New York project offers hope for native ash

Jillian McCarthy

Binghamton Press & Sun Bulletin

USA TODAY NETWORK

A propagation project in New York state may offer a way to protect native ash trees from an invasive species that is decimating woodlands across North America.

The ash saplings, planted at Cornell Botanic Gardens as part of the Nature Conservancy’s Trees in Peril project, are part of an effort to restore a disappearing species long valued for its lumber, which is used in baseball bats, tool handles, flooring and fireplaces.

Since its introduction, the emerald ash borer, a wood-boring beetle from Asia, has killed millions of ash trees across the United States and caused billions of dollars in damage and loss, according to the New York State Department of Environmental Conservation.

In New York, the first infestation was discovered by entomologist Mike Griggs, who worked on Cornell University’s campus. He spotted damaged trees – signs of infection include tree canopy die-back, yellowing and browning of leaves – farther west in the state in 2009.

Quarantine zones were put in place in an attempt to block the ash borer’s spread in 2015, but by year’s end, the conservation department found the beetles in traps set in additional towns.

Todd Bittner, director of natural areas for the Cornell Botanic Gardens, said the emerald ash borer was first detected in his local trees in 2018. Today, the ash borer has ravaged its way through virtually all of New York state.

There may still be hope for the ash trees, however.

A project to restore the population began with a significant discovery made by the U.S. Forest Service in Ohio. Researchers set up monitoring plots to track the emerald ash borer as the population moved across the state.

After the beetle population had been there awhile, researchers returned to the trees and made a crucial discovery.

'They found dead tree, dead tree, dead tree, dead tree and then, every once in a while, a relatively healthy-looking tree in the middle of a forest where all of these other trees had succumbed to the emerald ash borer,' Bittner said.

These surviving trees are now known as lingering ash, and researchers are trying to understand how they are able to persist. This discovery, Bittner said, could be the catalyst for repopulating the depleted ash population across the country.

Emerald ash borer larvae tunnel through the living tissues of ash tree trunks. With hundreds of thousands of insects in each tree, the ash borer essentially girdles the tree, making it unable to transport resources between the canopy and roots. Without the ability to complete photosynthesis, the tree dies.

Researchers have learned that some lingering ash have the ability to 'wall off' the larvae, preventing the insects from tunneling far enough to girdle the tree. That’s the first known mechanism of lingering ash resistance.

The second possible defense mechanism is related to the volatile organic compounds emitted by ash trees as part of their natural photosynthesis. Researchers believe emerald ash borers are able to use these compounds to detect where ash trees are located, Bittner said.

If an individual tree doesn’t produce those chemicals or produces them at low levels, the tree is essentially wearing a 'cloak of invisibility,' Bittner said, making it undetectable to the insects.

'We’re hoping that both of these mechanisms are true so in the future we can identify trees that have those traits and potentially cross them, so we have ash trees with both characteristics,' Bittner said.

These lingering ash trees are being propagated in protected sites because they are unlikely to persist in nature when the emerald ash borer population is elevated. When all of the other trees are dead, the remaining trees will have a disproportionate number of insects attempting to lay their eggs inside.

The propagation process, Bittner said, has the long-term goal of reintroducing resistant ash trees into the wild so the population can grow and thrive once again.

The Trees in Peril project is 'very long-term,' Bittner said, but it is well underway at the Cornell Botanic Gardens.

Newly planted trees are located at the Gardens’ conservation bank site, where they are maintained and protected. The project began with a scion, a twig sample, collected from the identified lingering ash. The scion is used to grow these new trees, which will stay within the facilities for about two years.

The goal of the project is to propagate 50 to 60 genotypes or individual parent trees of each of the three ash tree species − white, green and black ash. Right now, a total of 139 grafted trees have been planted into three conservation banks.

White ash is abundant, and the goal of getting 50 to 60 genotypes for the propagation center will be 'easily met,' he said. Green and black ash, however, are much less common − their habitat requirements are much narrower.

In about five to six years, when those trees are large enough, scions will be collected and the process will be repeated. The lingering ash will be planted in test sites along with trees known to be susceptible to the emerald ash borer. If they prove to be resistant, researchers will then cross the 'wall off' trees with the 'cloak of invisibility' trees, an intentional pollination to create a hybrid that has both genes.

Those trees would then be grown to reforest ash back into the environment.

'The hope is that we’re able to bring these species back through this dedicated work and restore ash species to our forest to support the environment and protect the cultural uses of them,' Bittner said.