Development of a black spruce (Picea mariana) shoreline stand in relation to snow level variations at Lake Bienville in northern Quebec

This study proposes a reconstruction of the past development of a forest stand submitted to long-term variations of snow levels. As of the 19th century, a gradient in tree-growth forms developed in a post-fire shoreline stand. This expansion was marked by three stages. (1) Prior to 1845, the effects of fire (between 1806 and 1826) increased the exposure stress on surviving trees, which started to develop irregular growth forms in response to niveo-eolian erosion. Post-fire regeneration expanded progressively toward the inner part of the island. (2) Afterwards (1845-1880), severe winter and summer conditions were marked by numerous unsuccessful snow-air interface breakthroughs, as shown by frequent loss of apical dominance. (3) Since 1880, the densification of above-snow tree structures contributed to the overaccumulation of snow that caused many injuries to trees (branch tearing, stem bending). The frequent damage (since the 1900s) and the raised level of above-snow erosional features (loss of apical dominance) indicate that increasing forest density merely exacerbated the rising trend of snowfalls in the forest studied. This trend, demonstrated earlier in the northern areas of the forest-tundra, was not yet documented at the limit of the southern boreal forest.