Dynamique d'une bordure forestière et variations récentes du niveau du fleuveSaint-Laurent

Abstract

The forested shoreline of the Saint Lawrence River upper estuary is frequently damaged by spring ice, currents, and waves during episodes of high water levels. A dendroecological analysis of the significant river floods, as recorded by ring-width patterns of uprooted woody plants, population growth and decay structures, and scars caused by ice on trees within the shore environment, provides direct evidence of a landward migrating shoreline. Regressive succession of vegetation is associated with a general rise in year-to-year flood levels. Plant community dynamics and shore sediment migration were investigated in a particularly exposed site between Grondines and Sainte-Anne-de-la-Pérade. Most of the oldest sublittoral trees are undergoing slow degradation and hydrophilous shrubby stands show extensive expansion within the shoreline habitat, which is associated with an important landward displacement of sediments. These ecological and geomorphological results concur with the general rising trend of flood levels of the Saint Lawrence during the last 30 years.