Climate Change Keeps Expanding Canada’s Unprecedented Epidemic Of Forest-Destroying Beetles

Since the late 1990s, climate change has driven a massive expansion of forest-destroying Mountain Pine Beetles in Canada, delivering the country one of the worst ecological disasters in its history. The insects are not technically invasive, and until recently they existed in a natural balance with their environment; killing off older trees and making room for new growth. But as a new documentary chronicles, climate change eliminated many of the natural limits on the beetles’ geographic spread and their rate of reproduction.

The Mountain Pine Beetles were historically contained to the pine forests west of the Canadian Rockies, which had adapted to the insects’ presence. Their ability to spread and reproduce is heavily effected by temperature: as the climate warmed, cyclical cold snaps killed off less and less of the population. They dispersed over greater geographic areas and into higher elevations as warmer temperatures rendered those areas more hospitable. They even began reproducing twice per year rather than once. As a result, midway through the 2000s, the beetles crossed the mountains:

Farmers on the eastern slope of the Rockies described huge clouds of insects. They could hear them pinging off their steel roofs. The swarms were so dense they gummed up the windshield wipers on the farmers’ vehicles.

It was an unprecedented eastward spread of the beetles into the boreal forests of north-central Alberta, as well as further north into the Yukon and other areas. These forests had historically been untouched by beetle infestations and thus hadn’t adapted many natural defenses, leaving them unusually vulnerable. Meanwhile, over the span of a decade, the beetles ate through 18 million hectares of the western Lodgepole Pine forests in which they originated:

The damage now extends throughout the rest of North America as well. The beetles have wiped out 70,000 square miles of the Rocky Mountain forests in just over a decade — an area equivalent to that of Washington State — bringing the threat of increased wildfires thanks to the forests of dead trees left behind. In Wyoming, specifically, milder winters since 1994 have reduced the beetles’ die-off rate in the cold season from 80 percent per year to less than 10 percent. All told, the number of beetles attacking in a given year has increased as much as 60 times over, resulting in the largest epidemic ever recorded.

Making matters worse, the beetles are also producing a positive feedback loop that worsens climate change. As forests are killed off, it means fewer trees are left to draw carbon dioxide out of the atmosphere. At the same time, the dead trees themselves release the carbon they had previously stored — 990 million tons of CO2 from the forests of British Columbia alone, as of the middle of last year. As for the boreal forests the beetles are moving into, estimates put the amount of carbon stored there at 703 billion tons — twice the storage capacity per unit of area as tropical forests.

The good news, if you can call it that, is that the beetles have been so successful at killing off the lodgepole pines that they may have undercut their own food supply, putting an upper limit on their increase. The eastern boreal forests are also less contiguous, making it harder for the insects to continue marching eastward. And some suppression efforts — such as burning infected trees and removing threatened threatened stands to cut off the beetles’ pathway — have shown results.

On the other hand, the beetles born in less adapted forests are healthier and larger according to scientists, some of whom worry the insects could make it all the way to the Atlantic Coast.