Quirks & Quarks

Can ash trees ever be reintroduced?

Dr. Dawn Hall, exhibition interpretation officer and science adviser at the Canada Science and Technology Museum in Ottawa, answers Chloe Cook's question.
The green emerald ash borer beetles are from Asia, and were first detected in Detroit, Mich., in 2002 before coming to Toronto. The pests are being blamed for killing thousands of Toronto's ash trees. (David Cappaert/Michigan State University)

Chloe Cook in Ottawa asks: "Almost 100 per cent of the ash tree population has been attacked by the invasive emerald ash borer. Will the areas affected eventually become unsuitable habitats for these insects due to lack of ash trees? If so, is there hope that ash trees might be reintroduced once the frontier of infection is suitably distant?"

Dr. Dawn Hall, the exhibition interpretation officer and science advisor at the Canada Science and Technology Museum in Ottawa, says the emerald ash borer — a type of a beetle native to Asia — decimates any ash tree populations it gets close to. 

The beetle originally hitched a ride to North America on wood products in the early 1990s, but it wasn't detected until around 2002. So far, they've been found mostly in northeastern United States, Ontario and some parts of Quebec.

They kill ash trees by cutting off nutrients coming down the tree from photosynthesis and the water coming up the roots by the larvae eating the tissue between the bark of the tree and the wood inside.

A study done near Windsor, Ont., where the original outbreak occurred found that even though almost 100 per cent of the mature ash trees were gone, there were still emerald ash borers present. They were living in the saplings — the young ash trees. In 2015, they were even discovered in another type of tree known as white fringe tree.

Ash trees could be reintroduced; they re-sprout very easily, so even though the large trees might die, they can still come back quickly. The end result might look more like a shrub, however.

Some tree species are showing resistance to the emerald ash borer, such as the blue ash tree, which is native to North America. Manchurian ash trees, which co-evolved with the emerald ash borer in China, has shown even more resistance than the blue ash. 

Researchers in the U.S. and Canada are now working to reduce the emerald ash borer population to a level that would still allow the trees to survive. There is also pathogenic fungus that can infect and kill them. And in China, there are tiny parasitic wasps — smaller than ants — that attack only emerald ash borers. Scientists in Canada are working towards bringing those wasps in to attack the ash borers to give the trees a chance to survive. 

So there is hope yet.