220 pull). None of the Terra Toggle™Earth Anchors came out of the ground during testing and the polypropylene strapping never broke. The strapping would usually slice into the lumber sup- ports approximately 1.27 cm (0.5 in), preventing it from sliding off the top of the wood. Occasionally, as tension on the straps increased, a lumber support would become displaced and the strapping would cut into the root ball. This did not appear to impact the strength of the system. Brooks Tree Brace in direction 2 (Figure 1) broke all five trees at the same spot just above the rubber pads. Brooks Tree Brace in direction 1 (Figure 1) was also unique; as the tree was being pulled, the front two braces in the direction of pull acted as lever arms because they were tightly secured around the trunk and began to lift the root ball out of the ground. The root ball remained aboveground level even after the tension from the pull- ing rope was removed. Brooks Tree Brace firmly secured the trunk allowing minimal movement, which has been shown to negatively impact tree height (Leiser et al. 1972; Mayhead and Jenkins 1992), taper (Svihra et al. 1999), and root growth (Stokes et al. 1995), at least in the short term. The 2 × 2’s in direction 1 (Figure 1) broke two trees approxi- mately 15.2 cm (6.1 in) from ground level. The most common mode of failure for 2 × 2’s in direction 1 was when the vertical braces were forced up on the tension side (opposite direction of pull) as the root ball rotated. This reduced the amount of down- ward force applied to the top of the root ball, allowing it to rotate more freely. The 2 × 2’s in direction 2 (Figure 1) failed on three trees when the horizontal brace on the side of the direction of pull broke as the trunk of the tree bent dramatically and was forced down into the lumber. Breakage of the horizontal piece probably accounted for the increased variability in maximum force among the ten replicates (as shown by the greatest coeffi- cient of variation; Table 2) because maximum force occurred after the lumber broke. The Tree Staple™, dowels, and T-stakes had relatively low force to failure values. The Tree Staple™could be improved by increasing the number of Tree Staples™that are used so that all sides of the tree are supported equally. The T-stake stabilization system could be improved by using longer (2.5 m [8.3 ft] or greater) stakes so that more of the support was in the ground. T-stakes could also be replaced with lodgepole pine or other polls for added rigidity. The low force to failure for dowels was the result of the root ball rotating toward the direction of pull and easily slipped off the wood dowels. This slipping might be re- duced by increasing the diameter of the dowels (2.5 cm [1 in] or greater), using rebar instead of dowels, and/or perhaps by fixing a flange on the end of the dowel on top of the root ball. Direction of pull and system design both influenced the pat- tern of system failure. Of the three best systems tested, Brooks Tree Brace took the least amount of time and effort to install but was also the most expensive, the Terra Toggle™ was the least expensive but the recommended installation method re- quired a water source to drive the anchors, and lastly, the 2 × 2’s could be made “in-house” but installation was the most labor- intensive (Eckstein 2007). The rebar and ArborTie, Duckbill, and ArborBrace guying systems were similar considering cost and their effectiveness relative to the other systems tested, and installation was time-consuming but not labor-intensive. The wood dowels, T-stakes, and Tree Staple™ were among the sys- tems that required the least amount of effort to install and, prob- ably not coincidentally, the three least effective systems. Apple- ©2008 International Society of Arboriculture Eckstein and Gilman: Landscape Tree Stabilization Systems ton’s (2004) work showed that aboveground systems can dam- age the trunk at the attachment point, which, combined with our results, suggests that rootball anchoring systems are the most effective tree stabilization systems. Future testing should cali- brate force to failure with wind speeds, giving a better under- standing of the effectiveness of the stabilization systems. Acknowledgment. We thank the TREE Fund and the Great Southern Tree Confer- ence for partial funding for this project. LITERATURE CITED Appleton, B.L. 2004. Tree stabilization at installation. SNA Research Conference 49:437–440. Burger, D.W., G.W. Forister, and P.A. Kiehl. 1996. Height, caliper growth, and biomass response of ten shade tree species to treeshel- ters. Journal of Arboriculture 22:161–166. Burger, D.W., P. Svihra, and R.W. Harris. 1991. Tree shelter use in producing container-grown trees. HortScience 27:30–32. Eckstein, R. Evaluation of landscape tree stabilization systems in simu- lated wind. University of Florida, Gainesville, Master’s Thesis. Gilman, E.F. 2006. Effect of planting depth on Cathedral Oak growth and quality in containers. University of Florida Great Southern Tree Conference 2006 Research Report, Gainesville, FL. Harris, R., A.T. Leiser, and W.B. Davis. 1976. Staking Landscape Trees. University of California Agricultural Extension leaflet 2576. Leiser, A.T., R. Harris, P. Neel, D. Long, N. Stice, and R. Maire. 1972. Staking and pruning influence trunk development of young trees. Journal of the American Society for Horticultural Science 97: 498–503. Leiser, A.T., and J.D. Kemper. 1968. A theoretical analysis of a critical height of staking landscape trees. American Society for Horticultural Science 92:713–720. Mayhead, G.J., and T. Jenkins. 1992. Growth of young Sitka Spruce [Picea sitchensis (Bong) Carr] and the effect of simulated browsing, staking, and treeshelters. Forestry 65:453–462. Niklas, K.J., and H.C. Spatz. 2000. Wind-induced stresses in cherry trees: Evidence against the hypothesis of constant stress levels. Trees (Berlin) 14:230–237. Peltola, H., S. Kellomaki, A. Hassinen, and M. Granander. 2000. Me- chanical stability of Scots pine, Norway spruce and birch: An analy- sis of tree-pulling experiments in Finland. Forest Ecology and Man- agement 135:143–153. Peltola, H., S. Kellomaki, A. Hassinen, M. Lemettinen, and J. Aho. 1993. Swaying of trees as caused by wind: Analysis of field mea- surements. Silva Fennica 27:113–126. Smiley, E.T., E. LeBrun, and E. Gilbert. 2003. Evaluation of extraction force for wooden guy anchors. Journal of Arboriculture 29:295–297. Stokes, A., A.H. Fitter, and M.P. Coutts. 1995. Responses of young trees to wind and shading: Effects on root architecture. Journal of Experi- mental Botany 46:1139–1146. Svihra, P., D. Burger, and D. Ellis. 1999. Effects of 3 trunk support systems on growth of young Pyrus calleryana trees. Journal of Ar- boriculture 25:319–324. Ryan Eckstein 1533 Fifield Hall Gainesville, FL 32611, U.S.
[email protected] Edward F. Gilman (corresponding author) 1533 Fifield Hall Gainesville, FL 32611, U.S.
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