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1905) § WHITFORD—FORESTS OF FLATHEAD VALLEY 201 
the meadows into the meso-hydrophytic forest in which the Engel- 
mann spruce predominates, so there is a similar change from these 
into a forest in which the western larch and Douglas spruce are the 
principal trees. Again, this difference is due to a change in the under- 
ground water level; in the meadows it is near the surface; in the 
Engelmann spruce stands it is slightly below the surface; and in the 
western larch-Douglas spruce combinations it is still farther below. 
Indeed, in this association the water level is so far below the surface 
in places that the roots of the trees do not reach it, but rather depend 
on the water in the surface layers that comes from the rains or by 
capillarity from the underground water level. Since there is a medium 
condition of water in the soil, the forests occupying these areas are 
known as the mesophytic formations (fig. 8). Other trees found 
with Larix occidentalis and Pseudotsuga taxifolia are Pinus Murrayana, 
Abies grandis, Pinus monticola, Picea Engelmanni, Thuja _plicata, 
and occasionally Abies lasiocarpa, Pinus ponderosa, and Tsuga 
heterophylla; also certain deciduous trees. 
Associated closely with the spruce and almost invariably sur- 
rounding stands of it, except where the lodgepole pine is present, is 
found a forest in which the silver pine and lowland fir are at their 
best. Thus on the west side of the bay-like area of meso-hydrophytic 
forest west of Ross Lake, the spruce is gradually replaced by a mag- 
nificent growth of lowland fir, silver pine, western larch, and Douglas 
spruce. The lodgepole pine occupies a good deal of the spruce 
stands that would otherwise have developed into a forest like that 
just mentioned, were it not for the influence of fires. In various 
other areas are found forests in which silver pine and lowland ‘fir 
form a more or less conspicuous element, especially in the area near 
the mouth of Meadow Creek. They are never unaccompanied by 
other species and seldom become the dominant trees, probably 
because the climate is not so congenial to them here as to some of 
the other dominant species. 
The silver pine closely resembles its relative the eastern white 
pine. As already stated, in Flathead valley it does its best in the 
Conditions surrounding the spruce stands, or where the water level 
1S not far below the surface. However, it spreads over nearly all the 
mesophytic region in Swan River valley and ascends the east slope 
