THE CEDAR-HEMLOCK FOREST. 217 



THE CEDAR-HEMLOCK FOREST. 



THUJA-TSUGA ASSOCIATION. 



Nature and extent. — This is much the more massive and continuous of the 

 two associations. The dominants are fewer and the composition less varied, 

 though the northern and southern extremes show striking differences from 

 the central portion. The trees are taller, the canopy denser, and the shrubby- 

 undergrowth often developed to form almost impenetrable thickets. The 

 most typical expression of the forest is found between the coast and the upper 

 slopes of the Cascade Mountains from southern British Columbia to northern 

 Oregon. The long extension to the northward in Alaska shows a more or less 

 similar ecological character, but becomes reduced practically to two domi- 

 nants, Picea sitchensis and Tsuga heterophylla. The southward prolongation 

 into California resembles the main portion in the presence of practically all 

 its dominants, but this narrow coastal strip is differentiated by the paramount 

 role of Sequoia sempervirens (plate 51). 



DOMINANTS. 



Tsuga heterophylla. Abies grandis. Abies nobilis. 



Thuja plicata. Sequoia sempervirens. Chamaecyparis nootkatensis. 



Picea sitchensis. Abies amabilis. Chamaecyparis lawsoniana. 

 pseudotsuga mucronata. 



Pseudotsuga mucronata is much the most important dominant with respect 

 to abundance. It is the typical species of burned areas, and hence has more 

 or less of the nature of a subclimax, particularly in view of its relatively low 

 tolerance. In addition, it is a major dominant of .the montane forest, and for 

 these reasons it is less characteristic of the association than Tsuga and Thuja. 

 The essential character is given by Tsuga, Thuja, Picea, and Sequoia, prac- 

 tically all of which attain their best development along the coast or in low- 

 lands. Abies grandis is almost equally important in the larch-pine association 

 and A. amabilis in the subalpine forest. Abies nobilis and Chamaecyparis 

 nootkatensis also occur to some extent in the subalpine forest. While the 

 latter ranges to the northern limits of the formation in Alaska, it drops out 

 in northern Oregon. Abies nobilis is restricted to western Washington and 

 Oregon and Chamaecyparis lawsoniana practically to the fog belt from Coos 

 Bay, Oregon, to Humboldt Bay, California. 



Groupings. — The typical grouping of the cedar-hemlock forest is Pseudo- 

 tsuga, Tsuga, Thuja, and Picea. According to Gannett (1900 : 14) Pseudotsuga 

 forms 64 per cent of the standing timber in western Washington, Tsuga 16 

 per cent, Thuja 14 per cent, and Picea 6 per cent. In western Oregon, the 

 figures are Pseudotsuga 81 to 85 per cent, Tsuga 6 to 7 per cent, and Thuja 

 1 to 2 per cent (1899 : 43), excluding the coast region where Picea occurs. 

 All of the four major dominants may form pure stands, but this is exceptional 

 for Thuja and frequent for Tsuga and Picea only in the north. It is more or 

 less common in the case of Pseudotsuga, though as a rule the other dominants 

 are scattered through this consociation. Near the coast from British Columbia 

 to California, Douglas fir and Sitka spruce are the chief associates, while in 

 California Pseudotsuga and Sequoia are most important. According to Sud- 

 worth (1908 : 147), the redwood is rarely pure, but usually forms 50 to 75 



