528 JOURNAL OF FORESTRY 



range {Sequoia zvashingtoniana) grow do not differ materially from 

 those characterizing the redwood belt. Moreover the groves of big 

 trees in the Sierras are so small relatively that they are of little 

 importance in this discussion. Consequently, they have not been con- 

 sidered separately. 



Douglas Fir Type 



This type possesses the heaviest precipitation of any forest type 

 in the United States with the possible exception of small areas of 

 sub-tropical growth in southern Florida. The average annual pre- 

 cipitation is 80 inches and the run-off and evaporation are only medium. 

 Furthermore the growing season is relatively long, approximately six 

 months in length. As a consequence not only does Douglas fir attain 

 a diameter of 24 inches and a total height of 154 feet, but the number 

 of trees per acre is relatively large, 115 in 100 years. The yield of 

 15,600 cubic feet in 100 years is the greatest for the United States. 

 Douglas fir is the dominant species in this type, but hemlock, red cedar, 

 and western larch are also found in small quantities. 



SUMMARY 



In order to bring out the relation between tree growth and climate, 

 it is necessary to arrange the various types discussed with reference to 

 the different factors. Taking the length of growing season first, the 

 following list shows the various types in descending order of length 

 of growing season: 1, southern pine type; 2, southern bottom land 

 type ; 3, sequoia type ; 4, southern hardwood types ; 5, sugar pine type ; 

 6, Douglas fir type; 7, western yellow pine type; 8, white pine type; 

 9, silver pine type; 10, lodgepole pine type; 11, northern hardwood 

 type; 12, Engelmann spruce type; 13, spruce type. 



Arranged in order of total annual precipitation, the types may be 

 listed as follows: 1, Douglas fir type; 2, southern hardwood types; 3, 

 southern pine type ; 4, southern bottom land type ; 5, spruce type ; 

 (j, sequoia type ; 7, northern hardwood type ; 8, white pine type ; 9, 

 Engelmann spruce type; 10, silver pine type; 11, sugar pine type; 12, 

 lodgepole pine type; 13, western yellow pine type. 



With reference to run-off, the classification is more difficult. The 

 following list is merely given as a tentative one proceeding from the 

 types that have the least run-off to those that have the most. Length of 

 growing season and steepness of slope were both taken into con- 

 sideration: 1, spruce type; 2, northern hardwood type; 3, southern 



