Conservationists in southwestern Ontario are working to fight back against an insidious, tree-killing canker that threatens butternut trees across Eastern Canada.
Never an overly abundant species, butternuts are revered by woodworkers and were an important food source for Indigenous people.
But a canker first found in Wisconsin in 1967 had, by the early 1990s, taken root in Ontario. Butternuts are found throughout Ontario and as far east as New Brunswick.
John Enright is a forester with the Upper Thames River Conservation Authority (UTRCA).
He’s also a big fan of the butternut tree. One reason? He believes the nuts they drop in the fall exceed walnuts when it comes to flavour.
“I know most people haven’t had a chance to eat a butternut but if you ever do get one, they are excellent, much better and sweeter than walnuts,” he said. “They’re a good nut for human consumption but also for wildlife.”
But the canker — a non-native fungal disease that causes the bark to crack — has pushed the butternut to the brink of extinction.
Butternuts are ‘definitely threatened’
It’s been so pervasive, the tree has been listed as endangered since 2007.
“I would say that over 99 per cent of the butternut on the landscape are showing some type of canker symptoms,” said Enright. “So it’s a species at risk, it’s definitely threatened here in Ontario.”
In 2009 the Forest Gene Conservation Association, a partner of the UTRCA, came up with a way to make a more robust butternut. The goal of the program: to maintain the genetics of healthy butternut that is tolerant to the disease.
They began to graft branches of healthy butternut trees onto samplings of black walnut, a tree similar to butternut but one resistant to the canker. After two years in the nursery, the trees were then planted at three butternut seed orchards across the province like the one outside of Woodstock, Ont., just south of Innerkip.
The seed orchards provide optimal growing conditions for the hybrid trees: a deer-fenced enclosure, regular watering and a spot on open ground where they don’t have to compete with other trees for light. There are currently 161 grafted butternut trees at the orchard. The oldest are now five years old, and some stand two metres tall. Between 30 and 70 new trees are added each year.
The hope is the trees will drop nuts this fall that contain seeds capable of producing a tougher butternut tree, one that will resist the canker that now threatens them. A similar program is underway to help save chestnut trees, another species threatened by canker.
There are no guarantees it will work and Enright concedes some of the hybrid trees may end up infected by the canker. But seeing the rows of healthy trees in the orchard has for Enright sprouted hopes that butternut trees may have a future.
“It’s very encouraging,” he said. “It’s pretty amazing that within five years we can have a tree that’s producing seed. It would be tragic if we lost butternut.”