When climate change leads to the migration of fauna and flora

The lizards take the train. Or rather they take the railway line. “On the Paris-Cherbourg line, I saw them arrive in around twenty years,” says Mickaël Barrioz. Based in the English Channel, this naturalist specializing in reptiles and amphibians coordinates the Climate Sentinels program for the Normandy region. “On each of my return trips to Paris by train, I scanned the ballast to spot the wildlife hiding there,” he says. Little by little, the wall lizard appeared, along with others. I first saw it at Lisieux station, then Caen, Bayeux, and finally Cherbourg, where it remained very rare until the 1990s.” For species that appreciate dry and warm rockeries, a railway line forms a ready-made corridor, with its refuges in the SNCF wastelands.

You have to have an eye to spot a lizard going into exile and verify that such a phenomenon is not anecdotal. Certainly, we will be surprised to hear a cicada singing north of Lyon (Rhône) one summer. But how do we know that a particular type of fescue was not among the grasses already present in our environment twenty years ago, or that there are fewer bumblebees than ten years ago? “It is imperative to go beyond empirical impressions, even those of naturalists! » advises Mickaël Barrioz.

A race against time

Only a scientific approach makes it possible to evaluate the migration of fauna and flora, by means of repeated monitoring protocols, statistics and delving into archives. “As much as the melting of the ice proves to be a clear marker, the migration of species is difficult to highlight and goes unnoticed,” notes ecologist Jonathan Lenoir, who devotes his research to this at the CNRS. “We rely on data recorded by previous generations of naturalists,” he says, going so far as to examine the observations of 18th century scientists to compare them with current findings.

On a planetary scale, the distribution areas of 12,000 species and the way in which they are redistributed over the decades were thus scrutinized. And in fact, to seek a cooler or more humid place to live, certain species of plants and animals did not wait to head towards the poles or the heights. The second option turns out to be the most effective: you have to travel 100 kilometers north to benefit from a drop in temperature comparable to that found by climbing 100 meters in altitude. But the speed of land movement of fauna (and even more so of flora) remains limited: 18 meters of difference in altitude per decade on average, one kilometer per year in the plains.

The rise in temperatures is evolving much more quickly. This discrepancy distresses entomologist Hugues Mouret, scientific director of the Arthropologia association, which campaigns for biodiversity and the protection of pollinating insects: “The previous major climate changes took place over one hundred and fifty thousand years, not less than one hundred and fifty like today ! Nature can never move fast enough. » Because mobility should not hide the fact that most species are suffering the situation and that their numbers will be dwindling.

For the adventurers, the journey appears strewn with pitfalls: fragmented habitats, scarred by roads, towns, industrial zones or impassable plains, when they are not quite simply destroyed. As for those who take refuge at altitude, what will they do once at the summit? And what about the trees, which cannot take their roots from their necks? Geneticist Brigitte Musch, national coordinator of forest genetic resources at the National Forestry Office (ONF), ensures that their descendants – pollen, seeds, cuttings – can grow a little further. The “move” takes place over several generations. At their pace, however, which is not that of a human life. An oak tree, for example, “reaches sexual maturity (the time when it produces the most acorns and pollen, Editor’s note) between 120 and 150 years old in a dense forest.

Should man speed up the movement by playing the mover? As a last resort, these specialists cry. Their first recommendation: “Let nature take its course!” » Let's stop artificializing the land, let's let as many spaces as possible “go wild” without intervening. “With time, space and the connection between spaces, it can go very quickly,” insists Hugues Mouret who, in ten years, has seen spontaneous insects, mammals, birds, shrubs and trees return to his own garden left in freedom, 30 kilometers from Lyon.

A little help

For public forests, the ONF also relies heavily on natural regeneration. The institution has developed an “assisted gene flow” program, which aims to expand the genetic richness of species in the hope of helping them adapt to new conditions. For this, tree seeds are harvested in areas subject to drastic climatic hazards, to be sown further north, among individuals of the same species. “We are betting that the encounter between each other’s genes will make future offspring more resistant,” explains Brigitte Musch.

In Normandy, as in Occitanie and Nouvelle-Aquitaine where it was launched, the Climate Sentinels program aims to model the impacts of climate change on regional natural environments where declining species live and to estimate whether, in 2050, or 2100, they will benefit from always favorable conditions. A critical case? Amphibians, half of which disappeared between 1960 and 1990. We do not know where these vertebrates dependent on wetlands could migrate. Especially since they return to reproduce in their place of birth…

“Amphibians have a very low dispersal capacity,” explains Mickaël Barrioz. It generally extends for less than 1 kilometer, rarely more than 5.” His team looked into the case of the yellow-bellied ringing toad, still present in Cotentin (Manche) and appearing on the international list of species ” critically endangered.” To ensure the conservation of the genetic profile of this amphibian, Norman naturalists resolved to breed it, before reintroducing it “in sectors which would be more favorable to it, with regard to the IPCC* scenarios”, i.e. more north, in Upper Normandy and Hauts-de-France. “A real dilemma,” admits Mickaël Barrioz, initially reluctant to the idea of ​​such a level of interventionism. His colleagues convinced him: man has such a deleterious influence on nature that he can afford a little help from time to time.

* Intergovernmental Panel on Climate Change; its website: ipcc.ch/languages-2/francais