1.0 



0.8 



o 

 c 



0.6 

 V) 



•I— 



o 



>. 



1 0.4 

 (0 



o 



0.2 



0.0 



Slope percent^ 



'o' 



.--''10 



y 5Q.- 



50 100 150 



Residual Basal Area (ft^/acre) 



200 



Figure 7 — The effect of residual overstory basal area and slope 

 for a south) aspect on predicted probability of stocking for an 

 fiih'ies grandis/Clintonia uniflora habitat type. 



The effect of western spruce budworm on the probability of stocking is not 

 very dramatic. This is not surprising since nonhost species stock plots as do 

 budworm host species. Lower rates of stocking over time occurred in the 

 Pseudotsuga menziesii, ThujalTsuga, and Abies lasiocarpa series, but not in 

 the Abies grandis series. Additionally, budworm defoliation in the 5 years 

 prior to harvest significantly decreased the probability of stocking in the 

 Abies lasiocarpa series. Figure 8 illustrates the probability of stocking over 

 time on the Pseudotsuga menziesii series. The upper line has no budworm. 

 The lower line illustrates the probability of stocking if budworm defoliation 

 occurred every year. After 20 years, the difference in the probability of 

 stocking is 0.07. 



Coefficients for spruce budworm effects in appendix B are sometimes not 

 significant at the 0.05 level. Budworm defoliation reduces the rate of stock- 

 ing of host species; it does not prevent stocking. For example, in the equation 

 for the probability of stocking for Pseudotsuga menziesii series (appendix B, 

 table 9), the coefficient for SQBWAF is 0.12913 (nonsignificant), and the co- 

 efficient for SQREGT is 0.21368 (significant). The effect of these two variables 

 is to break the number of years since disturbance into two components: a 

 significant increase when there is no budworm defoliation and a nonsignifi- 

 cant increase when there is budworm. 



Figure 9 illustrates the concepts of optimum aspect and amplitude. Both 

 are calculated from the interaction of slope and aspect using procedures devel- 

 oped by Stage (1976). The mathematical determination of the highest and 

 lowest points along the curve indicates the general directions of the optimum 



16 



