half of the tree species in the city are already weakened in France

This is unprecedented work: an international research team, involving the CNRS, studied how more than 3,000 species of trees planted in 164 cities around the world could adapt to climate change. They therefore concretely looked at how, in each of these 164 cities, the current trees could tolerate the temperature and drought levels expected locally for 2050. There is indeed a threat to urban green spaces: since at the global level, three-quarters of tree species are likely to suffer from climatic maladjustment in 30 years.

In France, researchers have studied the cases of Paris, Bordeaux, Montpellier, Grenoble and Lyon. Overall, in these five cities, two tree species out of three risk suffering from heat or drought in 2050, if they are not regularly watered and maintained by the municipalities. Half of the species are already weakened by climate change in France. We find among them: beeches, ashes, certain oaks, lime trees, or chestnut trees. This is why researchers recommend planting more suitable species now. If we take the case of Paris for example, we should plant more Mediterranean oaks such as kermes oak or cork oak. The olive trees will also be adapted to the climate of the capital in 2050.

Obviously, there is no question of cutting down the existing trees, which, if they are old, maintained and watered by the municipalities, will be able to adapt to the climate of 2050. But the interest is also to plant shrubs which will resist naturally, without too much additional water supply to temperatures in every city in 30 years. Because trees in the city will be more and more valuable: to store carbon, to capture certain pollutants as well as rainwater. And in terms of thermal regulation, studies have shown that green spaces can lower the temperature of a street or a park by 1°C to 5°C.