19 
The drier areas, such as the upper slopes and summits of sandy ridges, 
have a nearly pure forest of jackpine with a light undergrowth, making a 
rather open woods. On lower slopes and well-drained hollows, where the 
water table is nearer the surface and the soils have a somewhat greater 
water-holding capacity, Canada spruce forms dense forests, often of trees 
3 to 4 feet in diameter and over 100 feet in height. 
The main variations of these forest types occur over extensive areas 
that have been burned, and in such lesser areas as muskeg margins, dis- 
tricts that reach a considerable elevation above the general level of the 
surrounding country, and marginal situations subject to the influx of other 
species. The outstanding effect of fires has been the introduction of large 
quantities of aspen and poplar timber, Populus tremuloides and P. tacam- 
ahacca. These occur in nearly pure stands or in all sorts of combinations 
with the conifers, depending upon the nature of the fire and upon local 
soil and seed conditions. At muskeg margins black spruce Picea mariana, 
and larch Larix laricina, become predominant over the other trees. The 
jackpine, which is not far from its northern limit in this region, disappears 
upon the highest morainic ridges, where its place is taken by a park-like 
growth of Canada spruce such as occurs on sand-plains about the eastern 
arm of Great Slave lake (52). In Caribou mountains the jackpine is also 
absent. The higher levels in the mountains maintain an outlier of the Cor- 
dilleran forest, which involves the lodge-pole pine Pinus contorta (55) . This 
tree occupies open slopes in company with black spruce Picea mariana . At 
the southern margin of the park, in the upper delta of Athabaska river, is 
to be found the balsam fir Abies balsamea, a representative of the fir-spruce 
forests to the southeast. 
Muskegs 1 , with or without accompanying lakes, are regularly formed 
in undrained depressions throughout the region. They are characterized 
by very wet, bog-moss associations, grading off into the aquatic associations 
of open water, sedge marshes, or shrubby growths of willows Salix spp., and 
dwarf birch Betula glandulosa. Although common throughout the region, 
they have their greatest development in Wood Buffalo park, in the recently 
drained basin of Moose (Eight) and Bog (Thultue) lakes, between the Pine 
Lake upland and Caribou mountains. 
Semi-open prairies are to be found on clayey soils which are more or 
less localized in three districts: around the eastern base of Caribou 
Mountain plateau; in a strip of country extending from Grassy Slough 
district, north of Pine lake, northwestward to Little Buffalo river; and on 
the Salt Plain areas south and west of Fort Smith. These districts have 
a characteristic cover of herbaceous vegetation, chiefly grasses, dotted or 
separated by clumps of willows and the trees of the vicinity. Common 
grasses are the blue- joint Calamagrostis canadensis var. robusta, blue-grass 
Poa pratensis , vanilla-grass Hierochloe odorata, brome-grass Bromus spp., 
wheat-grass Agropyron spp., prairie June-grass Koelena cristata, and purple 
oat-grass Schizachne purpurascens. A wealth of other perennial herbs 
such as larkspur Delphinium scopulorum var. glaucum , mustard Erysimum 
cheiranthoides , cowslip Mertensia paniculata, and many others, accompany 
the grasses, giving the prairies a blaze of colour which changes with the 
l The term “ muskeg ” 
is universally applied to peat bogs in northern Canada. 
