University of Massachusetts Amherst ScholarWorks@UMass Amherst Doctoral Dissertations Dissertations and Theses 2-1-2020 The effect of pruning treatments on the vibration properties and wind-induced bending moments of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) in Singapore Daniel Burcham Follow this and additional works at: https://scholarworks.umass.edu/dissertations_2 Part of the Forest Management Commons Recommended Citation Burcham, Daniel, "The effect of pruning treatments on the vibration properties and wind-induced bending moments of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) in Singapore" (2020). Doctoral Dissertations. 1815. https://doi.org/10.7275/9rwz-5774 https://scholarworks.umass.edu/dissertations_2/1815 This Open Access Dissertation is brought to you for free and open access by the Dissertations and Theses at ScholarWorks@UMass Amherst. It has been accepted for inclusion in Doctoral Dissertations by an authorized administrator of ScholarWorks@UMass Amherst. For more information, please contact [email protected]. The effect of pruning treatments on the vibration properties and wind-induced bending moments of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) in Singapore A Dissertation Presented by DANIEL C. BURCHAM Submitted to the Graduate School of the University of Massachusetts Amherst in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY FEBRUARY 2020 Environmental Conservation © Copyright Daniel C. Burcham 2020 All Rights Reserved The effect of pruning treatments on the vibration properties and wind-induced bending moments of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) in Singapore A Dissertation Presented by DANIEL C. BURCHAM Approved as to style and content by: Brian C. P. Kane, Chair H. Dennis P. Ryan III, Member Wesley R. Autio, Outside Member Yahya Modarres-Sadeghi, Outside Member Curt Griffin, Department Head Environmental Conservation Timothy Randhir, Graduate Program Director Environmental Conservation DEDICATION To my grandmother, Ms. Diane K. Miller, who showed me love and loyalty. ACKNOWLEDGMENTS I thank my advisor, Dr. Brian Kane, for confidently supporting this project at its inception and maintaining that support over many years. I am thankful for his extraordinary insight on how to think about the science and practice of arboriculture, for his useful guidance on productive work habits, and for constantly guiding my efforts toward useful outcomes. He gave me a long lead, allowing me to pursue and explore my own interests, and gave instruction when I needed it. I am also grateful for the advice, instruction, and insight offered by my committee members, Dr. Wesley Autio, Dr. Kenneth James, Dr. Yahya Modarres-Sadeghi, and Dr. Dennis Ryan. This project could not have happened without support from the National Parks Board, Singapore, whose shared vision of a city in a garden lends significance to these efforts. The extraordinary foresight of Singapore’s first Prime Minister, Mr. Lee Kuan Yew and others inspired to advance his greening policies deserve much credit. I hope the insight offered by this project contributes positively to these ongoing efforts. I am also grateful for the practical contributions of many hardworking people. Field research in the equatorial tropics is hard work and progress is continuously opposed by rain, heat, and humidity. This project could not have succeeded without help from Rick Thomas, Lee Sheehan, Boo Ghim Yew, Martin Tay, Lau Lai Hock, Leonard Tan, Thomas Chua, Rajesh Singh Gill, and Joseph Oh from the Singapore Arboriculture Society; Nelson Abarrientos, Clayton Lee, Shirley Lim, Chia Choong Soon, and Daniel Heng from the National Parks Board; Lynette Sim, Syuhaidah Bte Mohamed Gapor, Joey Lim, Yeo Yong Ping, Chong Yan Huan, and Mohd Qurshairy Relferi Bin Mohd Hisham from Republic Polytechnic; Tan Eng Hwa, Samarth Kapoor, Jahnavi Mekala, Derrick Poh, Vincent Wei, Sven Yeo, and Kelvin Yong from BioMachines Pte. Ltd.; and Habib Mohd Ahasan, Mofazzel Jomadder, Ahamed Mohd Elroz, S. Sukan, A. v Velmurugan, Neaiveli Muthy, and Thongsai Phiraphon from Toh Kim Bock C-E Contractor Pte. Ltd. vi ABSTRACT THE EFFECT OF PRUNING TREATMENTS ON THE VIBRATION PROPERTIES AND WIND-INDUCED BENDING MOMENTS OF SENEGAL MAHOGANY (KHAYA SENEGALENSIS) AND RAIN TREE (SAMANEA SAMAN) IN SINGAPORE FEBRUARY 2020 DANIEL C. BURCHAM, B.S., OHIO STATE UNIVERSITY M.S., UNIVERSITY OF DELAWARE Ph.D., UNIVERSITY OF MASSACHUSETTS Directed by: Professor Brian Kane During pruning, arborists often intend to increase a tree’s resistance to wind loading by selectively removing branches, but there are few studies examining the efficacy of these interventions, especially for large, open-grown trees. In this study, the mass and vibration properties of Senegal mahogany (Khaya senegalensis) and rain tree (Samanea saman) were measured before and after the crowns of trees were incrementally raised or reduced between 0 and 80%. In addition, the wind-induced vibration and bending moments of Senegal mahoganies were monitored before and after the same pruning treatments. For both species, total mass and leaf mass both decreased faster on reduced than raised trees. The frequency and damping ratio of trees varied with the severity of pruning for reduced, but not raised, trees. The frequency of reduced trees generally increased with pruning severity. In contrast, damping ratio of reduced trees generally decreased with the severity of pruning, except for the unique increase in damping ratio on Senegal mahoganies reduced by 10 to 20%. Post-pruning vibration properties were significantly related to the post-pruning morphometric attributes of reduced, but not raised, trees. For reduced trees, most of the examined tree and branch attributes better explained variability in post-pruning frequency than damping ratio. vii At each pruning severity, Fourier energy spectra showed that raised trees continued to vibrate primarily at their fundamental mode. As the severity of pruning increased, however, reduced trees vibrated progressively less than raised trees at all analyzed frequencies. Similarly, the average 30- minute maximum bending moment associated with a given 30-minute maximum wind speed decreased more for reduced than raised trees at low pruning severities. For those seeking to decrease the likelihood of tree failure, the results suggest that arborists should reduce trees to change their vibration properties and wind loads, but trees should be reduced by small amounts to avoid the undesirable decrease in damping ratio. Although the observed changes on reduced trees contributed favorably to risk mitigation, there are many adverse biological consequences of some pruning methods, especially topping, that shorten tree parts without considering the anatomy of trees or remove an excessive amount of branches and leaves, and arborists should use good judgment when pruning trees to reduce their size without unnecessarily disturbing tree growth and development. Moreover, these mechanical properties will inevitably change as trees grow after pruning, and more work is needed to understand both the long-term biological and mechanical consequences of pruning treatments. viii TABLE OF CONTENTS Page ACKNOWLEDGMENTS ............................................................................................................... v ABSTRACT ................................................................................................................................... vii LIST OF TABLES .......................................................................................................................... xi LIST OF FIGURES ...................................................................................................................... xiv LIST OF FREQUENTLY USED SYMBOLS ............................................................................ xxxi CHAPTER 1 INTRODUCTION ........................................................................................................................ 1 2 LITERATURE REVIEW ............................................................................................................. 5 Tree Mechanics ............................................................................................................................ 5 Wind Mechanics ........................................................................................................................ 39 Wind-Tree Interaction ................................................................................................................ 48 Risk Mitigation Strategies.......................................................................................................... 56 3 MATERIALS AND METHODS ................................................................................................ 64 Experimental site and tree species ............................................................................................. 64 Tree and branch attributes .......................................................................................................... 65 Instrumentation .......................................................................................................................... 66 Measurement of mechanical properties ..................................................................................... 68 Measurement of wind-induced vibration and bending moments ..............................................