COMPOSITION OF FORESTS. 43 



lastly the southern exposures, which are very often grassy and have 

 only scattered trees, especially at high altitudes. 



Of the two great classes of trees which make up our northern forests 

 on the Pacific Slope the conifers are by far the most abundantly repre- 

 sented in point of individuals. They are also of the greater economic 

 importance. The deciduous trees are the most numerous as to species, 

 but form only an inconsiderable quantity in the forest growth, and their 

 commercial importance is as yet practically none. 



There are of the conifers 15 well-defined species. They are distributed 

 among the various genera as follows: pines, 4 or possibly 5j spruces, 1; 

 firs, 2; larches, 1; hemlock spruces, 1; arbor vita's, 1; hemlocks, 2; 

 yews, 1; junipers, 2. Thirteen among the 15 always attain the stature 

 of trees. One, the yew, is sometimes a tree, sometimes a trailing shrub. 

 Another, the alpine juniper, is always a low, spreading shrub. One, 

 the Western tamarack, is deciduous, shedding the leaves of the season 

 in late autumn, October and November. The others are evergreen. 



All the species are of wide range, occurring generally throughout the 

 forests of the Pacific Slope above the northern boundary of California. 

 It is uncertain how many of them range far enough east to enter the 

 Rocky Mountain region proper. I am inclined to think that they all do, 

 with the possible exception of the yew. 



The conifers are as follows: 



Pines, — Yellow or bull pine (Pinna ponderosa), white pine {Pinna monticola), black 

 pine (Piuus murrayava), white-burked pine (Piuus albicaulis). 



Spruces. — Engelmann spruce (Picea engelmanni). 



Firs.— White fir (Abies concolor), subalpine tir (Abies lasiocarpa). 



Larches. — Tamarack or Western larch (Larix occidentalis). 



Hemlock spruces , — Hemlock spruce, Douglas spruce, Oregon lir, red fir, etc. (Pseu- 

 dotsuga taxifolia). 



Arbor vita's. — Cedar (Thuja plicata) . 



Hemlocks. — Patton hemlock (Tsuga patiouiana), Mertens hemlock (Tsuga meriemi- 

 ana). 



Yews. — Short-leaved yew (Tarns brevifolia). 



Junipers. — Red cedar (Juniperus rirginiana), mountain juniper (Juniperus nana). 



YELLOW PINK. 

 I'inus ponderosa Dougl. 



The yellow or bull pine stands at the head of the list of the Cfleur 

 d'Alene trees as the most generally useful. It furnishes probably not 

 less than four-fifths of all the sawed lumber of the region. It is found 

 in all the larger valleys, in the bottoms and on the bench lands and f he 

 slopes of the abutting spurs. The mean elevation of its extreme alti- 

 tudiual range is 1,250 meters (4,100 feet). In some localities a few 

 trees will be found as high as 1,500 meters (4,000 feet), and in some 

 places it falls far short of its mean range. This is apparently due to 

 difference in precipitation, for the capacity of the yellow pine to endure 

 great atmospheric humidity is decidedly limited. The /one of its 

 7203— No. 1 4 



