

FJIGRICULTORE 



71 



ll<L_DEPJ OF AGRICULiui 



(U.S. FOREST Sct8$G& m«j 

 ^^^ OCT 3- 1963 



CURRENT SERIAL RECORDS 



1 



RESEARCH NOTE, LS-24^ 



LAKE STATES FOREST EXPERIMENT STATION •—U.-S^ DEPART ME NT OF AGRICULTURE 



f- '%'2'j'' /riealing Time for Pruning Wounds 



in a Red Pine Plantation 



In red pine plantations the branches are 

 persistent, and little knot-free lumber will be 

 produced in less than 80 years without ar- 

 tificial pruning. When applied judiciously in 

 managed stands, pruning should be a profit- 

 able investment. 



A pruning study on red pine was establish- 

 ed in Lower Michigan in 1950, and the effect 

 of pruning on height and diameter growth 

 was reported by Slabaugh. 1 This Note de- 

 scribes the effect of pruning date and other 

 characteristics on the healing time of pruning 

 wounds from that same study. 



The test was established in a 14-year-old 

 red pine plantation on a good site in Lower 

 Michigan. Trees were pruned on July 27, 

 September 25, and November 13 of 1950; 

 and on April 5, May 4, May 21, and July 31 

 of 1951. The trees, which averaged 3.4 inches 

 d.b.h. and 16 feet tall, were pruned to a 

 height of 6 to 8 feet, using a hand saw. All the 

 branches were alive when pruned. 



On trees pruned on the first six dates, 

 pruning wounds from whorls at heights of 

 3.0 and 4.5 feet averaged 0.84 inch in di- 

 ameter in July 1951. Most wounds were cov- 

 ered with pitch, but only those pruned on 

 April 5 or before showed much evidence of 

 healing at this time. In October 1953, two 

 growing seasons after pruning, the wounds 

 had begun to heal and averaged only 0.5 inch 

 in diameter. 



In April 1961, ten growing seasons after 

 pruning, three sample trees pruned on each 



1 Slabaugh, Paul E. Effects of live crown removal 

 on the growth of red pine. Jour. Forestry 55: 

 904-906, illus. 1957. 



of the seven pruning dates were felled, and 

 all the knots in the two sample whorls were 

 cut open in transverse sections to determine 

 the manner in which the annual rings grew 

 over the wounds. Wound width just after 

 pruning, branch stub length, and radial 

 growth of the bole during the 10 years after 

 pruning were measured to the nearest 0.05 

 inch on 183 sections and averaged 0.80, 0.28, 

 and 1.06 inches respectively. About one-third 

 of the wounds had not yet completely healed; 

 their healing times, on the basis of present 

 unhealed width and growth rate, were esti- 

 mated and averaged 13 years. For all wounds 

 the average number of years before clear 

 wood was produced, as determined by a ring 

 count, was 9.7 years. These data were used 

 to compute an equation for predicting wound 

 healing time. The equation is: 



Y = 11.115 + 4.380X X + 14.279X 2 ~8.382X 3 

 where Y = years before clear wood is pro- 

 duced 



Xi - wound width (inches) 



X 2 = stub length (inches) 



X 3 = radial growth during the 10-year 

 period after pruning (inches) 



Each of the independent variables was 

 highly significant (.01 level). Radial growth 

 accounted for a third of the variation in heal- 

 ing time while the three factors combined ac- 

 counted for half the variation. Predicted heal- 

 ing times, based on the measured values of 

 the three independent variables, were deter- 

 mined for all the wounds. The difference in 

 healing times between pruning dates was not 





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