At first glance, there are only oaks, lime trees and green hornbeams. «Nothing appealed to me, finally», recognizes Christophe Blanchet, volunteer of the movement «Together let’s save the forest of Chantilly» (Oise).

In contact with experts, this former aviation employee learned to raise his eyes to the tops of the trees. Their dry branches – many have lost their leaves – are a symptom of approaching death. More exposed to the sun and far from the roots, where the nutrients come from, the crown of the tree is the first to suffer from global warming.

In the Domaine de Chantilly, oak is the most widespread and most affected species. «It’s the master tree! When we see that they are in serious bad condition, that does something,» says Mr. Blanchet.

Since March, the group of volunteers, with 330 members, has been carrying out, with scientists and engineers from the National Research Institute for Agriculture, Food and the Environment (INRAE) in Nancy, a test campaign on the 6,300 hectares of the estate. Here, the average temperature has risen «by 1.5 degrees in 30 years», according to the director of the premises, Daisy Copeaux.

Two to three times a week, teams come to scrape the ground to define its characteristics, understand why certain «native» species are dying, and select those from elsewhere that will have to replace them.

A total of 13,000 samples will be collected by July 28 before being analyzed by a Bordeaux laboratory. The «little hands» like Jean-Michel Henrion, most retired, chain the hammer blows on their «corer», a metal tube used for taking samples.

– «Critical state» –

«We’re not young anymore,» he laughs, stuffing a clod of earth into a plastic bag. A «work of ants». But the learning in contact with the foresters and the feeling of contributing to the preservation of the forest to which they are all attached make them forget the aches of the evening.

Because the Chantilly estate, of which 40% of the trees are «affected by dieback», is in a «critical state», alert Daisy Copeaux. Difficult to survive on a sandy soil poor in natural groundwater, which does not retain rainwater. Thus thirsty and then baked by the sun, some are «unable to wake up in the spring».

Within a few decades, the Oise should have a climate similar to the South, estimates the scientist Hervé Le Bouler, nicknamed «the Druid» by the volunteers. The urgency is then to «migrate» species from the south, accustomed to heat waves, to the north. A process that would take «several thousand years if we let nature take its course», and the forest «does not have time to wait».

On an experimental plot, volunteer coordinator Jean-Charles Bocquet monitors «the adaptation of tree species from the South of France to Chantilly conditions». These «young hairy oaks of Albi» could repopulate the estate in the years to come.

It is not a question of «replacing everything with new species», specifies Mr. Bocquet. The idea being to «work in patchwork» to test the complementarity between the trees and the resistance of each to environmental hazards, while «favoring» the original flora.

– Insect Invasions –

But finding a response to the aridity of the soil is not the only challenge. Rising temperatures have also broken the cycles of «extreme cold» that regulated parasite populations. Protected from frost, beetle larvae «eat the roots» of trees and cut off their supply of nutrients.

Other «stinging insects» leave pockmarked trunks here and there. Small cavities, similar to drill holes, bear witness to the passage of bark beetles. These pests bore galleries in the wood, disrupting the flow of tree sap. Like a human in need of blood, they end up dying.

The consequences of global warming appear in Chantilly «5-10 years ahead» of the rest of France, warns Hervé Le Bouler. Hence the interest of having transformed this «sentinel» into an «open-air laboratory» and of developing solutions there that could «be of use to others».

Their quotas of “holes” filled, volunteers like Aline Hanshaw return whistling from the morning sampling session. Some will return in the afternoon. Without them, the experiment would be «impossible», conclude the INRAE ​​study engineers.