Les arbres habitats sont des éléments clés pour la biodiversité forestière

International audience; Habitat trees are defined as standing live or dead trees providing ecological niches (microhabitats) such as cavities, bark pockets, large dead branches, cracks or trunk rot. They are of prime concern for forest biodiversity as they can harbor many threatened species of flora and fauna. Habitat trees are a legacy of the past and are of exceptional importance given the hundreds of years such a tree might need to reach this status. The retention of habitat trees with a suitable distribution in the landscape is a challenge for forest management, because these trees generally do not match with forestry economic schemes and are sometimes thought to represent a potential danger for forest workers and visitors. Furthermore, the future of many habitat trees (and their microhabitats) will be highly dependent on changing forest policies for forest bioenergy purposes in many parts of Europe. If no conservation strategies are established, energy wood harvesting will lead to a strong decrease of habitat trees in managed forests, as quite all trees, even dead, can be harvested for this goal. Consequently, setting up a strategy of deliberate retention of habitat trees requires a shift in management objectives and practices towards encouraging the development of old-growth structures. At the stand level, at least 5 to 10 habitat trees per hectare should be retained in harvested stands to mitigate the effects of harvesting. Therefore, it would be of prime concern to establish harmonized measures relating to habitat trees and their microhabitats which could be adopted as biodiversity indicators in European forests.