11 



GEOGRAPHICAL DISTBIBUTIOIT. 



The coast form of Douglas fir grows in the coast ranges from 

 tiie head of Skeena River, in British Columbia, southward through 

 Washington and Oregon, and into California as far as the Santa 

 Lucia Mountains. It also grows along the Cascade and Sierra 

 Nevada mountains in these States to the headwaters of the San 

 Joaquin River, in Fresno County, Cal. The tree is of extremely 

 rare occurrence on the eastern slopes of this mountain chain, however, 

 from the southern extreme of its range to almost as far north as 

 Mount Hood, in Oregon. Its region of best development and great- 

 est abundance is in Washington and northern Oregon, Avest of the 

 Cascade Range. It reaches almost as large dimensions, however, 

 under the favorable climatic conditions offered by the humid western 

 slopes of the northern Sierra Nevada Mountains as it does on Puget 

 Sound. In dry situations in the Sierras its development resembles 

 that of the mountain form. 



The mountain form grows throughout the Rocky Mountain system 

 from Tacla Lake, British Columbia, latitude 55° north, southward 

 for at least 2,200 miles. It is absent or rare in the clf-y interior basins 

 and on the semiarid plateaus and minor mountain spurs lying be- 

 tween the principal ranges, especially toward the southern and east- 

 ern limits of its range. It is entirely absent from the high plateau 

 region of Nevada. In the drier parts of the Rocky Mountains, 

 especially in the south, it is confined almost exclusively to high 

 elevations. 



RELATION or ALTITUDE TO DISTRIBL'TIOX. 



From north to south both forms of Douglas fir occupy progres- 

 sively higher situations in the mountains. This results from their 

 demand for a certain amount of moisture in soil and air, which is 

 found at higher altitudes in the south than in the north. As a gen- 

 eral rule, the mountain form of Douglas fir grows at a higher eleva- 

 tion above sea level than the coast fir in the same latitude. This also 

 is due principal^ to moisture conditions, which are more favorable 

 to its growth at lower altitudes near the coast than in the mountains. 

 Where competing species are not influential in restricting its alti- 

 tudinal range its limits are climatically defined — loelow by lack of 

 moisture, and above chiefly by low temperature and shortness of the 

 growing season. 



The coast form grows in the Olympic Mountains in Washington 

 from sea level to an altitude of 3,500 feet, and in the Cascades from 

 the lowest elevations to 6,000 feet. In Oregon it grows in the Coast 

 Range between sea level and 6,200 feet, and is sometimes found in the 

 Cascades at an altitude of 7,200 feet. In the California coast moun- 



[Cir. 150] 



