318 University of California Publications in Zoology [ VOL - 16 



The alpine fir (Abies lasiocarpa) forms extensive forests on the 

 higher ridges of the Blue Mountains. It does not grow in the canons 

 or on the lower slopes, so it may be considered the characteristic tree 

 of the ridge forest. Alpine-fir forest is abundantly developed in many 

 of the sheltered coves near the tops of the ridges. In these coves the 

 ground is fairly moist. The forest developed is not dense, and there is 

 plenty of room to walk between the trees. The size reached by the 

 alpine firs is not very large and few of the trunks would measure over 

 fifteen inches in diameter. Some lodgepole pines (Finns murrayana) 

 are often mixed with the alpine firs and in places where new growth 

 is springing up lodgepole may be the dominant tree. There is usually 

 very little undergrowth under the alpine-fir forest, there being com- 

 monly only a few very low shrubs. On the ridges alpine fir is less 

 common and the forest is more open and commonly includes many 

 Douglas spruces (Pseudotsuga taxifolia). The ground here is drier 

 than in the coves and there is much exposure to sun and wind. The 

 trees occur singly or in small groups. Douglas spruce is the dominant 

 tree in the most exposed places. 



In many of the coves and on protected slopes near the tops of the 

 ridges forests of western larch (Larix Occident alis) are developed. 

 This may be developed as a pure forest or may be mixed with alpine 

 firs or Douglas spruces. The pure larch forest is very open and under- 

 brush is scanty and the forest floor may be covered entirely by grasses. 

 The trees reach a good size with trunks several feet in diameter. On 

 the damper slopes Douglas spruce usually dominates over the larch 

 and a rather dense forest is developed. This contains much more 

 underbrush and the ground is commonly quite damp. In such places 

 Engelmann spruces (Picea Engelmanni) may occur commonly. 



Although the alpine-fir association is made up of a considerable 

 number of forms very few are restricted to the association. Neither 

 do very many reach their greatest abundance in this habitat. 



Trapping in forest habitats on the ridges near Twin Buttes R.S. 

 on July 28, July 29, and August 3, 1914, produced 8 Peromyscus 

 maniculatus gambelii, 1 Microtus mordax mordax, 4 Evotomys gap- 

 peri saturatus, and 1 Eutamias amoenus amoenus from a total of 181 

 trap-nights. 



