64 



MISC. PUBLICATION 11, U. S. DEPT. OF AGRICULTUEE 



Table 7. — Rate of natural reproduction, cut-over loestern yelloic pine 



[Location, sec. 28, T. 10 S., R. 69 W. One acre plot established 1916, cut over 1915, recounted 1923 



and 1926] 





Trees ' Volume 



i 



Per cent 

 by volume 



Original stand. 



Number 1 Board feet 

 123 ; 5,630 

 34 3, 065 

 89 2, 565 



100 



Cut 



54.4 



Left 



45. & 







REPRODUCTION 





Under 1 foot 1 to 43^ feet 



4J4 feet to Scinches, 

 d. b. h. 





Year counted 



Western 



yellow 



pine 



Douglas 

 fir 



^5^- Douglas 

 pine 1 ^ 



Western 



3-ellow 



pine 



Douglas 

 fir 



Total 



1916 



50 

 74 

 29 



10 

 9 

 8 



! 

 88 1 4 

 80 6 

 68 6 



70 



88 

 81 



1 

 3 

 2 



22s 



1923 



260- 



1926 . . 



194 





1 









This represents a total increase of 37 trees in seven years, or 5.3 per year. 

 The loss shown in the 1926 count is due to the drought of 1924 and 1925. 



CALCULATION OF THE MEAN ANNUAL INCREMENT 



The present lack of adequate or reliable data makes impossible any accurate 

 determination of growth. For the purposes of this plan a rough calculation is 

 made, which can stand as conservative until a better basis is obtained. 



The available data consist of stand tables derived from a number of timber 

 surveys and the summary of experiments carried on at the Fremont experiment 

 station. The former lacks accuracy, but gives a rough estimate of what has 

 grown in the past ; the latter deals only with the total increment laid on, with 

 no reference to future merchantable increment, but serves as a valuable check 

 on the former. 



The calculation of increment is approached from three different angles — a 

 theoretical analysis based on growth in virgin stands, the probable second cut on 

 present timber sales, and a reduction of Bates's and Roeser's figures from total 

 increment to merchantable increment. These are considered in order. 



1. The basis for this discussion is the summary of the timber-survey stand 

 tables, which show that the average acre of virgin forest is comjwsed, in 

 rounded-ofl figures, of: 





Trees to i Trees to 



cut 10 1 leave 10 



inches and inches and 



over over 



Poles 

 6 to 10 

 inches 



Saplings 



Seedlings 



Number 



30 21 

 3, 040 930 



43 



141 



106 



Volume „ 













It is assumed that the 30 trees designated to cut range in age between 160 

 and 300 years, or, in other words, between the average ages of maturity and 

 death. The 160 has been accepted for years as approximately correct; the 

 300 is based on studies made by W. J. Pearce (Journal of Forestry, April, 

 1920), which have been checked by the judgment of the writer. 



These 30 trees represent the average maximum number of trees over 160 

 years old that the average acre of virgin forest can sustain constantly. This 

 is evident if the virgin forest is conceived to be a finely balanced organization 



