On either side of the path, imposing oak trees soar towards the sky, a few kilometers east of Fontainebleau (Seine-et-Marne). Beside them stand beech trees firmly anchored in the ground. And around them, more or less old shrubs and abundant ferns. A whole world of greenery, touched that day by one of the rare rays of sunlight at the start of autumn.
And when, by sweeping a pile of leaves with your foot, an oak shoot measuring around fifty centimeters appears, there is no room for doubt: this forest is in great shape! “Everything is fine here. If only the rest of Fontainebleau were like this,” immediately cools Matthieu Augéry, from the Île-de-France Est agency at the National Forestry Office (ONF).
Indeed, on the 21,000 hectares of the historic Ile-de-France region, not all plants are doing well. From this healthy plot, a five-minute drive north is enough to understand the situation. Gone is the impression of a warm and abundant forest. There, the oaks, much fewer in number, are visibly sick when they are not already dead. Their shortened branches only draw shadows against the sky that has turned gray again. It’s hard to believe that it’s the same forest.
Search for new suitable species
“This is the result of the difficulties that the trees undergo hereasks Matthieu Augéry. Global warming stresses populations with unusual episodes of drought or, like this year, an abnormal abundance of water. » In Fontainebleau as elsewhere, the ONF can only make this observation: certain species will not withstand the local climate of tomorrow.
According to the simulations, it will no longer really be suitable for sessile oak – the most common here – at the end of the century and even less for beech. Some species are even already very disturbed, such as the Scots pine, which covers a third of this national forest. Aerial shots reveal pieces of brown canopy, evidence of heavily damaged areas.
To reinvigorate the suffering plots, the Office is therefore replanting new species. Downy or tauzin oaks, respectively nicknamed Provence or Pyrenees oaks, are favored here in the hope that they adapt better to new climatic conditions. This diversification of tree varieties constitutes the first link in a more global strategy of the ONF: the mosaic forest. In other words, don’t put all your eggs in one basket.
Beyond species, this principle also applies to types of settlement and silviculture. The organization of the plots exploited for their wood varies between regular, irregular high forests or coppice. These arrangement methods aim to diversify the sizes and ages of the trees.
Finally, at the same time, the last aspect of diversification concerns developed biodiversity areas. In the mosaic, plots more dedicated to the ecological role of the forest are planned, such as so-called aging islands, which preserve old woods, or wetlands. Biological reserves are also planned. With different degrees of firmness, they form protected spaces.
Biodiversity reserves established
In Fontainebleau, this gives a patchwork covering all the categories of the mosaic forest concept. Particularity: a tradition of areas closed to the public to preserve landscapes – which dates back to the painters of the Barbizon school in the 19th centurye century – today leaves a thousand hectares without any human intervention. An additional thousand are classified as “managed biodiversity reserves”, in which foresters only work occasionally.
In one plot, for example, they cut down the few shoots of Scots pine to maintain a valuable heath for certain birds. “We must understand that a forest must be maintained to remain healthy and not be dangerous for visitors,” insists Matthieu Augéry. However, there are more and more of them in Fontainebleau, the most visited area in France with 15 million curious people per year.
“The mosaic forest can meet the three missions of the ONF: economic with the production of wood; ecological with the maintenance of biodiversity; social with the preservation of the forests that the French like to visit”explains the head of the ONF. The concept has been deployed for around five years across France, on a case-by-case basis, in the eleven million hectares managed by the Office, or around a third of French woods.
ONF staff under pressure
But this ideal faces headwinds. Since 2000, while the State’s requirements in terms of own revenue – that is to say the sale of wood – have increased, the workforce of the public establishment has fallen by 40%. However, in the face of global warming, the ONF can play a major role. The signals seemed to be more favorable in recent years, with the allocation of 60 million euros from the “France 2030” plan in 2021 and 2022. But the budget presented by the government envisages new sizes in the workforce: 95 full-time equivalents would be affected in 2025.
Inconceivable for the unions, who believe that if the mosaic forest is an ambitious project, it cannot be realized without additional hands. Point of view supported by the Court of Auditors which stated in September: “In the current state of its financial and human capacities, the ONF will not be able to respond alone to the challenges of ecological transition. »