After more than a decade, the mountain pine beetle epidemic that surged through British Columbia appears finally to be in remission. Having devastated the province's lodgepole pine forests, the insect is running out of food.
But forest managers now see new beetle infestations appearing at the edge of the Boreal Forest, in Alberta, and in the Yukon and Northwest Territories -- areas well outside the insect's historical range. As a warming climate lifts the temperature limitations that once kept the beetle in check, scientists fear it may continue its push across the continent, perhaps as far as the Atlantic Coast.
The threat of such an expansion is the subject of a new documentary, 'The Beetles Are Coming,' created by filmmaker David York and aired last week on CBC Canada.
In interviews with entomologists, biologists and residents of British Columbia, the film delves into the origins of the outbreak, which began in the 1990s but accelerated from 2004 to 2011 to become one of the worst ecological disasters in Canadian history.
"Most every scientist studying the beetle feels that [further expansion] is inevitable," York told CBC in the lead up to the film's release. "It's going to happen and we're going to have to adapt."
Once an ally, now an invader
British Columbia is home to the largest contiguous pine forests in North America, and the pine beetle is no stranger to the territory. In measured doses, the beetle can actually play a useful role in lodgepole forest ecology, attacking en masse every century or so and killing off mature stands so that fire and decomposition can clear the way for new growth.
These outbreaks have historically been limited by the cold northern climate in which lodgepoles typically grow. The beetle's life cycle is regulated by temperature, and cold snaps are one of the only sure ways of killing the insects off in large numbers. Since the late 1990s, however, temperatures in North America have held at levels well above the historical average, allowing MPB to explode through the province.
"In 2004, we had pine all over the place," said Staffan Lindgren, a professor at the Natural Resources and Environmental Studies Institute at the University of Northern British Columbia. "Now, if I drive around [the city of] Prince George and I see a mature pine tree, it's remarkable."
"We saw 90 to 99 percent die-off among mature pines in some areas," he added.
By 2006, clouds of beetles were swarming over the Rocky Mountains and coming down as much as 400 miles distant, the documentary notes. Farmers reported hearing sounds like hail on their roofs in the middle of summer, only to find that beetles were raining down out of the sky.
"The rate of expansion surprised virtually all of us," said Allan Carroll, an insect ecologist with the University of British Columbia's School of Forestry, whose work is featured in the documentary.
Moving to tree species that have few defenses
Since 2006 those dire projections have been revised downward. Roughly half of the province's lodgepole pine has been killed, but that number is projected to increase only slightly through the next decade, according to data from the BC Ministry of Forests, Lands and Natural Resource Operations.
While a sizable population remains in British Columbia, suppression efforts, such as removal of vulnerable stands, is keeping their spread in check, said Carroll. More importantly, though, the insect has largely exhausted its food supply in the province.
"We know that the rate of expansion from this point forward can be nowhere near what it was in British Columbia, because nowhere else are you going to find that kind of contiguous pine forest," he said. The beetle's ability to disperse is directly related to its population size during any given year, and with less pine trees to inhabit that population should be curbed in coming years, he added.
The larger threat lies on the other side of the Rocky Mountains, where the beetle has begun to infest the Jack Pine that mix with fir and spruce to form the diverse ecology of the Boreal Forest.
The beetles have begun to make their home in what scientists call 'naïve', or unadapted species of pines, said Lindgren. Having co-existed with MPB for millennia, lodgepole pines have multiple lines of defense they can use to fight back against the insect, such as sap secretions and toxins. In regions where MPB have not historically appeared due to temperature constraints, new research has found that trees are less able to repel the invaders, he said.
"We've seen quite a bit of evidence that beetles do better in [naïve] trees," he said. "The brood is more likely to survive," meaning more beetles emerge in the spring to attack other trees.
Other research has indicated that beetles born out of naive trees tend to be larger and healthier, meaning they are capable of laying larger broods. Scientists worry that these reproductive advantages may negate some of the disadvantages of a more limited food supply to the East.
In that scenario, while pine beetles may not explode through the boreal forest with the same speed that they moved through British Columbia, it is still possible that they could make their way through more gradually, using intermittent patches of Jack Pine as a ladder, Carroll said.
That could have serious implications for the biodiversity of the boreal forest and create new sources of ignition for wildfires, already projected to increase with global warming, he added.