DISCUSSION 



Partial cutting is useful in Engelmann spruce management as a reproduction method. 

 Although the partially cut stand observed in this study is small, it shows both advantages and 

 disadvantages of the method. 



On the credit side, both spruce and subalpine fir responded well to release even at the 

 advanced ages represented by the trees in this study. The spruce residual increased its gross 

 volume at a 2.4 percent per annum rate for 30 years. These residual trees during the regen- 

 eration period not only furnished an adequate, well-distributed seed source, but also provided 

 natural shade to aid seedling survival in the early years and good protection for the site. At 

 the same time, the residual trees returned a substantial increment. As illustrated in the re- 

 sults, the selection of good, vigorous spruce seed trees provided good control of the species 

 composition in the reproduction. 



On the debit side, however, the spruce residual presents the problem of risk from loss 

 by windthrow. Windthrow is not an insurmountable problem because, under proper conditions 

 of exposure, skillful cutting, and deep soil, spruce residuals can produce good net gains, as 

 shown by this study. Studies on the east side of the Canadian Rockies^ have shown that the 

 blow-down problem can be alleviated by light selection cutting where reasonable reserve stands 

 of 3,000 board feet or more per acre have been left. Further, these partially cut stands make 

 possible another cut on the area in 30 to 40 years. 



Subalpine fir, despite its good growth response to release by logging, is highly sensitive 

 to damage and mortality from sunscalding and insect attack, and suffers a high incidence of 

 heart rot. These facts make subalpine fir an extremely high risk in the residual stand unless 

 the trees are very young and vigorous. 



Suppression of the spruce reproduction by the residual stand, which is held for many 

 years beyond seedling establishment, constitutes another disadvantage of partial cutting. 

 Diameter and height growth of well-established spruce seedlings were retarded when compared 

 with seedling growth and development in the clearcutting. The extent to which the suppressed 

 reproduction may respond and fill the gap of lost increment when the old stand is removed is 

 not known. 



A further disadvantage of partial cutting is found in the difficulty of preparing seedbeds 

 under the residual trees. Mechanical scarification around the bases of spruce trees very often 

 damages roots close to the surface and, consequently, decreases vigor and increases the risk 

 of windthrow. Prescribed burning also often damages the shallow roots of spruce and some- 

 times causes death by damaging the cambium. The extent to which scarification and prescribed 

 burning may be modified to reduce their damaging effects is not known, but further investiga- 

 tion is highly desirable. 



On the basis of this study and present experience, clearcutting with seed-tree groups, 

 strips, or small blocks is not recommended. Seed sources of this kind are highly vulnerable 

 to wind damage. The transitory nature of the seed sources is a serious disadvantage not only 



^DeGrace, L. A. Management of spruce on the east slopes of the Canadian Rockies. 

 Canada Dept. of Resources and Development. Forest Res. Div. Silv. Res. Note 97, 55 pp. 

 1950. 



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