1238 
Journal of Agricultural Research 
Vol. XXVIII, No. 12 
Summarizing it may be said for all species that the method of slash disposal 
plays a minor part in germination and survival. Nor can the amount of slash 
scattered over the area be considered a criterion of the amount of immediate 
protection offered by logs, stumps, juniper, grass, twigs, and small litter, which 
furnish the seedlings protection through the critical period of the third year, 
when there is greatest danger from direct insolation. Again, although scattered 
slash effectively prevents grasses coming in after opening up the stand, nothing 
discovered in this study has indicated that grasses are detrimental to fir repro¬ 
duction; on the contrary, it has been found that the seedlings prefer to a sur¬ 
prising extent the protection offered by grasses. The number of survivors 
found and their general thrift indicate that the losses here are no greater than 
under slash. 
In 1919, 85 per cent of fir and 80 per cent of spruce had come up under immediate 
protection, irrespective of cleared and slash areas; in 1922 these figures were 87 
and 82 per cent, respectively. Evidently fir takes advantage of cover more than 
spruce does. Healthy 1917 and 1918 fir seedlings were more abundant under 
slash in 1919, while healthy spruce of the same age was more abundant in the 
open. This is attributed to the fact that the humus under slash is a trifle too 
deep for spruce. However, both species show the best thrift under protection, 
as defined above. As a whole, the seedlings naturally had more chance to come 
up near protection upon areas where the slash had been scattered, but the differ¬ 
ence was not a great one. 
HUMUS DEPTH AND ROOT LENGTH 
Though the principal factor in germination will be found to be moisture supply, 
survival is dependent to a great extent upon humus depth. There exists a definite 
relationship between drought and depth of humus and also between tolerable 
depth of humus and immediate protection. Protection permits about one-half 
inch of additional humus for fir, and less for spruce. A protected seedling may 
survive the first and crucial season in humus in which an unprotected, one would 
succumb. 
Since humus depth is important in governing the distribution and survival of 
fir and spruce seedlings, root length is of prime importance. The root must be 
able to push through the comparatively open, quickly desiccated layer of humus 
and secure a hold in the mineral soil beneath, where, if the seedling is to survive its 
first drought period, it must depend upon a more or less steady moisture supply. 
A study of root length in relation to humus depth was made in 1919. Only a 
limited number of trees were studied, but enough, it is believed, to reflect the 
general trend of the relationship. The following figures represent seedlings 
about one vear old: 
DOUGLAS FIR 
Average root 
length 
Average depth 
of humus 
Inches 
Inches 
Vigorous. 
3.94 
0.81 
Wilted.. 
2.74 
1.58 
Dead__ 
2.82 
2.40 
Average root length 2.75 inches. 
ENGELMANN SPRUCE 
Vigorous_ 
2. 75 
1.18 
Wilted... 
2.08 
1.04 
Dead.. 
1.51 
1. 71 
Average root length 1.80 inches. 
