Wood Quality and its Biological Basis

Transcription

1 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

2 Contents Contributors Preface xi xiii 1 Tree growth and wood quality 1 RODNEY ARTHUR SAVIDGE 1.1 Cambial growth Wood is a biosynthetic end product Zonation Bordered-pit development Secondary-wall lamellae Microfibrils and lignin Protoplasmic autolysis Cambial fusiform cell length and orientation Perennial cambial growth Episodic but variable cambial growth Tapering to the point in form and function Wood quality in perspective Defining wood quality Measuring wood quality Wood quantity versus wood quality Stem dimensions and quality G x E control of wood quality Variation taraplas within the tree Wood density Molecular and anatomical basis Enhancing wood density through silviculture Enhancing wood density through tree improvement Understanding the control of secondary-wall formation at the level of cell biology The larger picture An abundance of wealth The consumer is always right The technology of wood-quality assessment can be flawed Discussion: seeing the wood and the trees Philosophical and historical musings 22

3 vi CONTENTS Wood quality measured on a three-pan balance Lignin on the three-pan balance Looking back Looking forward 26 References 26 2 Wood anatomy in relation to wood quality 30 BRIAN G. BUTTERFIELD 2.1 Wood anatomy Softwoods and hardwoods Growth rings 2.2 The cell wall of softwood tracheids Cell wall structure The middle lamella The primary wall The secondary wall Cell wall and density Microfibril angle Determination of microfibril angle Microfibril angle variation and its effect on wood properties 2.3 The cell wall in hardwood fibres and vessel elements Fibres Vessels 2.4 Cell wall pits and perforations Pits Perforations 2.5 Vessel-less angiosperms Acknowledgements References Wood chemistry in relation to quality 53 HELENA PEREIRA, JOSE GRACA and JOSE C. RODRIGUES 3.1 Introduction Chemical composition of wood Cell wall structural components Cellulose Hemicelluloses 60

4 CONTENTS Vll Lignin Distribution in the cell wall Extractive components Terpenoid extractives Phenolic extractives Other wood extractives Variation of chemical composition Juvenile wood Heartwood Reaction wood Knotwood Wood chemical quality parameters depending on end-use 81 References 83 Wood density and growth 87 PEKKA SARANPAA 4.1 Importance of wood density Density of cell wall material Determination of density Water displacement method X-ray densitometry What causes variation in density? Within growth ring Within a tree Between sites Is there a correlation between density and growth rate? Effect of fertilisation on growth rate and wood density Conclusions 113 References Reaction wood 118 JOHN R. BARNETT and GEORGE JERONIMIDIS 5.1 Introduction Early studies of reaction wood formation Induction of reaction wood formation The role of auxin The role of ethylene The role of gibberellins The role of stress 124

5 viii CONTENTS 5.4 Structure and formation of reaction wood Compression wood Tension wood Opposite and lateral wood Reaction wood and wood quality 132 References Growth stresses 137 BERNARD THIBAUT and JOSEPH GRIL 6.1 Origin of growth stresses Geometric and mass growth: support stress Cell differentiation: maturation stress Growth stresses Role of growth stresses General models of growth stresses Measurement of growth stresses In situ peripheral measurement Measurement of residual stresses in logs Main results for normal maturation strain Growth stresses and reaction wood Consequence of growth stresses for quality Log-end cracks Lumber distortion Reaction wood Prediction and treatment Tree and log morphology Consequences of cutting operations Observation of reaction wood Conclusions 154 References Wood quality for pulp and paper 157 DENILSON DA SILVA PEREZ and THIERRY FAUCHON 7.1 Introduction Why wood? Wood versus non-wood fibres From wood to paper Wood as a raw material Wood-pulping process interactions Wood-pulp fibre relationships 164

6 CONTENTS IX 7.3 Resource management and biological decay Origin, supply of resources and pulp production Biological decay ~ Mill specifications and quality control measurement Wood-quality variability and its consequences for pulp and paper quality Wood species and mixtures Within- and among-tree property variation Within-ring variation Radial trends Variations from the base to the top Forestry practice, site index and growth conditions The future 184 References 184 The mechanical properties of wood 187 AUDREY ZINK-SHARP Introduction Advantages and disadvantages of wood as a structural material Advantages High strength and flexural rigidity in spite of light weight Available and renewable resource Requires less energy to process into structural material Ease of fabrication and conversion Dimensionally stable and durable if used correctly Low electrical, thermal, and acoustical conductivity Disadvantages Variability Natural built-in defects Dimensional instability Susceptibility to biological attack Anisotropy Combustibility Importance of density Mechanical properties important for structural applications Elastic properties Strength properties

7 X CONTENTS 8.5 Creep effects on deformation and fracture Defects affecting mechanical properties Naturally occurring defects: knots and sloping grain Knots Sloping grain Processing defects: checks and splits Checks Splits Problems with mechanical joints 204 References 209 Index 211