Clatsop County, Oreg., and in Pacific County, 
Wash., but no estimate of the loss from this out- 
During the period 1918-21 
another epidemic took place in Tillamook County, 
estimated to have killed 500 million board feet of 
standing timber on an area of approximately 27,000 
Fire followed the insects on much of this 
area, adding to the damage. 
break was ever made. 
acres. 
The most recent 
epidemic was one in 1929-31 in Pacific County, 
Wash., which the Bureau of Entomology and Plant 
Quarantine estimated covered about 52,000 acres 
and caused the loss of approximately 165 million 
board feet of standing timber, practically all 
western hemlock. Control measures are credited 
with hastening the termination of this epidemic. 
The native Douglas-fir bark beetle is commonly 
found in freshly felled or fire-killed trees, but 
occasionally this insect increases abnormally on 
burns and cut-over areas and attacks neighboring 
green timber, causing considerable damage. These 
outbreaks are usually of short duration and small 
extent. The annual damage to spruce by the 
aphis is usually small, although heavier infestations 
occur periodically. The Bureau of Entomology 
and Plant Quarantine estimates that during the 
period 1921-30 the abnormal forest drain due to 
epidemics of the hemlock looper and other insects 
averaged 80 million board feet per year. 
Abnormal losses from wind throw are difficult to 
estimate for a period as short as a decade, because 
they occur only sporadically and are likely to be 
catastrophic. The loss in the Olympic blowdown 
of January 1921 is estimated at 5 billion board 
feet, but there had probably been no storm damage 
like it for at least 75 years in this region. Losses 
averaging about 30 million board feet per year 
were reported for western Oregon in the decade 
1920-29. In April 1931 several hundred million 
feet of timber was reported to have been wind 
thrown during one storm, which did its greatest 
damage on the Mount Hood and Willamette 
National Forests in Oregon. In October 1934 a 
windstorm of unusual severity in western Wash- 
ington caused loss estimated at more than 300 
million board feet, practically all on State and 
private lands in King, Pierce, Skagit, and Sno- 
homish Counties. Fortunately a considerable part 
of this volume is salvable and it is therefore not 
considered as depletion. 
On the basis of such records and evidence as were 
available regarding windstorms, the quantity of 
saw timber blown down, including both bodies of 
timber and scattered trees, was estimated to average 
150 million board feet per year. It was further 
estimated that half of this fallen timber either was 
so scattered as not to affect total growth or would in 
the future be salvaged. If so, the net loss from 
wind throw was 75 million board feet annually. 
Assumed Future Depletion 
Undoubtedly all agents responsible for depletion 
in recent years will continue to be active in the 
future. By far the most important of the probable 
causes of future depletion is cutting. Beginning 
with 1933, the date of the inventory, the rate of 
depletion by cutting, fire, insects, and wind throw 
was estimated for each of three decades, 1933-42, 
1943-52, and 1953-62. The estimates are shown 
in table 20. 
TasLe 20.—Assumed future average annual forest depletion in the 
Douglas-fir region 
| 
Ejind of depletion and 10-year period National Gther Total 
: Miilion | Million | Million 
Cutting: board feet | board feet | board feet 
1933-42 22s Saree ee Re 215 6, 785 7, 000 
1943252 tam sae aoe eel kee e 498 7, 502 8, 000 
1953-6222 20 Ee eet ee eee ee ae 831 6, 169 7, 000 
Other: 
1933=42 7 Ee a St Soe os ee 242 507 749 
194352) ess ee ee eae 231 324 555 
1953622252 Re a 199 | 240 439 
Total: 
1933 40 ee ee eee eee ee eae 457 | 7, 292 7, 749 
OAS 55 Dis mene Pre ae cer oreo ee 729 7, 826 8, 555 
1953-62222 eee a Sb ee ee 1,030 | 6, 409 7, 439 
During the period 1925-33, the annual depletion 
by cutting of material of saw-timber size averaged 
approximately 7.9 billion board feet. It was con- 
siderably higher at the beginning of the period, but 
declined rapidly after 1929. A gradual increase 
over the cutting rate of the 3 years 1930-32 is 
anticipated during the decade 1933-42, but it is 
expected that the average for this period will be 
less than that for the period 1925-33. Therefore, 
it was estimated that the net annual depletion by 
cutting for 1933-42 would average 7 billion board 
feet. 
