Finally, a graphical analysis of radial increment to 

 determine past budworm activity in the stands was done 

 according to procedures developed previously (Carlson 

 and McCaughey 1982). 



RESULTS AND DISCUSSION 



Defoliation of Douglas-fir was much lower in the 

 thinned stand than in the unthinned stand (table 2). 

 Whole-tree defoliation (ground-based estimate) was only 

 15 percent in the thinned stand, whereas the unthinned 

 stand was 43 percent, and the difference was significant 

 at p < 0.05. Similarly, measured defoliation on current- 

 year midcrown shoots in the thinned stand was 44 per- 

 cent, significantly lower (p < 0.05) than in the unthinned 

 where defoliation averaged 66 percent. 



These two different estimates of defoliation differ sub- 

 stantially in magnitude but are similar to each other in 

 trend between the stands. It is not surprising that the 

 magnitudes of the estimates are different because they 

 estimate two different "types" of defoliation. The whole- 

 tree estimate reflects the observer's interpretation of 

 defoliation over all the needle age classes and crown 

 levels in a tree, whereas the shoot counts reflect a more 



accurate estimate but only on current year's needles 

 from midcrown. Thus, the whole-tree estimate likely is 

 more appropriate for long-term evaluation because it 

 reflects the current condition of the whole crown as 

 influenced by several years of budworm feeding and 

 probably closely reflects diameter growth. A detailed 

 analysis between shoot count and ocular methods of 

 estimating defoliation on balsam fir in eastern North 

 America showed that plot means of ocular estimates 

 were lower than shoot count estimates from the same 

 trees (MacLean and Lidstone 1982), similar to our obser- 

 vations at Lubrecht. MacLean and Lidstone (1982) con- 

 cluded that ground-based ocular methods gave reliable 

 estimates of budworm defoliation. 



Complementing this reduced defoliation in the thinned 

 stand, radial growth of both species accelerated in 

 response to thinning. In the unthinned stand, annual 

 radial growth of Douglas-fir paralleled that of ponderosa 

 pine between 1935 and 1966 (fig. 3). In 1967. however, 

 Douglas-fir radial growth declined, presumably in 

 response to the feeding pressure by budworm. whereas 

 ponderosa pine increased in response to the "biological 

 thinning" (defoliation) done by the insect. 



0.12 i- 



- 0.08 

 H- 

 Z 

 LU 

 S 

 LU 

 DC 

 O 



< 



lu 0.04 

 2 



UNTHINNED STAND 



PONDEROSA PINE 



DOUGLAS-FIR 



0.00 

 1935 



'45 '55 '65 



YEAR 



'75 



Figure 3.— Mean annual radial increment of 

 Douglas-fir and ponderosa pine in the 

 unthinned stand. Mean increment was simi- 

 lar for both species until the late 1950's 

 when the budworm infestation became 

 heavy. 



Table 2.— Comparison of mean defoliation (percent) of Douglas-fir trees 

 between the thinned and unthinned stands. Lubrecht 

 Experimental Forest 





Stand 



Statistics 



Variable 



Thinned Unthinned 



"t" Prob. 



Whole-tree defoliation 



15 43 



-8.23 



Measured current defoliation 



44 66 



-2.72 ,0.016 



4 



