, the USDA Forest Service Southern Research Station and North Carolina State University. The team studied data from around 30,000 localities, and they used a time range of 2020 through 2050. During that timespan, they estimated that 23 percent of urban areas “will experience 95 percent of all insect-induced” tree mortality.
According to the study’s authors, their findings are the “first nationwide spatial forecast of street tree mortality from invasive insects,” and it serves as a guide for city tree managers to know which tree species will be at the greatest risk from invasive insects.
“Many urban areas are dominated by a single tree species or genus, which means that a newly arrived insect for which those trees are a host can spread easily,” Dr. Frank Koch, a research ecologist at the USDA Forest Service and one of the study’s co-authors, said in a press release. “On top of this, there are usually fewer natural predators and warmer temperatures compared to nearby natural forests, which can benefit invasive insect development.”
Using a series of models, the researchers predicted the spread of 57 invasive insect species. They also noted which insects were more lethal than others to different tree species.
The team estimated that 1.4 million street trees will be killed by invasive sinecures from 2020 through 2050. They also analyzed the financial impact of tree removal and replacement in U.S. communities. The average annual cost of the damage caused by invasive insects during the time span studied in the U.S. was calculated at $30 million, they wrote.
New York City, Chicago and Milwaukee were singled out as tree “mortality hotspot cities” by the study’s authors.
The emerald ash borer (Agrilus planipennis) was identified as an especially destructive species. The researchers said 90 percent of the 1.4 million tree deaths would come as a result of the spread of this type of beetle. The ash borers are projected to kill “virtually all ash trees” in more than 6,000 urban communities.
The study’s lead author, Dr. Emma Hudgins of McGill University, also emphasized in the press release that cities are advised to avoid planting “what are essentially monoculture urban forests.” In other words, they should try to diversify the types of trees planted.
“These results can hopefully provide a cautionary tale against planting a single species of tree throughout entire cities, as has been done with ash trees in North America. Increasing urban tree diversity provides resilience against pest infestations,” Hudgins said.
