invasive insects are expected to kill 1.4 million trees across the United States over the next 30 years.

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.”

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