Wood Quality and its Biological Basis Edited by JOHN R. BARNETT School of Plant Sciences The University of Reading UK and GEORGE JERONIMIDIS Department of Engineering The University of Reading UK ib Blackwell Publishing CRC Press
Contents Contributors Preface xi xiii 1 Tree growth and wood quality 1 RODNEY ARTHUR SAVIDGE 1.1 Cambial growth 1 1.1.1 Wood is a biosynthetic end product 1 1.1.2 Zonation 1 1.1.3 Bordered-pit development 3 1.1.4 Secondary-wall lamellae 4 1.1.5 Microfibrils and lignin 5 1.1.6 Protoplasmic autolysis 5 1.1.7 Cambial fusiform cell length and orientation 6 1.2 Perennial cambial growth 6 1.2.1 Episodic but variable cambial growth 6 1.2.2 Tapering to the point in form and function 7 1.3 Wood quality in perspective 8 1.3.1 Defining wood quality 8 1.3.2 Measuring wood quality 8 1.3.3 Wood quantity versus wood quality 9 1.3.4 Stem dimensions and quality 9 1.3.5 G x E control of wood quality 9 1.3.6 Variation taraplas within the tree 12 1.4 Wood density. 14 1.4.1 Molecular and anatomical basis 14 1.4.2 Enhancing wood density through silviculture 14 1.4.3 Enhancing wood density through tree improvement 16 1.4.4 Understanding the control of secondary-wall formation at the level of cell biology 18 1.5 The larger picture 19 1.5.1 An abundance of wealth 19 1.5.2 The consumer is always right 21 1.5.3 The technology of wood-quality assessment can be flawed 21 1.6 Discussion: seeing the wood and the trees 22 1.6.1 Philosophical and historical musings 22
vi CONTENTS 1.6.2 Wood quality measured on a three-pan balance 23 1.6.3 Lignin on the three-pan balance 23 1.6.4 Looking back 24 1.6.5 Looking forward 26 References 26 2 Wood anatomy in relation to wood quality 30 BRIAN G. BUTTERFIELD 2.1 Wood anatomy 2.1.1 Softwoods and hardwoods 2.1.2 Growth rings 2.2 The cell wall of softwood tracheids 2.2.1 Cell wall structure 2.2.1.1 The middle lamella 2.2.1.2 The primary wall 2.2.1.3 The secondary wall 2.2.2 Cell wall and density 2.2.3 Microfibril angle 2.2.3.1 Determination of microfibril angle 2.2.3.2 Microfibril angle variation and its effect on wood properties 2.3 The cell wall in hardwood fibres and vessel elements 2.3.1 Fibres 2.3.2 Vessels 2.4 Cell wall pits and perforations 2.4.1 Pits 2.4.2 Perforations 2.5 Vessel-less angiosperms Acknowledgements References 30 30 32 34 34 35 36 37 37 38 38 40 43 43 43 45 45 48 48 49 49 Wood chemistry in relation to quality 53 HELENA PEREIRA, JOSE GRACA and JOSE C. RODRIGUES 3.1 Introduction 53 3.2 Chemical composition of wood 54 3.2.1 Cell wall structural components 55 3.2.1.1 Cellulose 55 3.2.1.2 Hemicelluloses 60
CONTENTS Vll 3.2.1.3 Lignin 64 3.2.1.4 Distribution in the cell wall 68 3.2.2 Extractive components 71-3.2.2.1 Terpenoid extractives 72 3.2.2.2 Phenolic extractives 74 3.2.2.3 Other wood extractives 76 3.3 Variation of chemical composition 76 3.3.1 Juvenile wood 79 3.3.2 Heartwood 79 3.3.3 Reaction wood 80 3.3.4 Knotwood 81 3.4 Wood chemical quality parameters depending on end-use 81 References 83 Wood density and growth 87 PEKKA SARANPAA 4.1 Importance of wood density 87 4.2 Density of cell wall material 87 4.3 Determination of density 90 4.3.1 Water displacement method 90 4.3.2 X-ray densitometry 91 4.4 What causes variation in density? 92 4.4.1 Within growth ring 93 4.4.2 Within a tree 97 4.4.3 Between sites 101 4.5 Is there a correlation between density and growth rate? 102 4.5.1 Effect of fertilisation on growth rate and wood density 109 4.6 Conclusions 113 References 113 5 Reaction wood 118 JOHN R. BARNETT and GEORGE JERONIMIDIS 5.1 Introduction 118 5.2 Early studies of reaction wood formation 121 5.3 Induction of reaction wood formation 122 5.3.1 The role of auxin 122 5.3.2 The role of ethylene 124 5.3.3 The role of gibberellins 124 5.3.4 The role of stress 124
viii CONTENTS 5.4 Structure and formation of reaction wood 125 5.4.1 Compression wood 125 5.4.2 Tension wood 128 5.4.3 Opposite and lateral wood 132 5.5 Reaction wood and wood quality 132 References 134 6 Growth stresses 137 BERNARD THIBAUT and JOSEPH GRIL 6.1 Origin of growth stresses 137 6.1.1 Geometric and mass growth: support stress 137 6.1.2 Cell differentiation: maturation stress 137 6.1.3 Growth stresses 139 6.1.4 Role of growth stresses 140 6.1.5 General models of growth stresses 140 6.2 Measurement of growth stresses 141 6.2.1 In situ peripheral measurement 141 6.2.2 Measurement of residual stresses in logs 142 6.2.3 Main results for normal maturation strain 142 6.2.4 Growth stresses and reaction wood 144 6.3 Consequence of growth stresses for quality 147 6.3.1 Log-end cracks 147 6.3.2 Lumber distortion 149 6.3.3 Reaction wood 150 6.4 Prediction and treatment 151 6.4.1 Tree and log morphology 151 6.4.2 Consequences of cutting operations 153 6.4.3 Observation of reaction wood 153 6.5 Conclusions 154 References 154 7 Wood quality for pulp and paper 157 DENILSON DA SILVA PEREZ and THIERRY FAUCHON 7.1 Introduction 157 7.1.1 Why wood? 157 7.1.2 Wood versus non-wood fibres 158 7.2 From wood to paper 160 7.2.1 Wood as a raw material 160 7.2.2 Wood-pulping process interactions 161 7.2.3 Wood-pulp fibre relationships 164
CONTENTS IX 7.3 Resource management and biological decay 165 7.3.1 Origin, supply of resources and pulp production 165 7.3.2 Biological decay 166 7.3.3 ~ Mill specifications and quality control measurement 170 7.4 Wood-quality variability and its consequences for pulp and paper quality 173 7.4.1 Wood species and mixtures 173 7.4.2 Within- and among-tree property variation 179 7.4.2.1 Within-ring variation 179 7.4.2.2 Radial trends 180 7.4.2.3 Variations from the base to the top 181 7.4.3 Forestry practice, site index and growth conditions 183 7.5 The future 184 References 184 The mechanical properties of wood 187 AUDREY ZINK-SHARP 8.1 8.2 8.3 8.4 Introduction Advantages and disadvantages of wood as a structural material 8.2.1 Advantages 8.2.1.1 High strength and flexural rigidity in spite of light weight 8.2.1.2 Available and renewable resource 8.2.1.3 Requires less energy to process into structural material 8.2.1.4 Ease of fabrication and conversion 8.2.1.5 Dimensionally stable and durable if used correctly 8.2.1.6 Low electrical, thermal, and acoustical conductivity 8.2.2 Disadvantages 8.2.2.1 Variability 8.2.2.2 Natural built-in defects 8.2.2.3 Dimensional instability 8.2.2.4 Susceptibility to biological attack 8.2.2.5 Anisotropy 8.2.2.6 Combustibility Importance of density Mechanical properties important for structural applications 8.4.1 Elastic properties 8.4.2 Strength properties 187 188 192 192 194 194 196
X CONTENTS 8.5 Creep effects on deformation and fracture 198 8.6 Defects affecting mechanical properties 199 8.6.1 Naturally occurring defects: knots and sloping grain 199 8.6.1.1 Knots 199 8.6.1.2 Sloping grain 200 8.6.2 Processing defects: checks and splits 203 8.6.2.1 Checks 203 8.6.2.2 Splits 203 8.7 Problems with mechanical joints 204 References 209 Index 211