Table Of ContentForest Products and Wood Science
An Introduction
Sixth Edition
Forest Products and Wood Science
An Introduction
Sixth Edition
Rubin Shmulsky
P. David Jones
Drawings by Karen Lilley
A John Wiley & Sons, Inc., Publication
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CONTENTS
Preface ix
Introduction xi
1. Tree Growth and Production of Woody Tissue 3
2. Macroscopic Character of Wood 23
3. Composition and Structure of Wood Cells 45
4. Softwood Structure 65
5. Hardwood Structure 79
6. Juvenile Wood, Reaction Wood, and Wood of Branches 107
7. Wood and Water 141
8. Density and Specifi c Gravity 175
9. Strength and Mechanics 197
10. Durability and Protection 229
11. Silvicultural Practices and Wood Quality 253
12. Lumber 289
13. Structural Composites 321
14. Nonstructural Composites 365
15. Pulp and Paper 397
16. Energy and Chemical Products 421
17. Global Raw Materials 443
Index 467
Appendices, review questions, and additional readings are located online at
www.wiley.com/go/shmulsky.
vii
PREFACE
This textbook is written as an introduction to the anatomical and physical nature of
wood and the relationship of these characteristics to its use as an industrial raw material.
Wood - based materials discussed include solid wood products, engineered composites,
energy, and paper and fi ber products. Also discussed are the basic processes involved in
the production of the principal wood products and how wood properties affect their
use and performance. Related issues examined herein include the use of wood for energy
and chemicals, environmental implications of wood- based materials, and the global
wood supply picture.
Given the high degree to which wood and wood- based products are embedded in
our culture, students of architecture, structural engineering, building construction, forest
management, and wood science and technology should develop an appreciation of the
many potential forms and uses for wood and other bio - based materials. Additionally, a
sound understanding of the keys to proper selection of raw materials for any wood- based
product, and of the type of wood product best suited for a given application, is extremely
important.
This text is divided into four parts. The fi rst part (Chapters 1 – 6 ) introduces the
growth and structure of hardwoods and softwoods, chemical and structural character-
istics, and inherent variability. The second part (Chapters 7 – 11 ) examines the physical
properties of wood, relates these properties to wood ’ s chemical and structural charac-
teristics, and explores how forest- related factors impact wood properties. The third part
(Chapters 12 – 15 ) discusses the major wood- based products, the basic manufacturing
processes associated with each, and how raw material selection affects product proper-
ties. The fi nal part (Chapters 16 and 17 ) focuses on the global raw materials picture,
the increasing use of wood as a source of energy and chemicals, and the environmental
implications of the use of wood.
Increasing sophistication of scientifi c tools that allow nanoscale measurement, visu-
alization, and manipulation of material building blocks continues to provide new insights
and possibilities across almost every fi eld, including tree physiology and wood and
materials science. Thus, even in such fi elds of inquiry as tree growth and wood struc-
ture — topics that have been extensively researched and reported over a long period of
time — knowledge of fundamental processes and structures continues to change. Simi-
larly, advancements relative to new product development, product enhancement, and
ix
x Preface
production technology are ongoing. Nanotechnology continues to slowly develop and
to show promise with respect to bringing positive change across society and throughout
the wood- based industries.
In many instances, the term “ wood products ” is being changed to “ bio - based prod-
ucts. ” In the United States, this broader term is often more environmentally benign. It
also includes other lignocellulosic materials such as paper and composites derived from
agricultural residues. It is not yet known whether this trend in name may be short lived
or long term. It is known, however, that regardless of any name change, wood and forest-
derived woody materials still account for the vast majority of all bio- based materials.
To paraphrase Shakespeare: A wood product by any other name is still a wood product.
This, the Sixth Edition, is a major revision of the Fifth Edition, which was published
in 2007. It has been substantially reorganized and pared down in an effort to augment
its acceptance, particularly to forestry students, as the primary introductory college level
text of this subject. This edition attempts to further broaden its international appeal in
response to the exponential growth of worldwide distribution. The fi rst edition of this
text was initially published nearly three decades ago in 1982. Through time, the authors
have sought to maintain the basic fundamental concepts while revising the time- sensitive
applications and technologies.
Many of the changes, updates, and improvements to the text are the result of the
addition of a new coauthor, Dr. Paul David Jones. This edition also marks the retirement
of Drs. John Haygreen and Jim Bowyer. This sixth edition marks nearly 30 years in
print. The authors express their sincere thanks to Drs. Haygreen and Bowyer for their
leadership and extensive contributions to this subject during the past three decades.
The authors also express their sincere thanks to reviewers who played a vital role
in this or earlier editions. These include Kent T. Adair, Terry L. Amburgey, Donald G.
Arganbright, James P. Armstrong, Stravros Avramidis, H. Michael Barnes, Thomas E.
Batey Jr., Frank C. Beall, B. Alan Bendtsen, Dwight W. Bensend, Evalgelos J. Biblis,
Brian H. Bond, Arthur B. Brauner, Charles C. Brunner, Ben S. Bryant, Honorio F. Carino,
Vincent L. Chiang, Poo Chow, Gilbert L. Comstock, Terry E. Connors, Harold A. Core,
John B. Crist, Bruce E. Cutter, Robert W. Erickson, Richard L. Folk, Charles E. Frazier,
David W. French, Douglas J. Gardner, Barbara L. Gartner, Roland O. Gertjejansen,
Irving S. Goldstein, Barry S. Goodell, Thomas M. Gorman, Robert L. Govett, Hans M.
Gregersen, Richard F. Helm, R. Bruce Hoadley, Peter J. Ince, Judson G. Isebrands, John
J. Janowiak, Fred A. Kamke, Philip O. Larson, Joseph R. Loferski, E.A. McGinnes,
Thomas M. Maloney, Timothy A. Martin, David J. Moorhead, Kenneth J. Muehlenfeld,
Wayne K. Murphey, Helmuth Resch, Irving B. Sachs, Simo Sarkanen, John F. Senft, Craig
E. Schuler, Tor P. Schultz, Audrey Zink Sharp, John R. Shelly, Todd F. Shupe, Richard
A. Skok, Douglas D. Stokke, Otto Suchsland, Edward I. Sucoff, Richard J. Thomas,
Ulrike Tschirner, Elisabeth A. Wheeler, Edwin H. White, Ed Williston, James B. Wilson,
K.C. Yang, Raymond A. Young, John I. Zerbe, and Steven C. Zylkowski.
Special thanks go to John B. Crist, Tor P. Schultz, Shane Kitchens, Ron Teclaw, John
P. Limbach, Elisabeth A. Wheeler, Mississippi State University, North Carolina State
University, and Trus Joist/Weyerhaeuser for their extensive photographic
contributions.
INTRODUCTION
In mid - 2007, it was estimated that the population of the world was approximately 6.7
billion, a 233 percent increase from just 50 years earlier. This dramatic increase has
created many problems and challenges for this and the next generation of leaders, includ-
ing those in the political, religious, and industrial arenas. The consumption of goods in
many areas of the world is today growing at a rate greater than that of the population.
Population and economic growth worldwide has resulted in substantial increases in
consumption of food and of raw materials needed to provide shelter, fuel, paper, packag-
ing, and durable and nondurable goods of all kinds. It is humbling to think that at any
given time, should farming cease, there is enough food in the world to last for only 40
days.
The long- term availability of crude oil has been a focus of concern since the 1970s,
with concerns magnifi ed by price trends since 2003. Energy concerns are likely to grow
in the decades ahead. In addition, the availability of nonenergy raw materials will likely
gain more attention going forward as consumption expands and as, in the case of non-
renewable minerals, supplies of the highest- grade and most accessible ores diminish. The
use of food as energy, such as the case of corn- based ethanol, remains an issue of great
contention. Supplies of wood, a renewable resource, are likely to expand, the result of
a long - term trend of growth exceeding removals in natural forests and tree plantations.
Conversely, concerns about forest amenities other than timber are likely to adversely
impact the availability of timber from natural forests.
As shown in Tables I .1 and I.2 , wood is a major raw material globally and within
the United States. Globally, in 2005, almost as much wood was used on a mass basis for
industrial products as steel. In the United States, more wood was used on a mass basis
in 2005 than any other basic material, and more than all metals and all plastics combined.
Yet, in most high school and college curricula, wood receives minimal attention.
The use of wood for energy is increasingly important. Wood has long been the
principal source of energy for heating and cooking in the less developed countries of the
world. Worldwide, about 53 percent of all wood consumed is used for home heating
and cooking, a reality that is revealed in the difference between the roundwood and
industrial roundwood numbers in Table I .1 ; the remainder is used in manufacturing an
array of wood products. In the United States, a much greater proportion of wood is
used as a raw material for wood products manufacture. Moreover, about 85 percent of
xi
xii Introduction
TABLE I.1. Annual world consumption of various raw materials (2005).
Billion metric tons Billion cubic meters
Roundwood 1.743 3 .5
Industrial roundwood 0.849 1 .7
Cement 2.220 2 .1
Steel 1.090 0 .13
Plastics 0.235 0 .21
Aluminum 0.031 0 .01
Source: Data for wood from the Food and Agriculture Organization of the United Nations
( 2006 ); for cement, aluminium, and steel from the United States Geological Survey (2 006 ); and
for plastics from the Association of Plastics Manufacturers in Europe (2 006 ).
TABLE I.2. Annual U.S. consumption of various raw materials (2005).
Million metric tons Million cubic meters
Roundwood 249 560
Industrial roundwood 227 516
Cement 126 114
Steel 122 154
Plastics 39.1 34.5
Aluminum 6.8 2.4
Source: Data for wood from Howard (2 006 ); for cement, steel, and aluminum from the
United States Geological Survey ( 2006 ); and for plastics from the American Plastics Council
( 2006 ).
the wood consumed for energy is used in the forest industries; the other 15 percent is
used for other heating needs, such as heating homes in rural areas. The extensive use of
wood energy by the forest products industries indicates that these interests have already
made the leap to green energy. Since the 1970s, forest industries have been increasing
the utilization of wood residues for the energy required to manufacture wood products.
Residues such as bark, sawdust, product trim, and pulping liquors are now almost
completely utilized. Currently, the primary wood products industries of the United States
are about 60– 70 percent energy self- suffi cient, meaning that only 30– 40 percent of the
energy used for the manufacture of wood - based materials is purchased from energy
providers or produced from fossil fuels. This is a very signifi cant advantage of wood as
compared with cement, steel, plastics, and aluminum. The use of wood for production
of commercial energy is likely to increase as interest in the development of alternative
energy grows. Current policies and “ green power” mandates make it economically
feasible to pelletize sawdust in the United States, ship it across the Atlantic Ocean, and
burn it for electrical power generation in parts of Europe. In the future, wood is certain
to play a larger role in the production of electricity and may provide a source of fuels
such as cellulosic ethanol, pyrolysis oil, torrifi ed wood, and liquid hydrogen as well.
It should be apparent that wood is an extremely vital and versatile raw material.
In addition to the economic and energy benefi ts of wood production, trees enhance the
aesthetic and environmental character of every region. The renewability of forests and
the assurance that with wise forest management a supply of wood will be available
indefi nitely favor its use as a basic raw material.
Introduction xiii
The use of wood for heat and as a material for shelter, dyes, tannin, and containers
dates back to the early days of human history. Historical transportation via wood boats
and ships, warfare that included long bows and catapults, wood- handled farming imple-
ments, and so on have shaped human culture for thousands of years. But the use of
wood in signifi cant volume goes back only about 150 years.
In colonial America, wood was the foundation on which society was built. Buildings
and furniture, spinning wheels and looms, dishes and pails, wagons and carriages, din-
ghies and ships, bridges and sidewalks, railroad ties, plows and hay rakes, milling
machinery and sawmills, and products of every kind and shape were made of wood.
Wood was also a major fuel source, used for heating and cooking and as the principal
fuel of industry. There is much basis for the axiom “ communities develop where forests
grow. ”
As an early English colony, America was prized for its abundance of tall pine trees,
from which ship masts could be fashioned. As the colonies gave way to rapidly expand-
ing cities, and as populations expanded, wood abundance in many areas turned to
scarcity as unrestrained wood use, combined with land clearing for agriculture, resulted
in greatly diminished forests. But as wooden wagon trains carried homesteaders steadily
westward, new forests were encountered and clearing of forests continued. Wood for
fencing of pastures alone required enormous volumes of timber, with some 3.2 million
miles of such fencing estimated to have been in existence in the mid- 1800s. Development
of the steam engine led to the need for great quantities of additional wood — for steam-
boat fuel and for railroad ties and trestles — and it provided a means of moving large
volumes of wood to population centers.
One of the early drivers of inquiry into whether things might be done to increase
the effi ciency of wood used was the tendency of wood to rot. The huge volumes used
for ships, fencing, ties, trestles, bridges, and telegraph line poles required replacement
after only a few years of use due to natural deterioration. As noted by MacCleery (1 993 ),
just replacing railroad ties on a sustained basis required from 15 to 20 million acres of
forest land in 1900. Interest in fi nding a way to preserve wood to eliminate or slow
decay processes provided an impetus to an early fi eld of inquiry in what would later
become known as the fi eld of wood science.
As the population of the United States grew— from an estimated 3 million in 1785
to 77 million in 1900— wood consumption grew rapidly (Fig. I.1 ); primary uses of wood
were lumber and fuelwood. Rapid growth in wood use continued for about another
decade, but then, despite ongoing increases in population, a dramatic shift in wood use
occurred.
First, lumber consumption declined almost as fast as it had increased. The causes
of the decline were many, including substitution of nonwood materials for many applica-
tions, increased effi ciency of wood use, and development of new technologies. Develop-
ment of wood preservatives and preservative treatments alone resulted in a substantial
reduction in the quantity of wood needed for the replacement of ties, poles, fencing, and
similar products. Another development— the invention of barbed wire — meant that as
the 3.2 million miles of wooden fencing estimated to have existed in the mid- 1800s
began to deteriorate, far smaller quantities of wood were needed for replacement. In
addition to declining lumber consumption, growth in the use of wood as a source of
energy leveled off at the turn of the century and then began to decline as fossil fuels
became increasingly more important. Wood energy rebounded during the Great
