E-mail : ann-catherine.laliberte.1@ulaval.ca

Dynamics of the maritime tree line and forest limit along the emerging coast of eastern Hudson Bay
 
Supervisor : Serge Payette

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The continental crust beneath the Laurentide inlandsis has been heavily compressed due to the important weight of glacial ice several km thick. The melting of glacial ice during deglaciation resulted in a compensatory, isostatic rebound of the crust particularly in the Hudson Bay (Canada) area. Postglacial uplift along maritime coasts is a major geophysical mechanism producing several collateral effects like the creation of new coastal habitats and correlative land colonization through the process of primary succession. In this study we have examined the patterns of vegetation dynamics along the rising coastline of eastern Hudson Bay in a context of primary succession. Because land emergence creates a primary chronosequence of stands which can be dated based on known rates of land uplift, it has been possible to analyze the colonization dynamics of white spruce (Picea glauca) as seedlings, tree-line trees and primary-forest trees along newly created raised beaches and terraces in 8 sites distributed along a 200-km latitudinal gradient. The main stages of primary succession developed along the emerging coast were common to all the sites studied whatever the latitude but at different altitudes above sea level. White spruce seedlings colonized near-shore beaches 2 m above sea level, whereas tree line and forest tended to form only at about 3-4 m and 4-8 m above sea level, i.e., 180-825 years and 310-1615 years after land emersion, respectively, assuming a mean emergence rate of 1.2 m century-1. White spruce establishment at tree line occurred about 50 years ago when climatic conditions were more favourable to tree colonization and growth than when the species established at the forest limit. Soil formation during primary succession was influenced mostly by distance from the seashore and altitude above sea-level, and podzolization was accelerated beneath the cover of white spruce trees. It is concluded that the current positions of tree line and forest limit on the coast correspond to ecological limits formed during the course of primary succession, in a context of changing climatic conditions.

Publication

Laliberté, A.-C., Payette, S. 2008. Primary succession of subarctic vegetation and soil on the fast-rising coast of eastern Hudson Bay, Canada. Journal of Biogeography, 35: 1989–1999.