A forest that needs fire
The Atikaki Boreal Wilderness, part of the Pimachiowin Aki UNESCO World Heritage site, is shaped by fire. Covering 3,981 square kilometers, this roadless expanse in Manitoba is a living laboratory for fire ecology. Here, lightning-ignited fires are a fundamental ecological process, creating a mosaic of burned and unburned patches that supports many species. The forest is dominated by trees that have adapted to survive fire, but to use it for reproduction.
One example is the jack pine (Pinus banksiana). Its cones are serotinous, meaning they are sealed shut by a strong resin. This resin only melts to release the seeds when exposed to the intense heat of a forest fire, typically at temperatures of 45 to 50 degrees Celsius or higher. A mature jack pine stand can store up to two million seeds per acre within these sealed cones, waiting for the next fire to clear the forest floor and trigger a mass germination. This ensures that a new generation of pines can sprout on the nutrient-rich ash bed with minimal competition. Black spruce (Picea mariana) also relies on fire to clear away competing vegetation and expose the mineral soil its seeds need to germinate.
Reading the scars of time
The long history of fire in Atikaki is recorded in the trees themselves. Scientists use a field called dendrochronology, or tree-ring dating, to reconstruct the region's fire history with remarkable precision. When a low-intensity fire sweeps through a forest, it may be hot enough to kill a section of a tree's cambium, the living tissue just under the bark, without killing the entire tree. As the tree continues to grow in subsequent years, it forms woundwood around this injury, creating a permanent fire scar.
By taking core samples or cross-sections from old living trees and fallen logs, researchers can count the annual growth rings to determine the exact year of each fire. When multiple trees across a wide area show scars from the same year, scientists can map the extent of ancient fires. This method has allowed for the creation of fire history maps stretching back 400 years in some parts of North America's boreal forest. The absence of fire suppression in such a large, remote area means these natural cycles continue largely as they have for thousands of years, a process the Anishinaabeg, the Indigenous people of the area, have understood and lived with for millennia.