ANALYSIS OF THE DATA AND RESULTS 



RESIDUAL STAND GROWTH 



In addition to providing a large controlled seed source and shade protection for the site, 

 partial cutting makes available high-quality, selected growing stock. Because part of the trees 

 are removed by logging, the success of the growing stock hinges to a large degree upon the 

 ability of the residual trees to accelerate and maintain good growth rates and to remain wind- 

 firm. The following analysis evaluates the growing stock in the partial cutting on the basis of 

 these criteria. 



Gross and net growth. --The original stand volume on the partial cutting averaged about 

 29,000 board feet Scribner per acre; about 7,000 feet per acre, chiefly Engelmann spruce, re- 

 mained in the residual stand in 1924. Subalpine fir was the principal associate, and only minor 

 quantities of other species were present. 



In partial cuttings, foresters aim to leave trees that can respond to release and make 

 good growth. The Engelmann spruce residual made a good net gain of 3 , 035 board feet per 

 acre in the 30-year period 1924-1954, but the subalpine fir sustained a net loss of 62 board feet 

 (table 1). Deductions for defect were not made from the volumes in table 1 because a quantita- 

 tive value for this factor was not available for the residual stand in 1924. However, defect as 

 determined by increment borings in 1954 was 6 percent of the volume in Engelmann spruce and 

 48 percent of the subalpine fir. Heart rot was chiefly responsible for the defect. The large 

 volume of defect in subalpine fir further accentuates the difference in the growth between the 

 two species shown in the table. 



Table 1. - -Thirty-year gross and net growth and mortality 



Species 



Residual : Volume 

 volume : in 

 in 1924 : 1954 



30 -year growth 



Periodic annual 

 growth 



Annual 

 mortality 



Net : Gross 



Net : Gross 



Board feet - -- -- -- -- -- -- - 



Engelmann spruce 5,906 8,941 3,035 4,255 101 142 41 

 Subalpine fir 1,082 1,020 -62 729 -2 24 26 



Values rounded to the nearest board foot; no deductions made for defect. 



Although Engelmann spruce usually is not windfirm, mortality in the residual stand in 

 this study was not unduly high. This may hav^ been because the stand was situated below the 

 crest of a ridge in a reasonably well-protected location. The annual mortality of 41 board feet 

 per acre of Engelmann spruce was caused primarily by windthrow, while much of the mortality 

 in subalpine fir appeared to be caused by sunscalding and insects. The following tabulation 

 shows the estimated percent volume loss by cause for both species. 



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