Development of a lichen-white spruce stand along the rapidly emerging coast of Hudson Bay in subarctic Quebec

Development of a lichen-white spruce stand along the rapidly emerging coast of Hudson Bay in subarctic Quebec. Population structure and tree growth of a white spruce stand (Picea glauca [Moench] Voss) were studied along the e merging coastline of Manitounuk Strait on the east coast of Hudson Bay. Iso static rebound in this area is still one of the most rapid in the world (1. 2 to 1.5 m/century). The study aimed to determine the relation between the development of a shoreline shrub fringe and the expansion of white spruce a nd to decipher the environmental changes that led to a scattered tree popul ation over the last century. The colonization of the raised shore by white spruce is closely dependent on the earlier development of a dense shrub fri nge. The shrubs form a narrow strip just above the tidal flat, where the su bstrate is maintained moist by the seepage of ground water from adjacent la nds. In winter, shrubs collect the wind-blown snow and protect the abondant white spruce seedlings locally. With the rapid land emergence, the waterta ble is lowered and the hygrophilous shrub fringe displaces slowly seaward. The degradation of shrubs change the snowpack depth at the position of the formerly established spruces. Only the most vigourous saplings survive. A s cattered population withstand this severely exposed environment. Its only p ossibility for further expansion is behind permafrost mounds that soon deve lop on surfaces exposed to the wind and behind raised beach ridges. The rai sed topography favours the accumulation of snow behind obstacles and white spruce takes advantage of such protected sites to expand. The steps of the colonization process are highlighted by the distribution of shrubs and tree s according to their age, the white spruce shoot elongation rates and tree- ring widths, and the recent vegetation changes indicated by the plant macro fossil remains since the end of the 19th century.