1146 
Journal of Agricultural Research 
Vol. XXVIII, No. 11 
Adverse climatic conditions, while still important influential factors, do not 
so completely dominate the reproduction problem in central Idaho as they do in 
the Southwest (0). Yet it is considered desirable to retain a sufficient number 
of trees to preserve forest conditions, in addition to insuring an adequate seed 
supply, since a heavy opening of the stand increases the danger from wind, 
excessive evaporation, deficient moisture, and frost injury (3, £)* 
As the result of special studies (5) failure of reproduction was found to be due 
more to high mortality the first three years following germination than to a lack 
of germination. By far the greatest mortality was found in seedlings less than a 
year old. Very few over 6 inches high die in any one year. A leaf disease, 
caused by Phacidium infestans , has caused a significant loss among seedlings 
and saplings of the fairly tolerant Douglas fir and promises to continue as a cause 
of mortality on the plots. Another leaf fungus (Hypoderma deformans) was 
frequently found to be the cause of fairly heavy losses of western yellow pine 
seedlings and saplings and ranks along with suppression as a cause of mortality 
in this species on northern aspects and in basins, especially where the cover is 
rather dense. 
The same field studies showed that the most serious causes of death, aside from 
the two diseases just mentioned, are in the order of their importance: Drought, 
browsing and trampling by grazing animals, especially sheep, girdling by rodents, 
winter-killing, including excessively low temperatures, frost injury, and rodents 
or birds which bite off the newly germinated seedlings. Seedlings and saplings 
15 to 20 years old were occasionally found girdled by rodents. Balanced against 
this is the fact that rodents render considerable aid in disseminating and burying 
the seed, thereby promoting favorable conditions for satisfactory germination. 
One of the most noteworthy results of these studies has been to emphasize 
the great importance of advance reproduction. The establishment of advance 
growth is a long slow process, doubtless requiring as much as 20 years or even 
more to secure adequate restocking on the poorer sites. Moderately heavy 
cuttings appear to be fully justified provided advance growth is reasonably 
abundant and provided healthy, vigorous seed trees are left as insurance against 
loss of the advance reproduction by fire. It is also evident that efforts to delib¬ 
erately change the composition of the stand by the method of cutting will produce 
few tangible results. Western yellow pine is holding its own on potential yellow 
pine sites and it can be succeeded by Douglas fir only in the tension zone between 
the two types or in the Douglas fir type. A large number of Douglas fir seedlings 
can be found, but owing to a heavier mortality extending over a longer period of 
years, fewer seedlings actually become established than in the case of western 
yellow pine. Where the two species occur in mixture, as in the basins, the pine 
in the juvenile stage grows faster than Douglas fir. However, these different rates 
of juvenile growth do not continue beyond about 40 years of age when Douglas 
fir surpasses the pine in diameter growth at least. 
APPLICATION OF RESULTS IN SILVICULTURAL PRACTICE 
When the national forests of the West were placed under Government ad¬ 
ministration, little exact information on the characteristics and requirements 
of the important native forest trees was available upon which to base rules for 
silvicultural practice. As a result of repeated fires, grazing, and insect infesta¬ 
tions, the forests were generally understocked and often had a preponderance 
of overmature and decadent timber and a deficiency of trees of the intermediate 
age classes from which to select vigorous, thrifty seed trees. All too often ad¬ 
vance reproduction was poorly distributed or lacking. In addition there was 
no sale for defective timber. 
