to meet the “society of trees” in the forests

Studying forests means discovering a connected world on all levels. Trees, plants, animals and all their cortege of microorganisms are in constant interaction, connected to each other. Trees form bonds between the community and the creatures that surround them, which will determine their life, survival and the balance of the ecosystem called the forest.

The real revolution of the last decade has been the evolution of genetic tools and mass sequencing. It allows us to discover the invisible world of microorganisms: fungi, bacteria, viruses…

Let’s take a boletus. What hides the invisible world?

Half…

Studying forests means discovering a connected world on all levels. Trees, plants, animals and all their cortege of microorganisms are in constant interaction, connected to each other. Trees form bonds between the community and the creatures that surround them, which will determine their life, survival and the balance of the ecosystem called the forest.

The real revolution of the last decade has been the evolution of genetic tools and mass sequencing. It allows us to discover the invisible world of microorganisms: fungi, bacteria, viruses…

Let’s take a boletus. What hides the invisible world?

Half of the forest’s living mass is under our feet. This is especially true for mushrooms: boletes, amanitas, cortinaria, ceps, russules… They are only the aerial part, the reproductive organs of the underground carpet, which makes up 99% of the mushroom itself. As you search for porcini mushrooms, you walk on a cotton-braided net a few centimeters below the ground’s surface. It occupies most of the territory. In symbiosis with trees, it absorbs nutrients to meet its needs.

An ode to the diversity of forests

Francis Martin, Emeritus Director of Research at the National Research Institute for Agriculture, Food and the Environment (INRAE) in Nancy (Meurthe-et-Moselle) studies the relationship between trees and fungi. A plant physiologist in his early days, he worked in molecular biology and built bridges with ecology, the science of interactions between species. With “La Forêt hyperconnectée” (ed. Salamander, 168 pp., €19.90), he signs an alphabet that opens a poetic window on forests while popularizing the latest knowledge about the functioning of these ecosystems.

What signals do these creatures send to each other?

Much of their communication takes place through volatile molecules. Trees send chemical signals to warn each other of danger and protect themselves from insect attacks. The same phenomenon works in soil. Tree roots are in contact with fungi, including fungi and tens of thousands of species – one gram of soil contains billions of bacteria. They interact, cooperate and/or compete. Some filamentous bacteria in soil use as weapons lipid molecules, fatty acids that are dispersed by rain and emit the “smell of rain” inhaled by forest walkers.

“Trees accumulate climate debt. Their rate of migration remains insufficient, either northwards or towards the highlands.

You write that “trees grow old”. Why?

We have almost no primary forests in Europe. They are domesticated. Planted forests such as the Landes massif, and even the large beech and oak forests characteristic of the state forests of the Loire and Central France, are the result of the forester’s “horticulture”. With this application, beech and oak can live between 100 and 150 years, while an oak can easily live for 500 years. However, only in forests where trees can die a beautiful death can the full spectrum of biodiversity be expressed. If we cut down 80-year-old pine trees and 150-year-old oak trees, the microorganisms associated with very old trees will never see the light of day. Some decaying fungi – polypores, known for their cantilever shape – appear only on trees over 250 years old. Dead trees must still remain on the ground for the wealth of living things to explode. Foresters have picked up bad habits over the past few centuries. They clear the forest. This is also the dream of many pedestrians.

“Trees have always been great nomads,” you say. But are they moving fast enough to avoid global warming?

Trees accumulate climate debt. Their rate of migration, whether northward or upward, remains insufficient, although the forest line in the Alps and Pyrenees has moved at a rate almost detectable by the human eye in recent decades. Climate change is ten times faster.

Beech, which is abundant in our forests, would have to migrate 100-200 kilometers north to resist. But with the geography of agricultural fields and cities, forests will not be able to move as they did thousands of years ago. Despite the help of corvids, jays, and squirrels that drive oaks north, there is little chance that oak populations can settle in more favorable areas without human help. It is for this reason that foresters develop assisted migration. We help nature adapt as if it had time.

What does it consist of?