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The Douglas-Fir Region 
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33 
HE Douglas-fir region, which includes those 
parts of Oregon and Washington west of the 
summit of the Cascade Range, was selected 
as the place to begin the Nation-wide forest survey 
(fig. 2). Extending 480 miles from north to south 
and varying in width from 100 to about 150 miles, 
this region has an area of more than 35 million 
acres, of which 29 million acres, or 83 percent, is 
forest land. Its long littoral exposure subjects most 
of it to humid westerly winds; its climate is charac- 
terized by equable temperatures, except in the 
high mountains, and moderate to heavy precipita- 
tion. Climatic conditions are particularly favor- 
able to conifer forest growth, and the region is noted 
for the luxuriance and density of its forest vegetation 
The forests of this region are almost exclusively 
conifer, and Douglas-fir (Pseudotsuga taxifolia) is the. 
predominating tree, forming 60 percent or more of 
the stand on more than half the forest land (fig. 1). 
Important species commonly associated with 
Douglas-fir are western hemlock (Tsuga_hetero- 
phylla), western redcedar (Thwa plicata), Sitka 
spruce (Picea sitchensis), Pacific silver fir (Abzes 
amabilis), and noble fir (A. nobilis). Exceptions to 
the predominance of Douglas-fir are found in the 
forests on the cool, humid western slopes of the 
Coast Ranges and the Olympic Mountains known 
as the fog belt, where western hemlock and Sitka 
spruce are the outstanding species and Douglas-fir 
is occasionally entirely lacking. Again, on the 
higher slopes of the Cascade Range and _ the 
Olympic Mountains and occasionally on those of 
the Coast Ranges, the stands are made up prin- 
cipally of western hemlock, Pacific silver fir, noble 
fir, mountain hemlock (Tsuga mertensiana), and 
western white pine (Pinus monticola). Latitudinally 
also, toward the cooler, northern extreme of the 
regicn, Douglas-fir forms a smaller percentage of 
the stand, western hemlock and other species in- 
creasing in frequency; and on the dry exposures of 
the interior valleys and foothills of southern Oregon, 
Douglas-fir gives way to ponderosa pine (P. 
ponderosa). 
F 325601 
Ficure 1.—Saw-timber stand of old-growth Douglas-fir near the 
Columbia River in western Washington averaging more than 40 
inches in diameter and having a gross volume of about 125,000 
board feet per acre. The trees in the picture measure from 5 to 
6 feet in diameter. 
