Arboriculture & Urban Forestry 34(1): January 2008 Arboriculture & Urban Forestry 2008. 34(1):13–19. 13 Effects of Pruning Dose and Type on Trunk Movement in Tropical Storm Winds Edward F. Gilman, Jason C. Grabosky, Scott Jones, and Chris Harchick Abstract. We built a machine with a propeller capable of generating 33.5 m/s (75 mph) winds to determine the influence of pruning dose and American National Standards Institute A300 pruning type on trunk movement of Quercus virginiana ‘QVTIA’ PP #11219, Highrise at various wind speeds. Trunk movement was regressed against wind speeds and pruning doses for each tree tested. Increasing wind speed increased trunk movement, and the magnitude of the increase depended on pruning dose and pruning type. Increasing pruning dose reduced trunk movement and the magnitude of the reduction was greater at higher wind speeds. The predicted trunk movement of thinned trees was statistically greater than movement of structurally pruned, raised, and lion’s tailed trees at wind speeds of 20.1 m/s (45 mph) and was greater than all pruning types at 26.8 m/s (60 mph). There was no difference in movement among reduced, raised, structurally pruned, and lion’s tailed trees; and there were no statistical differences in trunk movement among pruning types at the lower wind speeds. We found that thinning the outer edge of the crown was one of the least effective pruning types for reducing trunk movement in wind. Key Words. Crown raising; crown reduction; crown thinning; lion’s tailing; pruning dose; pruning type; structural pruning; wind. Mattheck and Breloer (1994) speculated that pruning can reduce damage from winds because it reduced the surface area of the tree crown, but Mayhead (1973) and others found mass to be a better predictor of drag than crown area. Duryea et al. (1996) noted that pruned trees withstood wind damage from Hurri- cane Andrew better than their unpruned counterparts; unfortu- nately, the pruning type or amount was not identified so inter- pretation is impossible. Ham and Rowe (pers. comm.) thought that despite losing over 4,800 street trees, damage to the city of Charlotte, North Carolina, U.S. from Hurricane Hugo was lessened by a program of routine maintenance, including prun- ing. Pruning is recommended as a means of reducing wind dam- age to trees (Matheny and Clark 1994; Gilman 2002; Harris et al. 2004). Research supporting recommendations for pruning trees to reduce wind damage is almost nonexistent in the primary literature. Moore and Maguire (2005) mention that the natural frequency and damping ratio of Douglas fir trees was not affected by re- moving low branches (crown raising) until more than 66% of the crown was removed. This may be attributable to mass damping and foliage drag in the lower crown and higher wind velocities at higher elevations. Rudnicki et al. (2004) and Vollsinger et al. (2005) reported that pruning did not influence streamlining (drag coefficients) in the coniferous or hardwood species tested. How- ever, they noted that their test specimens were small so the effect of streamlining was difficult to defend. One of the most recent studies showed that crown reduction reduced drag per unit mass removed about the same as crown thinning in wind speeds up to 20.1 m/s (45 mph) on Acer rubrum saplings (Smiley and Kane 2006). Increasing porosity in a conifer-shaped crown by thinning also predictably reduced drag (Hoag et al. 1971). The American National Standards Institute (ANSI; 2001) rec- ommends limits to pruning as defined by a percent of foliage removed within one growing season. However, ANSI provides no information about how to quantify the percent of foliage removed. Other resources refer back to the ANSI pruning stan- dard on questions of dose (Gilman and Lilly 2002). They also advise the practitioner to quantify pruning dose based on the desired objective or the appearance of the tree after pruning (Waring et al. 1982). Thus, the measurement of pruning dose by practitioners is largely qualitative and subjective, and there is no published measurement of the accuracy of visual estimates. The objective of this study was to determine the influence of pruning dose and pruning type on trunk movement at various wind speeds of tropical storm force velocity. Trunk move- ment below the bottom of the crown was used to evaluate prun- ing and wind effects because, everything else being equal, trunk deflection should be related to failure potential along this portion of the trunk. MATERIALS AND METHODS Trees Trees (clonal, cutting-propagated live oak trees, Quercus virgi- niana ‘QVTIA’ PP #11219, Highrise) were selected for physi- cal similarities described subsequently from trees at Marshall Tree Farm (Morriston, FL), U.S. Department of Agriculture (USDA) hardiness zone 8a. Wood properties vary very little among trees within a clone (Mosedale et al. 1996). Marshall Tree Farm (MTF) planted the trees from #5 containers [25 cm (10 in) wide at the top × 30 cm (12 in) deep] into Orlando fine sand or Sparr fine sand in June 2000. Trees were dug and placed in wire baskets January 2003. In May 2003, the following tree physical characteristics were evaluated from 50 trees: trunk diameter (caliper) 15 cm (6 in) from the ground; distance between top-most root and the lowest branch, total crown height (TCH) determined by measuring maximum height (distance from top of rootball to top of the crown), minimum height (distance from top of rootball to origin ©2008 International Society of Arboriculture
January 2008
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
