Arboriculture & Urban Forestry 35(1): January 2009 25 before removal of ash trees from emerald ash borer. Arboriculture and Urban Forestry 34:47–53. McPherson, E.G. 2000. Expenditures associated with conflicts between street trees root growth and hardscape in California. Journal of Arboriculture 26:289–297. McPherson, E.G., and P. Peper. 1995. Infrastructure repair costs associated with street trees in 15 cities. In: Watson, G.W., and D. Neely (Eds.). Trees and Building Sites: Proceedings of an International Workshop on Trees and Buildings. International Society of Arboriculture, Champaign, IL. Peper, P.J., and P.A. Barker. 1994. A buyer’s guide to root barriers, pp. 186–193. In: Watson, G.W., and D. Neely (Eds.). The Landscape Below Ground: Proceedings of an International Workshop on Tree Root Development in Urban Soils. International Society of Arboriculture, Champaign IL. Smiley, E.T. 2005. Root growth near vertical root barriers. Journal of Arboriculture 31:150–152. Figure 5. The number of large-diameter roots (greater than 10 mm [0.4 in]) that grew over the top of root barriers. Mean differences were not significant. DISCUSSION Root barriers have been found to be effective at altering root growth patterns under pavement (Gilman 1996; Smiley 2005, 2008). All five root barriers in this study significantly changed the growth patterns of the willow oak roots. Root growth in the area where a sidewalk would be located was greatly reduced compared with the control trees. Instead of growing horizontally outward, roots on the treated trees were directed underneath the barrier. This diver- sion of root growth resulted in fewer roots growing beyond the barrier as compared with the unimpeded control roots. In the 2002 harvest of roots, the DeepRoot Universal barrier appeared to be more efficient at redirecting growth below the bar- rier and the chemically treated barriers were more effective at sup- pressing root growth below the barriers (Smiley 2005). However, in the 2007 harvest, these differences were not apparent. In this study, there were no significant underground root growth differ- ences among any of the root barrier treatments. Roots growing over the top of barriers can cause significant damage to pavement (Smiley 2008). There were no significant differences in root overgrowth among the products tested. It is important that when installing barriers, the top of the barrier is above grade and that this portion of the barrier remains free of mulch and soil that would allow root overgrowth. LITERATURE CITED Barker, P.A., and P. Peper. 1995. Strategies to prevent damage to side- walks by tree roots. Arboricultural Journal 19:295–309. Costello, L.R., C.L. Elmore, and S. Steinmaus. 1997. Tree root response to circling root barriers. Journal of Arboriculture 23:211–218. Costello, L.R., and K.S. Jones. 2003. Reducing Infrastructure Damage by Tree Roots: A Compendium of Strategies. International Society of Arboriculture, Cohasset, CA. 119 pp. D’Amato, N.E., T.D. Sydnor, M. Knee, R. Hunt, and B. Bishop. 2002. Which comes first, the root or the crack? Journal of Arboriculture 28:277–289. Gilman, E.F. 1996. Root barriers affect root distribution. Journal of Arboriculture 22:151–154. ———. 2006. Deflecting roots near sidewalks. Arboriculture and Urban Forestry 32:18–22. Heimlich, J., T.D. Sydnor, M. Bumgardener, and P. O’Brien. 2008. Attitudes of residents toward street trees on four streets in Toledo, Ohio, ———. 2008. Comparison of methods to reduce sidewalk damage from tree roots. Arboriculture and Urban Forestry 34:179–183. Smiley, E.T., A. Key, and C. Greco. 2000. Root barriers and windthrow potential. Journal of Arboriculture 26:213–217. Wagar, J.A. 1985. Reducing surface rooting of trees with control planters and wells. Journal of Arboriculture 11:165–171. Wagar, J.A., and P.A. Barker. 1983. Tree root damage to sidewalks and curbs. Journal of Arboriculture 9:177–181. E. Thomas Smiley (corresponding author) Bartlett Tree Research Laboratory 13768 Hamilton Road Charlotte, NC 28278, U.S.
[email protected] Liza Wilkinson Bartlett Tree Research Laboratory 13768 Hamilton Road Charlotte, NC 28278, U.S. Bruce R. Fraedrich Bartlett Tree Research Laboratory 13768 Hamilton Road Charlotte, NC 28278, U.S. Résumé. Les barrières racinaires verticales sont utilisées pour rediriger la croissance des racines vers de plus grandes profon- deurs dans le sol ce qui permet de diminuer les dommages aux trottoirs. Cette étude a été menée pour examiner les patrons de développement des racines à proximité d’une variété de barrières racinaires. Trente chênes-saules ( Quercus phellos ) ont été plantés en novembre 2000 et l’un des dispositifs suivants a été installé sur deux côtés de chacun des arbres: Biobarrier, DeepRoot Universal Barrier, DeepRoot Uninversal Barrier avec Spin Out, Tex-R, Geotextile Typar 3801, et aucune barrière comme groupe témoin. En mars 2007, le second bloc de 15 arbres a été excavé afin de révéler le système racinaire au-delà de la barrière. Les cinq bar- rières ont permis de diminuer significativement la quantité de racines ayant poussé comparativement aux arbres du groupe- témoin. Il n’y avait pas de différence significative entre les dif- férents produits testés. Zusammenfassung. Vertikale Wurzelbarrieren werden ver- wendet, um das Wurzelwachstum umzulenken in tiefere Boden- schichten und damit den Schaden an Pflasterungen zu reduzieren. Dreisig Quercus phellus-Bäume wurden im November 2000 und jeweils eins der folgenden Behandlungen wurde beidseitig ©2009 International Society of Arboriculture
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