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The Anatomy and Biomechanical Properties of Bifurcations in Hazel

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The Anatomy and Biomechanical Properties of Bifurcations in Hazel The Anatomy and Biomechanical Properties of Bifurcations in Hazel (Corylus avellana L.) A thesis submitted to the University of Manchester for the degree of DOCTOR OF PHILOSOPHY in the Faculty of Life Sciences 2015 Duncan Slater This page intentionally left blank 2 Table of Contents Preliminary Sections Page No. Abstract 15 Declaration 16 Copyright Statement 16 List of abbreviations 17 Acknowledgements 18 Preface 19 Dedication 20 Chapter 1: Introduction 1.1 Introduction 22 1.2 Literature review 22 1.2.1 Definition of a tree bifurcation 1.2.2 Definitions of mechanical properties related to this study 1.2.3 Mechanical failure of bifurcations in trees 1.2.4 Bifurcations with included bark 1.2.5 Previous research into the mechanical performance of bifurcations in trees 1.2.6 The mechanical properties of greenwood (xylem) in relation to bifurcations 1.2.7 Previous research into the anatomy of junctions in trees 1.2.8 Trade-offs in xylem 1.2.9 Literature review summary 1.3 Research aims and objectives 42 3 1.3.1 Selected species and junction type for investigation 1.3.2 Thesis structure 1.4 References 49 Chapter 2: Determining the mechanical properties of bifurcations in hazel (Corylus avellana L.) by testing their component parts 2.1 Chapter Abstract 58 2.2 Introduction 59 2.3 Materials and Methods 65 2.3.1 Sample collection and organisation 2.3.2 Rupture tests 2.3.3 Calculation of bifurcation breaking stress 2.3.4 Three point bending tests 2.3.5 Sample size 2.3.6 Sampling for basic density testing 2.3.7 Statistical analysis 2.4 Results 74 2.4.1 Rupture tests of hazel bifurcations 2.4.2 Three point bending tests 2.5 Discussion 79 2.6 References 83 Chapter 3: The anatomy and grain pattern in bifurcations of hazel (Corylus avellana L.) and other tree species 3.1 Chapter Abstract 86 3.2 Introduction 87 4 3.3 Materials and Methods 90 3.3.1 Superficial examination 3.3.2 Internal anatomical investigations 3.4 Results 97 3.4.1 Superficial examination 3.4.2 Internal anatomy 3.5 Discussion 107 3.6 References 113 Chapter 4: Interlocking wood grain patterns provide improved wood strength properties in bifurcations of hazel (Corylus avellana L.) 4.1 Chapter Abstract 116 4.2 Introduction 117 4.3 Materials and Methods 122 4.3.1 Sample collection 4.3.2 Compression tests 4.3.3 Tensile tests 4.3.4 Basic density testing 4.3.5 Statistical analysis 4.4 Results 128 4.4.1 Compression tests 4.4.2 Tensile tests 4.4.3 Basic density 4.5 Discussion 131 4.6 References 135 5 Chapter 5: The level of occlusion of included bark affects the strength of bifurcations in hazel (Corylus avellana L.) 5.1 Chapter Abstract 138 5.2 Introduction 139 5.3 Materials and Methods 143 5.3.1 Sampling 5.3.2 Rupture tests 5.3.3 Three point bending tests 5.3.4 Measurements of included bark 5.3.5 Statistical analysis 5.4 Results 149 5.4.1 Effects of the extent and location of included bark 5.5 Discussion 156 5.6 References 162 Chapter 6: An assessment of the remodelling of bifurcations in hazel (Corylus avellana L.) in response to bracing, drilling and splitting 6.1 Chapter Abstract 166 6.2 Introduction 167 6.3 Materials and Methods 171 6.3.1 Selection of hazel bifurcations 6.3.2 Modification to the hazel bifurcations 6.3.3 Observations 6.3.4 Rupture testing 6.3.5 Basic density testing 6 6.3.6 Statistical analysis 6.4 Results 180 6.4.1 Specimen losses and mean specimen dimensions 6.4.2 Observations of bifurcations prior to testing 6.4.3 Rupture testing 6.4.4 Basic density at hazel bifurcations 6.5 Discussion 191 6.5.1 Discussion of results by bifurcation type 6.5.2 Basic density 6.5.3 Limitations of the study 6.5.4 Conclusions 6.6 References 197 Chapter 7: An assessment of the movement behaviour of bifurcations in hazel (Corylus avellana L.) under dynamic wind loading using accelerometers 7.1 Chapter Abstract 200 7.2 Introduction 201 7.3 Materials and Methods 205 7.3.1 Selection of hazel bifurcations 7.3.2 Accelerometry 7.3.3 Wind speed assessment 7.3.4 Observations 7.3.5 Rupture tests 7.3.6 Statistical analysis 7.4 Results 213 7.4.1 Summary of primary data 7.4.2 Observations 7.4.3 Regression analysis 7.4.4 Differences in movement related to bifurcation type 7.4.5 Rupture tests 7.4.6 The influence of bifurcation morphology and position 7 7.5 Discussion 225 7.6 References 229 Chapter 8: Discussion 8.1 Synthesis of research findings 234 8.2 Estimating the factor of safety for bifurcations in trees 238 8.3 Critique of methodologies used 243 8.4 Recommendations for further research work 246 8.4.1 Causes of differing bifurcation anatomy 8.4.2 Extending the study to other plant species 8.4.3 The relative risk of failure for bifurcations in trees 8.4.4 Opportunities for biomimicry of bifurcation anatomy 8.4.5 Advanced techniques for assessing bifurcations 8.4.6 Creating innovative remedial treatments for flawed bifurcations in trees 8.5 Implications of the findings of this study for arboricultural 253 practices 8.5.1 Pruning 8.5.2 Bifurcations and tree hazard management 8.5.3 Bark inclusions 8.5.4 Bracing 8.5.5 Split bifurcations 8.6 References 258 8 Table of Figures Chapter 1: Fig. 1.1 A bifurcation in hazel (Corylus avellana L.) 23 Fig. 1.2 Illustration of a yield point and breaking point of a hazel 26 bifurcation Fig. 1.3 Location of maximum bending stresses in branches and 27 bifurcations under bending Fig. 1.4 Failure of a bifurcation under wind-loading 31 Fig. 1.5 3D diagram of xylem cells formed in an angiosperm 34 Fig. 1.6 Shigo’s model of branch attachment 36 Chapter 2: Fig. 2.1 Types of tensile failure in tree bifurcations 60 Fig. 2.2 Observation of grain orientation on the fracture surface 61 of a hazel bifurcation Fig. 2.3 Location of the pivot point in calculating the maximum 62 breaking stresses of bifurcations Fig. 2.4 Illustration of the three components that contribute to 64 the mechanical strength of a bifurcation in a tree Fig. 2.5 Material removed in the two component tests 67 Fig. 2.6 Diagram illustrating morphological measurements taken 68 for each bifurcation Fig. 2.7 Rupture testing of hazel bifurcations and additional 69 measurements Fig. 2.8 Diagram of the three-point testing rig used 72 Fig. 2.9 Locations for extracting 5 mm wood cores from 25 73 hazel bifurcations for basic density testing and slide production Fig. 2.10 Boxplot of maximum breaking stress of all sample sets 75 in this study Fig. 2.11 Comparison of the anatomy of ‘junction wood’ and 78 normal stem wood 9 Chapter 3: Fig. 3.1 Implausible wood grain arrangements at the bifurcations 88 of woody plants Fig. 3.2 Sample preparation for CT scanning 93 Fig. 3.3 Determination of the inter-vessel tortuosity of the 96 vessels segmented out from the scanned hazel volumes Fig. 3.4 Visual observations of the wood grain orientation at de- 98 barked junctions and surfaces of fractures of split bifurcations Fig. 3.5 Visualisation of CT Scan output 104 Fig. 3.6 Contrasting form of rays in tangential view 106 Fig. 3.7 Simplified pattern of interlocking wood grain 109 Fig. 3.8 Schematic diagram of the arrangement of cell types at a 110 bifurcation Fig. 3.9 Whirled grain at a bifurcation in common ash (Fraxinus 111 excelsior L.) Chapter 4: Fig. 4.1 Two improbable wood grain arrangements at 118 bifurcations in trees Fig. 4.2 Comparison of vessel shapes in stem wood and junction 119 wood of hazel Fig. 4.3 Interlocking wood grain patterns at bifurcations in trees 120 Fig. 4.4 Diagram of compression test methodology 124 Fig. 4.5 Diagram of tensile test methodology 125 Fig. 4.6 Orientation of wood strength testing at a bifurcation 126 Fig. 4.7 Location for excision of tensile testing samples for bark- 127 included bifurcations Fig. 4.8 Remedial xylem growth at a bark-included bifurcation 133 10 Chapter 5: Fig. 5.1 Type I, Type II and branch failure modes of tree 140 bifurcations under tension across the bifurcation. Fig. 5.2 Potential development pathways for a bark-included 141 bifurcation Fig. 5.3 Measurements of the fracture surfaces of bark-included 146 bifurcations carried out in ImageJ Fig. 5.4 Categorisation of bifurcations with included bark into 147 two types Fig. 5.5 Failure modes in relation to the diameter ratio of the 150 bifurcation Fig. 5.6 Typical force/displacement graphs for specimen types 151 Fig. 5.7 Boxplot of mean yield stress of branches compared with 152 the mean breaking stresses of the normally-formed bifurcations and bifurcations with included bark Fig. 5.8 Boxplot of mean breaking stress of bifurcation types 154 Fig. 5.9 Suggested contrast in bending behaviour between a low 158 diameter ratio bifurcation and a high diameter ratio bifurcation Fig. 5.10 Weaker and stronger forms of bifurcations with 160 included bark Chapter 6: Fig. 6.1 Wood grain patterns at the apices of bifurcations 169 Fig. 6.2 Artificially-modified bifurcations left to grow in-situ for 174 two to four years Fig.
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