18 Gilman et al.: Effects of Pruning Dose and Type may be a bit less effective than other pruning types at reducing motion in strong tropical storm force wind speeds. These data indicate that it could require a lower wind speed to damage thinned trees along the portion of the trunk below the crown than trees pruned in other fashions. Effects of wind gustiness, quick change of directions, and other wind characteristics of a natural system that we did not measure in this study need to be tested in subsequent studies. It may not be wise to extrapolate these re- sults to larger trees using the trees tested here to represent branches or parts of a larger structure. Further testing is required to determine the effect of pruning on the aeromechanical behav- ior of individual branches when they are coupled as a continuous dynamic structure. This will be challenging. Figure 3. Predicted (from models in Table 1) trunk movement (averaged across pruning types) at increasing wind speed for five pruning doses. Interaction between pruning dose and wind speed was significant at P < 0.0001. The vertical axis is the least square means of trunk movement 137 cm (54.8 in) above the top-most root adjusted using Tukey’s method. Lines represent different pruning doses: circles = 0% foliage dry mass removed, triangles = 15%, squares = 30%, diamonds = 45%, and Xs = 60%. although as discussed previously, this effect may have been insignificant. We measured pruning dose as a percent of foliage dry weight removed because foliage is the crux of the ANSI standard. Mea- sured foliage removed [on those trees not subjected to geometric dictation of foliage removal (i.e., those not in the original blocks)] corresponded to targeted (estimated) foliage removed better on lower pruning doses (targeted 15%, measured 17.9%; targeted30%, measured35.9%) than at the largest dose (targeted45%, measured52.8%). This provides some comfort to arborists attempting to visually estimate pruning dos- age, although Smiley and Kane’s (2006) visual estimates of per- cent crown removed appeared to vary from actual measurements more than ours. Trees generally moved similarly in the wind regardless of ANSI pruning type applied. Our results indicate that thinning Table 3. Least squares means of predicted trunk movement by pruning type and wind speed. Trunk movement [cm (in)] 1.4 m (54 in) above topmost rootz Pruning typey ST RA LT RE TH 6.7 m/s (15 mph)x NS NS NS NS NS 13.4 m/s (30 mph) NS NS NS NS NS ST structural; TH thinning. x Means in a column with different letters are significantly different (P < 0.001) from each other. NS not significant; there were no differences within that column. w ©2008 International Society of Arboriculture 20.1 m/s (45 mph) 3.3 (1.31) aw 3.8 (1.50) a 3.8 (1.51) a 4.5 (1.77) ab 5.3 (2.07) b 26.8 m/s (60 mph) 5.3 (2.05) a 5.7 (2.25) a 6.1 (2.39) a 6.9 (2.70) a 8.4 (3.32) b zAverage trunk movement predicted from regression models in Table 1. yPruning types: LT lion’s tailing; RA raising; RE reducing; Wind speed at which trunk movement was predicted from regression models. Acknowledgments. Partial funding for this work was supported by the TREE Fund and Marshall Tree Farm, Morriston, Florida. LITERATURE CITED American National Standards Institute. 2001. American National Stan- dard for Tree Care Operations—Tree, Shrub and Other Woody Plant Maintenance—Standard Practices (Pruning) (A300, Part 1). Tree Care Industry Association, Manchester, NH. Duryea, M.L., G.M. Blakeslee, W.G. Hubbard, and R.A. Vasquez. 1996. Wind and trees: A survey of homeowners after Hurricane Andrew. Journal of Arboriculture 22:44–50. Gilman, E.F. 2002. An Illustrated Guide to Pruning, 2nd edition. Delmar Publishers, Albany, NY. Gilman, E.F., and S.J. Lilly. 2002. Best Management Practices: Tree Pruning. International Society of Arboriculture, Champaign, IL. Grant, P.F., and W.G. Nickling. 1998. Direct measurement of wind drag on vegetation for application to windbreak design and modeling. Land Degradation and Development 9:57–66. Harris, R.W., J.R. Clark, and N.P. Matheny. 2004. Arboriculture: Inte- grated Management of Landscape Trees, Shrubs, and Vines, 4th edi- tion. Prentice Hall, Upper Saddle River, NJ. Hoag, D.L., R.B. Fridley, and J.R. Hutchinson. 1971. Experimental measurement of internal and external damping properties of tree limbs. Transactions of the American Society of Agricultural Engi- neers 14:20–28. Jones, S. 2005. Effect of pruning type, pruning dose, and wind speed on tree response to wind load. Master’s thesis, University of Florida. Leiser, A.T., and J.D. Kemper. 1973. Analysis of stress distribution in the sapling tree trunk. Journal of the American Society for Horticul- tural Science 98:164–170. Matheny, N.P., and J.R. Clark. 1994. A Photographic Guide to the Evaluation of Hazard Trees in Urban Areas, 2nd edition. International Society of Arboriculture, Urbana, IL. Mattheck, C., and H. Breloer. 1994. The Body Language of Trees: A Handbook for Failure Analysis. Department of the Environment, Transport and the Regions, London, U.K. Mayhead, G.J. 1973. Some drag coefficients for British forest trees derived from wind tunnel studies. Agricultural and Forest Meteorol- ogy 12:123–130. Moore, J.R., and D.A. Maguire. 2005. Natural sway frequencies and damping ratios of trees: Influence of crown structure. Trees— Structure and Function 19:363–373.
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