A RECENT DOWNWARD EXPANSION OF SHORELINE SHRUBS AT LAKE BIENVILLE (SUB-ARCTIC QUEBEC)

The regeneration patterns of Alnus crispa (Ait.) Pursh. in response to water level lowerings were studied along the shores of Lake Bienville (898 km(2)) in subarctic Quebec. During a period of high waters in the 1970s, pruning by drifting ice was important and contributed to sprouting and crown densification of well-established shrub individuals. Low water levels prevailed between 1980 and 1985 when massive shrub colonization along the lakeshores occurred. Shrub establishment was favored on shorelines where geomorphic activity (ice pushes and wave action) was moderate or low. Well-established shrubs have undergone moderate ice-push damages since 1985, which limit the expansion of the population by seeds, but favor the densification of the stem metapopulations. Interannual and decennial fluctuations in water levels of northern basins should be studied more closely to better understand hydroclimatic regimes and causes of periods of low hydraulicity, especially in regions where the potential for hydroelectricity is high.