Impact de L'anthropisation Ancienne sur la Biodiversité d'un Habitat de Hêtraie-sapinière Montagnarde

Abstract

Several studies have shown the considerable impact effect of ancient human activity on the forests of the Pyrenees, affecting the boundaries and spatial location of stands, and their species composition. Two of the most noticeable effects are the almost universal rarefaction of silver fir and, more locally, the substitution of the potential montane beech-fir forest by mixed sessile oak-birch stands. In a test forest, we tried to assess the impact of these changes on taxonomie biodiversity, 1- In a beech-fir stand left unmanaged for about a century, a survey of tree microhabitats shows silver fir to be less accommodating than beech. The insect and fungal associations for the two species are different, and are abundant for fir in some groups. Rarefaction of silver fir has therefore probably reduced the overall taxonomic diversity of beech-fir stands. 2- In a sessile oak stand of the montane belt, sampling of saproxylic beetle and syrphid populations revealed the presence of very few uncommon insects while the successions are much impoverished by comparison with those of oak stands in the collinean belt. On the other hand, 60 % of bats observed in the forest studied were encountered in the oak stands. The conclusion reached is that, in the montane belt of the Pyrenees, beech and fir should be allowed to spontaneously re-colonize oak stands while silver fir should be encouraged to repopulate beech stands.