24 



20 - 



Q 



o 



O 



< 12 - 



4 - 



RATE OF GROWTH 

 (RINGS PER INCH) 



0.5 1.0 1.5 



PRUNING WOUND WIDTH (INCHES) 



2.0 



Figure 1. — Relationship between pruning wound 

 width, bole radial growth, and time until clear 

 wood is formed in a red pine plantation ( branch 

 stub length constant at 0.25 inch). 



significant when the residuals were tested by 

 analysis of variance. 



In this study the branch stub length was 

 measured from the cambium. Branches cut 



flush with the bark had a stub length equal 

 to the bark thickness or about 0.25 inch. In- 

 creasing the average stub length another 0.25 

 inch would have increased the healing time 

 3.6 years, but increasing the wound width 

 0.25 inch would have increased the healing 

 time only 1.1 years. For rapid wound heal- 

 ing, therefore, the branch stubs should be 

 short, even though the wound width is in- 

 creased slightly. 



A series of regressions to show the rela- 

 tionship of wound width and growth rate to 

 healing time was computed from the equation 

 above. These regressions (fig. 1) show the 

 importance of growth rate on healing time. 

 A 1 -inch-wide pruning wound, for example, 

 was healed in 7 years where the growth after 

 pruning was 7 rings per inch, but 12 years 

 were required where the growth was 12 rings 

 per inch. Thus, for the early formation of 

 clear wood over pruning wounds the trees 

 had to grow fast. 



As a rule of thumb, the wounds of average 

 width were usually healed when a layer of 

 wood about as thick as the width of the wound 

 had been formed. The thickness of the layer 

 required was slightly less than the wound 

 width for the larger wounds and more than 

 the wound width for the smaller wounds. 

 Thinning pruned plantations will stimulate 

 diameter growth on the remaining trees, 

 thereby reducing the time required to heal 

 the pruning wounds and increasing the re- 

 turn on the investment in pruning costs. 



£• 



July 1963 



RICHARD E:. LOHREY 

 Research Forester 

 (Forest Management) 



