TREE GROWTH AND CLIMATE IN THE UNITED STATES 527 



dominant species. The climatic factors which make more rapid growth 

 and higher yields possible in this type are heavier precipitation, less 

 rapid run-oflf, and evaporation. The mountain ranges in the northern 

 part of Idaho upon which this type occurs are in the direct path of 

 the moisture laden winds from the Pacific Ocean and the cooling 

 which occurs as the winds rise in crossing the mountain ranges results 

 in an area of relatively high precipitation in northern Idaho and north- 

 western Montana in spite of the fact that eastern Washington and 

 Oregon are desert-like in character. The total annual precipitation, for 

 example, at Murray. Idaho, is 40 inches. The short growing season 

 retards run-of¥ and evaporation. 



Sugar Pine Type 



The dominant species are sugar pine, incense cedar, and yellow 

 pine. Sugar pine under virgin conditions attains a diameter of 24 

 inches and a total height of 111 feet in 100 years, while yellow pine 

 and incense cedar reach 20 inches and 94 feet, and 14 inches and 65 feet, 

 respectively, in the same length of time. The average yield will not 

 exceed 2,000 cubic feet per acre in a 100-year rotation. The growing 

 season is relatively long, from five to seven months, the precipitation 

 medium, about 35 inches, and the run-ofif and evaporation medium to 

 large. Consequently the available moisture is not great. This is evi- 

 denced by the relatively open stands. 



Sequoia Type 



While there are groves of sequoias in the Sierra range, the largest 

 areas of trees of this genus occur in the California coast ranges imme- 

 diately east of the Pacific Ocean. These are the famous redwoods of 

 northwestern California and southwestern Oregon. The climate of the 

 redwood region is characterized by a long growing season, seven 

 months, total annual precipitation ranging from 25 to 50 inches, and 

 relatively rapid run-ofif and evaporation. As a consequence the total 

 amount of available moisture is approximately the same as in the 

 sugar pine type, but the longer growing season permits of greater 

 individual development. As a consequence the trees attain the largest 

 size of any on the American continent. It is estimated that in 100 

 years a redwood will reach a diameter of 35 inches and a total height 

 of 150 feet. No yield figures are available, but it seems reasonable to 

 assume that a yield of 10,000 cubic feet per acre is possible in 100 years. 



The climatic conditions under which the big trees of the Sierra 



