26 Gilman et al.: Pruning Affects Tree Movement in Hurricanes flexible reconfigured crown that appeared to move more or less as a single mass in the wind. This could have protected many leaves from direct wind exposure such as occurs in a nonthinned forest (Gardiner et al. 2005). In reduced and thinned trees, wind was blowing against areas of the crown where the trunk was more upright than on raised trees, which were bending over more near the top of the tree (Figure 5). This resulted in branches on reduced and thinned trees projecting straighter into the wind field instead of being pushed up against the single trunk as occurred on raised trees. This could have allowed more wind to flow into the reduced and thinned crowns causing more defoliation. Few others have stud- ied this, although Zhu et al. (2000) reported that wind speed inside the crown of a nonpruned Japanese pine (Pinus thunber- gii) was approximately half that experienced on the outside of the crown. This probably explains why foliage was not lost from the leeward side of the crown. Branches broke on the windward side of the lower crown on several trees. Longitudinal compression cracks were evident on all broken branches; tension cracks appeared on only a few bro- ken branches. Cracks appeared at the point where branches twisted or bent dramatically while reconfiguring in the wind. There were no differences in the number of broken branches among pruning treatments (data not shown); however, thinned trees had more bark damage on branches than other treatments. Watching the video of each tree showed that branches on thinned trees moved more than branches on all other treatments. In conclusion, removing branches from the crown of live oak Figure 6. Tree that was not pruned bending with 45 m/s (110 mph) wind. The lower (just below canopy) and middle (in- side canopy) orientation sensors are shown mounted on a bracket constructed of metal and wood. The top sensor is hidden higher in the crown. Three wires are shown on the trunk and ground; each sends sensor data to the Multifunc- tion DAQ. because foliage was lost (data not shown). This indicates that the mass and projected frontal area of trunk, branches, and twigs played a large role in trunk movement of live oak in wind, although force on the trunk in the dormant season for deciduous trees was reported much lower than in summer (Baker 1997). Raised trees appeared to have lost the least amount of foliage, although this was not measured. This may have occurred because most of the branches in the crown were bent over in a stream- lined fashion similar to a nursery tree or conifer tied up for shipping. This form probably allowed wind to pass under and up the reconfigured crown. At high wind speeds, air was essentially pushing up the bent trunk oppressing branches against the single trunk (Figure 6). With most or all branches and twigs aligned with the wind on raised trees, leaves could have been oppressed to the twigs in a fashion that compressed the axial bud. Foliage may be better connected to the twig when subjected to forces in this direction than in other directions (Niklas 1996). In addition, small twigs and branches on raised trees were packed into a tight, ©2008 International Society of Arboriculture reduced trunk movement in wind. Although this result was ex- pected, we quantified the relationship showing that removal of 33% of the foliage with reduction or thinning pruning types resulted in less than half the movement compared with non- pruned trees. Reduced motion likely resulted in lesser forces transferred to the trunk (Kerzenmacher and Gardiner 1998) and reduced likelihood of trunk failure in wind. This effect is likely a combination of reduced frontal area, reconfigured crown shape, and mass damping (James et al. 2006). Thinning and reduction appeared most effective at reducing trunk movement in the upper crown. Lions tailing or crown raising appeared ineffective at reducing upper trunk movement in windstorms. All pruning types reduced lower trunk movement by the same amount compared with nonpruned trees. Much more research is needed, including the testing of different species, different prun- ing doses, larger trees, gusty winds, and testing the effect of wind for longer durations. In addition, we know nothing about how long the pruning effect on movement described will last. 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). National Arborist Association, Inc., Manchester, NH. Baker, C.J. 1997. Measurements of the natural frequencies of trees. Journal of Experimental Botany 48:1125–1132. Bertram, J.E.A. 1989. Size-dependent differential scaling in branches: The mechanical design of trees revisited. Trees Structure and Func- tion 4:241–253. Brudi, E., and P. van Wassenaer. 2002. Trees and statics: Nondestructive failure analysis. In Tree Structure and Mechanics Conference Pro- ceedings. Smiley, T.E., and Coder K. (Eds.). Intern. Soc. Arboricul- ture, Champaign IL.
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
