Results 



The diameter-growth response of western redcedar to 

 release from overstory and surrounding competition 

 was related to site, stand, and tree characteristics. 

 Because tree and stand characteristics such as number 

 of trees per acre, tree heights, and stand basal area per 

 acre could not be estimated for past growth periods, 

 these characteristics were used only in the regression 

 models for the 1975-1979 growth period (table 4). Other 

 variables such as stand elevation, slope percent, and 

 slope configuration, were used in the regression models 

 for all periods. The dependent variable in the models 

 was the difference between the observed 5-year diam- 

 eter growth and the predicted nonreleased 5-year diam- 

 eter growth. 



ZERO TO FIVE YEARS AFTER RELEASE 



Five years after release, cosine of the aspect times the 

 slope, natural log d.i.b.. b.h. tree age, and the predicted 

 nonreleased diameter growth had significant (P<0.05) 

 relationships with the difference between observed dia- 

 meter growth and predicted nonreleased diameter 

 growth of western redcedar. The best response of 

 western redcedar occurred on the steep north-facing 

 slopes and the poorest response occurred on steep 

 south-facing slopes (fig. 2). Tree d.i.b. had a significant 

 positive relationship with the diameter growth response 



90 180 270 360 



ASPECT AZIMUTH (DEGREES) 



Figure 2.— The 5-year growth response of 

 western redcedar on two slopes for three 

 periods after stand treatment. 



of western redcedar as indicated by the positive sign of 

 the regression coefficient for the natural log d.i.b. term 

 in the 0- to 5-year regression model (table 4). The posi- 

 tive sign of the natural log d.i.b. term indicated that the 

 larger diameter western redcedar had the better 

 response to release from competition, as compared to 

 the smaller diameter trees. In contrast, the regression 

 coefficient for b.h. tree age in the 0- to 5-year regression 

 model was negative, denoting that as b.h. tree age 

 increased, the diameter growth response of western 

 redcedar to release decreased (table 4). Likewise, the 

 negative coefficient for the predicted diameter growth 

 variable provided evidence that the predicted slower 

 growing trees had better diameter growth response to 

 release than those with the predicted faster growth 

 rates. 



FIVE TO TEN YEARS AFTER RELEASE 



Slope and aspect, along with b.h. age, had significant 

 relationships with the difference between observed 

 diameter growth and predicted nonreleased diameter 

 growth of western redcedar 5 to 10 years after stand 

 treatment. The diameter growth release response for 

 the 5- to 10-year growth period was better on the steep 

 north-facing slopes than on steep south-facing slopes 

 (fig. 2) and is similar to the results for the 0- to 5-year 

 growth period. In the 5 to 10 years after release, tree 

 age continued to have an inverse relationship with tree 

 response as indicated by the negative regression coeffi- 

 cient in the model for the 5- to 10-year period (table 4). 



TEN TO FIFTEEN YEARS AFTER RELEASE 



Predicted nonreleased diameter growth, sine-aspect 

 transformation, cosine-aspect transformation, natural 

 log d.i.b., and b.h. age were all significant (P<0.05) 

 variables in the observed minus predicted diameter 

 growth model for the 10- to 15-year period (table 4). 

 Predicted nonreleased diameter growth and tree age 

 with negative regression coefficients remained inversely 

 related to diameter growth release response, while 

 natural log d.i.b. continued to have a positive rela- 

 tionship with the release response of western redcedar. 

 The response to release 10 to 15 years after treatment 

 continued to be the best on north-facing slopes and the 

 poorest on south-facing slopes (fig. 2). 



1975-79 PERIOD OF GROWTH 



All of the site, stand, and tree variables were used in 

 the regression models for the 1975-79 growth period. 

 The number of years between the time each stand was 

 treated and the 1975-79 growth period ranged from 10 

 to 45 years, with a mean time of 21 years. Stand crown 

 competition factor, CCF, predicted nonreleased diam- 

 eter growth, natural log d.i.b., b.h. age, and habitat 

 type were variables significant in the regression model 

 (table 4). The results for this period were similar to the 

 results of the other growth periods, with both b.h. age 

 and predicted diameter growth having an inverse rela- 

 tionship with the difference between actual tree 

 diameter growth and predicted nonreleased tree diam- 

 eter growth (table 4). Total stand CCF was significant 

 (P<0.05) and also had a negative regression coefficient 



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