Originally, the planting was justified by the fact that trees are carbon sinks, they absorb CO2 through photosynthesis and store it outside the atmosphere, which allows human emissions to be at least partially neutralized.
Planting new trees on a massive scale was considered a miracle solution to offset CO2 emissions and fight pollution, but this widespread practice, long considered positive, is increasingly being called into question.
In recent years, this method has been widely used by large companies to offset their high greenhouse gas emissions. Airlines in particular are singled out by environmentalists for this practice. At the end of 2019, Air France announced the compensation of CO2 emissions from its 450 daily domestic flights by doing so.
Quoted by ‘Le Monde’, Anne Rigail, the company’s general director, mentioned projects such as “tree planting, forest protection, energy transition and even the safeguarding of biodiversity”. But some observers consider tree planting by companies to be a “greenwashing” strategy, as this action does not directly cancel out the consequences of a polluting activity.
Myrtho Tilianaki, from the French NGO CCFD-Terre Solidaire, observed, by studying the carbon strategies of several companies, that these actions often hide an absence of measures to reduce emissions.
And certain practices can be abusive: “We have had cases in the past of carbon offset projects which led to intimidation, evictions, land grabbing phenomena,” adds Myrtho Tilianaki, quoted by ‘France 24’.
Is tree planting at least effective in its role as a carbon sink?
This is not the view of a growing number of scientists and public figures. Bill Gates declared, during a conference organized by the ‘New York Times’, that he does not plant trees, calling the practice “complete nonsense”.
The opinion of the founder of Microsoft is confirmed by a study cited by ‘Geo’, published on October 3: according to its authors, British and South African scientists, the massive planting of trees would have more disadvantages than benefits, particularly in tropical regions.
“Society has reduced the value of these ecosystems to a single parameter: carbon,” they write in the journal ‘Trends in Ecology and Evolution’. However, carbon capture is “a small element of the essential ecological functions that tropical forests and grassland ecosystems perform”.
The tree species chosen are, moreover, not varied enough. In some countries, previously very diverse forests have become “homogeneous masses”, according to an Oxford researcher, cited by ‘AFP’.
This homogeneity makes the trees very vulnerable to diseases while having a negative impact on local biodiversity, according to the Oxford scientist.
Trees are selected for their speed of growth or for their value in wood or paper pulp. They will therefore be cut down sooner or later, which will release carbon and cancel out the positive impact of the plantation.
Another adverse effect: planting trees reduces available agricultural space, which leads to an increase in the price of food and can cause the undernutrition of millions of people on the planet.
How can we realize the absorption potential of trees without inflicting collateral damage on ecosystems? The Royal Botanic Gardens, Kew, United Kingdom, and the organization BGCI (Botanic Gardens Conservation International) have proposed ten golden rules.
The first of these is to better protect existing forests, taking into account the time they need to recover, before starting to replant. It is also advisable to avoid meadows and wetlands to plant new forests, and to select resistant tree species rich in biodiversity.
On September 21, 2023, the member states of the European Union agreed to prohibit declarations of neutral or positive environmental impact based exclusively on the compensation of CO2 emissions. Indeed, compensation often consists of planting trees without concern for effectiveness. Priority is now given to directly reducing companies’ CO2 emissions.