Ash Trees Face Imminent Threat of Extinction in North America

An invasive insect species has brought a number of North America’s most prominent ash trees to the brink of extinction, and scientists are raising the alarm. 

In an update to the annual Red List of threatened and endangered species from the International Union for Conservation of Nature, biologists warn that six of North America’s most prevalent ash tree species now face the threat of extinction — and five of these species are critically endangered.

Green ash, white ash and black ash are included in this list. These trees are the most abundant ash varieties in the U.S., with estimates suggesting that, together, they make up nearly nine billion trees across forested land. White ash is also considered to be one of the most valuable commodities for furniture and wider timber use.

But that could all change if the decline in ash trees continues.

“Our activities as humans are pushing species to the brink so fast that it’s impossible for conservationists to assess the declines in real time,” IUCN Director General Inger Andersen explained. “Even those species that we thought were abundant and safe — such as antelopes in Africa or ash trees in the U.S. — now face an imminent threat of extinction.

But what is causing this decline in ash trees?

Imports, invasions and climate change create the perfect storm

Emerald ash borer. Photo credit: U.S. Department of Agriculture.

Emerald ash borer. Photo credit: U.S. Department of Agriculture.

A primary threat to ash trees comes from the beautiful but ravenous emerald ash borer — pictured above. The beetle is native to Asia, and it was likely — and accidentally — transported  to North America in wooden cargo packing materials in the 1990s. The beetle was first observed in the United States in Michigan in 2002.

When fully grown, the beetle only measures about half an inch long. Emerald ash borers use ash trees as a main source of sustenance for their larvae. The larvae will burrow into the tree and gorge themselves on the tissue that allows the tree to transport water and other nutrients.

An infestation isn’t easy to detect at first, but the tree will soon start showing signs like yellowing and thinning of foliage, fissures in the bark, an increase in woodpecker activity as the birds search for beetle larvae and characteristic D-shaped holes that the beetles bore as they emerge from the tree in their adult state.

Once these symptoms become obvious, most ash trees will succumb to the beetle within two to three years.

It’s estimated that infestations have now reached 30 states in North America. In just the past few months, local governments in both New York and Minnesota have announced ash tree monitoring and removal plans, as they attempt to battle the emerald ash borer.

It’s now estimated that the emerald ash borer may be one of the most expensive threats of its kind – largely because ash is such a common tree in urban areas. Each time the emerald ash borer is detected, large swathes of trees have to be removed, disposed of in ways that prevent the spread of larvae and then replaced with new trees.

And these efforts aren’t just financially costly. Ash trees help birds, small mammals and other insects thrive, and their disappearance certainly has a damaging impact. Some biologists suggest that tens of millions of trees have already been affected by the ash borer, with up to 80 percent of all ash trees in the U.S. and Canada likely to face infestation.

Unfortunately, there are signs the problem may still get worse. That’s because scientists have seen that, as areas of North America warm, places where ash trees were previously safe from infestation are beginning to experience an increase in emerald ash borers. Essentially, climate change is making this beetle’s life considerably easier.

It isn’t all bad news, however. Systemic insecticides work against the emerald ash borer. While insecticides carry significant drawbacks and no one approach will be a perfect solution, they may be a necessary evil for treating isolated outbreaks in order to prevent a wider infestation.

Researchers are also exploring ”biocontrol measures” for handling the infestation, in which natural predators or parasites could control the emerald ash borer population. Introduction of such organisms needs careful planning and strict guidelines to ensure no adverse impact on other wildlife. So far three parasites have been identified to potentially reduce emerald ash borer numbers, with small field trials showing promising results.

And, clearly, such action cannot come soon enough.

Photo credit: Thinkstock.


Marie W
Marie W16 hours ago

Thanks for sharing

Kelsey S
Kelsey S4 months ago


Jan S
Jan S4 months ago

Thanks for sharing this

Angela K
Angela K5 months ago

Thanks for sharing

H M5 months ago

We had to remove a backyard tree due to this. Hope birches and Korean Sun Pears aren't the next to go.

Dan Blossfeld
Dan Blossfeld5 months ago

Anne P.,
Good question. Since the ash borer was only introduced some 25 years ago, we may never know.

Jan S
Jan S5 months ago

Thank you

Anne P
Anne P5 months ago

Insects have destroyed so much of Alaskan timber it is beyond disgusting. Climate change warming weakened the trees' resistance to the beetle.

I wonder: had we the solid climate - the seasons, cold, etc we used to have - would that have helped against the ash borer?

We can't blame Everything on Climate Change, at least not Directly . . .

Telica R
Telica R5 months ago

Thanks for sharing

Past Member
Past Member 5 months ago