BOG AND LAKE STUDIES ON THE LAURENTIAN SHIELD IN MONT TREMBLANT PARK, QUEBEC

Abstract

The study includes five bogs and one small lake. Preferred kettletype bogs were located very effectively by plane. The deepest section of the kettle lake was determined with a Bendix Depth Finder. The initial tree invaders in the whole park were chiefly jack pine (Pinus banksiana), paper birch (Betula papyrifera), a minor representation of spruce–fir (Picea–Abies), and oak (Quercus) characterized by an attention-demanding minor peak. After one or two foot-levels spruce–fir increased to considerable prominence, then declined to negligible representation in all bogs and in the lake by mid-profile. The pine peak at about mid-profile was uniformly very prominent over the whole area. In the topmost one-third to one-fifth of the profiles, pine declined steadily. The small representation of pine at topmost levels pictures very well its status in the region today. Mont Tremblant Park is a forest transition zone. In the range of 50 miles from Lac Puant bog to Lac Tacoma bog, abundance of spruce and fir pollens (especially that of black spruce) increase markedly as one proceeds northward. Pollens of beech (Fagus), oak, maple (Acer), and especially hemlock (Tsuga) and yellow birch (Betula lutea) show marked decrease northward. In the southern half of the transect hemlock is represented in the profiles by a decided pine–hemlock peak. Paper birch has erratic fluctuations in its prominent representation over the whole profile. From the forest type indicated at lowest levels we must infer an initial warm period. This is attributed to ocean invasion of the St. Lawrence Valley and slow retreat of continental glaciers. The combination of these factors delayed the forest invasion of the Canadian Shield until the boreal spruce–fir period, so characteristic of lowest levels in bogs farther south, had passed. Slight deterioration of climate thereafter with development of local glaciers on the Shield apparently accounts for the first minor rise of spruce and fir. A warm–dry period at mid-profiles is indicated by the universal prominent pine peak accompanied by extreme decline of spruce and fir. The succeeding increase in hemlock and white–red pine (later replaced by minor peaks of beech–maple) suggests a monster climate with increasing coolness. Continued cooling during more recent times in turn favored spruce, fir, and yellow birch. Pine, hemlock, beech, and oak declined to a status of minor elements in the forest association. The erratic fluctuations of paper birch and its abundance at all levels show little correlation with major climatic changes.