Frédéric Joignot, The Guardian
“Man is senescent, that is to say is programmed to die, but a plane tree is not,” says French botanist Francis Hallé. After its leaves have fallen, life begins again in the spring and the tree recovers its youthful genomes. If it is not subjected to accidents, diseases or humans, the plane tree could live for centuries.
The botanist knows of a 2,000-year-old olive tree in Roquebrune-Cap-Martin on the Côte d’Azur
Humans, with a mere 2 square metres of skin, underestimate the surface area of a tree. To calculate that you need to measure both sides of each leaf, add the surface of the trunk, the branches and boughs, the perennial and feeder roots and the absorbent root hairs, not forgetting the bark pockets. A 15-metre tree in leaf would cover a total area of 200 hectares, which is the size of Monaco. A tree doubles its weight when wet, and its entire surface breathes and allows us to breathe.
Hallé believes that arboreal photosynthesis is our best ally in the fight against global warming. Buffon’s plane tree, like all trees, absorbs quantities of carbon dioxide, responsible for greenhouse gases, and between 20% and 50% of matter produced by the tree, including wood, roots, leaves and fruit, is composed of CO2. When trees breathe they clean the atmosphere and retain CO2 and urban pollutants such as heavy metals, lead, manganese, industrial soot and nitrous oxide. These are stored in the wood. That is why we should refrain as much as possible from cutting down old trees. The older they are, the better they control pollutants.
At the same time, trees release oxygen that allows us to live. An adult human consumes about 700g of O2 per day, or 255kg per year. In that time, an average tree produces 15kg to 30kg, so about 10 trees are required to provide oxygen for one person. Trees also humidify and cool the atmosphere by evaporation and transpiration. A wooded area of 50 square metres brings the temperature down by 3.5C and increases the humidity by 50%. Leaf movement, especially in conifers, releases negative ions that are supposed to have beneficial effects on health and mood.