Very fashionable, is the massive planting of trees an “absurdity” to combat global warming? Like Bill Gates, a growing number of scientists are openly expressing their doubts.
The American billionaire sparked controversy last month by brushing aside this method of planting forests to capture CO2.
Asked about his way of offsetting his carbon emissions, during a conference organized by the New York Times, he said: “I don’t plant trees”. This technique, whose “effectiveness is one of the least proven”, is a “total absurdity”, he insisted, before asking the question: “are we scientists or are we idiots?” »
Across the world, tree plantations have become a preferred way for businesses and individuals to offset their greenhouse gas emissions.
Even US Republicans, notoriously skeptical of climate change, have introduced a bill to support the planting of a trillion trees worldwide.
Bill Gates’ comment “can really set us back”, blasted X Jad Daley, director of the NGO American Forests, who “dedicated the last 16 years [sa] life to ensure that forests are part of the climate solution.”
But Bill Gates is far from the only one to doubt the benefits of such ambitious plans.
On September 21, EU member states agreed on legislation that bans claims of neutral or positive environmental impact based solely on offsetting carbon emissions, which often amounts to tree plantings, ineffective practice according to the text, compared to the direct reduction of CO emissions2 of the company.
A group of scientists warned Tuesday that mass tree planting risks doing more harm than good, particularly in tropical regions, where monoculture can lead to the disappearance of complex ecosystems.
“Society has reduced the value of these ecosystems to a single parameter: carbon,” write the scientists from British and South African universities.
Carbon capture is “a small part of the essential ecological functions that tropical forests and grassland ecosystems perform,” they explain in an article published in the journal Trends in Ecology and Evolution.
One such scientist, Jesus Aguirre Gutierrez, cites examples in southern Mexico and Ghana, where once diverse forests “transformed into homogenous masses.” This makes them “very vulnerable to disease and has a negative impact on local biodiversity,” says the researcher from the Institute of Environmental Change at the University of Oxford.
Risks to the ecosystem
These plantations are dominated by five species of trees chosen largely for their value in wood and paper pulp, or for their speed of growth. The trees will eventually be cut down, releasing carbon.
Among these species, teak, which can take precedence over the original species, “posing additional risks for native plants and the ecosystem,” adds Mr. Aguirre Gutierrez.
Other criticisms relate to the lack of space on a global scale for the numerous massive planting projects, the planting of poorly adapted seedlings or the inappropriate use of meadows and wetlands in forest areas.
So is there no value in planting trees? Not so fast, says Daley, whose American Forests organization claims to have planted 65 million trees. It is Bill Gates’ postulate that is false, he believes.
“No one says that forests alone can save our environment,” he says.
But he castigates “sketchy” critiques that ignore carefully calibrated projects involving native species in areas to be reforested.
“A lot of reforestation is driven by the loss of forests that won’t regenerate without help,” he emphasizes, “we don’t just plant trees wherever we want to capture carbon.”
Some strive to reconcile the pros and the antis, such as the Royal Botanic Gardens of Kew (United Kingdom) and the organization BGCI (Botanic Gardens Conservation International), which propose ten “golden rules for restoring forests”.
It advises in particular to avoid meadows or wetlands, to give priority to natural regeneration and to select resistant trees rich in biodiversity.
And on the first of these golden rules, everyone can agree: first protect existing forests. “These forests can take more than 100 years to reestablish themselves, so it is essential to protect what we already have before planting more.”