From the Field

Fading Forests: The High Cost of Invasive Pests

Invasive forest pests threaten ancient hemlock groves in the East. Photo: © Kent Mason

Sarah Johnson, a conservation GIS analyst for The Nature Conservancy in Pennsylvania, tells a story familiar to anyone who deals with non-native forest pests.

Staff at the Woodbourne Forest Preserve in northeastern Pennsylvania knew it was coming: emerald ash borer, an incredibly destructive and invasive beetle. A beetle that could quickly devastate the native ash trees growing there.

And they knew there was nothing they could do to stop it. The pest had already been confirmed in eastern Pennsylvania, and once the emerald ash borer is established in an area, there is little that can be done to prevent its spread.

In March, the emerald ash borer was found on Woodbourne by a forest crew. “I wasn’t at all surprised,” says Johnson. “We have been searching for it, knowing it was coming. But it can be a very difficult pest to locate.”

Still, that knowledge – that certainty that the forest pest would show up, probably sooner than later – didn’t make its discovery easier to take.

“We’re scientists. We’re practical and we understand forest ecology and invasive species,” says Johnson. “Still, it can be very emotional. You know it’s going to get there; you know it’s going to have consequences. But it still hits you in the gut.”

Across North America, new non-native forest pests are appearing and other ones are spreading, altering our forests and the wildlife and industries that depend on them. It will take the action of policy makers, businesses and individuals to stop the spread. But what does that look like?

That question is answered in a new comprehensive report released this week, Fading Forests III. Coauthored by Faith Thompson Campbell of The Nature Conservancy and Scott E. Schlarbaum of the Department of Forestry, Wildlife and Fisheries at The University of Tennessee, the report investigates the damage done by invasive forest pests, and what must be done to solve this problem.

The report is an update of Fading Forests II, a similar report published twelve years ago. The sobering reality is a lot has changed, and not for the better.

“A lot of bad things have happened for forest conservation since that report was published,” says coauthor Campbell. “Some of the biggest invaders have rapidly expanded their range, and we have confirmed 28 new pests that are damaging forests.”

The report records the high ecological and economic costs of pest introductions. For instance, it cites a study estimating that municipalities and homeowners spend $2.7 billion annually on removing trees killed by non-native pests, and that homeowners lose another $1.5 billion in property values.

The ecological costs can be even more devastating. As the report notes:

“These estimated costs, while substantial, nevertheless underestimate the full range of costs because they do not include ecological impacts arising from the death of entire tree taxa and impacts from a significant number of pests, including all the pathogens and thousand cankers disease.”

A tree-lined Toledo street before and after an infestation. Photo: Dan Herms/Ohio State University
A tree-lined Toledo street before and after an infestation. Photo: Dan Herms/Ohio State University

One of the risks of forest pests is what ecologists call shifting baseline syndrome: when people accept as normal the conditions they’re familiar with, even if those conditions are damaged or degraded. When hemlocks disappear, people begin to consider a forest without hemlocks as normal.

But, Campbell argues, these changes are not always gradual. You can likely see the influence of forest pests all around you. “There were many really beautiful groves of hemlock trees in Shenandoah National Park,” she says. “It’s sad to look across those same gorges that used to be dark with big, beautiful trees and see it now all weedy.”

As scientists at Woodbourne Forest Preserve know, stopping the spread of some forest pests – like the emerald ash borer – is impossible once the pest is entrenched.

Can anything be done?

The report’s authors lay out some concrete plans for stopping the trend, including strengthened requirements governing imports, particularly wood packaging. Researchers believe that the emerald ash borer and other pests have arrived on these shipping crates.

“Americans rely on imports, but we haven’t addressed some of the hidden costs associated with them,” says Campbell. “We could require pest-exclusion treatments and be much more vigilant in detecting and reporting pests arriving on shipping containers.”

The report also includes recommendations for regulating firewood, as people can inadvertently transport forest pests by moving infested wood from one location to another.

“People can decide to do things differently,” says Campbell. “The costs of invasive forest pests are clear and well documented, as we lay out in this report. And we can take concrete steps to reverse the trend. Our forests and our quality of life depend on it.”

Read the full report here.

Opinions expressed on Cool Green Science and in any corresponding comments are the personal opinions of the original authors and do not necessarily reflect the views of the Nature Conservancy.

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  1. I have Emerald Ash Borer in one of my trees. Can I get State aide to have the tree cut down?