the same volumes as tJie unthiimed plot, while the other two have nearly caught up. To do this, 

 it was necessary for the thinned crop trees to grow faster than those in the unthinned plot. It is 

 expected that this trend will continue , and all the thinned plots may exceed the unthinned plot 

 10 to 15 years hence. 



The cost of thinning by the D+4 rule in the West Fork area amounted to 20. 1 man-hours 

 per acre as contrasted with 15.0 for the crown thinning. These costs are further broken down 

 as follows: 



The D+4 thinning cost more because it resulted in removing more trees than the crown thinning. 



Western larch and ponderosa pine trees were pruned to a height of one log at an average 

 rate of 14 trees per hour. This cost was obtained on the ^-acre plots in the West Fork study. 

 Consequently, it may not completely represent practical average rates for such work on larger 

 areas. The crew was better than average; consequently the cost estimate is probably 

 conservative . 



No cost records were kept for the low thinning in the Pattee Canyon plots . 



These studies show that the main benefit from thinning is obtained by concentrating the 

 growth on fewer stems. The net result is that trees grow to a larger size earlier, and usable 

 volume is realized earlier in the life of the stand. For example, if the present growth rates 

 continue on the Pattee Canyon plots, the thinned trees will reach a 10-inch average diameter at 

 stand age 135 years. The unthinned trees, on the other hand, will not reach this average size in 

 less than 200 years, or times as long. 



Recommendations for thinning western larch: 



1. Early thinning should be the rule in managing larch stands. Growth response of thinned 

 stands is related to stand structure and stocking prior to thinning. Growth that is lost on individ- 

 ual trees through years of overstocking cannot be regained by thinning. In fact, response to 

 thinning will be slow until the thinned trees develop good crown and root systems. Therefore, 

 stands should be thinned early, before serious competition for moisture and light occurs. 



2. The best results are obtained from larch thinnings when first consideration is given to 

 selecting good crop trees. Correct spacing is important, but secondary to crop-tree selection. 

 Dominant and codominant trees consistently show the greatest response to thinning. Therefore, 

 the best practice is to thin from below and reserve the more dominant trees with well -developed 

 vigorous crowns . 



3. Where crop-tree thinning is desirable, the D+4 rule applied to individual crop trees as 

 a spacing guide is suggested. If the management objective is to grow sawtimber on a 140-year 

 rotation, crop trees should be selected at the rate of 120 to the acre for site index 65 or more, 

 and 140 to the acre for under site index 65. 



Cost 



Cutting 



Girdling 



Poisoning 



64.3 trees per man-hour (trees less than 5 inches d.b.h. only) 

 23.6 trees per man-hour (trees more than 5 inches d.b.h. only) 



18.4 trees per man-hour (trees more than 5 inches d.b.h. only) 



DISCUSSION AND RECOMMENDATIONS 



10 



