How Wildfires are Changing Boreal Forests and Increasing Emissions

The devastating fires that had stricken California and Australia this autumn, though unprecedented, stay true to the wildfire stereotype. They are seasonal fires that had occurred in the dry, fire-prone regions of the world. However,  the climate crisis has been influencing changes in the world’s fire patterns. Parts of northern United States and Canada have experienced this first hand.

Much of the summer haze, air pollution, and carbon emissions in the north now come from boreal forest fires. Because, unfortunately, under the circumstances of the above-average temperatures, northern conifers can fuel even stronger fires than fire-prone vegetation of the Southwest. 

The turning point came in 2004 when 2.6 million hectares of boreal forests burned down in Yukon and Alaska. What looked like an incidental event soon turned into a pattern repeating across the American North, fulfilling the predictions of climate models – that individual forests are much more likely to burn today than hundreds and thousands of years ago.

Consequently, the boreal forests of today might be altered dramatically because of the cascade of changes the frequent fire activity brings about. Increasing fire activity in the boreal forest is consistent with projected responses to climate change.

This means that individual forests are likely to burn more frequently then they have in the past hundreds, even thousands, of years. The fires could change the face northern boreal forests as we know them, and the mechanisms are pretty straightforward.

• Frequent burning can affect tree cover. The fires that are too frequent impede the regeneration of slow-growing conifers such as the Black Spruce (Picea mariana), the most abundant tree of North American boreal forests that doesn’t produce its first seeds until it’s about 25 years old. Although their cones are actually adapted to release the seeds when they are ignited by fire, if the trees burn at a young age, chances are that they won’t get to reproduce. Consequently, in warmer areas, a boreal forest will shift to a deciduous forest dominated by aspen or birch. In colder areas, it will morph into a tundra. A single fire event can trigger the ecosystem shift.

• Once the shift has taken place, it is very difficult for the original forest ecosystem to recover, as elements that are needed for the return of the forest – the Black Spruce seeds and the original soil – go missing.
• Boreal forests are critically important for biodiversity, including flora ad fauna. They are habitats of the species such as caribou which are completely adapted to (and therefore dependent on) boreal forest ecosystems. For example, the disruption in lichen understory of conifer forests that occurs after the fires affects caribous, who overwinter in the forests feeding on the lichens. Further up the ecosystem’s food network, the caribou population decline affects the predator populations. And that includes humans too. Caribous have always been a traditional food source for indigenous people of the North.

Besides the biodiversity decline, the visible airborne direct pollution, and all other forms of visible damage, there is another major issue that comes with the increased fire activity in the global North.

Forests are natural carbon sinks, soaking in the carbon dioxide from the atmosphere and storing it for a long time, mostly in the soil and plant tissue. The fires are burning the forests from carbon sinks to major carbon emitters. This is especially true for boreal forests that have efficient ancient carbon storage in the deeper, wet layers of soil. Now the increased frequency and intensity of fires are putting those layers at risk to be exposed and release their millennia-old stashes of carbon.

One thing is certain – boreal forests are changing along with our climate. Climate disruption has various consequences for the ecosystem – from drought stress to pest invasions. Still, when the fire strikes, it seems to belittle all of the forementioned consequences. It remains the ultimate challenge in managing forests.

While various strategies to mitigate the effects of these disasters are evolving, how the world will handle the climate crisis itself remains a key question for the survival of natural complexes across the world, including the North American boreal forests.

The study

Walker, X. J., Baltzer, J. L., Cumming, S. G., Day, N. J., Ebert, C., Goetz, S., … & Turetsky, M. R. (2019). Increasing wildfires threaten historic carbon sink of boreal forest soils. Nature, 572(7770), 520-523. doi:10.1038/s41586-019-1474-y

More frequent fires could dramatically alter boreal forests and emit more carbon, The Conversation. August 29, 2019

Boreal Forest Fires Could Release Deep Soil Carbon, NASA Global Climate Change, August 22, 2019

Related

• Arctic Permafrost is Now Releasing More Carbon Than it Stores
• New Study Maps Out the Global Pattern of Soil-based Carbon Storage
• Looking at Centuries of California’s Climate to Understand Fire Risk

Related: Map of Wildfires Around the World