SPEUCE AND BALSAM FIR TREES. 27 
ever, alpine fir requires less soil moisture than Engelmann spruce, but 
grows in places too wet for this spruce ; it also grows on soils suitable 
for Douglas fir, where Engelmann spruce will not succeed. 
Alpine fir occurs in pure small stands and in mixture with other 
trees. At the North it is associated more or less with mountain hem- 
lock, Engelmann spruce, lodgepole pine, white-bark pine, limber 
pine, and Lyall larch. At the south it is mingled commonly with 
Engelmann spruce, lodgepole pine, cork fir, and aspen, and less 
frequently with bristle-cone pine. 
Alpine fir is only slightly less tolerant of shade than Engelmann 
spruce, and, except the mountain hemlock, it can live under deeper 
shade than any of its associates. Saplings long suppressed by heavy 
shade recover and grow rapidly with the admission of top light. 
Abies lasiocarpa is a moderately prolific seeder, beginning to bear 
cones as early as the twentieth year. Some seed is produced locally 
every year, but heavy production occurs only at intervals of about 
3 years. The seed has a rather high rate of germination, but very 
transient vitality. Seedlings spring up abundantly on exposed min- 
eral soil in the open and also on thin and heavy moist duff under 
light or heavy shade. Usually, however, they grow most thickly 
on the north side of groups of trees or forests and under the branches 
of mother trees. Abundant reproduction nearly always occurs in 
shaded openings among seed trees. At high elevations branches 
lying on the ground and partly covered with earth or moist duff occa- 
sionally take root, from which, however, the production of new trees 
is probably very rare. 
LONGEVITY. 
Alpine fir is moderately long-lived. Trees from 10 to 20 inches 
in diameter are from 140 to 210 years old. The considerably larger 
trees which occur are not likely to be more than 250 years old. 
CORK FIR. 
Abies arizonica Merriam. 
COMMON NAME AND EAKLY HISTOKY. 
Most authors consider this fir a form only or a variety of the 
alpine fir (Abies lasiocarpa). For the present, however, it is here 
maintained as specifically distinct from the alpine fir, to which it is 
very similar in crown form and in the general appearance of its 
foliage, but from which it is at once distinguished by its soft, corky 
bark (compare Pis. XIII and XV), differences in the shape of the 
