Publisher Summary This chapter reviews the rates at which Coarse Woody Debris (CWD) is added and removed from ecosystems, the biomass found in streams and forests, and many functions that CWD serves. CWD is an important component of temperate stream and forest ecosystems and is added to the ecosystem by numerous mechanisms, including wind, fire, insect attack, pathogens, competition, and geomorphic processes. Many factors control the rate at which CWD decomposes, including temperature, moisture, the internal gas composition of CWD, substrate quality, the size of the CWD, and the types of organisms involved. The mass of CWD in an ecosystem ideally represents the balance between addition and loss. In reality, slow decomposition rates and erratic variations in input of CWD cause the CWD mass to deviate markedly from steady-state projections. Many differences correspond to forest type, with deciduous-dominated systems having generally lower biomass than conifer-dominated systems. Stream size also influences CWD mass in lotic ecosystems, while successional stage dramatically influences CWD mass in boat aquatic and terrestrial settings. This chapter reviews many of these functions and concludes that CWD is an important functional component of stream and forest ecosystems. Better scientific understanding of these functions and the natural factors influencing CWD dynamics should lead to more enlightened management practices.

Ecology of Coarse Woody Debris in Temperate Ecosystems

Progress and recent trends in biofuels

Wood density (Dt), an excellent predictor of mechanical properties, is typically viewed in relation to support against gravity, wind, snow, and other environ- mental forces. In contrast, we show the surprising extent to which variation in D t and wood structure is linked to support against implosion by negative pressure in the xy- lem pipeline. The more drought-tolerant the plant, the more negative the xylem pressure can become without cavitation, and the greater the internal load on the xylem conduit walls. Accordingly, Dt was correlated with cavi- tation resistance. This trend was consistent with the maintenance of a safety factor from implosion by nega- tive pressure: conduit wall span ( b) and thickness (t) scaled so that (t/b) 2 was proportional to cavitation resis- tance as required to avoid wall collapse. Unexpectedly, trends in Dt may be as much or more related to support of the xylem pipeline as to support of the plant.

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Trends in wood density and structure are linked to prevention of xylem implosion by negative pressure

1 Basic Wood-Moisture Relationships.- 1.1 Introduction.- 1.2 Saturated Vapor Pressure.- 1.3 Relative Humidity.- 1.3.1 Use of the Psychrometric Chart.- 1.3.2 Measurement of Relative Humidity.- 1.3.3 Control of Relative Humidity.- 1.4 Equilibrium Moisture Content and the Sorption Isotherm.- 1.5 The Effect of Changes in Pressure and Temperature on Relative Humidity.- 1.6 Specific Gravity and Density.- 1.7 Specific Gravity of the Cell Wall and Porosity of Wood.- 1.8 Swelling and Shrinkage of the Cell Wall.- 1.9 Swelling and Shrinkage of Wood.- 2 Wood Structure and Chemical Composition.- 2.1 Introduction.- 2.2 The Cell Wall.- 2.3 Structure of Softwoods.- 2.4 Types of Pit Pairs.- 2.5 Softwood Pitting.- 2.6 Microscopic Studies of Flow in Softwoods.- 2.7 Structure of Hardwoods.- 2.8 Hardwood Pitting.- 2.9 Microscopic Studies of Flow in Hardwoods.- 2.10 Chemical Composition of Normal Wood.- 2.10.1 Cellulose.- 2.10.2 Hemicelluloses.- 2.10.2.1 Introduction.- 2.10.2.2 Softwood Hemicelluloses.- 2.10.2.3 Hardwood Hemicelluloses.- 2.10.3 Lignins.- 2.11 Chemical Composition of Reaction Wood.- 2.11.1 Introduction.- 2.11.2 Compression Wood.- 2.11.3 Tension Wood.- 2.12 Topochemistry of Wood.- 3 Permeability.- 3.1 Introduction.- 3.2 Darcy's Law.- 3.3 Kinds of Flow.- 3.4 Specific Permeability.- 3.5 Poiseuille's Law of Viscous Flow.- 3.6 Turbulent Flow.- 3.7 Nonlinear Flow Due to Kinetic-Energy Losses at the Entrance of a Short Capillary.- 3.8 Knudsen Diffusion or Slip Flow.- 3.9 Corrections for Short Capillaries.- 3.10 Permeability Models Applicable to Wood.- 3.10.1 Simple Parallel Capillary Model.- 3.10.2 Petty Model for Conductances in Series.- 3.10.3 Comstock Model for Softwoods.- 3.10.4 Characterization of Wood Structure from Permeability Measurements.- 3.11 Measurement of Liquid Permeability.- 3.12 Measurement of Gas Permeability.- 3.13 The Effect of Drying on Wood Permeability.- 3.14 Treatments to Increase Permeability.- 3.15 The Effect of Moisture Content on Permeability.- 3.16 The Influence of Specimen Length on Permeability.- 3.17 Permeability of the Cell Wall.- 3.18 Zones of Widely Differing Permeabilities in Wood.- 3.19 General Permeability Variation with Species.- 4 Capillary and Water Potential.- 4.1 Surface Tension.- 4.2 Capillary Tension and Pressure.- 4.3 Mercury Porosimetry.- 4.4 Influence of Capillary Forces on the Pressure Impregnation of Woods with Liquids.- 4.5 Collapse in Wood.- 4.6 Pit Aspiration.- 4.7 The Relationship Between Water Potential and Moisture Movement.- 4.8 Notes on Water Potential. Equilibrium Moisture Content, and Fiber Saturation Point of Wood.- 5 Thermal Conductivity.- 5.1 Fourier's Law.- 5.2 Empirical Equations for Thermal Conductivity.- 5.3 Conductivity Model.- 5.4 Resistance and Resistivity Conductance and Conductivity.- 5.5 Derivation of Theoretical Transverse Conductivity Equation.- 5.6 Derivation of Theoretical Longitudinal Conductivity Equation.- 5.7 R and U Values Convection and Radiation.- 5.8 Application to Electrical Resistivity Calculations.- 5.9 Application to Dielectric Constant Calculations.- 6 Steady-State Moisture Movement.- 6.1 Fick's First Law Under Isothermal Conditions.- 6.2 Bound-Water Diffusion Coefficient of Cell-Wall Substance.- 6.3 The Combined Effect of Moisture Content and Temperature on the Diffusion Coefficient of Cell-Wall Substance.- 6.4 Water-Vapor Diffusion Coefficient of Air in the Lumens.- 6.5 The Transverse Moisture Diffusion Model.- 6.6 The Importance of Pit Pairs in Water-Vapor Diffusion.- 6.7 Longitudinal Moisture Diffusion Model.- 6.8 Nonisothermal Moisture Movement.- 6.9 Measurement of Diffusion Coefficients by Steady-State Method.- 7 Unsteady-State Transport.- 7.1 Derivation of Unsteady-State Equations for Heat and Moisture Flow.- 7.2 Derivation of Unsteady-State Equations for Gaseous Flow in Parallel-Sided Bodies.- 7.3 Graphical and Analytical Solutions of Diffusion-Differential Equations with Constant Coefficients.- 7.3.1 Solutions of Equations for Parallel-Sided Bodies.- 7.3.2 Solutions of Equations for Cylinders.- 7.3.3 Simultaneous Diffusion in Different Flow Directions.- 7.3.4 Significance of Flow in Different Directions.- 7.3.5 Special Considerations Relating to the Heating of Wood.- 7.4 Relative Values of Diffusion Coefficients.- 7.5 Retention.- 7.6 Unsteady-State Transport of Liquids.- 7.6.1 Parallel-Sided Bodies, Permeability Assumed Constant with Length.- 7.6.2 Parallel-Sided Bodies with Permeability Decreasing with Length (Bramhall Model).- 7.6.3 Cylindrical Specimens.- 7.6.4 Square and Rectangular Specimens.- 7.7 Unsteady-State Transport of Moisture Under Noniso-thermal Conditions.- 7.8 Heat Transfer Through Massive Walls.- References.- Symbols and Abbreviations.

Transport processes in wood

Mechanisms of liquefaction and pyrolysis reactions of biomass

This is a technical volume designed for use as a reference book and as a textbook. The first part deals with the formation, anatomy and properties of wood. The second part is important for the numerous means of identifying woods which it contains. There are discussions of the identification of wood by anatomical means, structural features, physical characteristics, figure as it is related to the various planes of cut, and by chemical means. Keys for identification are offered as are descriptions by species and complete physical data for woods native to the U.S. and Canada. Also included is a section on the identification of wood by its fiber. -- AATA

A. J. Panshin

Papers

Textbook of Wood Technology

Textbook of wood technology. Vol. I. Structure, identification, uses, and properties of the commercial woods of the United States.