340 FOREST TREES OF THE PACIFIC SLOPE. 



From western Wyoming to Montana (western slopes Rocky Mountains), Idaho 

 (Coeur d'Alene Mountains), Oregon (eastern Blue Mountains), and southward (through 

 Wasatch Mountains and ranges of the Great Basin) to California (eastern slopes Sierra 

 Nevada and northern slopes of San Bernardino Mountains), and to northern New Mexico 

 and Arizona. 



OCCURRENCE. 



Arid mountain slopes ; in poor, dry, gravelly and rocky soils, or less often in moist, 

 richer soils, where it is of largest size (hills of central Nevada). In pure open, or 

 rather dense stands, or mingled with chaparral ; commonly with one-leaf pinon. 



Climatic Conditions. — Undetermined, as are also its silvical characteristics. Appears 

 to be decidedly intolerant of shade throughout life. 



Birch-leaf Mahogany; Mountain Mahogany. 

 Cercocarpus parvifolius Nuttall. 



DISTINGUISHING CHARACTERISTICS. 



Birch-leaf mahogany is usually shrubby, with several long, sparingly branched 

 fctems, and under 10 feet in height ; occasionally a tree 15 to 25 feet high, with 

 a rounded crown of straight, upright, stiff, slim branches and a short trunk 

 £ to 8 inches in diameter. The bark of large limbs and small trunks is smooth 

 and dull gray to brownish ; that of large trunks is thin, flaky, and reddish-brown. 

 The more eastern form appears to have much firmer bark with shallow seams, 

 and its scales are much less easily detached. Mature leaves (fig. 159), with 

 prominent straight veins, are thickish, smooth, sometimes minutely hairy, deep 

 yellowish-green on their top sides and whitish, occasionally brownish, beneath. 

 Leaves of a season's growth persist as a rule for about two seasons ; very com- 

 monly, however, they persist only for one summer and winter, falling as the new 

 ones appear the succeeding spring. The long-tailed, hairy fruits are inclosed in 

 a tubular case which has a distinct slender stem, instead of being stemless like 

 the preceding species. The silky young twigs have a pleasant slightly aromatic 

 flavor. Twigs of the low shrubby forms of this species are often extensively 

 eaten by cattle, in some sections furnishing a considerable part of the mountain 

 browse on which range animals depend for food. Wood, of somewhat lighter 

 weight, is otherwise very similar to that of the preceding tree ; rarely used 

 except locally for firewood. 



Longevity. — Very slow-growing tree. Stems from 5 to 6 inches thick are 

 from 50 to 60 years old. Further study of its growth and age limits is desirable. 



Three varieties of this species have been described. These are distinguished 

 on the basis of characters which the writer believes to be only such natural 

 modifications in leaves and fruit as are to be expected in individuals growing 

 under varying soil and climatic conditions. Through all of the forms it seems 

 possible to trace the marks of one variable species ; no essential differences can 

 be found in the wood of the different trees. Cercocarpus parvifolius betuloides 

 (Nuttall) Sargent, the California coast and Sierra foothill form, has wider 

 leaves, smooth above, and larger fruit than are produced elsewhere. Cercocar- 

 pus parvifolius breviflorus b (Gray) Jones is distinguished by very small flowers 

 and small, narrow leaves with entire slightly curved or very finely toothed 



° See footnote under preceding species. 



6 This is Dr. Gray's Cercocarpus breviflorus, which, by inadvertence or otherwise, is 

 frequently written C. brevifolius. 



