Tatiana Giraud: “Biodiversity is a vital fuel”

In your latest book, you seek to correct a certain stereotyped image of biodiversity. What is it?

When we talk about biodiversity today, it is mainly the large emblematic mammals that are mentioned, such as tigers, pandas or whales. More rarely birds and flowers. And much more rarely, the micro-organisms which are essential to soil fertility.

Furthermore, in the collective imagination, biodiversity is often perceived as a library, where species are juxtaposed with each other, like books on a shelf. On the contrary, they form a set of constant and complex interactions.

Biodiversity is a dynamic balance, like when you ride a bike: you have to be in motion so as not to fall. Life is sustained on Earth because diversity allows species to constantly evolve and change. This is the fuel of evolution. A static vision of biodiversity risks leading to false solutions.

Which ones for example?

French forests are hard hit by climate change, with an 80% increase in tree losses in 2024. Some believe they can save their genetic varieties by saving seeds. But if we replant them in soil that no longer contains the microorganisms with which they create symbioses, the trees will not be able to grow. The mushrooms in fact provide water and nutrients to the tree, which provides them with sugar in return.

Forests also cannot survive without pollinators or birds that eat pests. It is therefore an entire ecosystem that must be protected. Plants evolve with their environment, constantly adapting to new pathogens.

If seeds are stored cold, as is the case in the Global Seed Vault in Svalbard, Norway, they cannot be reintroduced into an environment where they will encounter new diseases with which they have not coevolved.

By reading you, I learned that there are 2.15 million species known and described, and probably 4 times more in total. Does humanity really need all this to live?

We don’t know exactly which ones we have and will need! If biodiversity is thought of as a library, we can say that, if a book is missing, continuing to live is possible by reading the others. A better analogy would be an airplane, where the rivets hold the metal sheets together.

It takes several rivets to hold a sheet of metal, such as species in an ecosystem like a forest or wetland. You can lose a few rivets, there is redundancy and the plane still holds. Until we lose a rivet, we don’t know in advance which one, and then nothing holds. That’s what biodiversity is: losing a few species doesn’t immediately have any consequences, then, at one point, the imbalance is too strong.

What are the concrete consequences?

Impacts on human health and the economy, for example. In 2025, an American study focused on bats sick with an invasive pathogen that caused their noses to turn white. As a result of this disease, their population collapsed. At the end of the chain, this increased pediatric cancers by 8%. For what ? Because the bats were no longer there to eat the crop-destroying insects.

The farmers concerned therefore increased the doses of pesticides, without however managing to restore previous yields, and these products deteriorated the health of neighboring populations, starting with that of children.

You warn of the ongoing collapse of biodiversity. It’s a strong word. What indicators do you rely on?

The rate of disappearance of species is very rapid. Since 1980, depending on the animal group concerned, it has been 15 to 165 times higher than during the last known extinction on Earth, 65 million years ago. The decline in population abundance within each species is also of great concern. Mammals have lost three quarters of their individuals in thirty years. The smaller the populations, the less genetic diversity there is, and the less able species are to adapt.

What are the main causes?

These are the destruction of natural environments, the overexploitation of resources, pollution of all kinds, climate change and the introduction of invasive species. In France, the leading cause of species disappearance is pesticides. The problem has worsened since the 1990s as they are increasingly used in the form of seed coatings. 70% of the product leaves with precipitation, polluting water and soil. Note also that 30% of these coated seeds are eaten by birds or rodents, and poison them directly. These molecules designed to kill have a very wide range of action. It is absurd to use them for prevention and no longer just for treatment of diseases on plants. It’s like taking antibiotics to avoid getting sick. It is urgent to stop this use and move towards an exit from pesticides. However, whether at the European or French level, we are taking the opposite path. Some would like to believe that the agricultural emergency bill (which relaxes regulations on pesticides and water retention, editor’s note) under discussion in Parliament supports small farmers. In reality, it goes in the direction of agro-industry, to the detriment of the common good.

How to do otherwise?

We cannot do without pesticides overnight. But the transition to an agroecological model is realistic. We must reintroduce diversity into crops and livestock to put an end to these very simplified agricultural systems which open avenues to pathogens. The whole challenge is to support farmers by redirecting subsidies from the Common Agricultural Policy, which today mainly go to large farms and intensive livestock farming.

Do you see today in France a denial of this collapse, just as there is a denial of climate change and its human causes?

Yes, biodiversity also has its “merchants of doubt”. It is true that this collapse is less perceptible than the disasters linked to climate change, due to a form of generational amnesia. Younger generations rarely perceive the extent of the loss, while older ones can compare the quantity of butterflies fluttering in the garden or insects crushed on windshields with what they observed in their youth.

The collapse is here and it is already having concrete consequences, even if they are little publicized. Who knows that floods in France are linked to the disappearance of wetlands and part of the biodiversity that absorbed water?

In recent years, the fall in the number of pollinators has also led to a drop in the yield of several crops, such as blackcurrants in Burgundy.

Is it easier to restore biodiversity than to stabilize the climate?

Biodiversity can indeed return very quickly, as we see in the pilot rewilding experiments carried out in Scotland, or in the Millière valley, in Yvelines. Provided that the soils are not too degraded and that the species are left alone. It is also possible in cultivated areas, as we see in organic farming plots, especially if there are hedges and a diversity of production.

Mushrooms are at the center of your research. Why do they interest you so much?

These microscopic organisms seem insignificant, even disgusting to some. However, they are essential to the life of three quarters of plants, with which they create symbioses. They are also nature’s scavengers, the only living organisms capable of recycling dead wood, for example.

In Chernobyl, where there are no more fungi in the ground, dead wood accumulates. I also worked on the domestication of these fungi called molds, which develop the aroma of our cheeses. Without them, we would have no wine, no beer, no bread, no Camembert or Roquefort! I am fascinated by the gap between their apparent insignificance and the importance they have in the grand cycle of life. Even on our plates.