SPRUCE AND BALSAM FIR TREES. 37 
White fir is very tolerant of shade throughout its life, but it en- 
dures more shade from the seedling to the pole stage than at any 
other period. Such growths survive long suppression under heavy 
shade, but with slow progress, and recover readily when overhead 
light is admitted. White fir appears to be most tolerant of shade in 
moist soil, where usually it is able to endure more than any associated 
species except Engelmann spruce and alpine fir. Owing to its great 
tolerance, white fir has a closely branched crown, and the trunks lose 
their branches rather slowly. 
White fir is a fairly prolific seeder, producing large crops of cones 
periodically. Good seed years occur only at irregular intervals of 
from two to four years, but some seed is produced nearly every year. 
As a rule, seed production begins mostly at a rather advanced age, 
but pole-size trees in dense stands may bear seed when their leaders 
reach full light. Seed bearing continues for many years, but it is 
more abundant during the period of rapid height growth (between 
the ages of 50 and 100 years) than at maturity. The seed has only a 
moderately high rate of germination (often under 40 per cent) and 
transient vitality. Reproduction is usually abundant, large dense 
groups of seedlings often resulting from a single tree's heavy seed 
crop. 
The character of the seed bed is apparently of little importance, 
for seed germinates on moist, heavy litter and humus as well as in 
mineral soil. However, fairly abundant soil moisture is essential 
during the first few months following germination in order that the 
seedlings may become established. Indifference to the kind of seed 
bed renders this tree more than ordinarily agressive, reproduction 
occurring over denuded lands adjacent to seed trees as well as imme- 
diately under their own shade. 
Large quantities of seed of this fir are eaten by squirrels 1 and 
probably also by other rodents which doubtless avail themselves of 
1 The remarkable sagacity of pine squirrels is shown by an incident observed by the 
writer in connection with their " cutting " of white fir cones in the Manzano National 
Forest, N. Mex. Part of the cones " cut " from a tree had necessarily fallen directly into 
a shallow pool of spring water beneath the tree, and it is equally certain that part of 
them fell on the border of the pool. The latter supply of cones had, however, evidently 
been dragged to the abrupt edge of the pool and pushed into the water. Altogether a 
bushel or more of cones were thus cached in the water. Evidence that the squirrels had 
deposited part of the cones in the water appeared in the fact that cones were especially 
numerous in the water at the edge of the pool. None were to be found anywhere on the 
ground about the pool. While the squirrels were not actually seen at work, the position 
of the tree with reference to the pool was such that only a part of the cones " cut down " 
could have fallen directly into the water, while the remainder clearly must have reached 
the ground. The writer was informed by a settler's lad who frequently passed the pool 
that he had seen the squirrels dragging cones to the water's edge. The effect of placing 
ripe fir cones in water is to prevent them from breaking up and liberating their seeds, 
which occurs when the cones are left on the ground exposed to the air. While it is 
believable that the placing of these cones in the water may have been in accordance with 
the instinct of squirrels and many other rodents to cache their winter supply of food, it 
seems quite unbelievable that the squirrels could know and profit by the fact that 
immersing fir cones in water temporarily preserves them intact. 
