530 JOURNAL OF FORESTRY 



amount of available moisture due to heavy precipitation or retarded 

 run-off or evaporation. 



Yield is the result of the three factors of diameter growth, height 

 growth, and density, but density seems to be the most important of the 

 three, since the stands that yield the highest are the ones with the 

 greatest density per acre. 



Climatic and soil factors will not entirely account for the differ- 

 ences on yield. Specific dift'erences also enter into the problem. Some 

 species seem so well adapted to their environment that they grow rapidly 

 and densely in spite of untoward conditions. For example, the eastern 

 white pine seems peculiarly fitted for its role in rate of growth, toler- 

 ance, and reproductive capacity. Were all types of the same composi- 

 tion, the exact effect of the climatic and soil factors would come out 

 more clearly, but each has its own tree species which thrive best under 

 the peculiar and complex conditions which differentiate it from other 

 types. 



Using the data given above as a basis, it is possible to determine 

 the relative values for forest production of the land in the types which 

 have been discussed. In making this calculation it will, of course, be 

 necessary to make the conditions uniform. Therefore, it is assumed 

 that the rotation is 100 years, the rate of interest 3 per cent, no returns 

 are expected from thinnings, but no allowance is made for losses from 

 fire, insects, and fungi. The stumpage value at the end of the rotation 

 is estimated to be $10 per M, $10 per acre is allowed for regeneration, 

 and 50 cents per acre for annual expenses. The following yields per 

 acre for the different types have been used. The value per acre for 

 forest production purposes is also given. Arranged in descending order, 

 they are : 



Yield Per Acre 



Type Cubic Feet Board Feet Productive Value 



Douglas fir 15,600 90,000 $22 



White pine 14,700 84,000 19 



Southern bottom land 1 2,000 7 2,000 1 2 



Hardwood cove 10,000 60,000 6 



Silver pine 10,000 60,000 6 



Sequoia 10,000 60,000 6 



Northern spruce 7,400 44,000 -3 



Northern hardwoods 7,000 44,000 



Southern pine 7,000 42,000 



Engelmann spruce 6,000 36,000 



Hardwood slope 5,000 30,000 



Lodgepole pine 5,000 30,000 



Sugar pine 2,000 12,000 



Western yellow pine 1,500 9,000 



Hardwood ridge 1,000 6,000 



