'The essential is invisible to the eyes (Saint Exupery): Application to forest soil biodiversity' ; ' L'essentiel est invisible pour les yeux » (Saint-Exupéry) : Application à la biodiversité des sols forestiers' ; ‘The essential is invisible to the eyes (Saint Exupery): Application to forest soil biodiversity’; ‘The essential is invisible to the eyes’ (Saint-Exupéry): Forest soil biodiversity application”

International audience ; Mediterranean forests are known for their exceptional biodiversity, especially for plants. But they form a complex system of which we can directly see only a tiny part: trees first, 3 to 12 species at best per hectare in our regions, numbering a few tens to a few thousand individuals; then other higher plants, a few tens to a hundred species with sometimes several tens of thousands of individuals per hectare. Finally, large animals complete the picture, sometimes dozens of species: birds, mammals, reptiles. But we really need to take a closer look… Just with a magnifying glass, life is much richer: ants, termites and other micro-insects, arachnids, mushrooms, worms. It is then per square meter that we discover thousands or tens of thousands of individuals, i.e. millions of individuals per hectare from a few hundred to more than a thousand species. But under the microscope biodiversity increases exponentially: in each gram of forest humus, bacteria number in the tens to hundreds of millions (for several thousand species), fungi, protozoa and microalgae in the tens or hundreds of thousands. Thus, taken together per square meter, tens of billions of individuals and, per hectare, up to tens of thousands of billions. And although they are still very poorly known and little studied, viruses would still be far more numerous than bacteria. The richness of the soil is the key to this incredible diversity and, reciprocally, this diversity and abundance and the activity of all these tiny beings together condition the fertility of the soil, its quality and, therefore, the life and survival of the forest: its productivity, its ability to sequester carbon, capture water and provide us with so many other services. Consequently, protecting the soil is an absolute necessity in the management and restoration of forests (this is, of course, also true for all agricultural and urban soils worldwide). Much remains to be done to know and understand this infinite hidden biodiversity and how it works, the better ...