WeatherImpact Earth


Pests, rising temperatures threatening Aspen trees in northern Arizona

NPS Oyster Shell Scale.png
Posted at 6:34 PM, Jan 31, 2022
and last updated 2022-02-01 09:42:55-05

PHOENIX — Arizona's aspen trees are an iconic symbol of fall, drawing thousands of hikers and photographers to the high country every year.

However, research out of Northern Arizona University suggests that the effects of a warming climate and an invasive pest, known as an oystershell scale, are putting the trees at risk.

Connor Crouch, a Ph.D. student in the School of Forestry at NAU, said there's a concern that in some areas, oystershell scales could be a death knell for aspens.

Oystershell scales, which are no bigger than a sesame seed when fully grown, have been in North America for more than 200 years, attaching themselves to a tree's bark and sucking the sap out, severely damaging or killing them in the process.

For years, they were predominately a pest on fruit orchards and trees in lower elevations, but in 2017, they were spotted on aspen trees for the first time in both the Coconino and Kaibab national forests.

Amanda Grady works for Forest Health Protection, a group within the U.S. Forest Service, and said it's a significant situation.

"This emergent pest has migrated into the natural forest setting and is causing really severe damage as well as tree mortality," she said.

One reason this is likely happening, according to Grady, is a warming climate, saying one of the main natural controls was freezing temperatures that would be cold enough to kill oystershell scale eggs.

"We have to accept that the landscape is changing because of climate," said NAU School of Forestry professor Kristen Waring.

NAU and the U.S. Forest Service are partnering up to conduct research on the invasive insects, learning more about their life cycle, aspen trees' lifespan once infested, and potential treatments for infested trees.

As of now, the oystershell scales haven't reached aspen stands above 8,500 feet, which Waring said might be due to colder temperatures at that elevation. Research on that topic is still ongoing.