Modifications morphologiques de l'Épinette blanche soumise à la sédimentation éolienne en milieu dunaire, Québec subarctique

Abstract

The characteristic growth forms of white spruce (Picea glauca (Moench) Voss) were studied within a dune located north of Whapmagoostui (Subarctic Québec). Thirty-two trees (14 living and 18 dead) were excavated and their morphology and ring patterns are described. Adventitious root development at the base of buried stems and spindle-like trunks (diameter smaller at collar than at higher levels) were the most important morphological modifications in response to slow sedimentation rates (close to 5 – 6 cm/year), as long as total sedimentation did not exceed a depth of approximately 1.25 m. The decrease in radial growth with depth was most likely due to low temperatures caused by long-lasting snow lenses within the niveoeolian sediment during the growing season. Tree dieback occurred when the sedimentation rate rose to 8 cm/year. The combined weight of sand and buried snow caused severe mechanical damage to the trees (e.g. branch and stem breakage). Life expectancy of tall trees was about 50 years under such high stress conditions. The dune moves towards the north at a rate of 0.74 m/year. The mean sedimentation rate is 7.65 cm/year. These values are similar to those found in coastal dunes in Finland. The ultimate fate of these trees is death through dune displacement.