By reconstructing 12,000 years of history of a representative area of these forests, a recent study notes a surprising parallel between contemporary forest fires and those that occurred 7,000 years ago.
“We are going to see more and more losses in forest ecosystems. We are going to have to redevelop our forests if we want them to become more resilient to fires,” says Martin Girardin, researcher in forest modeling and productivity at the Laurentian Forestry Centre.
Subscribe to our newsletter!
To not miss any scientific news and learn everything about our efforts to fight fake news and disinformation!
7,000 years ago, frequent fires reduced the extent of the boreal forest and impacted land use.
The researchers were particularly interested in the region of Lake of the Woodsa large freshwater system located on the borders of Ontario, Manitoba and Minnesota.
They analyzed sediment cores from the bottom of six lakes to follow the evolution of this area after glaciation. hemiborealwhich today marks the southern limit of the North American boreal forest.
“The amount of coal tells us about the history of fires. And the pollen tells us about the evolution of vegetation and the advance of more heat-tolerant species, such as pines,” adds the researcher.
His team traced the different ecosystems there, including mixed forests with savannahs, grasslands and wetlands.
A change spread over 2000 years
However, about 7,000 years ago, a decisive change occurred when the boreal forest – similar to the one we know today – became an ecosystem of barren oaks and pines. This change lasted about 2,000 years, before returning to its “natural” state of spruce, fir, birch and aspen.
Researchers notice a decrease in pollen inputs into lakes. Oaks and grasses become dominant.
“The burning was frequent and there was a gradual increase in average annual temperatures of about 2 degrees. This warmer and drier climate significantly modified the ecosystem at the time,” explains Mr. Girardin.
The researchers also looked at the size of the human population at the time, using archaeological databases. They noted that their presence reflects fluctuations in forest fires, meaning that it decreases with increasing frequency of fires.
The people of the time were even absent when the fires were particularly intense.
Today, in this area bordering the boreal forest, more frequent fires pose the problem of the natural renewal of certain species (such as red pine) to the benefit of those better adapted to fires (such as jack pine).
The increase in aridity and the reduction in the southern extent of the boreal forest, observed with global warming, show that it will be necessary to review the forest management of this “ecotone”, this ecological transition zone between two ecosystems.
To limit the climatic impacts linked to fires, it will be necessary to consider arrangements that are less conducive to the spread of fires (firebreaks, cleaning chores, etc.) and to focus on reseeding.
“The particularity of this area is to be on the border of two environments and therefore to be very diverse in its biodiversity: moors, broadleaf trees, conifers. And this is where we will see the main changes,” notes the researcher.
A previous study tracing nearly a century of wildfires—between 1920 and 2010—showed that human density did not increase fire risk. The level of burning in eastern North America was actually lower during that century.
A timely study for our times
The study combines unpublished empirical paleo-ecological data (recording of coal and pollen from lake sediments), outputs from paleo-climatic models and the analysis of an archaeological database, comments the holder of the Canada Research Chair in Integrative Biology of Northern Flora at UQAR, Guillaume de Lafontaine.
And the “subject of the study is particularly timely. In a context of a global awareness of the impact of global changes and recent seasons of large fires, this study addresses precisely the interaction between fires, vegetation, climate and the size of human populations, in a historical perspective,” he adds.
However, he questions the generalization of the results to the entire hemiboreal zone: “the southern limit of this zone is far from uniform. Further east, the meadow is replaced by temperate forest (for example, maple and beech groves). However, fires are very rare in the temperate forest, which is rather boosted by windthrow.”
The expert also notes that inferences about climate and human population are not made at the same spatial scale as for fires and vegetation.
Guillaume de Lafontaine adds that “the approach of reconstructing the history of fires from coals from lake sediments remains relatively young and we still know very little about the origin and the processes that lead to the accumulation of coal buried in the sediments.”
This research therefore opens the door to others: “For example, we can ask ourselves how the accumulation of charcoal will depend on the type of fuel, erosion, the size of the fire, the distance from the fire.”
