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NATURALISTS GUIDE TO THE AMERICAS 



resulting in dense impenetrable thickets 

 which show very slow growth. This 

 forest is composed of trees of small 

 diameter and has a low volume produc- 

 tion compared with the Idaho forests, 

 thereby reflecting the lesser annual 

 precipitation in Montana than in Idaho. 

 This type grows under a mean annual 

 air temperature ranging from 35 to 40 

 and annual precipitation of 20 in., while 

 the snowfall is about 150 in. The flora 

 and fauna are quite similar to those 

 found in the Douglas fir-western larch 

 type. Since this type embraces the 

 major portions of the forests of central 

 and southern Montana there is quite a 

 local demand for the timber for mines, 

 railroads and for building material, but 

 there is no immediate danger of excessive 

 cutting such as would eliminate natural 

 virgin areas. Grazing is very important 

 in this part of the state, especially on 

 the open grasslands at lower elevations. 

 The Douglas fir-lodgepole pine type 

 occurs on most of the National Forests 

 in northern Idaho and Montana but 

 may be studied to best advantage on the 

 following : 



SUBALPINE FORESTS 



Above 5500 ft. in altitude in Idaho 

 most of the forest trees mentioned in 

 the cedar-hemlock-grand fir type give 

 way to mountain hemlock (Tsuga merten- 

 siana), whitebark pine (Pinus albicaulis), 

 alpine fir (Abies lasiocarpa) } Douglas fir 

 and lodgepole pine continue upward 

 above 5500 ft. Engelmann spruce 

 usually lines the water courses on north 

 aspects. Alpine fir is more generally 

 distributed but prefers northern and 

 eastern aspects. Mountain hemlock is 

 the climax species on the broad ridge 

 tops in the Clearwater basin while white- 



bark pine and lodgepole pine are most 

 abundant on the upper sunny aspects. 



At these elevations the summer is 

 short but warm and much clear weather 

 prevails. The mean annual air tempera- 

 ture at Roosevelt in the Thunder Moun- 

 tains of Idaho at 7000 ft. averages 36.4; 

 the annual precipitation is 26.5 in. 



Wherever the mountain hemlock holds 

 sway on high ridges, as in the Clearwater 

 drainage, Engelmann spruce is largely 

 wanting. Perhaps the dry summer 

 winds coming from the Snake River 

 desert limits it to the more northern 

 and eastern forests. In the subalpine 

 forest to the east of the Bitterroot 

 range, limber pine (Pinus flexilis} 

 replaces whitebark pine (Pinus albi- 

 caulis) . 



In this type or belt the vegetation 

 varies greatly according to soil moisture 

 and aspect. The fauna does not differ 

 greatly from that of the cedar-hemlock- 

 grand-fir type. Blue grouse, fool hen, 

 grosbeak, hawk are found, in addition. 



This type of forest may be studied to 

 advantage on the following National 

 forests : 



ALPINE FORESTS AND BARRENS 



Points above 8000 ft. elevation repre- 

 sent alpine conditions. Such areas are 

 marked by permanent glaciers and bar- 

 rens and are found in the northern sec- 

 tion of the main Rocky mountains, and 

 on the Beartooth National Forest. The 

 forest at these high elevations is repre- 

 sented by more or less dwarfed Engel- 

 mann spruce and Lyall larch (Larix 

 Lyallii), the latter not occurring east of 

 the main Continental Divide in northern 

 Montana. The alpine flora of the 

 Yellowstone National Park has been 

 listed by F. Tweedy. This list shows 

 several species also found in similar 

 situations in Europe and Asia. The 



