E-mail : guillaume.de-lafontaine.1@ulaval.ca

Population dynamics of subalpine white spruce
Supervisor :
Serge Payette 


White spruce (Picea glauca) stands  possess a unique distribution in eastern North America. They are found at the tree limit along the eastern coast of Hudson Bay, as well as along the coast of Labrador. In addition, stands are found at the altitudinal tree limit of the high summits in the mountainous regions of Manicouagan (Monts Otish, Monts Groulx and Montagnes Blanches, and the Chics-Chocs in Gaspésie). White spruce is also a relatively abundant companion species found in the southernmost balsam fir (Abies balsamea) forests. Subalpine populations of white spruce form the treeline in the high summits of the Manicouagan region. The bare summits above the treeline are characterized by an alpine tundra with krummholz forms of both white and black spruce (Picea mariana). On the flanks of these mountains some balsam fir stands grow amongst the black spruce forests, which represent the regional forest matrix. The subalpine white spruce stands possess several forms. Some stands are pure and are represented exclusively by young trees, giving the impression of a recent colonization. Other populations form equilibrium stands with a greater species richness and several different tree age classes. The objective of this thesis is to determine both the historical origin and current dynamics of the subalpine white spruce located on the high summits in the Manicouagan region. We hypothesize that the subalpine stands dominated by white spruce are the result of an ecological sorting (by ecosystem processes that will be identified and analyzed) within the boreal fir forests where white spruce is well-established but generally in lower abundance. Several multidisciplinary methods will be used to test this hypothesis. Genetic markers will be used to determine the phylogeography of the species by analyzing the genetic distance between white spruce populations of the high summits and those within the boreal fir forests. Paleoecological techniques, charcoal analysis, and 14C dating will be used to determine the composition and relative abundance of species along with the date of fire events. This will permit an in situ reconstruction of the fire chronology and the development of the post-fire forest vegetation through time. Finally, analyzing the age structure of both living and dead trees along with their tree rings will aid in determining the mechanisms that white spruce use to colonize the high summits from the lower slopes. The results of the genetic markers analysis should show that the post glacial advance of white spruce occurred simultaneously with the expansion of the boreal fir forest. At the elevation of the high summits, the paleoecological analysis should show a reduction in the intensity and frequency of forest fires with altitude related to the orographic effect. The high summits of the massifs receive more precipitation that corresponds to less frequent fires, resulting in the establishment of balsam fir forests to the detriment of black spruce forests. The black spruce forests, which are better adapted to fire, are thus displaced to the foot of the mountains, which are drier and more prone to fire. White spruce, which are probably more tolerant to extreme climates, appear to be the first species to colonize the high summits and have the capacity to establish in conditions that are adverse to the growth of balsam fir. A relatively recent advance of pure white spruce stands could be related to a more clement climate over the last few decades.


de Lafontaine, G. 2005. Protocole de suivi des populations d'aster du Saint-Laurent, Symphyotricum laurentianum, aux Îles-de-la-Madeleine. Canadian Field-Naturalist 119 (4): 556-568.