|Publication Type:||Journal Article|
|Year of Publication:||2006|
|Authors:||Asselin, H, Payette, S|
|Keywords:|| Evolution,  Ecology: environmental biology - General and methods,  Ecology: environmental biology - Bioclimatology and biometeorology,  Ecology: environmental biology - Plant,  Musci,  Sphagnobrya,  Coniferopsida,  Cyperaceae,  Development and Embryology - General and descriptive,  Plant physiology - Growth, Angiospermae, black spruce, Bryophyta, Carex: genus [Cyperaceae], climate warming, Climatology: Environmental Sciences, common, Coniferopsida: Gymnosperms, Cyperaceae: Angiosperms, development, Dicranum: genus [Musci], differentiation, Environmental Sciences, Eriophorum: genus [Cyperaceae], Evolution and Adaptation, growth rate, Gymnospermae, long-term dynamics, Monocots, Monocotyledones, Musci: Bryophytes, Nonvascular Plants, Picea mariana: species, Plantae, Plants, seed [Coniferopsida], Spermatophyta, Spermatophytes, Sphagnobrya: Bryophytes, Sphagnum: genus [Sphagnobrya], Terrestrial Ecology: Ecology, Vascular plants|
The basic unit of the forest-tundra landscape is a toposequence extending from a wet, forested valley to a xeric, deforested hilltop; the contact zone between these two environments being called a subarctic tree line. Dendrochronological analysis of living, dead, and subfossil black spruce, and radiocarbon dating of peat samples were used to reconstruct the dynamics of a subarctic tree line since its post-fire origin about 1000 y ago. Fire is not the sole disturbance to have influenced the dynamics of the toposequence. A regional-scale flooding event ca. 1120 AD killed many black spruce trees, growth of permafrost during the Little Ice Age, and its subsequent degradation in the 20(th) century. also had major consequences. The climate was favourable to black spruce growth between ca. 300 and I 100 AD, as evidenced by large growth rings and tree growth forms. Ring widths then decreased markedly between the 12(th) and 19(th) centuries and trees were replaced by stunted growth forms. Although climate warming during the 20(th) century resulted in increased ring widths. black spruces have still not produced tree growth forms, a necessary condition for viable seed production and eventual re-colonization of deforested hilltops.