88 A Study of the Vegetation of 
the deeper strata are very moist. Outside of meso-hydrophytic 
situations it does not flourish in the region and even here it does 
not reach the usual size of the species. It sometimes forms a 
very broken and fragmentary zone between the alder-willow com- 
munity and the climax cedar forest. Its ability to tolerate shade 
to a greater degree than Douglas fir or tamarack probably ac- 
counts for the presence of its seedlings in drier situations, for I 
have shown that conditions under typical stands of white fir and 
tamarack are, as regards the seedling stage, fairly mesophytic. 
Likewise, its power to germinate in the open, providing there is 
sufficient soil moisture, accounts for its presence, often in dense 
stands, in situations where drifts of melting snow keep the soil 
well moistened in otherwise apparently rather dry, rocky situ- 
ations. Like other shade-enduring species, it makes a more rapid 
growth in these situations than in the shade. 
The Thuja Consociation 
The climax forest community of the region and the one in the 
xerosere with the lowest light intensity, greatest soil and air 
humidity as well as lowest temperature, is that dominated by the 
cedar, Thuja plicata. The best protected and most mesophytic 
mountain slopes as well as the well watered ravines are clothed 
with a growth of this cedar. These often form 90 per cent. or 
more pure stands and the trees may reach diameters of 3-5 feet. 
In such well developed forests, the light intensity ranges from 
0.015 to 0.005 and even to 0.003, and except for the seedlings of 
the cedar the ground may be quite bare. But usually the forest 
canopy is sufficiently open to permit a growth of a few shade- 
enduring shrubs and numerous herbs. Of these the following are 
typical of the consociation: 
Ribes lacustre Rubus parviflorus 
Aconitum columbianum Circaea pacifica 
Anemone piperi Claytonia asarifolia 
Asarum caudatum Clintonia uniflora 
Athyrium cyclosorum Coptis occidentalis 
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