Arboriculture & Urban Forestry 34(2): March 2008 many species cannot tolerate cutting close to the trunk (Hamilton 1998). A one-third reduction in force was found with 50% root re- moval and a linear tangential root cut at the trunk. This may indicate that trenching tends to cut more of the oblique roots and that roots directly opposite the force are far more important to stability than those perpendicular to the direction of force. Under dynamic wind conditions, in which wind intensity and direction may change rapidly, the impact of 50% root removal would be expected to be greater than a one-sided linear root cut near the trunk. The dynamic osculation of the wind forces are known to cause a progressive failure at lower wind velocities (O’Sullivan and Ritchie 1993; James et al. 2006) Cutting large-diameter roots may make the root more suscep- tible to root decay. The maximum size root that can be cut that will not readily decay has yet to be determined. It is possible that cutting roots at a distance of three times the trunk diameter makes the roots more susceptible to decay than cutting roots at a greater distance. Therefore, to be safe when linear root cuts are made, cuts should be at the greatest distance possible from the trunk. Caution should be exercised in extrapolating these findings to large trees in urban areas. These results are only on one species and the trees were relatively small. More research is needed to see if the conclusions presented here will hold up for other species and larger trees. More information is also needed on the forces that wind exerts on the tree so that pull forces could be correlated with wind speed. Acknowledgments. Thanks to Robert A. Bartlett Jr. and the F.A. Bart- lett Tree Expert Co. for their continuing support of tree care research and Dr. Bruce Fraedrich, Director of the Bartlett Tree Research Laboratories. For conducting these experiments: Liza Wilkinson, Research Techni- cian; Richard Herfurth, Safety and Training Coordinator Hookset NH; Drew Zwart, Plant Diagnostician; Eric Honeycutt, Manager Plant Diag- nostic Laboratory, Bartlett Tree Research Lab. Technical assistance from Dr. Brian Kane, University of Massachusetts and manuscript ed- iting by Dr. Jim Clark, HortScience. Drawings by Renee Byrd, Clemson University. LITERATURE CITED Brudi, E., and P. van Wassenaer. 2002. Trees and statics: Nondestructive failure analysis. In Smiley, E.T., and K.D. Coder (Eds.). Tree Struc- ture and Mechanics Conference Proceedings. International Society of Arboriculture, Champaign, IL. 184 pp. Busgen, M., E. Munch, and T. Thomas. 1929. The Structure and Life of Forest Trees. Chapman and Hall, London, U.K. Coutts, M.P. 1983. Root architecture and tree stability. Plant and Soil 71:171–188. Crook, M.J., and A.R. Ennos. 1996. The anchorage mechanics of deep rooted larch, Larix europea × L. japonica. Journal of Experimental Botany 47:1509–1517. Dupuy, L., T. Fourcaud, and A. Stokes. 2005a. A numerical investiga- tion into factors affecting the anchorage of roots in tension. European Journal of Soil Science 56:319–327. ———. 2005b. A numerical investigation into the influence of soil type and root architecture on tree anchorage. Plant and Soil 278:119–134. Ennos, A.R. 1993. The scaling of root anchorage. Journal of Theoretical Biology 161:61–75. Fraedrich, B.R., and E.T. Smiley. 2002. Assessing the failure potential of tree roots. In Smiley, E.T., and K.D. Coder (Eds.). Tree Structure and Mechanics Conference Proceedings. International Society of Ar- boriculture, Champaign, IL. 184 pp. 127 Genet, M., A. Stokes, F. Salin, S.B. Mickovski, T. Fourcaud, J.F. Du- mail, and R. van Beek. 2005. The influence of cellulose content on tensile strength in tree roots. Plant and Soil 278:1–9. Hamilton, W.D. 1988. Significance of root severance on performance of established trees. Journal of Arboriculture 14:288–292. Harris, R.W., J.R. Clark, and N.P. Matheny. 2004. Arboriculture Inte- grated Management of Landscape Trees, Shrubs and Vines. Prentice Hall, Upper Saddle River, NJ. 580 pp. ITFD. 2007. International Tree Failure Database web site. http:// ftcweb.fs.fed.us/natfdb/reports.aspx (accessed 4/3/2007). James, K.R., N. Haritos, and P.K. Ades. 2006. Mechanical stability of trees under dynamic loads. American Journal of Botany 93: 1361–1369. Matheny, N.P., and J.R. Clark. 1994. A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas. International Society of Arboriculture, Champaign, IL. 85 pp. Mattheck, C., and H. Breloer. 1994. The Body Language of Trees. The Stationary Office, Norwich, U.K. 239 pp. Mattheck, C., M. Teschner, and J. Schafer. 1997. Mechanical control of root growth: A computer simulation. Journal of Theoretical Biology 184:261–269. Mickovski, S.B., and A.R. Ennos. 2003. Anchorage and asymmetry in the root system of Pinus peuce. Silva Fennica 37:161–173. Mickovski, S.B., and R.A. Ennos. 2002. A morphological and mechani- cal study of the root system of suppressed crown Scots pine. Trees— Structure and Function 16:274–280. Miller, F.D., and D. Neely. 1993. The effect of trenching on growth and plant health of selected species of shade trees. Journal of Arboricul- ture 19:226–229. O’Sullivan, M.F., and R.M. Ritchie. 1993. Tree stability in relation to cyclic loading. Forestry. 66:69–82. Smiley, E.T. 2005. Root growth near vertical root barriers. Journal of Arboriculture 31:150–152. Smiley, E.T., B.R. Fraedrich, and N. Hendrickson. 2002. Tree Risk Management. Bartlett Tree Expert Co., Charlotte, NC. 44 pp. Smiley, E.T., A. Key, and C. Greco. 2000. Root barriers and windthrow potential. Journal of Arboriculture 26:213–217. Smiley, E.T., T.R. Martin, and B.R. Fraedrich. 1998. Tree root failures. In Neely, D., and G.W. Watson (Eds.). The Landscape Below Ground II. Proceedings of an International Workshop on the Tree Root De- velopment in Urban Soils. International Society of Arboriculture, Champaign, IL. 265 pp. Stokes, A. 1999. Strain distribution during anchorage failure of Pinus pinaster at different ages and tree growth response to wind-induced root movement. Plant and Soil 217:17–27. Stokes, A., J. Ball, A.H. Fitter, P. Brain, and M.P. Coutts. 1996. An experimental investigation of the resistance of model root systems to uprooting. Annals of Botany 78:415–421. Stokes, A., and C. Mattheck. 1996. Variation of wood strength in tree roots. Journal of Experimental Botany 47:693–699. Watson, G.W. 1988. Tree growth after trenching and compensatory crown pruning. Journal of Arboriculture 24:47–53. E. Thomas Smiley Arboriculture Researcher Bartlett Tree Research Laboratory 13768 Hamilton Road Charlotte, NC 28278, U.S.
[email protected] Résumé. Le but de cette étude était d’examiner deux types de taille des racines et de déterminer l’impact de la perte en racines sur la stabilité de l’arbre. Les troncs des arbres ont été tirés à un angle de 1° de la verticale au moyen d’une force mesurée. Un tiers des arbres étudiés ont été tirés jusqu’au point de rupture afin de déterminer une corrélation ©2008 International Society of Arboriculture
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