More than a third of the world’s trees are threatened with extinction, researchers recently announced at COP16 on biodiversity. This observation seems to contradict NASA images, which show that the Earth is increasingly green. “Who to believe? », asks a reader.
Published at 6:00 a.m.
Last month, at the Cali conference, the International Union for Conservation of Nature (IUCN) released an updated report on the state of the world’s trees. According to new data gathered by more than 1,000 experts, 38% of tree species are now included on the IUCN Red List, which lists species according to their risk of extinction.
These predictions raise the eyebrows of our reader Marc McDonald, who attaches to his email NASA satellite data from a study published in 2019 in the journal Nature Reviews Earth and Environment. According to this study, since the beginning of the 1980s, the planet has gained 5% plant cover, which may seem like good news.
How to reconcile the two?
“It’s like trying to compare an orange with an apple seed. We have to be very careful,” says Christian Messier, professor of forest management and biodiversity at the University of Quebec in Outaouais.
According to the expert, who is also a member of the Center for the Study of Forests and the Canada Chair on the Resilience of Forests in the Face of Global Change, “the planet has greened a little, especially in China and India.”
The planet is becoming greener in three ways, he explains. There is intensive agriculture, as is the case in India, which has greatly increased greenery. In China, an intensive tree planting program is contributing to the phenomenon, while greening is increasing in the north with the melting of permafrost.
In India, for example, 82% of the greening observed is attributable to the increase in the surface area of intensive crops, specifies another study published in the journal Nature Sustainability.
In China, they have made colossal efforts to plant trees, reduce places where there was deforestation and that is really good news. This is a significant success. The only downside is mainly monocultures, plantations of a single species over huge areas which aim to produce more wood.
Christian Messier, professor of forest management and biodiversity at the University of Quebec in Outaouais
“These are not natural forests that we have reproduced, these are environments that will be productive for the production of wood,” points out Christian Messier.
We also notice that there is vegetation growing in the northern regions, in the north of Canada and Russia, because of global warming, mentions Mr. Messier. The problem is that this vegetation appears due to the melting of permafrost, a phenomenon which releases significant quantities of methane into the atmosphere.
Methane is a greenhouse gas with a much greater short-term warming potential than carbon dioxide.
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Christian Messier, professor of forest management and biodiversity at the University of Quebec in Outaouais
We may think that it is good news that there are greener regions, but emitting a lot of methane will accelerate climate change.
Christian Messier, professor of forest management and biodiversity at the University of Quebec in Outaouais
We must be very careful with these data on the greening of the planet, maintains the researcher, and especially not put them in opposition to the decline of tree species. “It’s never all black and white, obviously. »
We are going to lose more and more species of trees on a global level, but the most important thing is the loss of tropical environments. In the Amazon, 50 hectares can contain 500 to 1000 species of trees.
Christian Messier, professor of forest management and biodiversity at the University of Quebec in Outaouais
The situation is not necessarily catastrophic, he adds, but could become so if the decline continues.
Several tree species have approximately the same functions, he explains. We can therefore lose a certain number of tree species without losing important properties in ecosystems. “But if we continue like this, eventually, we will lose important species and that is worrying. »
Consult NASA’s fact sheet about the greening of the planet (in English)
