Shoreline Shrub Population Extension in Response to Recent Isostatic Rebound in Eastern Hudson Bay, Quebec, Canada

Abstract

The response of littoral shrub populations to recent land emergence along the eastern coast of Hudson Bay was studied as an indirect estimate of the minimum rate of isostatic rebound in the area. Evidence of a rapid downward displacement of shrub populations is borne out (1) by the zonation in population structures ranging from a clear expanding semilogarithmic distribution close to water to an irregular multimodal pattern backshore, (2) by the zonation pattern in shrub vitality showing healthy individuals in the expansion zone at water edge and a declining zone backshore, and (3) by the progressive displacement of the lower limit occupied by the different species as suggested by the distribution of the oldest individuals along the sloping shore. Average lateral displacement varies among species, ranging between 1.3 and 2.9 m yr- . The downward movement ranges between 0.7 and 1.2 m yr-1, which is an extension rate close to the current land emergence rates obtained by projection of 14C-dated uplift curves in the area (between 1.0 and 1.3 cm yr-1).