Hknky and Flood — The Douglas Firs. 75 



Colorado aud Utah to Arizona, New Mexico, and northern Mexico. In this 

 region the daily and seasonal ranges of temperature are great, the winter 

 being long and severe, with frequent periods of extreme cold, the tempera- 

 ture falling sometimes to -30'^ F. The summer is hot, and often very dry. 

 The annual precipitation in tlie Douglas Fir zone is 15 to <!5 inches, largely 

 in the form of snow. The growing season is short, often less than three 

 mouths. The region is characterized by the occurrence of Picea Engelmanni 

 and Pinus ponderosa scopulorum throughout, with Pinns Murrayana in the 

 north aud extending as far south as central Colorado. lu the southern parts of 

 the Rocky Mountains, as in New Mexico, the climate is more moderate, with 

 a smaller range of temperature (-10^ to 95° F.), heavier rainfall, and a longer 

 growing season. Here the Douglas Fir becomes a larger tree, and possibly 

 constitutes a distinct variety. (See note, p. 91.) 



The Rocky Mountains Douglas Fir is much less susceptible to injury 

 from drought than the Coast species ; but in arid regions it grows best on 

 cool northern slopes, and in deep valleys where moisture in the soil and air 

 is retained. It bears without injury very severe cold in winter, but is liable 

 to attack by spring frosts, whicli damage the young shoots after growth has 

 begun. In the Rocky Mountains it grows well Ijoth on dry sandy tracts 

 and on moist loamy soils, but does not succeed on clay, on coarse gravel, or 

 in poorly drained situations. It does not bear shade as well as Engelmann 

 Spruce or Abies lasiocarjxi. 



In its native home it is very slow in growth, and rarely attains over 

 90 feet in height aud li feet in diameter. Yield tables are not available ; 

 but figures given by Frothinghami show that at its best in the wild state it 

 reaches about 90 feet in 150 years. On account of its slow growth, the 

 volume of timber per acre yielded by this species in the liocky Mountains is 

 very small ; and it usually forms an open forest of small trees, with tapering 

 stems and persistent branches. 



Pseudotsuga macrooarpa, Mayr, Wald. Nordamcr. 27S (1890). 



This species attains a height of 70 or 80 feel. Branchlets reddish brown 

 in the first year, grey in the second and third years, variable in jjubescence, 

 either quite glabrous or with scattered short hairs ; puhini only slightly 

 raised. Buds more or less coated witli resin. 



Leaves pectinate, not glaucous, curved, 1 to 1^' nich long, usually tipped 

 with a cartilaginous point ; median groove on the upper surface indistinct ; 

 lower surface with raised broad midrib, and two depressed whitish bauds, 



' U. S. Vepl. Ayiic. Forest Circular No. 150, p. 30 (190D). 



