Vital for the future of the planet, the boreal forest, this immense ring of greenery which encircles the Arctic, is in danger, threatened like the Amazonian forest by global warming.
Deployed in Canada, Scandinavia, Russia and Alaska, the so-called taiga is weakened by increasing fires, melting permafrost, insect epidemics made more virulent by milder temperatures. .
And the experts are formal, its northern part gains on the tundra, while in the south it is nibbled by the meadows.
In his cabin in Quebec, in a corner near the St. Lawrence River, Jean-Luc Kanapé, a member of the Innu people, lives in communion with the aspen trees and the black spruces with “the energy of the wind, of the cold”, there where the Milky Way ignites the sky on summer nights.
“When I’m in the heart of the forest, I feel like I’m part of it. The trees are like my roots,” the 47-year-old colossus told AFP.
But the man who dedicates his life to the defense of caribou, whose habitat is threatened by the disappearance of the oldest forests under the effect of global warming and deforestation, is worried.
“Often, we say we have to save the planet, but that’s not true,” he warns, “it’s our own decline” that is at stake.
This forest – whose name comes from Boreas, the titan of Greek mythology who personifies the north wind – covers 10% of the land surface and has a decisive influence on the oceans in the north of the globe and on the global climate.
With its 1.2 billion hectares, the largest wilderness area in the world (almost a third of all forested areas) slows global warming by absorbing a significant part of the carbon dioxide released into the atmosphere.
In total, it stores twice as much carbon as all the tropical forests, it also stores an astonishing volume of fresh water.
The boreal forest, where human intrusion is limited by extreme conditions, has always been subject to natural disturbances.
But scientists are now worried that they are happening more often, or even becoming the new norm.
– “Monster” of fire –
The dead trunks soar towards the sky. They stand like ghosts, creating huge white spots in the intense green of the forest. At their feet, small shrubs and grasses are the symbol of nature’s struggle to regain its rights.
“Never in my lifetime will I see a spruce tree in these hills again,” said Harvey Sykes, 70, a former oil worker, sadly.
In the middle of the boreal forest, the region of Fort McMurray in Alberta in western Canada, known to be the largest industrial tar sands complex in the world, still bears the scars of the gigantic fire of May 2016.
“This fire was a monster,” says the man, red checkered shirt on his back, pointing to the surrounding hills through which the fire came.
A wall of flames, clouds of smoke, reduced visibility for kilometers and, in the middle, nearly 90,000 inhabitants trying to flee in the chaos by the only access road.
“A fire like that, you don’t face it. You get up, you get out of there”, recalls Harvey Sykes who, like many, lost everything at the time, his house, his possessions, the memories of a life.
This fire remains the biggest disaster in the history of Canada with more than 2,500 buildings destroyed and a cost of nearly 10 billion Canadian dollars (7.30 billion euros).
A trauma in the country which saw, for the first time, its inhabitants being directly hit by the consequences of global warming on the boreal forest.
Today, these mega-fires are multiplying in Alaska, Canada or Siberia. They are one of the greatest dangers to the northern forest.
– Extreme heat waves –
Quite a paradox because fires are an integral part of its history.
Like the sun or the rain, they are essential to its evolution. Not least because they release valuable nutrients found in the forest floor and create pierces of light in the canopy that stimulate the growth of new trees.
In the boreal forest, crown fires dominate, more intense and difficult to fight than surface fires. Bog fires can last all winter under snow, producing large amounts of smoke and carbon monoxide emissions.
Resistant to the great cold, all the plants have adapted to the fire, such as the aspen poplars which burn quickly but regrow easily thanks to underground discharges.
Some are even dependent on it, such as jack pine or black spruce whose cones open and release seeds when the flames pass.
But data collected over the past decades indicate that the frequency of fires and their intensity have reached an abnormal level.
“We end up with a fire season that is longer, more severe. They are more intense and cover larger areas,” notes Yan Boulanger, researcher in forest ecology for the Canadian Ministry of Natural Resources.
The fires destroy twice as much forest cover in the world as at the beginning of the century and 70% of the surfaces devoured by the flames in 20 years concern the boreal forests, confirmed in August satellite data compiled by the Global Forest Watch (GFW ), the World Resources Institute (WRI) and the University of Maryland.
Extreme heat waves are now five times more likely than a century and a half ago, experts say. And the warming is particularly affecting the northern regions, including the boreal zone, since temperatures are increasing there two to three times faster than on the planet as a whole.
Excess heat leads to more lightning, which often starts the most devastating fires, said Yan Boulanger, 42, a weather enthusiast with a long brown beard.
The destruction of the forest by these fires leads to massive emissions of greenhouse gases, which further aggravates climate change by self-sustaining it.
And while fires are one of the extreme manifestations of rising temperatures, its consequences are wider still.
– “Drunken trees” –
For a while they lean: they are called “drunken trees”. Then the ground ends up giving way under their roots. So they end up falling.
Experts call this high latitude phenomenon “thermokarst”.
These land subsidences which cause deep depressions before tilting the trees are due to the destabilization of the permafrost – this basement which remains permanently frozen for two consecutive years – on which rests part of the boreal forest.
“With permafrost thawing, you have the potential for big changes,” worries Diana Stralberg, researcher in Edmonton in western Canada for the Department of Natural Resources.
“These areas are suddenly flooded and lose forests” to become peat bogs or lakes, she explains.
While in the thawing ground, bacteria break down biomass stored for thousands of years, leading to emissions of carbon dioxide and methane, greenhouse gases which in turn accelerate global warming.
Elsewhere, in the northern boreal forest, trees are colonizing the tundra where they now find conditions more conducive to their development.
Recently, scientists discovered that white spruces had moved north from Alaska into an area of arctic tundra that hadn’t seen such trees in millennia. They would advance at a rate of four kilometers in a decade.
At the same time, to the south, the boreal forest is rapidly drying up and turning into tall grasses and shrubs.
“In the west, we could end up with forests that simply turn into grasslands since the degree of drought or the frequency of disturbances is too great to support a population of trees”, explains Yan Boulanger.
Diana Stralberg remembers the first maps modeling the effects of global warming she saw drawing on her computer when she started working on boreal forests a few years ago.
“I said to myself there is a mistake because it seemed to me too extreme to be true”. But little by little, his colleagues came to the same conclusions: the forest is rising rapidly, absorbing part of the tundra in the north, eaten by the prairie in the south.
Moving an ecosystem is not neutral.
“You can lose a forest much faster than it can grow and provide habitat for wildlife,” continues the discreet 52-year-old scientist.
When the mercury rises, evaporation occurs more easily and plants lose water at a high rate through transpiration. They then close the pores of their leaves and fight for their survival. By slowing their growth, they also lose some of their ability to remove carbon dioxide from the atmosphere. A vicious circle.
– “Runaway phenomenon” –
Here, “we want to measure the resilience of the carbon pool that is the soil of boreal forests”.
The sun had a hard time breaking through to the ground, the trees compete to catch the light. Thousands of pine needles cover the moss.
In western Quebec, forest carbon specialist David Paré and his teams are interested in litter, the decomposing plant debris that forms the soil of forests.
The quantity of CO2 stored for hundreds of years in this litter is five to six times greater than that retained by plants. It is the carbon sink of the boreal forest.
To understand how it works and simulate the future, experiments are multiplying in Canada: in places the basement is heated, in others the quantity of litter on the ground is modified or the roots of trees are cut…
Planted in the pine needles fallen to the ground, dozens of small orange flags and wooden bins indicate the various experiments in place for six years.
“We want to understand how much carbon accumulates in the soil and how,” David Paré, researcher for the Canadian government, told AFP.
“Because if with the warming, this reservoir decreases, it will create more warming”, adds this 59-year-old cross-country skier, with a broad smile.
“A runaway phenomenon” feared by scientists. Ultimately, this could cause boreal forests to lose their status as carbon sinks. Especially since the vegetation there is threatened by another phenomenon that has appeared with the rise in temperatures: the proliferation of insects.
– “Hemlock looper” –
It is a surprising landscape: in the middle of a hill populated by very green and very alive trees, a square made up of skeletons of trees, stripped of their horizontal branches but whose trunk remains erect towards the sky.
“It’s as if a bomb had exploded, all the trees are dead in this area, killed by the hemlock looper”, notes David Paré, hard hat on his head.
The looper is a “very virulent insect that will eat all the needles and also the leaves in a single season”, explains the researcher, advancing with difficulty in the middle of the raspberry bushes which have colonized the space to the delight of the bears fond of the small pink fruit.
Several phenomena seem to come into play to explain the multiplication of insect epidemics, which are also found in Scandinavia: trees already “stressed” by the lack of water are less resistant and insects benefit from winters that are less cold or longer summers.
Hundreds of thousands of hectares of forest are also eaten away by the spruce budworm, an insect that mainly attacks fir trees in Canada.
“With global warming, the budworm now has access to territories where it was not or very little present in the past”, explains researcher Louis De Grandpré, who has been studying the forest for 30 years.
The main thing now is to measure the long-term effects of these epidemics “because we are really in the unknown about the future of these forests”, slips the scientist.
– “Resilience” –
“There is a limit to what trees can take,” warns David Paré.
At this stage, the question of whether the boreal forest can reach a “tipping point”, a climatic threshold beyond which the release of CO2 and methane is inevitable and the change in the ecosystem irreversible, remains a question in the scientific circles.
There remains, for the experts, the hope of the “resilience” of this ecosystem which has already been able to adapt.
It is still possible to reduce the damage, believes Diana Stralberg.
“We studied areas that will remain cooler and wetter in a warming world, such as the shores of large inland lakes, large bog complexes and north-facing hillsides,” she explains.
“These are areas where we can buy time for cold-adapted species like spruces and caribou to adapt to short-term climate change.”
Monitoring, reforestation, legislation, technological progress and above all ancestral techniques can contribute to maintaining this carbon sink.
“So-called cultural burning can be one of the solutions combined with some of the new technology,” says Amy Cardinal Christianson, a Canadian Forest Service researcher who studies the effects of fires in Indigenous communities.
Practiced for millennia by the natives, these controlled burnings can help reduce the importance of forest fires by eliminating in particular part of the vegetation on the ground. It’s “a slow fire, which is a good fire”, says this member of the Métis people.
Unlike the Amazon, in this cold forest with inhospitable conditions, direct human action – such as deforestation or the exploitation of oil sands – is less to blame than “natural disturbances” due to global warming.
The solution, so that it continues to play its essential role for the health of the planet, can only be global, underline the experts.
We must, says Yan Boulanger, keep “faith in the generation that follows”.
