Migratory woodland caribou

• Although it is too early to establish a precise assessment of this extreme episode, recent research allows us to place it in a broader context.
• In North American boreal forests, several million hectares can go up in smoke in a single year.
• The results of our research contradict the common wisdom about North American boreal forests — that they burned more in the past than they do today.
• But before we go into more detail about this, we feel it’s important to provide some background and context.

What causes a forest fire?

• For example, large areas of dense coniferous forest are more likely to burn down than are deciduous forests with wetter undergrowth, or less dense forests.
• However, this combination of favourable conditions, itself, is not enough to generate a forest fire; there also needs to be a trigger.
• Although humans have been the cause of most fires started in recent decades in Canada, lightning has actually been responsible for the largest area of burned forest.

Impacts on society

• Fires also have an economic impact on the forestry industry, as they consume millions of trees originally destined for mills.
• Moreover, fires accelerate climate change, as the burning of vegetation causes a massive release of CO2 into the atmosphere.

A strong influence on ecosystems, but not necessarily negative

• This is the case for certain species such as the Woodland Caribou, which depend on the presence of mature coniferous forests to survive.
• But, on the other hand, fires have always been part of forests, and are sometimes even essential to their ecological functioning.
• This is the case notably of jack pine and black spruce, which the forestry industry loves.
• Additionally, as is often the case, it is also a question of balance…

Reconstructing the history of fires over the last centuries

• Accurate records required to reconstruct the history of forest fires in Canada only go back to the 1960s.
• So how can we reconstruct the history of burned areas over the last few centuries?

A downward trend in burned areas over the past few centuries

• We gathered 16 studies that had independently applied the same method to different areas across North American boreal forests, from Alaska to Québec.
• In the earliest period covered by our data, between 1700 and 1850, the annual area burned was between two and more than 10 times greater than what has been observed over the past 40 years.
• What explains this long-term downward trend?
• A better understanding of why fires have decreased or increased over the past few centuries will give us a head start in predicting what to expect from future climate change.