38 Smiley and Kane: Effects of Pruning Type on Wind Loading branch failure when decay is present (Matheny and Clark 1994), further investigations must be conducted to deter- mine whether reduction pruning is more effective at reducing the risk of tree failure than thinning. Additional studies are under way that incorporate larger trees and higher wind velocities. These studies are necessary in light of Mayhead (1973), who noted that trees shorter than 3.5 m (11.6 ft) were morphologically different from larger trees, and this difference affects how much trees bend under wind load. A study modeling failure of loblolly pine (Pinus taeda) did not detect differences among treatments to reduce tree mortality until wind velocity exceeded 40 m/sec (89.5 mph) (Hedden et al. 1995). The current study nevertheless provides a baseline for much-needed data on this important aspect of arboriculture and urban forestry. Compared with the same trees prior to pruning, the center of pressure height was significantly lowered on thinned and reduced trees, while the center of pressure height did not change on lion-tailed trees. Lion tailing has been discredited as a viable pruning technique because of its adverse physiological consequences and tendency to reduce branch taper over time (Lilly 2001; Gilman and Lilly 2002). Poor taper has been suggested as a likely cause of stem failure from wind (Cremer et al. 1982; Putz et al. 1983; Petty and Swain 1985) and snow loading (Petty and Worrell 1981). This study makes the point that for the amount of foliage removed, lion tailing is not a good method of reducing the effects of wind. LITERATURE CITED American National Standards Institute. 2001. American National Standard for Tree Care Operations—Tree, Shrub, and Other Woody Plant Maintenance—Standard Practices (Pruning) (A300, Part 1). Tree Care Industry Association, Manchester, NH. 9 pp. Baker, C.J. 1997. Measurements of the natural frequencies of trees. Journal of Experimental Botany 48(310):1125–1132. Baker, C.J., and H.J. Bell. 1992. The aerodynamics of urban trees. Journal of Wind Engineering and Industrial Aerodynamics 41–44(1992):2655–2666. Ball, J. 2003. Topics in Plant Health Care: The role of pruning. Arborist News 12(2):13–14. Beer, F.P., and E.R. Johnston. 1988. Vector Mechanics for Engineers: Static (5th ed.). McGraw-Hill, New York, NY. 472 pp. Bertram, J.E.A. 1989. Size-dependent differential scaling in branches: The mechanical design of trees revisited. Trees 4:241–253. Cannell, M., and M. Coutts. 1988. Growing in the wind. New Scientist 21:42–46. ©2006 International Society of Arboriculture Cremer, K.W., C.J. Borough, P.H. McKinnel, and P.R. Carter. 1982. Effects of stocking and thinning on wind damage in plantations. New Zealand Journal of Forest Science 12(2):244–265. Fraser, A.I. 1962. Wind tunnel studies of the forces acting on the crowns of small trees. Report on Forest Research. HMSO, London, UK. pp. 178–183. Gardiner, B.A., and C.P. Quine. 2000. Management of forests to reduce the risk of abiotic damage—A review with particular reference to the effects of strong winds. Forest Ecology and Management 135:261–277. Gilman, E.F. 1997. An Illustrated Guide to Pruning. Delmar, New York, NY. 178 pp. Gilman, E.F., and S.J. Lilly. 2002. Best Management Practices: Tree Pruning. International Society of Arboriculture. Champaign, IL. 35 pp. Hedden, R.L., T.S. Fredericksen, and S.A. Williams. 1995. Modeling the effect of crown shedding and streamlining on the survival of loblolly pine exposed to acute wind. Canadian Journal of Forest Research 25:704–712. King, D.A. 1986. Tree form: Height growth, and susceptibility to wind damage in Acer saccharum. Ecology 67:980–990. King, D.A., and O.L. Loucks. 1978. The theory of tree bole and branch form. Radiation and Environmental Biophysics15:141–165. Landsberg, J.J., and G.B. James. 1971. Wind profiles in plant canopies: Studies on an analytical model. Journal of Applied Ecology 8(2):729–741. [tom: Landsberg and James 1971 not cited in article] Lilly, S.J. 2001. Arborists’ Certification Study Guide. International Society of Arboriculture. Champaign IL. 222 pp. Marini, R.P. 1999. Are nonsignificant differences really not significant? HortScience 34(5):761–762. Matheny, N.P., and J.R. Clark. 1994. A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas (2nd ed.). International Society of Arboriculture. Champaign, IL. 85 pp. Mayhead, G.J. 1973. Some drag coefficients for British trees derived from wind tunnel studies. Agricultural Meteorology 12:123–130. Mayhead, G.J., J.B.H. Gardiner, and D.W. Durrant. 1975. A Report on the Physical Properties of Conifers in Relation to Plantation Stability. Forestry Commission Research and Development Division, Roslin, Midlothian, UK. 39 pp. Moore, J.R., and D.A. Maguire. 2001. The mechanics of trees under wind loading. In Smiley, E.T., and K.D. Coder (Eds.). Tree Structure and Mechanics Conference Proceedings: How Trees Stand Up and Fall Down. International Society of Arboriculture, Champaign, IL. 184 pp.
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