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Research ArticleArticles

Branch Pruning Wound Closure

Dan Neely
Arboriculture & Urban Forestry (AUF) August 1991, 17 (8) 205-208; DOI: https://doi.org/10.48044/jauf.1991.049
Dan Neely
Center for Biodiversity, Illinois Natural History Survey, 607 East Peabody Drive, Champaign, IL 61820
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Abstract

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Branches were pruned from 10 species of trees by the “Shigo” and the conventional methods. The branches (four per tree, five trees per species) averaged 50 to 75 mm (2 to 3 in) in diameter. Wounds from conventional cuts were 30 to 50 percent larger than wounds from Shigo cuts. There was little closure of Shigo wounds during the first year. After four years, the conventional wounds were smaller than the Shigo wounds on six species, approximately the same size on one species, and larger on three species.

Wounds to trees are detrimental because they expose the xylem to invasion by insects or disease or decay organisms. Branch pruning wounds can be especially undesirable because wood growth after the cut, remains exposed for many years. The exposed sapwood may be invaded by borers or systemic fungi (2, 3). Infection of the sapwood and heartwood by other primary and secondary invaders may result in wood discoloration and decay (5). Bleeding from diseased heartwood following branch removal is not uncommon (1).

Yet, branch removal is a sound and often essential horticultural practice. Crossing and hazardous branches should be removed. Regulations may require that lower or obstructing tree branches be removed to accomodate pedestrian or vehicular traffic. When branch removal is necessary, rapid closure of pruning wounds is desirable. Closed wounds complete the last annual growth ring, reduce the likelihood of invasion by external agents, and increase tree stability.

The placement of the final cut in branch removal recently has been discussed by various researchers. The dialogue centers on whether rapid closure (4) or discloration and decay (7) should be the primary consideration in placement of the cut. Two criticisms of an earlier paper (4) demonstrating rapid closure from conventional branch pruning were that the data came from only three tree species and that the branches removed were quite small. They, therefore, may not have been representative of branches on larger trees. The objective of the present study was to confirm or refute the previous study by pruning much larger branches from additional species of trees.

Materials and Methods

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The trees used in this study were located in the Street Tree Collection of the Morton Arboretum near Lisle, Illinois. The trees were planted in 1958 with 15m (50 ft) between trees in a row and 15m between rows. The trees ranged from 12 to 20 m tall in 1986. Ten cultivars within seven genera were chosen (Table 1). Four branches on each of five trees of each cultivar were selected for pruning. The branches’ diameters were measured with a steel tape approximately 8 cm from the trunk. Two branches on each tree were pruned beyond the branch shoulder using the “Shigo” method (6), and two branches were pruned through the branch shoulder using the conventional method (4) on September 22, 1986. The width of xylem exposed on each wound was measured on April 27, 1987, and again in mid-October of 1987, 1988, 1989, and 1990. The amounts of closure each year on each species were analyzed using Student’s test for paired samples.

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Table 1.

Mean diameter of branches pruned from trees with Shigo or conventional cuts and the width of resultant xylem exposed*.

Results

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The average branch diameters and the average widths of wounds are given in Table 1. The widths of the wounds from conventional cuts were significantly larger than those associated with the Shigo cuts. The width of xylem exposed after a Shigo cut was sometimes even less than the branch diameter (e.g., 94 percent of branch diameter for Liquidambar and 96 percent for Fraxinus). With conventional cuts, the wound width was often 45 percent larger than the branch diameter (e.g., 151 percent of branch diameter for Acer (1) and 147 percent for Acer (2) and Gleditsia).

The average closures in the widths of wounds for each of the four growing seasons are given in Table 2. Closure of the Shigo cuts was slight or nonexistent in 1987 for all 10 cultivars and averaged 3.1 mm. By contrast, only on Quercus was the closure of conventional cuts limited in 1987, and closure of conventional cuts averaged 8.4 mm. With exception of Quercus in 1987 and 1990, the conventional cut wounds closed more each season on each cultivar than did the Shigo cut wounds.

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Table 2.

Average closure of the branch pruning wounds from Shigo or conventional cuts during four growing seasons, 1987-1990.

At the end of the 1990 season, the conventional wounds were smaller than the Shigo wounds on Acer (1), Acer (2), Acer (3), Liquidambar, Platanus, and Ulmus; they were essentially the same size on Acer (4); and they were larger than the Shigo wounds on Fraxinus, Gleditsia, and Quercus (Fig. 1). Of the 100 wounds of each type on all species, 17 Shigo cuts and 12 conventional cuts were closed after four seasons.

Figure 1.
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Figure 1.

The widths of wounds resulting from pruning of branches by the Shigo and conventional methods and the resulting widths during four years of wound closure.

Discussion

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The specifications for a Shigo cut as used in this test were those recommended in 1984. The angle of the final cut was equal to that formed by the branch bark ridge and the vertical. Since then, Dr. Alex L. Shigo has stated, “Proper pruning of a living branch is a cut as close as possible to the branch collar. There is no set angle for a proper cut” (7, page 29). Had the 1989 specifications been used in this study, the results may have been different. Both Shigo and I include the warning—do not leave branch stubs!

The decision that must be made by the arborist or tree owner is whether to make the final cut either through or outside of the branch shoulder. A conventional cut through the shoulder will result in a more aesthetically pleasing and faster growing callus. A cut outside of the shoulder or collar will possibly reduce discloration and decay in the stem or trunk from which the branch was removed. Both objectives are desirable, but only one is obtainable.

Acknowledgment

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The cooperation of the Morton Arboretum staff, especially Drs. Gary W. Watson and Thomas Green, is gratefully acknowledged.

  • © 1991, International Society of Arboriculture. All rights reserved.

Literature Cited

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  1. 1.↵
    1. Carter, J.C.
    1945. Wetwood of elms. Illinois Natural History Survey Bulletin 23(4):407–448.
    OpenUrl
  2. 2.↵
    1. Johnson, W.R. and
    2. H.H. Lyon
    . 1988. Insects that Feed on Trees and Shrubs. Second edition. Cornell University Press, Ithaca, New York. 556 pp.
  3. 3.↵
    1. Juzwik, J.,
    2. D.W. French, and
    3. J. Jeresek
    . 1985. Overland spread of the oak wilt fungus in Minnesota. J. Arboric. 11(11):323–327.
    OpenUrl
  4. 4.↵
    1. Neely, D.
    1988. Closure of branch pruning wounds with conventional and ‘Shigo’ cuts. J. Arboric. 14(11):261–264.
    OpenUrl
  5. 5.↵
    1. Shigo, A.L.
    1967. Successions of Organisms in Discoloration and Decay of Wood. International Review of Forest Research 2. Academic Press, Orlando, Florida. 65 pp.
  6. 6.↵
    1. Shigo, A.L.
    1984. Homeowners guide for beautiful, safe, and healthy trees. U.S. Department of Agriculture, Forest Service NE-INF-58-84. 8 pp.
  7. 7.↵
    1. Shigo, A.L.
    1989. Tree Pruning. Shigo and Trees Associates, Durham, New Hampshire. 186 pp.
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Arboriculture & Urban Forestry (AUF)
Vol. 17, Issue 8
August 1991
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Branch Pruning Wound Closure
Dan Neely
Arboriculture & Urban Forestry (AUF) Aug 1991, 17 (8) 205-208; DOI: 10.48044/jauf.1991.049

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Branch Pruning Wound Closure
Dan Neely
Arboriculture & Urban Forestry (AUF) Aug 1991, 17 (8) 205-208; DOI: 10.48044/jauf.1991.049
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