Stanley Park looper moths kill many hemlock trees

An ongoing moth outbreak is killing a large number of hemlock trees in Vancouver’s Stanley Park.

Many trees in the popular park are dotted with hemlock looper moths. They hatch in the spring and then feed aggressively on the trees with the same name.

The moths kill the trees, resulting in safety hazards to people who may be visiting the park.

Francis Klimo, a certified arborist with Klimo & Associates, says we’re at the end of a four-year looper moth outbreak. Most of the damage they do happens between July and October.

This comes as trees in the area are already facing challenges after a hot and dry summer.

“Obviously we can see that there is a significant amount of western hemlocks that are declining,” explained Klimo. “These moths, they latch onto the needles, which forms a canopy of the hemlocks. They basically feed on it, to an extent until these needles turn brown and eventually fall off and scatter around the forest edge.”

Many hemlock trees in Vancouver’s Stanley Park have been killed amid a looper moth outbreak. (CityNews Image)

Richard Hamelin, the department head of Forest Conservation Sciences at UBC, says the last big outbreak was in the early 2000s.

“Even though it’s a native insect … it’s still quite impactful. Even ecologists think that we’d be better off letting nature do its own thing. So these outbreaks can come every 20 years, there’d be some defoliation. Other tree species are naturally going to replace them,” Hamelin told CityNews.

The other option, he says, is to intervene, for example by spraying insecticides. But it may be too late by this point to do that.

“Naturally, these populations crash after about four years — between three and four years — and this is the fourth year, so most likely this will resolve itself and next year we won’t talk about it,” he added.

Meanwhile, the Vancouver Park Board says affected trees are now being looked at and that it will determine which ones need to be cut down for public safety reasons.

“A significant portion of the park is affected, particularly near Lions Gate bridge. This outbreak is also heavily affecting parts of West and North Vancouver, where many trees are showing signs of infestation,” the board says in a statement.