Old trees are the guardians of forests

With Mathilde Fontez, editor-in-chief of scientific magazine Epsiloon, at a time when we talk a lot about deforestation, even reforestation, we are now interested in ancestors essential for the balance of our planet: old trees. A new study has clarified how urgent it is to preserve them.

franceinfo: It is not enough to plant rows of new trees. Because for a forest to be healthy, it must have old trees?

Mathilde Fontez: Yes, it is a study that sings the praises of the most venerable of living beings on Earth. They are several hundred years old. Sometimes more than a thousand. And they hide in the heart of preserved forests. They are 10 to 20 times older than the average of the other trees around them.

They are very few, they represent only 1% of the population of a forest. And yet, they are the ones who guarantee its stability, its resistance to climate change and to all environmental pressures. Old trees are the guardians of the forest.

They act on the entire ecosystem?

This is the conclusion reached by Charles Cannon, researcher at the Morton Arboretum, near Chicago. To get there, he did not conduct a field study. It’s just not possible. These very old trees are too few in number for us to hope to identify and sample them, as is done for traditional ecological studies.

The researcher therefore carried out a numerical study. Using field data on tree populations, in particular mortality rates, he modeled the evolution of virtual forests, over 150,000 years – like a demographic study of trees in a way. Then he varied the environmental conditions, the climatic cycles. And what he sees is that, indeed, forests that do not have old trees resist less well.

And do we know why?

We suspect it. It’s quite logical actually. Because these trees, during their long life, have adapted particularly well. They have survived lightning, fire, pest attacks, droughts, frost. Each time, by adapting genetically.

Especially since the genetics of trees is very plastic: they can modify their DNA on each branch permanently. They don’t have a single genome like us. It is undoubtedly this phenomenon, multiplied over hundreds of years, which gives them an incredible resilience. And they transmit it around them, sowing new trees from year to year, strengthening the whole forest.