Secular climate change in old-growth tree-line vegetation of northern Quebec

Abstract

The climate of the Northern Hemisphere changed during recent centuries, as shown by the Little Ice Age episode1 and the warming trend of the past 100 years2,3. The ecological impacts of these changes have yet to be evaluated in several terrestrial ecosystems, incorporating direct evidence such as detailed botanical field observations4. We report here results of the analysis of a ∼600-year response of a lichen–spruce woodland to this long-term trend, which are thought to be the first extensive illustration of these impacts in the Subarctic. It suggests that tree-line vegetation is in a dynamic equilibrium with climate in the absence of other external disturbances; this is emphasized by spruce reaction through phenotypic adaptation—a shift from stunted individuals (krummholz) to normal trees (forest)—and differential regeneration. This study produces evidence that marginal northern forests can persist through time and that successional processes, in the absence of fire, perpetuate the original lichen–spruce facies. The longest tree-ring chronology (AD 1398–1982) yet available in eastern North America was constructed from living and dead spruces found in the lichen woodland of our study.