46 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
be utilized at 25 years of age for pulp wood. At that age little 
heartwood has been formed, and a harvest of about 2,500 cubic feet 
to the acre could be obtained from good stands. At 35 years of 
age stands of this character would yield up to 2,000 posts to the acre, 
and at 45 years of age there would be 350 to 400 trees to the acre 
suitable for ties. At 55 years the stand would average about 110 
feet in height and would be suitable for poles and piles. On favor- 
able sites Douglas fir may yield 40,000 board feet to the acre at 60 
years of age. Stands of 100 to 200 years make an annual growth of 
500 to 1,000 board feet to the acre. This excellent growth diminishes 
little until the trees have reached the age of about 200 years, but 
from that time on it is much less. At about 250 years the timber 
begins to show the effects of decay. After this age growth in the 
forest may not be greater than the loss resulting from the death 
of trees from disease or other causes. ; 
The best growth occurs on the gentle, well-drained slopes and 
benches at the lower altitudes west of the Cascades and in the Coast 
Mountains. In middle age the more densely stocked stands occur on 
the south or exposed slopes, and the least dense on the cool north 
slopes. Humidity is an important factor in promoting this phe- 
nomenal growth. Consequently, the best growth occurs in the coast 
regions, where fogs are comparatively common. 
SILVICULTURAL MANAGEMENT. 
MATURE AND OVERMATURE FORESTS. 
The present merchantable forest of Douglas fir generally consists 
of a mature or overmature stand. (Pl. XVI.) Management in these 
forests for the purpose of securing a second crop and protecting 
the existing young stands requires proper methods of cutting, slash 
disposal, and fire protection. 
METHODS OF CUTTING. 
Clear cutting is the most feasible method with the present system 
of logging, and it also produces the best results from a silvicultural 
standpoint. All trees and snags that are large enough to remain 
standing through a slash fire should be cut whether they are mer- 
chantable or not, unless they are to be left as seed trees. A diameter 
limit is not a satisfactory basis for classifying the material to be 
felled, because such a limit would have to be different in different 
places or even within the same area. The important thing is to get 
all the material on the ground before the slash fire. Trees up to 
about 12 inches in diameter at breast height are usually torn down 
by the cables in the areas through which a large number of logs are 
skidded. On the outside of the settings, however, the logs are pulled 
out in more direct lines, and a large percentage of small trees remain 
standing after the logging is completed. This is the principal reason 
why a diameter limit would not solve the problem satisfactorily. 
Material left standing after all operations are completed should be 
felled before the slash is burned. If trees and snags are left after 
the slash fire, they form a fire hazard for the entire area and add 
to the cost of fire protection. Standing trees are generally killed 
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