Late Holocene opening of the forest tundra landscape in northern Quebec, Canada

Aim Previous studies conducted at the tree line in northwestern Quebec suggested that the forest tundra was created over the last 3000 years by deforestation as a result of the combined action of forest fires and climatic cooling. Our objectives were to: (1) validate at a larger spatial scale the time frame of the last 3000 years; (2) verify if the opening process was more pronounced during particular time periods; and (3) confirm that fire was the triggering mechanism. Location Seventeen lakes from the forest tundra of northern Quebec. Methods Pollen records were analysed to determine the date of landscape opening, as interpreted by the time of decrease towards present-day values of the ratio of Picea pollen percentage to pollen percentage of the taxa typical of open forest tundra landscapes (Betula, Ericaceae, Cyperaceae and Poaceae). Results Landscape opening in northern Quebec started c. 3220 cal. bp (calibrated years before present) and was more pronounced between c. 2040 and 890 cal. bp. No spatial pattern was observed in the dates of landscape opening. Main conclusions The suggestion that landscape opening in the forest tundra occurred over the last 3000 years was validated at the scale of northern Quebec. A period of more pronounced opening was identified between 2040 and 890 cal. bp and could be related to increased fire occurrence. Absence of a spatial pattern in the dates of landscape opening provides further confirmation that fire was the triggering mechanism.