Table 4. --Growth per acre of all trees in Pattee Canyon plots, 1932-1959 



Treatment 

 and 

 plot number 



: D.b.h. 



Height 

 ■ 1949-1960^ ■ 



Basal area : 



Volume 





Inches 



Feet 



Sq. ft. 



Cu. ft. 



Thinned (1) 



1.8 



7.8 



74.8 



2,006 



Unthinned (2) 



1.7 



4.7 



57.6 



1,625 



Unthinned (3) 



1.2 



5.6 



38.4 



1,152 



^ Since check plots were not measured until 1949, height growth for 11 years 

 only was available for comparison with the thinned plot. 



The effect of thinning on diameter growth in the Pattee Canyon plots was even greater when 

 comparison was based upon equivalent of the 150 largest trees per acre. This comparison 

 showed 56 percent larger diameter growth on the thinned trees than on the unthinned. This 

 indicated that the larger trees responded better to thinning than the smaller trees. 



The effectiveness of thinning can be evaluated by comparing actual growth with potential 

 growth for the proper site and age conditions and optimum stocking. A study of normal yield 

 data for western larch has led to the development of a set of curves showing diameter growth 

 of crop trees by age and site index and adjusted for optimum stocking.'*' These curves provide 

 our best estimate of potential growth with a moderately intensive level of management in stands 

 that have never been seriously suppressed. 



By determining the section of curve covering the growth periods (age 50-60 in West Fork 

 and age 30-57 in Pattee Canyon) involved in the thinning studies and adjusting to plot site index, 

 the potential diameter curves for the growth period were developed. (See A and B, fig. 2.) For 

 example, curve A in figure 2 is the potential diameter growth curve for crop trees (dominant 

 and codominant trees) at site index 52 and an optimum level of stocking for age 50 to 60 years , 

 Thus the potential 10-year d.b.h. growth for the growth period would be equal to the difference 

 between the 50- and 60 -year diameters, or 10.8 inches (60 years) minus 9.0 inches (50 years) 



^, , actual d.b.h. growth X 100 , , u . j 



= 1.8 inches . The ratio of , , , , ■ equals the extent to which the stands 



potential d.b.h. growth 



have reached this potential. 



By comparing actual growth on each plot to the potential growth, the relative improvement 

 due to thinning is evident (table 5). For example, the D+4 treatment increased the diameter 

 growth to 78 percent of the site potential in the first 10-year period following thinning- -22 

 percent closer to the potential goal than the check. During this 10-year period, the trees re- 

 sponded to increased growing space by enlarging their crowns and root systems . About 3 years 

 after thinning, ring width increased noticeably. If the trends continue, greater attainment of 

 the potential goal is expected. 



Unpublished data, files of Intermountain Forest and Range Experiment Station. 



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