Bark Beetles and Wildfires

Hello again! After taking down all our traps in Burnt Cabin Bog Ecological Reserve, we packed up and drove for two days up to Kluane National Park and Reserve. While the drive was long there was plenty of scenery to see along the way. While driving North on the Stewart-Cassiar highway, we passed through a region of forest where two wildfires had recently occurred, in 2010 and 2011. These fires were sparked by lightning and grew quickly due to hot, dry weather, strong winds as well as the propensity of spruce trees to catch fire. The fires were allowed to burn and expand naturally for the most part, however certain areas were extinguished to protect the highway.

Evidence of a recent forest fire along the Stewart-Cassiar highway in northern British Columbia
Evidence of a recent forest fire along the Stewart-Cassiar highway in northern British Columbia.

The tendency for spruce to catch fire is increased by the spruce bark beetle (Dendrocthonus rufipennis), found naturally in Kluane National Park and across Canada. The larvae of this beetle bores through the bark of spruce which damages and can kill the trees. These damaged and dead trees are dry and are therefore much more likely to catch fire than living trees. This beetle, like many other forest pests, goes through cycles of population explosion, which leaves exceptionally high numbers of dead spruce trees behind in these explosion years and subsequently increases the risk of wildfires. However, the occurance of wildfires reduces the risk of future insect outbreaks by killing insects and breaking up stretches of forest with suitable habitat.

Spruce trees damaged by the spruce bark beetle in Kluane National Park.
Spruce trees damaged by the spruce bark beetle in Kluane National Park.

Here in Kluane, the forests are dominated by white spruce and while hiking through the forest we have come across many dead and damaged trees. We have even caught a few spruce bark beetles while hand collecting and we may find more in our traps! We also pulled apart some of the dead spruce trees to investigate and found the intricate tracks left in the bark by spruce beetle larvae. There has not been a major fire in Kluane for many years and the build up of dead trees over the years continues to increase the risk.

While it may sound like beetle pests and wildfires are bad for the forests in the park, forest fires are actually beneficial for the forest ecosystem. First of all, fires create a natural firebreak against future fires limiting their spread. Wildfires also create a mosaic landscape with different species of trees and trees of different ages, which increases overall biodiversity. Nutrients are recycled back into the soil through ashes which encourages the growth of new plants, ideal forage for wildlife. Fires can also create a more resilient forest by thinning forest cover and creating space for shrubs and grasses. This mix of habitats can respond better to disease and insect outbreaks. Interestingly, some insects (some flat-footed flies, dance flies, long-horned beetles and jewel beetles) are attracted to forest fires, more specifically to the smoke, and lay their eggs in recently burned wood. These insects help break down the dead trees to humus after a fire.

Tracks left in spruce bark by the spruce bark beetle.
Tracks left in spruce bark by the spruce bark beetle.

One of our three sites set up here in Kluane is in a spruce and aspen forest. After visiting the site a few times, we  started noticing more and more burnt trees in the area, evidence of a forest fire from many years ago. It was exciting to notice the signs of a forest fire and to see a forest in the recovery stages. It will also be interesting to see the community of insects we find living in this fascinating ecosystem.

–        Beverly