Reconstructing the late-Holocene history of a subalpine environment (Charlevoix, Québec) using fossil insects

Abstract

In southern Quebec (Charlevoix, Canada), reconstructions of the subalpine insect assemblages were made in environments that were transformed by fire during the late Holocene (since 4500 BP). The ecological requirements of beetle species likely to be found as fossils were studied by collecting living beetles in pitfall traps in forest, suibalpine and alpine environments. The late-Holocene changes of insect assemblages were reconstructed by recovering fossil insects from 13 peat sections. Modem beetle assemblages are valuable indicators of tree cover. Well-developed podzol soils under peat, as well as numerous spruce charcoal remains overlaying the podzol in all sampling sites, suggest that a dense spruce cover was present before the beginning of the accumulation of peat, and was eliminated by fire (4570-800 BP). Ground beetle and bark beetle assemblages at the base of the peat sections contained a mixture of forest and open-environment species, indicating that the postfire environment was a subalpine one with a tree cover of 30-50%. The most recent fire in the area (AD 1915) increased the openness of the landscape (tree cover <30%) Forest ground beetles and bark beetles disappeared almost completely; only open-environment species remained. The late-Holocene history of the Charlevoix mountains as reconstructed using fossil insects is similar to that reconstructed using charcoal remains. However, fossil insects add significant information (tree cover, health of trees, forest composition) that is difficult to obtain using other macrofossils. This opens up new opportunities for palaeoecological studies in the boreal forest, which was formed during the Holocene epoch, and was frequently disturbed by fire and insect outbreaks.