Other pests pose problem for B.C. forests

While British Columbia’s timber industry is occupied with the mountain-pine-beetle infestation’s aftermath, forest managers haven’t lost sight of other pest problems looming among the trees in a changing climate.

News this summer has been dominated by mill closures and production cuts as companies adjust to timber supplies depleted by the unprecedented infestation that killed off pine trees in up to 18,000 square kilometres of forests.

At the same time, the province is closely watching an outbreak of spruce beetles chewing through trees across hundreds of square kilometres of forests to the north and east, Douglas fir beetles are wreaking havoc in Cariboo forests around Williams Lake and 100 Mile House along with other pests such as the spruce bud worm.

“We wouldn’t expect (the spruce beetle infestation) to be at the same scale as the mountain pine beetle,” said entomologist Jeanne Robert. “That said, this is a large outbreak, so we are going to keep monitoring it very carefully.”

Robert added that scientists believe the spruce-beetle infestation peaked in 2017 when it spread across 3,420 square kilometres of northern-interior forests. In 2018, the spread was smaller at about 2,420 square kilometres. The estimate for 2019 won’t be complete until November, she said.

Aerial surveys are the province’s front-line tool for keeping tabs on all things related to forest health, said Robert, regional entomologist for the Ministry of Forests, Lands and Natural Resource Operations in the Omenica and North East region. That includes all bark beetles, such as the mountain pine, spruce, Douglas fir and western balsam beetles – all close relatives – and are all natural disturbances in forest ecosystems, Robert said, so she cautioned that it is difficult to characterize the outbreaks “as all bad.”

In smaller-scale outbreaks, bark beetles attack the oldest and sickest trees first, Robert said, which helps open gaps in forest cover to allow for new trees to grow and increase a forest’s diversity of species.

“This is actually how ecosystems have evolved into what we see today (in B.C. forests),” Robert said, “which is very useful for humans.”

It is a combination of factors, however, ranging from insects to forest fires that forest managers, First Nations and timber companies need to worry about, said Allan Carroll, director of the forest science program in the University of B.C.’s department of forest and conservation sciences and a professor in insect ecology.

“But the one big bow that can be wrapped around all of this is the issue of a warming environment,” Carroll said.

The mountain pine beetle, for instance, took hold so well and in areas it had never been before because interior forests rarely experience the deep winter cold snaps that normally kill the insects off, keeping them in check, Carroll said.

Then the large number of dead trees left over from the infestations contributed to a buildup of fuels in forests for successive years of record forest fires.

And fire-damaged trees became susceptible to pests such as the western spruce bud worm, which weakened forest stands making them less resistant to more damaging threats, such as the Douglas fir beetle.

“Forests and forest ecosystems are so super complex that things that happen at one point in time can have an echo effect for many, many years – decades – to come,” Carroll said.

In response, Carroll said scientists are learning that people need to focus on how to re-establish resiliency in forests, which will require considerable patience.