Distribution of the Alpine Flora
There is a natural temptation to call upon "the great ice age" for an explanation, for it seems to be a sort of universal solvent of geological mysteries.
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The alpine flora of Glacier and Waterton parks is composed of different elements. Predominant is the arctic-alpine element, consisting of those species that have both an arctic and an alpine distribution. In the arctic most of these species are circumpolar or nearly so. Their southern, or alpine, distribution is interrupted and discontinuous. Why these two areas of distribution contain similar species and why they are separated by an area where arctic-alpine plants are absent is a subject of disagreement. Johnson and Packer (1974) believe it is best explained by "supposing an essentially circumpolar arctic-alpine tundra flora during the Tertiary upon which Pleistocene events have been superimposed." Hult6n (1964, 1971) expressed the same theory and added that the flora of the arctic area is younger than that of the alpine areas. He also pointed out that wide separations in the distribution of disjunct species "are not due to sudden recent extensions of the area [of the species] but to reductions" (Hult6n 1937). The Loves (1974) believe that the occurrence of arctic-alpine species in areas such as Glacier and Waterton may be due to southward dispersal during glaciation. They also suggest that the ancestors of these species are relics from Tertiary times. These relics still exist in the mountains of central and southern Asia. Whatever its origin, it does seem certain that the arctic-alpine element of today is a fragment of an ancient flora. Current distribution is the result of successive advances and recessions of Pleistocene glaciation.
The endemic element of the alpine flora is best explained by assuming the survival of some species and the emergence of others as distinct species during continental glaciation. Packer (1971) hinted at the existence of refugial areas during glaciation in southwestern Alberta and in adjacent parts of British Columbia and Montana. He suggested that these refugia held the endemics of today. Later research confirmed the theory of ice-free areas in and near Glacier and Waterton during the time of greatest (most southern) advance of the Laurentide Ice Sheet about 18,000 years ago. Other advances stopped short of the parks area but it is important that the advance of 18,000 years ago penetrated south of the 48th parallel in central Montana and to and perhaps over the continental divide in the vicinity of the 49th parallel. Later Laurentide advances, corresponding to the most southerly advance of the Cordilleran Ice Sheet, left an ice-free corridor in the vicinity of the continental divide for a distance of about 300 miles north of the 49th parallel (Dyke and Prest 1987).
The third element, as Packer (1974) suggests, is made up of species of local origin. This element can be subdivided into lowland elements, species more common below treeline; cordilleran elements, species that are usually alpine but not arctic-alpine, and a few Pacific northwest elements (Pemble 1965).
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