Old-growth forests: artificial intelligence put to the test in the field in the Dronne valley

Since 2024, the Périgord-Limousin Regional Natural Park has been conducting a program to identify old-growth forests in the Dronne watershed. After an initial analysis phase based on the use of aerial images and the latest technologies, fieldwork is currently being carried out to map these remarkable environments.

Gain a better understanding of the most mature forests in the area

Characterized by the presence of large trees, deadwood, and numerous microhabitats, mature forests constitute reservoirs of biodiversity particularly valuable but have become rare.

The study area covers a 240 km² catchment area, approximately half of which is forested. Of these wooded areas, nearly 40% are considered old-growth forests, meaning forests that have existed for several centuries without interruption of forestry use. However, An ancient forest is not necessarily an old forest. : ecological maturity results from a long process during which trees age, accumulate dead wood and develop habitats favorable to many species.

An innovative method for targeting the most promising sectors

In order to identify the areas most likely to harbor mature forests, the Park has used a method developed by the consulting firm i-Sea, based on artificial intelligence, aerial image analysis and LiDAR data.

Of the approximately 12,000 hectares of forest in the watershed, this approach identified around 300 hectares of potential old-growth forest. After a phase of further analysis and mapping verification, 90 forest polygons were selected for field surveys. This campaign required the contact made with 170 owners representing more than 360 cadastral parcels.

The initial results are particularly encouragingCompared to an approach based solely on visual analysis of aerial photographs, the i-Sea method significantly improves the ability to identify areas with characteristics favorable to forest maturity. The detection rate of structural potential thus increases from approximately 7% to over 80%.

The field remains essential

Since spring 2026, interns at the Park have been conducting surveys according to the protocol of the South Atlantic National Botanical Conservatory. To date, 115 plots with a radius of 20m were inventoried. within 50 forest polygons.

Observations show, however, that for the time being, the analysis of successive aerial photographs is not sufficient to guarantee the presence of old-growth forest. Inventories reveal that approximately 60% of the areas studied correspond to forests that are still relatively immature. But about 30% can nevertheless be classified as pre-old-growth forests, that is to say, stands that already exhibit certain attributes of maturity and whose ecological value could increase further over time. Less than 10% of the surveyed polygons now reach the status of old-growth forest, which tends to confirm the rarity of these environments in the territory.

These results serve as a reminder that the forestry history of the Périgord-Limousin region, marked by centuries of exploitation and multiple uses, has profoundly shaped the current stands. They also show that many forests possess significant potential for evolution when trees are preserved to advanced ages.

The inventories will continue until the end of the summer to refine the mapping of mature forests in the watershed. This study already confirms that, when it comes to old-growth forests, artificial intelligence is a powerful targeting tool, but that the naturalist expertise of the field remains essential to revealing the true forest treasures of the region.