Arboriculture & Urban Forestry 33(5): September 2007 365 the remaining branches at the next harvest interval for a shape analysis to further define these response effects. The data would suggest that the anatomic changes at branch attachments (Sachs and Cohen 1982; Lev-Yadun and Aloni 1990), the concept of a branch protection zone (BPZ) (Gilman 2002) and the associated concept of hydraulic seg- mentation of the tree stem to branch (Tyree et al. 1993), which governs the natural target pruning approach (Shigo 1983) in removal pruning cuts, may also play a role in re- duction pruning. The role of the internal BPZ architecture is twofold. Much as the BPZ is thought to limit ingress of decay from a removal cut, this internal structure would impact the attenuation of a discoloration zone downward from a reduc- tion cut, thus potentially limiting discoloration depth. The ability to restrict flow into the branch may also influence the nature of discoloration and decay from trunk to branch if lateral spread of decay moves below the BPZ and into the hydraulic flow column of the remaining lateral branch (de- fined here as column jump), then moving upward along the pith of the lateral branch assuming the terminal leader. This column jump was observed in seven shumard oak sites and one live oak site. Column jump occurrence was not related to any parameter in the study. If the suggested role of the BPZ in limiting reduction cut discoloration is accepted for the purpose of this study, several responses fall into place. The trunk–branch dimensioning re- lationships related to BPZ presence and hydraulic segmenta- tion should follow the relationships observed in this study. Morphologic indicators such as aspect ratio and branch col- lars as well as the section views of the discoloration zones collaborate earlier data on the same field of live oak (Eisner 2001; Eisner et al. 2002) for hydraulic partitioning through the branch connection zone. Discoloration from removal cuts branch to stem were limited by a BPZ and in a similar manner hydraulic segmented in flow stem to branch. Three- dimensional sectioning of the remaining reduction cuts will attempt to better define and clarify the nature of decay es- tablishment in these species. The data do not provide any explicit validation for the current preferred target angle of reduction pruning cut. Angle of dieback was associated with the actual cut angle in both species and had little if any influence on tree growth response or discoloration. It is noteworthy, however, that discoloration in the less efficient compartmentalizing species (shumard oak) was related to cut surface, but not to cut angle, so a crosscut perpendicular to the growth axis, minimizing cut surface, may be preferred over the angle bisect method for the that species in this study. There was no relationship between aspect ratio and discol- oration in the 3 years after pruning. The data suggest that reduction cuts can be made back to lateral branches as small as one-third the diameter of the removed stem. Acknowledgments. We thank Scott Jones and Nathan Eisner for their assis- tance in data collection while graduate students at the University of Florida. We also thank Chris Harchick, research field manager at University of Florida, for his work maintaining the site, coordinating labor, and data collection assistance. Partial funding of this project from The Great Southern Tree Conference and the TREE Fund. LITERATURE CITED ANSI (American National Standards Institute). 2001. ANSI A300 (part 1)—2001 American National Standard for tree care operations standard Practices (Pruning). New York, ANSI. Bauch, J., A.L. Shigo, and M. Starck. 1980. Wound effects in the xylem of Acer and Betula species. Holzforschung 34: 153–160. Duchnesne, L.C., M. Hubbes, and R.S. Jeng. 1992. Biochem- istry and molecular biology of defense reactions in the xylem of angiosperm trees. In Defense Mechanisms of Woody Plants Against Fungi. Biggs, A.R., Ed. Berlin, Springer-Verlag. 458 pp. Eisner, N.J. 2001. The effect of branch junction morphol- ogy on tree wound compartmentalization and hy- draulic segmentation. MS Thesis. University of Florida. 74 pp. Eisner, N.J., E.F. Gilman, and J.C. Grabosky. 2002. Branch morphology impacts compartmentalization of pruning wounds. Journal of Arboriculture 28:99–105. Gilman, E.F. 2002. An Illustrated Guide to Pruning. 2nd ed. Albany, NY, Delmar Publishing. 330 pp. Gilman, E.F., R.J. Black, and B. Dehgan. 1998. Irrigation volume and frequency and tree size affect establishment rate. Journal of Arboriculture 24:1–9. Gilman, E.F., and S. Lilly. 2002. Best management practices: Tree pruning. Champaigne, IL, International Society of Arboriculture. 35 pp. Harris, R.W., J.R. Clark, and N.P. Matheny. 2004. Arbori- culture: Integrated Management of Landscape Trees, Shrubs, and Vines. 4th ed. Upper Saddle River, NJ, Prentice-Hall. 579 pp. Lev-Yadun, S., and R. Aloni. 1990. Vascular differentiation in branch junction: circular patterns and functional sig- nificance. Trees 4:49–54. Sachs, T., and D. Cohen. 1982. Circular vessels and the con- trol of vascular differentiation in plants. Differentiation 21:22–26. Santamour, F.S. 1979. Inheritance of wound compartmental- ization in soft maples. Journal of Arboriculture 5: 220–225. Schwarze, F.W.M.R., J. Engels, and C. Mattheck. 2000. Fungal strategies of wood decay in trees (translated by Linnard, W.). Berlin, Springer. 185 pp. ©2007 International Society of Arboriculture
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