SPRUCE 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 EAELY HISTOEY. 



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 



