Ecologie des coléoptères saproxyliques dans les forêts de l’étage montagnard des Alpes du nord françaises

Abstract

Ecology of the saproxylic beetles in mountain forests of the northern French Alps. Both saproxylic beetles and deadwood stocks were studied in order to detect special deadwood features important for these organisms, and to better understand their ecology. A total of 37 window traps were used in ten stations covering four mountain forests in the French northern Alps. In the same time, the deadwood stocks were inventoried in the ten stations. 181 m3 of deadwood (1219 fragments) were measured and 4268 individuals belonging to 235 saproxylic species were trapped. The deadwood volume ranges from 21.1 to 233.6 m3/ha and the number of beetle species from 27 to 113. A positive relation was observed between the stand age, the whole volume of deadwood and the species richness of saproxylic beetles. However, in some deadwood rich sites the beetle diversity is not as high as expected. This was explained by the negative influence of the management history of the forest. The compositions of saproxylic communities depend also of some characteristics of the deadwood stocks. Xylophagous and zoophagous species prefer “not lying and recently dead softwood” while the mycophagous and saproxylophagous species are strongly dependent on fungi growing on hardwood, respectively under “large surfaces of barks” and in “large woody debris”. Surprisingly, the majority of the saproxylic beetles living on softwood does not depend on the most represented resinous deadwood type: the “decayed and lying softwood”.