40 BULLETIN 1200, U. S. DEPARTMENT OF AGRICULTURE. 
are equally unfavorable at these different distances. In localities 
where moisture and soil are more favorable, as in some sections of 
the Willamette Valley in Oregon, the forest makes more substantial 
progress through migration, because the percentage of seedlings 
established is greater. The distance covered by each seeding genera- 
tion, however, is not greatly increased. 
CHARACTER OF SECOND-GROWTH FORESTS. 
Usually the same forest type that existed before the action of 
the disturbing or destroying agencies is reestablished. An imme- 
diate forest succession without the usual intermediate stages results 
either from dormant seed left after the removal of the previous 
forest or from other exceptionally favorable conditions for reseed- 
ing. Immediate succession is characteristic in burns in the Pacific 
Northwest. In successions of this character the forest which was 
removed by fire, cutting, or other agencies is replaced by the identical 
species of the original forest, although usually in different pro- 
ortions. Wherever reproduction is found coming in after a fire 
which killed the entire forest, the dead trees and snags of the same 
species were also found. ; 
The extensive, unbroken forests of Douglas fir in the Pacific 
Northwest have developed primarily through fires. If this region 
were left without fire for 600 or 700 years, the forest of Douglas fir 
would be greatly reduced in area, and the best Douglas-fir soils 
would be occupied by western red cedar and western hemlock. With- 
out artificial interference, such as fire or logging, Douglas fir can not 
compete with western red cedar and western hemlock, whose ability 
to endure shade permits them to form an understory which crowds 
out the less shade-enduring Douglas fir. (Pls. XIII and XIV.) 
Tf the Douglas fir trees mature or are killed by any agent other 
than fire, and the western red cedar and western hemlock remain 
uninjured, the openings made by the removal of the Douglas firs 
are immediately filled by the understory of western red cedar and 
western hemlock. For this reason a Douglas fir forest seldom main- 
tains a pure stand after the first generation, and sometimes is en- 
tirely replaced at the end of the first generation. Stands of Douglas 
fir 50 years old with clear, straight boles and well-developed crowns 
sometimes have a complete understory of western red cedar and 
western hemlock of practically the same age. Although the Douglas 
fir may be 100 to 130 feet tall, the western red cedar and western 
hemlock understory is only 20 to 30 feet tall. But this understory 
is not suppressed beyond recovery; and as soon as the forest is 
opened the suppressed trees renew their growth and form the forest 
stand. Although there may be a number of veteran Douglas firs in 
a forest consisting mostly of western red cedar and western hemlock, 
there is no chance for the replacement of Douglas fir unless the en- 
tire forest is removed. On the other hand, it has been found that 
some stands which originally contained only about 5 per cent of 
Douglas fir have been succeeded after a fire by young growth which 
contained as high as 50 per cent. 
Tf the enormous quantities of seed produced almost annually by 
the western red cedar and western hemlock had the same chances of 
succeeding as the Douglas fir, the entire forest would soon consist 
of these species. From the small seeds produced by the western 
