On the gene, species, or ecosystem scale, biological diversity is one of the factors the forest ecosystem uses to adapt to constricting global changes, particularly climate changes. While in this sense it can condition the very perpetuity of the forest, biodiversity can be profoundly modified by how the forest is managed. Notably because of the reduction in the quantity and quality of dead wood in harvested zones, 20%–40% of forest life forms dependent on this dead wood are today threatened with extinction in several European countries. In France, with a forest cover of 15.3 million hectares (27.1% of the land surface), forest bird populations may have diminished by 18% between 1989 and 2004.

Taking biological diversity into account in sectorial policies and management choices is a priority outlined in the Convention on Biological Diversity, ratified by France in 1994. However, the tools and data necessary to quantify the impact of forest harvesting on biodiversity have not been sufficiently developed to date, especially given the high stakes involved. To offset this deficiency and test the relevant indicators, Cemagref scientists in Nogent-sur-Vernisson are developing a statistical approach based on field data measuring the response of the biodiversity in seven different groups of species (animals, plants, fungi) to forest harvesting. Conducted in collaboration with the ONF and the RNFs, the study compares harvested and unharvested zones:
-  untouched by any human intervention for at least 20 years¹
- belonging to the same forest areas in metropolitan France, located in both the lowlands and the mountains. This project is a first in France, where there has been no comparative study of this size since the 1960s.

Within the Auberive-Chalmessin (Haute-Marne), Fontainebleau (Seine et Marne), and Ventron (Haut-Rhin) forest areas, 61 sample plots were chosen in spring 2008, then described in detail (quantity of dead wood, species composition, tree stand size, etc.). The inventory and analysis of the flora and fauna are continuing today, so that a true “zero condition” of biodiversity can be established by comparing harvested zones with those that have evolved naturally in each forest area. The moss, mushroom, vascular plant, insect, bird, and bat species are being inventoried by networks of naturalists from the ONF and the RNF as well as by Cemagref’s scientists. The field data will then be processed statistically and modeled. This work on the three forest areas forms a pilot project designed to validate the work methods. In the near future, Cemagref, the ONF and the RNF hope to extend this inventory to 20 forest areas and enlarge the project’s scientific partnerships.

By the end of the project, the comparison of harvested and unharvested forests should make it possible to identify the factor(s) that can best explain the variations in biodiversity observed: the harvesting itself, the structure of the forest stand, the quantity of dead wood (presence of cavities, microhabitats), and the characteristics of unharvested forests. The project therefore aims to test the relevance of the different indicators of sustainable forest management to determine the proportion of biodiversity that these indicators represent most faithfully, including the optimal intensity levels and management conditions. Integrating unharvested forests into the project will make it possible to demonstrate the effect of factors that could not have been considered in an analysis limited only to harvested forests.