526 JOURNAL OF FORESTRY 



dry climate, and the run-ofif is greatest in the southwest on account 

 of the longer growing season and the torrential character of the rains. 

 No satisfactory growth figures exist for this type, so that it is only 

 possible to say in a general way that the individual trees grow rela- 

 tively slowly, all mature stands are very open, and the yield in 100 

 years will not average better than 1,500 cubic feet. 



Lodgcpole Pine Type 



This type grows immediately above the western yellow pine type 

 and is characterized by a shorter growing season, slightly heavier pre- 

 cipitation, more rapid run-off on account of the steeper slopes, but 

 less rapid evaporation. Hence there is a slightly larger amount of 

 available moisture. In 100 years lodgepole pine will attain under 

 favorable conditions a diameter of 12 inches and total height of TO 

 feet. No figures exist for its associated species, Douglas fir and 

 alpine fir. The yield can only be estimated, but it seems safe to say 

 that it will not exceed 5,000 cubic feet in 100 years. 



Engelmann Spruce 



This type is confined to the summits of the Rocky Mountains. As 

 a consequence it is characterized by a short growing season, not more 

 than 35 inches of precipitation, medium run-off and evaporation, and 

 shallow soils. The amount of available moisture is greater than in 

 the lodgepole pine type because of the heavier precipitation and less 

 rapid run-off and evaporation due to the long winters. Satisfactory 

 growth and yield figures are not available for this type, so that it can 

 only be stated in a general way that the individual trees do not reach 

 such large size as in the lodgepole pine type, but the number of trees 

 per acre is greater so that the yield will probably be larger than in 

 the lodgepole pine type. It is estimated to be 6,000 cubic feet. 



Silver Pine Type 



In northern Idaho the climatic conditions are such that the silver 

 pine and red cedar grow abundantly. Both these species will attain, 

 under favorable site conditions, a larger size in 100 years than is 

 possible in the other Rocky Mountain types. Likewise the density and 

 yield per acre are heavier ; as a consequence it is estimated that this 

 type will yield approximately 10,000 cubic feet in 100 years. The 

 characteristic species are silver pine and red cedar, although Douglas 

 fir, western larch, and alpine fir are also found in association with the 



