Late Holocene climate of the James Bay area, Quebec, Canada, reconstructedusing fossil beetles

We used fossil beetles recovered from three peatlands of the James Bay area (Radisson, northern Quebec, Canada), and the mutual climatic range (MCR) m ethod, to produce a quantitative reconstruction of summer temperatures duri ng the last 5000 yr. Our main objective was to test the hypothesis that a s ignificant climatic cooling episode occurred during the late Holocene epoch , leading to the opening up of the boreal forest, and to the progressive re placement of black spruce (Picea mariana) forests by jack pine (Pinus banks iana) stands. Beetle assemblages in the Radisson area were very stable duri ng the late Holocene epoch. We used a total of 22 beetle species to conduct the MCR analyses. Reconstructed mean July temperatures ranged from 14.5 to 17.5 degreesC, which is close to the present-day (A.D. 1977-1996) temperat ure range found in the Radisson area. The general stability of beetle assem blages, and the MCR analyses, suggest that there was no major change in Jul y temperatures during the last 5000 yr in the Radisson area. This study pro vides no evidence that the progressive replacement of black spruce forests by jack pine stands in the Radisson area during the last 2700 yr can be exp lained by a long-term climatic cooling episode affecting the postfire regen eration potential of trees. Consequently, an alternative hypothesis (more f requent fires favoring jack pine) should be seriously considered to explain the late Holocene changes in the forest environment of the Radisson area.