Boreal forest. Credit: dvs from Vermont, USA, CC BY 2.0 , via Wikimedia Commons


In 2015, Ellen Whitman bushwhacked her way through a section of boreal forest in the southern Northwest Territories, near Fort Smith, and stepped into an open landscape, dotted with leafy trees. The area had once been thick with white spruce and some jack pine, but instead, Dr. Whitman saw trembling aspens surrounded by grassland.

“It was almost like a savannah,” said Dr. Whitman, who is a forest-fire research scientist at Natural Resources Canada in Edmonton. “It was a big change.”

Two fires had torn through the area less than 15 years apart. The first one burned the dense coniferous forest of older trees. The second killed off the young conifers that had sprouted after the first fire. The interval between the fires was too short for the trees to produce mature seeds and regenerate the forest on their own, allowing grasses, shrubs and deciduous trees to take root instead.

It’s a shift that threatens to recur across Canada’s boreal forest. As wildfires increase in size, severity and frequency, against a backdrop of warmer temperatures and persistent drought, the boreal is beginning to give way to birch, aspen, shrubs and grasses.

Wildfires have burned a staggering 15.4 million hectares so far this year, an area roughly the size of lakes Superior and Michigan combined. It is by far the worst wildfire season on record in Canada, where in an average year 2.1 million hectares burn.

Historically, wildfire has been an important element in renewing the boreal. It clears out dead trees and other dry fuels and creates the conditions for fire-adapted tree species such as black spruce to distribute seeds and grow a new forest that resembles past ones. Wildfire also temporarily reshapes the forest for birds and other animals, creating open spaces for flycatchers and other insect eaters, and leaving behind dead trees that become larvae buffets for woodpeckers.

But drought and warmer temperatures because of climate change have created hot and dry conditions that are causing fires to ignite more easily, grow larger and spread faster. Those changes to the fire regime are driving long-lasting shifts in the boreal.

“Our forests are going to change,” said Jill Harvey, the Canada Research Chair in Fire Ecology at Thompson Rivers University in Kamloops, who studies repeat wildfires, historical fire regimes, drought and regeneration.

“Forests need time to recover following wildfires. They need years for trees to germinate and time for trees to grow. … With drier conditions and more wildfires, we will see change in our forests, their structure and their function.”

Read the rest of the story at The Globe and Mail.

Written by Hannah

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