Late Holocene deforestation and tree regeneration in the forest–tundra of Québec

Abstract

Reconstructions of climate in the Holocene rely heavily on palaeoclimatic indicators such as altitudinal and latitudinal tree-line movements¹ inferred either from direct (macrofossil), or indirect (pollen), evidence of sites more or less distant from the present treelines^2–8. Long-term trends in tree regeneration on well-drained sites of the forest–tundra—the transition zone between the Boreal forest and the Arctic tundra zones—may also be used as ecological indicators of Holocene climatic changes. Charcoal found in soils of treeless or forest vegetation in the transition zone indicates respectively, failure or success in the post-fire regeneration of trees; as regeneration is influenced by climate, radiocarbon-dated charcoal can be used as a record of palaeoclimate. We suggest here that the widespread occurrence of treeless sites is the result of late Holocene deforestation involving climate–fire interactions and that disjunct lichen-forest sites are the outcome of successful regeneration sometime during the last 1,000 yr. This climatically induced process is acting at the site and the species levels, south of the present tree line.