Formation and 

Properties of 

Juvenile Wood in 

Southern Pines 

A Synopsis

Philip R. Larson 

David E. Kretschmann 

Alexander Clark III 

J. G. Isebrands 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

General 

Technical 

Report 

FPL−GTR–129 
Abstract 

To satisfy the increasing demand for forest products, much 

of the future timber supply will be from improved trees 

grown on managed plantations. This fast-grown resource 

will tend to be harvested in short age rotations and will 

contain higher proportions of juvenile wood than that of 

current harvests. In anticipation of this resource, definitive 

information is needed on the influence of juvenile wood on 

lumber properties so that grading rules and the associated 

allowable design stresses can be modified as needed. This 

document reports the results of an extensive review of the 

literature on juvenile wood in southern pines. This report 

defines and discusses the extent, occurrence, and characteristics of juvenile wood. It reviews the effects that environment 

and silviculture have on the amount of juvenile wood produced. Finally, the impacts that juvenile wood has on mechanical properties were quantified. The results of this quantification are significant to all producers of fast-grown 

plantations. Research has clearly shown that juvenile wood 

will have a detrimental impact on allowable design stresses 

for visually graded lumber. It is critical that methods are 

developed to more carefully manage fast-grown plantation 

wood for its most efficient use. This review should serve as 

an overall collection of knowledge pertaining to juvenile 

wood research in southern pines and should help in the 

decision-making efforts to improve seedling selection techniques and silvicultural practices to maximize the potential 

for fast-grown plantations of southern pines. 

Keywords: juvenile wood, southern pines 

September 2001 

Larson, Philip R.; Kretschmann, David E.; Clark, Alexander III; 

Isebrands, J.G. 2001. Formation and properties of juvenile wood in 

southern pines: a synopsis. Gen. Tech. Rep. FPL-GTR-129. Madison, WI: 

U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 

42 p. 

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Acknowledgments 

We thank Union Camp Corporation, Savannah, Georgia, for 

financial assistance to conduct this work. 
ii 

Preface 

This paper is the last scientific writing of Dr. Philip R. Larson’s distinguished career as a pioneering scientist and project leader 

at the USDA Forest Service, North Central Forest Experiment Station, Rhinelander, Wisconsin. Larson grew up in North 

Branch, Minnesota, and after a 4-year tour of duty as a Navy pilot in the Pacific theater in World War II, he began his career at 

the University of Minnesota, Department of Forestry. He received his B.S. and M.S. degrees in 1949 and 1952 and took his first 

professional position with the Southeastern Forest Experiment Station at Lake City, Florida. While in Florida, he conducted 

research on naval stores production in southern pines before returning to graduate school for a Ph.D. at Yale University, where

he studied wood formation in southern pines. He graduated in 1957 and took a position at the North Central Forest Experiment 

Station in Rhinelander, where his first duties included designing and coordinating the building of the Northern Institute of 

Forest Genetics completed in 1960. In 1962, he was designated the USDA Forest Service’s first pioneering scientist, permitting 

him freedom of research. He became the world’s leading authority on the physiology of wood formation and the Forest Service’s first super grade scientist. 

Since his retirement in 1986, Larson continued scientific writing by completing a monumental book in which he synthesized the 

historical aspects of the concept of The Vascular Cambium: Development and Structure. It was published in 1994 by Springer–

Verlag, Berlin. 

His final scientific work was a result of a Cooperative Research and Development Agreement (CRADA) between the Forest 

Products Laboratory in Madison, Wisconsin, and Union Camp Corporation, Savannah, Georgia. Union Camp managers asked 

Larson and the Forest Service coauthors to synopsize the current knowledge on juvenile wood formation in southern pines. The 

CRADA final report was completed in 1998. This document represents our edited version of that report. 

Larson and his wife Yvonne are retired and reside in Surprise, Arizona. 

J.G. Isebrands 

Rhinelander, Wisconsin 
ii 

Contents 

Page

Introduction ...........................................................................1

Crown–Stem Relationship .....................................................2

Juvenile Wood Defined .........................................................3

Radial Extent and Occurrence ...............................................4

Characteristics of Juvenile Wood ..........................................4

Growth Ring Width ...........................................................4

Growth Ring Age...............................................................5

Growth Ring Uniformity ...................................................5

Summerwood Percentage ..................................................6

Specific Gravity.................................................................6

Tracheid Diameter and Wall Thickness.............................8

Tracheid Length...............................................................10

Microfibrillar Angle.........................................................10

Other Wood-Related Properties...........................................11

Branches, Knots, and Knotwood .....................................11

Compression Wood .........................................................12

Spiral Grain......................................................................13

Extractives .......................................................................13

Heartwood .......................................................................14

Stem Form and Taper ......................................................14

 Page 

Effects of Environment....................................................... 14

Stand Density.................................................................. 14

Site.................................................................................. 15

Geographic Location ...................................................... 15

Effects of Silviculture......................................................... 16

Thinning.......................................................................... 16

Pruning............................................................................ 16

Fertilization..................................................................... 17

Irrigation and Drainage................................................... 17

Cultivation ...................................................................... 17

Mechanical and Strength Properties ................................... 18

Shrinkage........................................................................ 18

MOR and MOE............................................................... 18

Tensile Strength.............................................................. 19

Shear Parallel to Grain and Compression and 

Tension Perpendicular to Grain ...................................... 19

Conclusion.......................................................................... 19

Discussion........................................................................... 19

Literature Cited................................................................... 21 

Appendix—References....................................................... 25

Key Words ..................................................................... 25

References Read in Preparing This Report..................... 26 
Formation and Properties of 

Juvenile Wood in Southern Pines 

A Synopsis 

Philip R. Larson, Chief Plant Physiologist (retired)

USDA Forest Service, North Central Forest Experiment Station, 

Forestry Sciences Laboratory, Rhinelander, Wisconsin

David E. Kretschmann, Research General Engineer 

Forest Products Laboratory, Madison, Wisconsin

Alexander Clark III, Wood Scientist

USDA Forest Service, Southern Research Station, Forestry Sciences Laboratory, Athens, Georgia

J. G. Isebrands, Project Leader 

USDA Forest Service, North Central Forest Experiment Station, 

Forestry Sciences Laboratory, Rhinelander, Wisconsin 

Introduction 

To address the problem of juvenile wood quality, one must 

first address the questions of how wood is formed and why a 

tree produces juvenile wood. All wood is produced by the 

cambium, a zone of dividing cells situated between the wood 

and the inner bark. Cell division by the cambium and differentiation of the wood cells produced by the cambium are, in 

turn, regulated by physiological processes originating in the 

foliar organs of the tree crown. Consequently, changes in the 

characteristics we recognize as wood quality are indirectly 

controlled by the size, distribution, and efficiency of the 

foliar organs. This process, which tree physiologists refer to 

as crown control, is the key to understanding the variability 

in wood quality. 

In pine species, such as loblolly and other southern pines, 

the beginning of cambial activity in the spring coincides with 

bursting of the winter buds and new shoot extension. The 

breaking of winter dormancy is temperature dependent, 

although in very moderate climates the winter buds might 

resume growth at any time of year if temperature conditions 

are favorable. Once activated, the cambium produces 

springwood (earlywood) during the period of shoot extension and new needle elongation. The transition to summerwood (latewood) approximately coincides with the cessation 

of terminal shoot extension and reduction of soil moisture. 

Summerwood formation begins at the base of the tree and 

proceeds upward in the new growth ring. However, in rapidly growing trees, the transition and its upward progression 

can be delayed because of vigorous needle growth. Moreover, in multiple flushing species, such as loblolly pine, 

each new flush of growth produces new springwood, which 

often occurs before summerwood has been initiated. Therefore, the transition from springwood to summerwood will 

vary not only with environmental conditions, particularly 

soil moisture, but also at different height levels within the 

tree stem. 

Springwood and summerwood cells (tracheids in pines) are 

easily identified in mature wood, but in juvenile wood, the 

intervening transition zone is often extremely diffuse. The 

transition zone in juvenile wood consists of cells with large 

radial diameters typical of springwood but with secondary 

walls of varying thickness approaching those of summerwood. Radial cell diameter and secondary wall thickness 

vary independently, and they are controlled by different 

physiological processes within the crown. Cambial cell 

division and radial cell expansion respond to hormonal 

signals emanating primarily from the new shoots and needles 

of the uppermost crown. Secondary wall thickness, on the 

other hand, is dependent on the photosynthetic production of 

the foliage on the older branches of the mid to lower crown. 

The foregoing generalizations are obviously subject to numerous interactions too detailed to dwell on here. We do 

have good knowledge as to how the foliar organs control 

wood formation on the stem and, if the stand history is 

known, we can explain with a high degree of confidence 

how wood quality was affected by past growth conditions. 

Unfortunately, however, because of the complexity of interacting factors, our confidence level for predicting either 

wood quality values or changes in these values is greatly 

diminished. 
2 

In the following sections, we define the most important 

wood quality characteristics and describe how they are 

affected by external growth conditions. We also explain, to 

the best of our knowledge, the interacting effect of these 

growth conditions on tree crown development and wood 

formation. Emphasis will be placed on loblolly pine with 

occasional references to the other southern pines and radiata 

pine. 

The objectives of this report are to 

1. briefly describe how a tree grows and, in so doing, clarify 

the relationship between development of the foliage organs in the tree crown and the formation and quality of 

wood produced in the stem (emphasis will be on juvenile 

wood characteristics), 

2. demonstrate how external growth conditions, both naturally occurring and silviculturally imposed, influence the 

aforementioned relationship, 

3. relate wood quality characteristics of juvenile wood to 

published values of mechanical strength, 

4. suggest what wood quality changes might be anticipated 

by various silvicultural and management options, 

based on available knowledge, and 

5. suggest what wood quality changes might be anticipated 

by genetic improvement, based on available knowledge. 

Crown–Stem Relationship 

A young tree with living branches extending almost to 

ground level is essentially all crown. Because of the strong 

regulatory influence of the crown, springwood-type cells are 

produced throughout most of the growing season. In some 

trees, the innermost growth rings consist exclusively of 

springwood-type cells. Springwood cells are produced during the period of terminal shoot extension, and the transition 

to summerwood production approximately coincides with its 

cessation. However, in the lower stems of young trees and 

the upper crowns of older trees, springwood cell production 

continues while the newly formed needles are elongating. 

The springwood–summerwood transition is a complex 

growth phenomenon. Springwood cells are thin-walled and 

large in radial diameter with large lumens, whereas summerwood cells are thick-walled and narrow in radial diameter 

with narrow lumens. Although these changes in cell dimensions occur concomitantly during the transition from springwood to summerwood, radial cell diameter and wall 

thickness are regulated by entirely different physiological 

processes highly influenced by environmental factors such 

as soil moisture. When active shoot extension is underway 

during high soil moisture, a growth hormone is produced 

that promotes radial cell expansion characteristic of springwood. When soil moisture is reduced and shoot extension 

ceases, hormone production diminishes and the narrowdiameter cells characteristic of summerwood begin to form. 

Cell wall thickening, on the other hand, is regulated by 

photosynthetic processes occurring in the foliage organs of 

the crown. In the early part of the season, the photosynthates 

produced by the older needles are predominantly used in 

growth of the newly expanding shoot and elongating needles. Thus, relatively little photosynthate is available for wall 

formation of the rapidly enlarging springwood cells. Later in 

the season, the photosynthates produced by both the newly 

matured needles and the older needles become available for 

wood formation. It is at this time that wall thickening typical 

of summerwood occurs (Larson 1964, Gordon and Larson 

1970). 

Because radial cell expansion and cell wall thickening are 

regulated by different physiological processes, they can and 

do vary independently. It is this independence that is responsible for the “transition tracheid” characteristic of the growth 

rings in juvenile wood. Transition tracheids are neither 

springwood nor summerwood. They consist of largediameter cells typical of springwood with walls of varying 

thickness typical of summerwood. Transition tracheids occur 

in young, vigorously growing trees with full crowns. The 

vigorous growth of these trees and the short, clear bole 

lengths permit large-diameter cell production to continue 

until late in the season while excess photosynthates are 

simultaneously shunted to cell wall formation. An extreme 

example of this was observed by Schmidt and Smith (1961) 

in slash pine growing in southern Queensland, Australia, 

where growing seasons are exceptionally long. Because 

wood formation continued almost year round, true summerwood formed for a very short period when terminal growth 

was dormant. Springwood formed during the remainder of 

the year, but the cells were essentially all transition tracheids 

due to the continuous, high level of photosynthetic activity. 

As a tree grows in height during the sapling and pole stages, 

its crown recedes upward and the length of clear bole increases. The increase in distance from the active terminal 

shoot contributes to more readily recognizable summerwood 

cells as well as a wider summerwood zone in each successive growth ring of the lower stem. However, the cambium 

within the crown, which remains in close proximity to the 

active shoot, continues to produce growth rings with wide 

zones of springwood and transition wood. With increasing 

tree age and growth in height, the lower stem becomes farther removed from the most active foliar organs of the 

crown. Consequently, springwood and summerwood cells 

become more sharply differentiated and the transition zone1

____________ 

1

The term transition tracheids refers to the intermediate type 

cells between true springwood and summerwood. The term 

transition zone refers to the actual cell boundary between 

springwood and summerwood. The term transition wood 

refers to the annual rings produced after the juvenile wood 

or crown-formed wood but before the rings have the 

properties of mature wood. 
3 

more abrupt. This process of growth ring maturity, which 

begins at the stem base, progresses upward in the stem with 

each new increment of growth. However, crown-formed 

wood, which has characteristics similar to juvenile wood, 

continues to be produced within the upper crown. The concomitant upward progression of mature wood and the upward regression of juvenile wood result in a core of juvenile 

wood extending throughout the bole. Although juvenile 

wood produced by a young tree is not identical to the crownformed wood produced by an older tree, they are sufficiently 

similar in characteristics to be considered identical. 

The southern pines have inherently adapted to take advantage of the long growing seasons and abundant moisture of 

the regions in which they naturally occur. This favorable 

combination contributes not only to rapid juvenile growth 

but also to the many vagaries in wood formation and quality 

associated with such growth. Many pines, such as loblolly 

and slash, produce multiple flushes of growth during the 

season that are a response to available soil moisture. A succession of strong second or third flushes immediately following the first flush will produce a renewed surge of 

springwood that might extend to the stem base. In this case, 

springwood would follow springwood with no intervening 

summerwood. If, however, the second flush or a later flush 

is weak, it might extend only part way down the stem. In 

this case, the cambium responding to the renewed surge of 

growth would produce a partial growth sheath consisting of 

springwood at upper stem levels that grades imperceptibly to 

summerwood in the lower stem. Multiple growth flushes of 

varying intensity are responsible for the formation of false 

growth rings that frequently occur in juvenile wood. In older 

trees, false rings are commonly found in the upper stem but 

are generally absent at the stem base. As a contrary example, 

in extremely suppressed trees, even the first flush might be 

incapable of producing a springwood-forming stimulus 

sufficient to reach the stem base. In this case, in some parts 

of the lower stem, summerwood follows summerwood with 

no intervening springwood (Larson 1956, 1957). In severely 

suppressed trees, entire growth rings might be absent at the 

stem base but fully formed in the upper stem. 

When one examines how the crown in its development 

influences wood formation, it becomes clear how changing 

growth conditions can affect this relationship. As we demonstrate in later sections of this report, stand conditions and 

silvicultural practices can markedly influence the quality of 

wood by altering the crown–stem relationship.

Juvenile Wood Defined 

Juvenile wood is commonly defined as the zone of wood 

extending outward from the pith where wood characteristics 

undergo rapid and progressive changes in successively older 

growth rings. Older wood beyond the juvenile core has been 

referred to as mature wood, adult wood, and outer wood. 

Juvenile wood differs from mature wood in that it has a 

lower percentage of summerwood, lower specific gravity, 

shorter tracheids with larger fibril angles, and occasionally 

disproportionate amounts of compression wood, distorted 

grain patterns, and pitch deposits. 

The term juvenile wood is an unfortunate misnomer. True 

juvenile wood is produced during the first 1 to 3 years of 

growth. Thereafter, similar but not identical wood is produced in the central core of wood at all height levels in the 

stem. This wood has been referred to more appropriately as 

core wood. It has also been referred to as crown-formed 

wood because it is produced either within the living crown 

or in proximity to physiological processes emanating from 

the living crown. The term juvenile wood will be used in this 

report as a synonym for core wood, pith-associated wood, 

and crown-formed wood. 

As shown in subsequent sections, the extent of juvenile 

wood can only be defined by arbitrary criteria. Outward 

from the pith, identifiable wood characteristics undergo 

rapid and progressive changes with increasing growth ring 

age, but the rates of change are not the same within a single 

stem cross section nor within cross sections from different 

trees. For example, Bendtsen and Senft (1986) estimated the 

juvenile period for loblolly pine to be 12 years based on 

values for specific gravity, modulus of elasticity (MOE), 

modulus of rupture (MOR), and compressive strength of the 

wood. However, tracheid length continued to increase rapidly for 18 years, and fibril angle had not yet attained a 

constant value at 30 years. 

Paul (1957, 1960) challenged the concept of juvenile wood. 

He argued that juvenile wood, or core wood, was not necessarily inherent to tree growth because wood characteristics 

of these centrally located growth rings were under silvicultural control. His argument was based on the fact that core 

wood did not contribute to either longitudinal shrinkage or 

distortion in the southern pines when the growth rings were 

narrow (1/8 to 1/10 in. (3.2 to 2.5 mm)). On the contrary, 

both structural defects were excessive when growth rings in 

the core wood were wide (>1/4 in. (6.4 mm)). Paul’s argument is tempting, and it is supported by numerous studies. 

However, as proven by so many other studies, slow growth 

does not eliminate juvenile wood but simply confines it to a 

smaller core. Both narrow- and wide-core wood rings retain 

their juvenile characteristics compared with narrow and wide 

mature rings, respectively. 

Paul, however, did correctly interpret the effects of early 

stand competition on the reduction of springwood formation, 

hence the increase in summerwood percentage in the juvenile growth rings. Early stand competition reduces crown 

size and encourages rapid upward retreat of the live crown 

both of which restrict springwood formation. This silvicultural option is open to forest managers if they are willing to 

sacrifice volume production for the more favorable small 

diameter of core-wood growth rings. 
4 

Radial Extent and Occurrence 

In the southern pines, radial extent of the juvenile wood zone 

is most commonly based on visual estimates of summerwood 

percentage, although specific gravity values are sometimes 

relied on (Hodge and Purnell 1993). As a rule of thumb, 

McAlister and Powers (1992) judged the transition to mature 

wood to be those growth rings that consistently attained 50% 

summerwood. However, in practice they found that 15-yearold loblolly pines growing in seed orchards with average 

diameter at breast height (DBH) of 10 to 16 in. (254 to 

406.4 mm) had still not attained 50% summerwood values. 

Similar results were obtained by Ying and others (1994). 

The transition to mature wood is gradual and therefore arbitrarily defined. In a study of loblolly pines, Zobel and others 

(1959) estimated the extent of the juvenile zone solely on 

visual appearance. The number of juvenile growth rings 

based on this method varied from tree to tree. In most trees, 

the juvenile zone appeared to consist of the first eight rings, 

but because of uncertainties, another two rings of transition 

wood were added to the estimates. Two to four rings of 

transition wood are now widely recognized as part of the 

juvenile core, and the ten innermost growth rings, including 

transition wood, have generally been accepted as the juvenile zone by most investigators of loblolly pine. 

As noted in the definition, a juvenile core of wood is produced at all height levels in the stem. Zobel and others 

(1959) found that the juvenile core in nine 17-year-old loblolly pines was almost cylindrical. Core diameter decreased 

from 4.4 in. (111.8 mm) at DBH to 3.4 in. (86.4 mm) at the 

45-ft (13.7-m) level. The juvenile core averaged 3.6 in. 

(91.4 mm) in diameter in a larger sample of 670 trees. The 

amount of juvenile wood in a loblolly pine tree on a volume 

basis decreased from 85% at age 15 to 55% at age 25 and 

then to 19% at age 40 (Zobel and others 1972). That is, the 

older and larger the tree, the lower the volume of juvenile 

wood even though the size of the juvenile core remains 

unchanged. Obviously, all these values will vary according 

to growing conditions of the trees, but they do provide working estimates. According to Franklin (1987), variations in the 

amount of taper of the juvenile core with height in the tree 

are insufficient to materially affect sawtimber values. 

Despite the many factors that can and do influence the formation of juvenile wood, its radial extent appears to be fairly 

consistent and developmentally conservative. Szymanski and 

Tauer (1991) examined the age of transition from juvenile to 

mature wood in 36 loblolly pine seed sources planted in 

Arkansas. The seed sources originated from throughout the 

entire range of loblolly pine. Their analyses were based on 

wood specific gravity values of 2-year ring segments sampled outward from the pith. Juvenile wood extended to age 6 

with a transition period of rapidly increasing specific gravity 

from ages 6 to 12 and mature wood beyond. The mean transition age averaged for all 36 seed sources was 12.61 years 

with negligible variation among seed sources. The generally 

recognized transition age of 10 years for loblolly pine therefore appears to be an acceptable average for most purposes. 

Characteristics of 

Juvenile Wood 

The wood of a southern pine tree consists of several kinds of 

anatomical elements, only one of which, the tracheid, will be 

of concern in this report. Pine tracheids, sometimes erroneously referred to as fibers, serve two primary functions—to 

transport water and nutrients from roots to crown and to 

strengthen tissue for support of the crown. The tracheids that 

perform these functions are structurally different. Springwood tracheids with their wide lumens and thin walls provide efficient transport pathways between the roots and the 

newly elongating shoot and needles. The later-formed 

summerwood tracheids with their narrow lumens and thick 

walls, on the other hand, provide strength to the new growth 

sheath and support for the expanding crown. The width of 

the growth ring, the relative proportions of springwood to 

summerwood, and the structure of the individual tracheids 

within the growth ring are regulated in various ways by the 

foliage organs of the crown and the vigor or health of these 

organs. Crown vigor, in turn, is entirely dependent on the 

tree’s growth environment (temperature, soil moisture, nutrients), age, and parentage. Therefore, to understand how 

wood is formed and how wood quality varies, one must first 

understand how trees grow. 

Wood quality is an arbitrary term that applies to certain 

wood characteristics that can be quantified and analyzed and 

then used to evaluate a final wood product. In southern 

pines, the most meaningful wood characteristics are associated with the tracheids either individually or collectively. 

Although these wood characteristics are interrelated to varying degrees, they are discussed separately so that their relative importance to the final product can be more readily 

evaluated. 

Growth Ring Width 

Growth ring width, often reported as rings per inch of radial 

growth, is an excellent measure of overall tree health and 

growing conditions. Growth ring width by itself, however, 

provides no reliable evidence of wood quality. When sampled at breast height (4 ft (1.2 m)), ring width usually increases radially for an indefinite number of years before 

either leveling off or decreasing. This pattern reflects both 

growing conditions and proximity to the living crown. In 

vigorous trees free of competition, wide rings will be produced until the living crown advances upward beyond a 

critical level. In trees from closely spaced stands where 

competition is established early, ring widths are reduced 

concomitant with the degree of competition. Thus, the radial 

extent of the juvenile core cannot be estimated on the basis 
5 

of ring width patterns. Trees freed of competition by early 

and frequent thinnings or whose growth is enhanced by 

fertilization and cultivation can maintain wide growth rings 

well beyond the generally accepted juvenile period. On the 

contrary, trees subject to competition early in life might 

exhibit narrow growth ring patterns suggestive of mature 

wood. 

Irrespective of how trees are grown, ring width will eventually decline. As a tree increases in diameter, the wood volume of each annual increment increases. For example, a 

1/2-in. (12.7-mm) ring at age 3 produces far less circumferential volume growth than a 1/2-in. (12.7-mm) ring at age 

10. It is impossible for a tree to maintain extremely wide 

growth rings throughout, or much beyond, the juvenile 

period. However, Burton and Shoulders (1974a,b) grew 

loblolly pines to sawlog sizes in 27 years. They maintained 

growth at an average of 3.6 rings per inch (1.4 rings/cm) 

by frequent thinning. 

Although ring widths eventually decline at breast height, 

they increase at higher levels in the stem. For example, if 

ring number ten is followed upward in the stem, its width 

will increase to a maximum and then gradually decrease to 

the stem top. As a tree ages and the live crown advances 

upward, the level in the stem where the maximum ring width 

occurs also advances upward. The point of maximum ring 

width is often considered to be the base of the live crown. 

However, this point is more typically found at a slightly 

higher level where more vigorous branches contribute to 

stem growth. The fact that maximum ring width shifts progressively upward accounts for changes in stem taper, and as 

shown in the section Stem Form and Taper, stem taper can 

be altered by changing growth conditions. Thus, growing 

conditions not only determine diameter growth at the stem 

base but also at higher levels in the stem, and consequently 

they affect yield and quality of the final product. 

Obviously, growing conditions dramatically influence 

growth ring widths, and abrupt changes in these conditions 

can contribute to nonuniform radial growth rates. Nonuniform growth rates during the juvenile period, although not 

directly influencing wood quality, are nonetheless associated 

with other wood characteristics that do contribute to the 

quality of solid wood products. 

Growth Ring Age 

The accepted method of determining growth ring age in 

wood quality investigations is to count the number of growth 

rings outward from the pith at the level of sampling in the 

tree. Ring age as determined by this method is not to be 

confused with chronological age in which case the first 

growth ring next to the pith would be the oldest. 

In most wood quality investigations, ring ages are counted 

on increment cores or wood disks taken at breast height in 

the tree. Such determinations do not always accurately reflect the true physiological age of the tree. Most loblolly and 

slash plantation-grown trees are 3 to 4 years old before a 

growth ring is discernible at breast height, and in naturally 

established stands, the true physiological age is often unknown. Moreover, ring counts near the pith are often difficult to identify in trees from stands of unknown age because 

of false and indistinct growth rings. For most purposes, the 

physiological age at breast height is perhaps of little or no 

significance but generally is reliable in planted stands. However, heritability estimates and evaluations of wood quality 

characteristics have been made on 2- to 3-year-old seedling 

and clonal material. The question must be raised as to 

whether such estimates are representative of the generally 

accepted values for juvenile wood. 

Ring age within the juvenile core of wood is a function of 

annual height increments. At a given height, for example, the 

18-ft (5.5-m) level, a tree averaging 3 ft (0.9 m) per year of 

annual height growth would show more annual growth rings 

in the juvenile core than one averaging only 2 ft (0.6 m) per 

year. Again, the physiological ages of the growth rings 

comprising the juvenile cores of the two trees at the 18-ft 

(5.5-m) level would be different. Wood quality characteristics within the juvenile core undergo appreciable changes 

with sampling height in the stem, and some of this change is 

undoubtedly due to physiological ages of the growth rings. 

Growth Ring Uniformity 

In wood quality investigations, uniformity refers to consistency in the value of a wood characteristic with increasing 

growth ring age on a stem cross section. That is, the wood 

characteristic either maintains a stable pattern or a gradually 

changing pattern with no abrupt deviations. With regard to 

juvenile wood, uniformity usually refers to width of the 

growth rings, the implication being that a uniform growth 

ring pattern signifies uniformity in the accompanying wood 

characteristics. Nonuniformity of juvenile wood, on the 

contrary, implies highly variable wood characteristics and 

undesirable structural properties. For example, this can result 

in “lathe chatter” (vibrational forces on a veneer lathe), 

which increases surface roughness and decreases gluability. 

To achieve growth ring uniformity, it is necessary that a 

uniform growth rate be maintained not only during the juvenile period but also during the juvenile–mature transition and 

beyond. A uniform growth rate, however, does not mean 

equal ring widths in successively older growth rings. It is 

obviously impossible to maintain ring width equality as a 

tree increases both circumferentially and volumetrically. 

What uniformity does mean is that despite the inherent 

decrease in ring width with age, the rate of growth established in the juvenile core should be maintained to the extent 

possible. One of the main objectives of tree breeding is to 

increase wood uniformity (Zobel and others 1983). 
6 

Authors of a number of spacing studies have suggested how 

growth ring uniformity can be maintained throughout a 

rotation in the southern pines (Bassett 1969, Burton and 

Shoulders 1974a,b). In the case of rapid juvenile growth, 

ring uniformity requires early and frequent thinning. The 

alternative is nonuniform wood when competition intensifies 

and growth rate declines in unthinned stands. Uniformity 

achieved by judicious thinning will not eliminate the undesirable properties of juvenile wood. Thinning simply minimizes structural problems associated with a juvenile–mature 

transition exacerbated by a nonuniform growth ring pattern. 

Some forest managers have recommended management 

systems that not only maintain uniformity but also minimize 

the effects of juvenile wood. Under these systems, juvenile 

growth would be minimized by close initial spacing and this 

growth rate would be maintained by frequent, light thinning. 

Although this method presumably should minimize juvenile 

wood, rotation length would be increased and volume of 

production decreased. 

Summerwood Percentage 

Summerwood percentage is the most easily determined, 

therefore the most widely used, wood quality characteristic. 

Because it is highly correlated with wood specific gravity 

and provides a visual index of strength and structural properties (Koch 1972), it is also an important component of lumber and timber grading rules. 

Juvenile wood is inherently low in summerwood. As pointed 

out in the section Characteristics of Juvenile Wood, springwood formation is favored during juvenile growth because 

of the predominating influence of the tree crown. In fact, in 

some trees, the first several juvenile growth rings appear to 

be all springwood (Hiller 1954). In many other trees, the 

prevalence of false growth rings combined with a broad, 

indistinct band of transition tracheids make it impossible to 

distinguish springwood from summerwood. Consequently, 

summerwood percentage in the rapidly grown juvenile wood 

of southern pines is difficult and sometimes impossible to 

quantify. Most researchers simply make visual estimates 

based on changes in apparent growth ring density and color 

changes in the wood (Zobel and others 1959). 

The older the growth ring relative to the pith and the greater 

its distance from the active crown, the more distinct the 

springwood–summerwood transition and the larger the 

percentage of summerwood. Beyond the first several growth 

rings nearest the pith, summerwood percentage increases 

rapidly within the juvenile core. Selection of 10 years as the 

arbitrarily defined juvenile period for loblolly pine is based 

on the assumption that mature summerwood values will be 

produced thereafter. For example, McAlister and Powers 

(1992) considered a growth ring with 50% summerwood to 

be a good rule of thumb for defining the transition. However, loblolly pine in the northern portion of its range may 

not produce 50% summerwood at any age. Thus, 40% 

summerwood might be a better rule of thumb for defining 

the transition to mature wood. 

Summerwood percentage in mature growth rings varies 

widely with environmental conditions and silvicultural 

practices and, of course, with inherent growth potential. 

Variations in summerwood percentages attributable to these 

factors are discussed in the respective sections of this report. 

Summerwood percentage is simply an index of wood quality 

that is more appropriately evaluated by other wood characteristics. The patterns of specific gravity variation discussed 

in the following section, Specific Gravity, quite accurately 

reflect similar patterns of variation encountered in summerwood percentage. Specific gravity, in turn, is a fairly reliable 

index of the combined effect of tracheid radial diameter and 

wall thickness. 

Specific Gravity 

Specific gravity is perhaps the oldest and most widely used 

criterion for evaluating quality of wood and its strength 

properties. Specific gravity itself is dimensionless. It is the 

ratio of the weight of a wood sample to the weight of a equal 

volume of water at a standard temperature. Specific gravity 

is usually based on the ovendry weight and green volume of 

the wood sample. Although wood density and basic density 

are derived differently, the terms are often used synonymously with specific gravity. Because of the utility of specific gravity as a predictor of the quality and strength properties of wood, researchers have searched over the years for 

some readily definable relation between specific gravity and 

the growing conditions of trees. 

During the early years of research on wood quality, beginning about 1880, it was widely believed that slowly grown, 

narrow-ringed wood of conifers was superior in quality to 

that of rapidly grown, wide-ringed wood. In trees from the 

naturally established stands prevalent at that time, most of 

the wide rings occurred in the growth zone we now refer to 

as juvenile wood. Silviculturists therefore recommended 

planting trees at close spacings followed by frequent stand 

thinning to maintain uniform ring widths. Most of this research was based on data from natural stands and closely 

spaced plantations in northern Europe (Larson 1962), although similar recommendations were made for the southern 

pines in the United States (Paul 1930, 1932a,b). Despite the 

objections of some, these ideas prevailed until about 1950 

when researchers, primarily in South Africa and Australia, 

began examining fast-grown wood from wide-spaced plantation trees. Results of this and later research proved that 

growth ring width, per se, was not a valid criterion for 

evaluating wood quality. The research also demonstrated 

that close initial spacing of trees simply masked the effects 

of juvenile wood by confining these growth rings to a small 

core of wood near the pith where their influence on structural properties was minimized. 
7 

Numerous investigations conducted on the southern pines 

and other Pinus species have conclusively demonstrated that 

wide growth rings are not necessarily associated with a 

reduction in wood specific gravity. Summerwood percentage, which is highly correlated with specific gravity, increases radially outward from the pith, and within the juvenile zone, the increase is both progressive and rapid. This 

age-related pattern in summerwood percentage and specific 

gravity is inherent, and it occurs in both fast- and slowgrown trees. A typical age-related specific gravity pattern for 

loblolly pine in the Piedmont of South Carolina, based on 

data from Zobel and others (1972), is shown in Table 1. 

Realistic average values for loblolly pine range from 0.36 to 

0.45 for juvenile wood and 0.42 to 0.64 for mature wood 

(Zobel 1972). In another study of more than 2,000 loblolly 

pines, Zobel and McElwee (1958) obtained average values 

of 0.45 and 0.59 for juvenile and mature wood, respectively. 

Similar specific gravity values have been reported by other 

researchers. 

Although the age-related pattern is inherent, it is not invariable. As shown later in this report, it can be modified by 

environmental conditions and silvicultural measures that 

affect crown size and development. In a similar way, the 

lack of a correlation between ring width and specific gravity 

requires clarification. Growth rings of the same age from the 

pith but differing in width do not as a rule differ appreciably 

in specific gravity. However, when growth rings of approximately equal widths but of widely different ages are 

compared, for example, from juvenile and mature wood 

zones, the specific gravity of the older rings will almost 

always be greatest because of the inherent radial increase in 

summerwood percentage. 

Lack of a correlation between ring width and specific gravity 

only applies within reasonable limits of comparability. Extremely wide rings are often rich in springwood and extremely narrow rings poor in summerwood. Consequently, 

wood from trees that had greatly different juvenile growth 

rates often differ in specific gravity. Comparisons of this 

nature are illogical when making management decisions. 

Such an error was sometimes unknowingly committed in 

past investigations of the southern pines when juvenile wood 

from open-grown, old field trees was compared with that 

from close-grown, natural stands (Paul 1929). 

The relationship between growth ring width and specific 

gravity within the juvenile zone can be restated. Within a 

rather broad range of ring widths, the rate of juvenile growth 

should exert a negligible effect on wood specific gravity and 

can be ignored for most end products. However, this conclusion does not mean that wide-ringed juvenile wood is comparable in quality with wide-ringed mature wood. 

With reference to the relationship between ring width and 

specific gravity, the weak correlation between these two 

variables is due not only to variations in the percentage of 

summerwood but also to the great disparity in the specific 

gravities of springwood and summerwood. For example, 

Ying and others (1994) found that summerwood percentage 

and wood specific gravity in loblolly pines rapidly increased 

from 15% and 0.39, respectively, at 1 year old, to 53% and 

0.51, respectively, at 10 years old. Considering the withinring variation, Paul (1958) reported that the specific gravity 

of springwood averaged 0.310, whereas that of summerwood 

averaged 0.625 for 12- to 13-year-old loblolly pines averaging 3.7 rings per inch (1.5 rings/cm). These values compare 

favorably with those of Pew and Knechtges (1939), Goggans 

(1964), Megraw (1985), and Hodge and Purnell (1993). 

Goggans reported specific gravity values of 0.29 and 0.63 

for springwood and summerwood, respectively, in an 8-yearold Georgia progeny test. 

The innermost growth rings next to the pith have been found 

to be atypical by some researchers, and these rings were 

therefore deleted from their analyses. That is, the rings either 

lacked recognizable summerwood tracheids or they appeared 

to possess other unacceptable characteristics such as tendencies for compression wood or spiral grain formation, excessive extractive contents, or extremely short tracheids with 

high fibril angles. The atypical nature of these growth rings 

is undoubtedly attributable to physiological age as discussed 

in the section Growth Ring Age. Again, one might question 

heritability estimates based on the first one to several growth 

rings when their physiological ages either have not been 

accounted for or are unknown. 

Within the juvenile zone, specific gravity increases rapidly 

with increasing ring age. Beyond the juvenile zone, specific 

gravity continues to increase but the increase is usually more 

gradual because of a more consistent percentage of 

summerwood associated with increasing ring maturity. 

Summerwood percentages are not invariable, however, and 

mature wood specific gravity values can therefore fluctuate 

quite widely with seasonal weather patterns and changing 

stand conditions. 

Radial specific gravity patterns observed at breast height are 

repeated at different heights in the stem. Although the patterns are similar, the values differ because the rings at higher 

stem levels are both physiologically older and in closer 

proximity to the living crown. A typical pattern for loblolly 

pine, as reported by Pearson and Gilmore (1971), is shown 

in Table 2. 

Table 1—Variation in specific gravity of merchantable wood with age 

Specific gravitya 

10 

years 

15 

years 

20 

years 

25 

years 

30 

years 

40 

years 

0.385 0.409 0.425 0.438 0.449 0.466 

a

Values based on a regression equation based upon 

100-tree sample 
8 

In most studies of juvenile wood, specific gravity is an average value based on a composite of juvenile growth rings 

rather than individual rings within the juvenile core. When 

based on average values, specific gravity will vary with site, 

geographic location, stand conditions, and silvicultural 

practices, as will be shown later in this report. Nonetheless, 

irrespective of the method of group comparison, there is 

usually more variation between individual trees within a 

group than there is between group averages. These differences provide the impetus for genetic improvement. 

Specific gravity is an excellent index of both the anatomical 

characteristics and structural properties of dry wood. Anatomically, it is most closely correlated with the percentage of 

summerwood in the annual growth ring, which in turn is 

related to characteristics of the springwood and summerwood tracheids. Structurally, specific gravity is a important 

component of the grading rules for Southern Pine lumber 

and timbers. However, as we will discuss in the Conclusion 

of this report, it appears to be of limited usefulness in evaluating the quality of juvenile wood for solid wood products. 

Tracheid Diameter and Wall Thickness 

Tracheid radial diameter and wall thickness are the primary 

determinants of summerwood percentage. Springwood 

tracheids are large in radial diameter with relatively thin cell 

walls whereas summerwood tracheids are narrow in radial 

diameter with relatively thick cell walls. The transition from 

springwood to summerwood in mature growth rings of 

southern pines is usually abrupt, and often a springwood cell 

is immediately followed by a distinct summerwood cell. 

Such a transition occurs either in older trees in which the 

active crown is far removed from the stem base or in relatively slow-growing trees. 

In contrast to mature growth rings, the transition from 

springwood to summerwood in wide, juvenile growth rings 

is extremely gradual and diffuse. The difficulty in determining the springwood–summerwood boundary in juvenile rings 

is due to the transitional nature of the mid-ring tracheids. 

These so-called transition tracheids, which are neither 

springwood nor summerwood, often comprise the major part 

of extremely wide juvenile rings. Transition tracheids are 

produced when growth conditions are favorable for the 

prolongation of terminal shoot growth and foliage development and also for the promotion of high levels of photosynthetic activity. Transition tracheids can either gradually 

decrease in radial diameter, increase in wall thickness, or 

both. The most common pattern is for tracheid radial diameter to remain essentially constant (that is, wide lumened) and 

for wall thickness to gradually increase. The measurable 

decrease in lumen radial diameter, typical of true summerwood, occurs in the outermost part of the juvenile growth 

ring. 

The wide zone of transition tracheids is not only a distinguishing characteristic of juvenile wood but also a major 

determinant of wood quality. By modifying the structure of 

these tracheids, dramatic changes can be made in both wood 

quality and structural properties. As we have repeatedly 

emphasized, the tree crown regulates wood formation on the 

stem. Since springwood tracheids are large-lumened, thinwalled, and structurally weak, a reduction in springwood 

formation should contribute to an improvement in quality of 

the wood. Minimizing juvenile ring width can reduce 

springwood. A reduction in ring width always affects 

springwood more drastically than summerwood. A reduction 

in ring width, however, will not necessarily increase the 

amount of summerwood, although it will increase the percentage of summerwood. 

Reduction of juvenile springwood occurs primarily by 

reduction in the width of transition tracheids, which are 

usually classified as springwood. The more drastic the 

decrease in growth rate and ring width, the narrower the 

width of transition tracheids in the growth ring. In relatively 

narrow rings, such as those produced by close initial tree 

spacing, transition wood might be absent in the outer rings 

of the juvenile core. These rings often have the outward 

appearance and visual characteristics of mature rings, 

suggesting to some workers that the juvenile core consists of 

only the innermost six to eight rings. 

It is difficult to generalize as to how the springwood–

summerwood relationship will be affected by either an increase or decrease in ring width. Although both radial tracheid diameter and wall thickness are used to differentiate 

springwood from summerwood, the two characteristics vary 

independently during growth ring formation. That is, radial 

tracheid diameter and wall thickness have been found to be 

under the control of entirely different physiological processes (Larson 1964). Therefore, an environmental factor or a 

silvicultural practice might either increase or decrease wall 

thickness while having no effect on radial lumen diameter. 

However, both the springwood–summerwood ratio and 

wood specific gravity values would be significantly altered, 

as Bethel (1950) pointed out in his work on loblolly pine. 

Tangential tracheid diameter does not vary significantly 

within a growth ring nor appreciably within a tree, and it is 

therefore of no concern in wood quality investigations. 

Table 2—Typical pattern for loblolly pine juvenile wood 

specific gravity with height in stem 

 Specific gravity 

Type of wood 3 fta 13 ft 23 ft 33 ft 43 ft 

Juvenile wood 

(10 years) 

0.474 0.428 0.408 0.405 0.409 

Mature wood 0.525 0.484 0.404 0.434 0.439 

a

Height in stem (1 ft = 0.3048 m). 
9 

This digression into the relative structures of springwood 

and summerwood, and especially of transition tracheids, in 

juvenile growth rings is necessary to place specific gravity in 

proper perspective. Variations in wood specific gravity are 

frequently related back to variations in percentage of 

summerwood. But both of these wood characteristics are 

arbitrary indices dependent almost entirely on the radial 

diameter and wall thickness of the individual tracheids comprising a growth ring. Because of the importance of these 

interrelations to our final conclusions, two highly pertinent 

studies will be briefly summarized. 

In the first study, Pew and Knechtges (1939) examined the 

variation in tracheid diameter and wall thickness in fast- and 

slow-grown loblolly pines. Neither the cross-sectional 

dimensions nor wall thickness of springwood tracheids 

varied appreciably between the fast- (2.9 rings per inch 

(1.1 rings/cm)) and slow- (10 rings per inch (3.9 rings/cm)) 

grown trees either at breast height or at several height levels 

in the stems. Similarly, the cross-sectional dimensions of 

summerwood tracheids did not vary greatly between fastand slow-grown trees, but in the slow-grown trees, summerwood tracheids had slightly thicker walls and wall thickness 

decreased with sampling heights in the stems. 

These authors also examined two loblolly pine upper-stem 

logs, both about 8 years old and of comparable growth rates 

but varying significantly in wood specific gravity. The data 

revealed little variation in cross-sectional dimensions but 

large variations in wall thickness between the high and low 

specific gravity wood samples (Table 3). 

In all samples tested by Pew and Knechtges, specific gravity 

of springwood remained rather constant at 0.28 whereas that 

of summerwood varied widely with variations in wall thickness. They concluded that woods with high and low specific 

gravity values often appear strikingly similar in visual appearance and the underlying differences cannot be detected 

with the naked eye, for example, by grading rules. 

In the second example, McMillan (1968) approached the 

problem differently but arrived at somewhat similar conclusions. His data, based on 40 loblolly pine trees, is summarized in Table 4. Again, it can be seen that the most important variable is summerwood wall thickness. McMillan 

concluded that since springwood wall thickness remained 

constant with distance from the pith while radial tracheid 

diameter increased, the amount of wood substance per unit 

area decreased. Therefore, specific gravity of a unit volume 

of springwood must decrease with distance from the pith. In 

contrast, radial diameters of summerwood tracheids remained essentially constant with increasing distance from 

the pith while wall thickness increased. Therefore, because 

the amount of wood substance per unit cross-sectional area 

increased, the specific gravity of summerwood must increase 

with distance from the pith. 

The main point to be gained from this exercise is that 

springwood and summerwood are independently related to 

specific gravity. Therefore, the characteristic increase in 

wood specific gravity with distance from the pith is determined not only by the relative amounts of springwood and 

summerwood in the growth rings but more importantly by 

Table 3—Variation of specific gravity and cell wall thickness with high and low specific gravity 

1⁄2-in. (13-mm) test samples 

Entire disk 

 

Specific gravity Wall thickness (μm) 

Specific 

gravity 

Rings per 

incha Specific gravity 

Rings 

per inch 

Summerwood (%) Springwood Summerwood Springwood Summerwood 

High 2.7 0.460 2.5 54 0.28 0.68 4.1 8.7 

Low 2.1 0.38 1.8 60 0.28 0.49 3.0 5.8 

a

1 ring per inch = 0.4 ring/cm. 

Table 4—Radial tracheid diameter and cell wall thickness as a function of growth ring

Growth ring number

1–10 11–20 21–30 

 Springwood Summerwood Springwood Summerwood Springwood Summerwood 

Radial tracheid diameter (μm) 52.8 32.8 55.3 33.6 56.7 33.8 

Wall thickness (μm) 4.5 9.4 4.6 9.4 4.6 10.0 
10 

the wall thickness of the individual tracheids and to a lesser 

extent their radial diameters. These conclusions can be reinforced by referring back to the section on specific gravity. 

Tracheid Length 

Tracheid length is of special importance to the pulp and 

paper industry, and for this reason, extensive literature exists 

concerning its variation within and among trees. As a general rule, tracheid length increases rapidly from rings nearest 

the pith to the outer rings of the juvenile core. Thereafter, it 

might continue to increase rapidly, do so more slowly, or 

vary unpredictably. Similar patterns occur in rings of the 

juvenile core at different height levels in the stem, although 

the actual length values often differ. 

Tracheid lengths are quite closely correlated with growth 

ring width. In the juvenile core, tracheid length increases 

more rapidly in narrow than in wide growth rings. In mature 

wood, tracheids are generally longer in narrow than in wide 

rings. 

Within a growth ring, summerwood tracheids are longer than 

springwood tracheids. In radiata pine, tracheid length has 

been found to increase rather abruptly at the springwood–

summerwood transition, attain a maximum in the mid- to 

late-summerwood zone, and then decrease sharply at season’s end (Nicholls and others 1964). The wider the growth 

ring, the more gradual the increase at the springwood–

summerwood transition, particularly in juvenile rings with 

broad bands of transition tracheids. Similar patterns have 

been observed in other conifers, including loblolly pine (Ifju 

and Labosky 1972). 

Reported values for tracheid lengths within and among 

loblolly pine trees are extremely variable. Because of the 

manner in which cambial cells divide and the new wood 

cells then elongate, a population of tracheids is produced 

that varies widely in length. Research has shown how this 

population of tracheids originates and why it is so variable. 

Briefly, the changes are related to how rapidly the cambial 

cells must divide to accommodate the circumferential growth 

of the tree. The process is complex and is of no immediate 

concern in this report. The subject has been thoroughly 

covered in Larson (1994, chap. 6). 

In addition to variation with age and position within stems of 

individual trees of loblolly pine, tracheid length has also 

been found to vary among trees according to stand density, 

site, geographic location (Zobel and others 1960), and different silvicultural practices. Tracheid length also varies 

widely among individual trees and is considered a highly 

heritable trait. 

Although tracheid length has been found to be correlated 

with summerwood percentage, possibly due to the withinring pattern, it is either poorly or sometimes negatively 

correlated with wood specific gravity according to Zobel and 

others (1960). 

Tracheid length, by itself, is of little or no importance in 

evaluating strength or structural properties of products made 

from mature wood. However, longer tracheids in juvenile 

wood appear to impart increased MOE and tensile strength. 

Longer tracheids are also associated with smaller fibril 

angles (Megraw 1985). Some typical tracheid length values 

for loblolly pine are given in Table 5. 

Microfibrillar Angle 

The secondary, or S2, layer is the main wall layer comprising 

the bulk of a pine tracheid. Research has shown that the 

compound middle lamella and the S1 and S3 layers remain 

essentially fixed, while variation in volume of the S2 is 

solely responsible for change in total cell wall thickness 

(Cave 1976). The secondary wall is not solid wood substance. Rather, it consists of helically arranged cellulose 

microfibrils oriented in the long axis of the tracheid. Orientation of the microfibrils in juvenile wood tracheids varies 

widely both within the same tree and among different trees. 

Table 5—Tracheid lengths for loblolly pine 

Tracheid length (mm) 

Reference Juvenile wood Mature wood 

Springwood Summerwood Springwood Summerwood 

McMillan (1968) 3.52 3.79 3.91 4.13 

Taylor and Moore (1981) 2.92 3.14 4.15 4.17 

Cole and others (1966) 2.58a

 3.45a

Zobel and Blair (1976) 2.56a

 3.41a

Kellison (1981) 2.98a

 4.28a

a

These values were average values for both springwood and summerwood. 
11 

In mature loblolly pines, the microfibrillar or fibril angle is 

small, averaging about 5° to 10° as measured by deviation 

from the vertical. In juvenile wood, the fibril angle is large, 

averaging 25° to 35° and often up to 50° in rings next to the 

pith, then decreasing outward in the juvenile core. However, 

the decrease in fibril angle often continues well beyond the 

juvenile core. For example, Ying and others (1994) found 

that fibril angles in tracheids of fast-grown loblolly pines 

decreased from 33° at age 1, to 23° at age 10, and to 17° at 

age 22. Bendtsen and Senft (1986) reported that loblolly 

pines had not yet attained stable fibril angles at age 30. 

Within the juvenile zone, fibril angle varies with growth 

rate. As a general rule, fibril angles are larger in wide than in 

narrow growth rings. Pillow and others (1953), for example, 

found that fibril angles in the juvenile wood of open-grown 

loblolly pines averaged almost 20° larger than those in a 

closely spaced natural stand. Fibril angles of springwood 

tracheids are also larger than those of summerwood. This 

difference between springwood and summerwood fibril 

angles accounts for the fact that fibril angles have been 

reported to be negatively correlated with both summerwood 

percentage and specific gravity, although not always so. 

The negative correlation is much stronger between fibril 

angle and wall thickness. The angle of orientation of the 

microfibrils tends to increase from the inner to outer parts 

of the secondary wall. And so, the thicker the secondary 

wall, the smaller the fibril angle. Hiller (1964) found that 

wall thickness accounted for 64% to 81% of the variation 

in fibril angle. 

Fibril angle is negatively and strongly correlated with 

tracheid length in growth rings of mature wood (the longer 

the tracheid, the smaller the fibril angle). Although this 

relationship also holds in the juvenile growth rings, the 

correlation is weaker and it is for this reason that fibril angles often continue to decline in slope outward in the stem 

long after tracheid length values have stabilized. 

A strong relationship exists between fibril angle and longitudinal shrinkage. Tests by Harris and Meylan (1965) on 

juvenile wood of radiata pine showed that longitudinal 

shrinkage increased sharply while tangential shrinkage 

decreased at fibril angles greater than 25°. More specifically, 

longitudinal shrinkage was low as fibril angles decreased 

below 25°, whereas tangential shrinkage increased as fibril 

angles decreased below 15°. Ying and others (1994) confirmed these data by showing that fibril angles of 25° or 

greater corresponded to the outer boundary of the 10-year 

juvenile core in loblolly pine. 

Compression wood tracheids, which are both abnormally 

short and thick-walled, also have excessively large fibril 

angles. Compression wood growth rings with extremely 

large fibril angles show a higher degree of longitudinal and a 

lower degree of tangential shrinkage than normal wood for 

comparable fibril angles (Harris 1977). For example, at a 

fibril angle of 40°, longitudinal shrinkage of radiata pine 

compression wood was 2.5%, whereas that of normal wood 

was only 1%. In trees with strongly expressed compression 

wood in the juvenile core, longitudinal shrinkage of 

summerwood was 3% to 5% and that of springwood was 

2%. This apparent contradiction, with summerwood shrinking more than springwood, is due to the fact that compression wood is essentially a summerwood phenomenon. 

Shrinkage is due to several interrelated factors but is primarily due to the removal of moisture from between the microfibrils and from within the cellulosic microfibrillar matrix. From a practical standpoint, wood shrinkage can be 

related to microfibril angle with a high degree of certainty. 

Other Wood-Related Properties 

Branches, Knots, and Knotwood 

Loblolly pine has relatively small branches and exhibits 

good self-pruning, especially for lower stem branches. According to von Wedel and others (1967), branches in the 

lower crowns of loblolly pines 8 to 11 years old, planted 7.8 

by 7.8 ft (2.4 by 2.4 m) apart, essentially stopped growing 

after the third year. Reduced growth, however, does not 

necessarily mean branch death. For example, Paul (1957) 

estimated that loblolly branches remain alive for about 

7 years in the lower 20 ft (6.1 m) of stem, although a more 

reliable estimate might be 4 or 5 years. 

This pattern of branch death and senescence continues upward in successive branches as long as height growth remains strong and crown competition persists. However, 

when height growth begins to slow, branches of the upper 

crown remain alive longer because of the reduced competition for sunlight. These upper-crown branches are usually 

larger in diameter and have steeper branch angles relative 

to the main stem than lower-crown branches. In general, 

fast-growing trees have steeper branch angles than slowgrowing trees, although all branch angles tend to flatten 

as a branch ages. 

Both branch longevity and branch size can be controlled to a 

large degree by stand density. Close initial spacing encourages small branches and early mortality, whereas wide initial 

spacing encourages large, persistent branches. Close initial 

spacing significantly reduces radial stem growth, but it also 

confines knotwood to a smaller juvenile core. Any management practice that stimulates overall crown and foliage 

development, such as thinning or fertilization, will prolong 

the life and invigorate the growth of existing branches 

(de Villiers 1965, 1966). For example, Burton and Shoulders 

(1974a) observed that lower branches developing in heavily 

thinned loblolly pine stands were so large that artificial 

pruning was required to ensure an outer cylinder of clear 

wood. Another closely related effect of heavy thinning or 

fertilization in young stands is the stimulation of height 

growth. An increase in height growth can be accomplished 
12 

by an increase in the number of branch whorls (growth 

flushes), by an increase in the distance between whorls, or 

both. An increase in the number of whorls would, of course, 

increase branch number and knot volume. 

Another important branch characteristic is the number of 

branches per whorl. Paul (1957) considered two to four, 

sometimes five, branches per whorl to be typical of loblolly 

pine. von Wedel and others (1967) arrived at a similar conclusion, although they observed differences among selected 

progenies. Apparently, a tree can satisfy its foliage needs by 

either producing a small number of relatively large branches 

per whorl or a larger number of small branches. 

Branch death is not the same as self-pruning, which is the 

elimination of dead branches from the stem. Loblolly is a 

fairly efficient self-pruning species. Nonetheless, the propensity for self-pruning decreases upward on the stem as 

branch sizes and branch angles increase. The longer the dead 

branch remains intact on the stem, the larger the core of 

knotty wood. Retention of dead branches with acute branch 

angles are especially deleterious because the resulting knots 

not only are larger but also pass through a larger volume of 

stem wood. 

Publications by von Wedel and others (1967, 1968) contain 

a wealth of information, including knot sizes, volumes, and 

distributions, on loblolly pine. Knot volume is considered a 

better measure of potential lumber degrade than knot size. 

Knot volume includes the effects of branch or knot angle as 

well as associated defects such as compression wood, grain 

distortions, and pitch deposits. 

Knots in the juvenile core contribute to serious degrade of 

solid wood products. Large knots are sites of weakness in an 

already substandard wood, particularly if the wood is rapidly 

grown. Trees with high knot volumes also have high 

amounts of compression wood (von Wedel and others 1967). 

The volume occupied by knotwood and compression wood 

increases upward in the stem, contributing to lesser value of 

upper-stem logs. On a total tree basis, the compression wood 

associated with knotwood averaged 7.1% of the stem 

volume of 11-year-old loblolly pine trees (von Wedel and 

others 1967). 

Pearson (1988) examined knotty and knot-free stud samples 

cut from the juvenile cores of loblolly pines. Knotty studs 

had slightly higher specific gravities than clear studs because 

of the higher density of knots. Nonetheless, the mean maximum crushing strength of the knotty studs was only 41% of 

the species mean value compared with 52% for the clear 

studs. Interestingly, he found that the continuity of grain and 

swelling of the trunk around large knots in loblolly pine 

stemwood tended to counteract, to some extent, the reduction in crushing strength caused by the knots. Other structural properties were similarly reduced by the presence of 

knots. For example, MOR in upper-stem logs was reduced 

outward from the pith due to the larger knots. 

Compression Wood 

Compression wood, or reaction wood, occurs on the lower 

sides of leaning coniferous stems, on the undersides of 

branches, and below the level of branch insertion on a stem. 

It is a gravitational response, and its formation tends either 

to return a leaning stem to an upright position or to maintain 

the position of a branch within the crown. Tree lean in 

young pines can be attributed to many causes such as poor 

planting procedures, spongy soils with poor root holding 

ability, persistent prevailing winds or wind storms, and 

heavy thinning or sudden release cutting (see Timell 1986 

for an exhaustive review of compression wood). 

All degrees of compression wood can be encountered in the 

juvenile cores of southern pines. When lean is excessive and 

tree growth is vigorous, the stem cross sections will appear 

eccentric because of the unusually wide growth rings that 

develop on the underside of the lean. Compression wood is 

produced primarily during summerwood formation, and the 

extra-wide summerwood zone is preceded by a broad band 

of transition tracheids that resemble summerwood. Compression wood is easily recognized in eccentric growth rings. 

However, it can also be present in growth rings that show 

little or no eccentricity. In such cases, compression wood 

can only be visually detected by the dark coloration of transition tracheids that appear as a crescent or eccentric arc in 

an otherwise normal appearing growth ring. It is most easily 

detected by its greater opacity when viewed with transmitted 

light. 

Young loblolly pines are highly susceptible to compression 

wood formation, especially during the first few years of 

growth (Zobel 1961, 1976; Bendtsen and Senft 1986). In 

some rapidly grown trees, compression wood arises without 

any observable cause and it often appears in young trees 

showing no evidence of lean (Cown 1974, Harris 1977). 

Compression wood is known to be caused by an excess of 

growth hormones produced by elongating shoots and foliage 

organs of the crown, and the combination of rapid growth 

and short branch-free stems in young, upright trees accentuates the response. Anatomically, the innermost rings of the 

juvenile core in fast-grown trees resemble compression 

wood, and physiologically, the processes responsible for 

both types of wood are remarkably similar. 

Compression wood often occurs in the wood of young pines 

after heavy fertilization and/or thinning even in trees that are 

apparently free of lean (de Villiers 1965, 1966; Smith 1968). 

For example, in radiata pine, heavy thinning increased the 

incidence of compression wood by 20% in butt logs that 

showed no evidence of eccentricity (Cown 1974). 

The specific gravity of compression wood is usually reported 

as being higher than that of normal wood, possibly because 

of the higher proportion of summerwood in the growth rings. 

According to Shelbourne and Ritchie (1968), the specific 

gravity of springwood compression wood was the same as 
13 

normal wood after extraction. However, the specific gravity 

of summerwood compression wood was slightly lower than 

normal due to intercellular spaces, larger tracheid lumens, 

and spiral checking in the secondary wall layer. These tracheid characteristics are typical of compression wood. The 

intercellular spaces are formed by the circular rather than 

hexagonal-shaped tracheids when viewed as cross sections, 

and the spiral checking is related to the high fibril angle. 

Tracheids of both springwood and summerwood are shorter 

than normal in compression wood. 

Physical properties of compression wood are similar to those 

of juvenile wood but are more extreme due to the accentuated tracheid characteristics. For example, normal, green 

Southern Pine lumber shrinks longitudinally about 15 parts 

in 10,000; compression wood is often 10 times that (Manwiller 1966). Stresses in boards with both juvenile and compression wood may be so severe as to cause splitting. This 

combination can be particularly damaging in boards or 

planks consisting of only a few growth rings as often encountered in the juvenile core. Compression wood is also 

associated with warp, bowing, and other distortions in lumber that appear during drying. In radiata pine with strongly 

expressed compression wood, longitudinal shrinkage in 

summerwood of the juvenile core was about 3% to 5% in 

contrast to almost zero shrinkage in normal summerwood 

(Harris 1977). Longitudinal shrinkage of springwood was 

about 2%, not appreciably different than normal springwood. 

Longitudinal shrinkage has been found to be highly correlated with fibril angle. Compression wood tracheids have 

abnormally large fibril angles. But for the same fibril angle, 

compression wood shrinks longitudinally more than normal 

wood. The difference is believed to be related to the thicker 

secondary wall layers, lower cellulose content, higher hemicellulose content, and the spiral checking in the secondary 

wall of compression wood. Longitudinal shrinkage results 

during drying when moisture is removed from between the 

microfibrils and the spiral checks in the secondary wall. 

Transverse shrinkage responds differently to changes in 

fibril angle. Again, in radiata pine, longitudinal shrinkage 

increased sharply at fibril angles greater than 25° while 

tangential shrinkage decreased with increasing fibril angles 

just as it did in normal juvenile wood (see Microfibrillar 

Angle section). Longitudinal shrinkage was low at fibril 

angles less than 25°, whereas tangential shrinkage was highest below 15° (Harris and Meylan 1965). 

Spiral Grain 

Spiral grain is a defect in which the tracheids within a 

growth ring are aligned at an angle to the vertical, that is, the 

normal stem axis. It is not to be confused with fibril angle, 

which involves the orientation of the microfibrils comprising 

the tracheid walls. When severe, spiral grain can exert an 

adverse effect on solid wood products because of differential 

drying resulting in warping, checking, and cracking. 

Spiral grain is an inherited characteristic, and it therefore 

varies considerably among trees. It also varies among species with slash and loblolly being affected to a much lesser 

degree than radiata pine. However, in all species, certain 

trees express a proclivity for spiral grain formation in juvenile growth rings nearest the pith. The tendency usually 

disappears in older rings, although it might persist if growth 

is exceptionally rapid. 

The occurrence of spiral grain in the innermost rings of the 

juvenile core might be difficult to silviculturally control in 

rapidly growing young trees. However, because of the strong 

inherited potential, trees with excessive spiral grain in the 

juvenile core should be eliminated as parents. 

Extractives 

Extractives in southern pines are essentially resin acids in 

turpentine. They often saturate growth rings near the pith to 

varying extents. When present in large amounts in solid 

wood products, extractives can create problems in painting, 

finishing, and the penetrability of preservatives. Although 

extractives exert little or no influence on either the strength 

or physical properties of wood, they do significantly affect 

specific gravity values. For this reason, alcohol–benzene 

extraction is recommended before specific gravity determinations are made. 

Typically, specific gravity in the juvenile core of southern 

pines increases rapidly in the radial direction. However, in 

unextracted wood, specific gravity values of the first several 

rings nearest the pith are abnormally high because of resin or 

pitch deposits. These growth rings not only have an abundance of resin ducts but the ducts are well distributed 

throughout the growth rings (Larson 1994, chap. 9). Wildfires or controlled burns that severely scorch the bark can 

cause release of the resin. Stem swaying by strong winds can 

have a similar effect. For some unknown reason, pitch deposition increases in growth rings of the juvenile core as trees 

increase in size and age. Such depositions are unpredictable, 

and large tree to tree variations have been reported for the 

southern pines (Goggans 1961). 

Taras and Saucier (1967) estimated that unextracted increment cores overestimated specific gravity by 6.0% to 7.5%. 

Similar values were obtained by Cole and others (1966) in a 

10-tree sample of loblolly pine. The extractive content averaged 3.06% for juvenile wood and 2.67% for mature wood. 

Unextracted and extracted specific gravities were 0.430 and 

0.413 for juvenile wood and 0.553 and 0.540 for mature 

wood, respectively. 
14 

Heartwood 

Heartwood formation, like extractives content, exerts little or 

no influence on both the strength and physical properties of 

solid wood products. However, the deposition of minerals 

and other biochemical constituents associated with the death 

and dissolution of ray cells during heartwood formation can 

significantly affect specific gravity values. Heartwood deposits also serve as preservatives for certain solid wood 

products. 

Alcohol–benzene extraction removes most heartwood deposits along with the resins. However, in older trees with significant heartwood formation, specific gravity values for 

rings in the juvenile zone often remain high even after extraction (Zobel and others 1959). Although the cause is 

unknown, these higher values are probably due to residual 

minerals and other insoluble constituents. 

The time of heartwood initiation varies among the southern 

pines. In slash pine, it might begin as early as 8 years, 

whereas it might be delayed until age 30 in loblolly pine 

(Zobel and Blair 1976). Zobel and others (1959) concluded 

that heartwood in loblolly pine was of little significance 

during a rotation age of 25 to 45 years. Paul (1952) reported 

that heartwood is initiated earlier in weak or suppressed trees 

than in co-dominant or dominant trees. Moreover, it can first 

appear at an isolated position on a stem cross section or at 

varying height levels in the lower stem. Once initiated, 

heartwood formation gradually spreads outward in rings of 

the juvenile core and beyond. The denser the stocking and 

slower the growth, the larger the inner core of heartwood 

relative to the outer sapwood. Consequently, rapidly grown 

trees often retain wide sapwood bands well into maturity. 

Based on analysis of increment cores from 577 loblolly and 

519 longleaf pine trees sampled across the South, Clark 

(1994) also reported that the more rapid growing trees contained a wider band of sapwood than the slower growing 

trees. However, he also found that the faster growing trees 

on the good sites contained a wider core of heartwood at an 

earlier age than the slower growing trees on the poorer sites. 

Stem Form and Taper 

Stem form generally relates to straightness of the stem. In 

this sense, defects include stem crooks, bowing, and other 

deformities. Such defects, unless severe, have little effect on 

most wood quality characteristics other than the possibility 

of induced compression wood. However, any deviation in 

stem straightness will affect not only the total yield of solid 

wood products but also the lengths of straight boards cut 

from logs. In one study, separation of 165 loblolly pines into 

five straightness categories resulted in 5% more lumber 

recovery from straight trees than from the average tree in the 

stand (Kellison and others 1985). Tree straightness is one of 

the easiest qualities to improve genetically, and estimated 

gains of 24% have been attained in one generation. 

Another interpretation of stem form involves stem taper, a 

measure of the degree of cylindricity of a stem (Larson 

1963). Lumber yield of strongly tapered stems is decreased 

because of the diameter difference between the log bottom 

and top. Strongly tapered stems also produce shorter poles of 

lesser quality. 

Stem taper is related to crown size and its distribution on the 

stem and also to rate of growth. In general, rapidly growing 

trees with deep, full crowns have greater stem taper than 

slower growing trees with high-setting crowns. Thus, artificial pruning, which reduces crown length, tends to increase 

cylindricity and decrease stem taper. On the contrary, heavy 

thinning or sudden tree release, which retards branch decline 

and increases crown size, tends to decrease cylindricity and 

increase stem taper. In the former case, growth would shift 

upward toward the new crown base, whereas in the latter 

case, growth would shift downward in response to renewed 

crown vigor. Loblolly pine growing on a good site and 

expressing strong height growth would undoubtedly show 

minimal taper in the first log. Consequently, changes in stem 

taper following judicious thinning should be negligible. 

Effects of Environment 

Stand Density 

Stand density regulation is the most powerful tool available 

to the silviculturist for controlling wood formation and 

quality. Stand density regulation is, in essence, a form of 

crown control, as mentioned in the Introduction. 

In plantation management, stand density is determined by 

initial stocking density and thereafter by the frequency and 

intensity of thinning, if any. Initial stocking densities are 

management decisions with important consequences relative 

to both the quantity and quality of the final product. Once a 

plantation is established, silvicultural practices can modify 

the initial stocking level in a desired direction but they are 

expensive to employ and of limited effectiveness. 

The effect of stocking levels on crown competition can be 

illustrated by contrasting the growth response of loblolly 

pines at two widely different initial spacings. At a 12- by 

12-ft (3.7- by 3.7-m) spacing, tree crowns develop unimpeded to their full potential. Lack of competition permits 

vigorous foliar development and the formation of large, 

persistent lower-stem branches. These crown attributes 

continue until crown closure eventually causes the lower 

branches to decline and then die for lack of sunlight. Up to 

this time, however, the large, vigorous crowns will have 

contributed to large juvenile cores of wide-ringed, knotty 

wood that tapers upward in the stem. Irrespective of how the 

stand is managed in later years, these juvenile core attributes 

will persist. 

The wide-ringed wood that forms in the juvenile core of 

these trees typically has high proportions of springwood and 
15 

transition wood, low specific gravity, short tracheids with 

relatively large fibril angles, and in some trees, abnormal 

amounts of compression wood and extractives. Collectively, 

these wood characteristics contribute to substandard grades 

of solid wood products. 

At the other extreme, for example, a 4- by 4-ft (1.2- by 

1.2-m) spacing on a good site, noticeable crown competition 

might begin within a few years after planting. As competition intensifies, the lower, shaded branches die and branch 

senescence gradually advances upward on the stem. These 

dead, lower-stem branches, which are small in diameter, will 

be confined to a relatively small juvenile core. The small 

juvenile core is the result of the narrow growth rings produced by restricted crown development not the tendency for 

close spacing to accelerate the transition to mature wood 

formation. The influence of initial spacing on the date of 

transition from juvenile to mature wood of loblolly pine was 

examined at breast height for loblolly pine planted at 6 by 6, 

8 by 8, 10 by 10, and 12 by 12 ft (1.8 by 1.8, 2.4 by 2.4, 

3.1 by 3.1, and 3.7 by 3.7 m) in the Piedmont of Georgia and 

slash pine planted at 6 by 6, 8 by 8, 10 by 10, and 15 by 15 ft 

(1.8 by 1.8, 2.4 by 2.4, 3.1 by 3.1, and 4.6 by 4.6 m) in the 

Coastal Plain of Georgia (Clark and Saucier 1989). Results 

show that planting density does not significantly affect the 

age of transition from juvenile to mature wood but does 

affect the diameter of the juvenile core. 

The narrow-ringed wood that forms the juvenile core of 

loblolly pine planted at close spacing typically has a relatively narrow band of transition tracheids. However, because 

summerwood formation is also restricted, the specific gravity of these narrow rings seldom differs from that of growth 

rings produced at wider spacings. Yet, the summerwood 

tracheids usually will be longer and fibril angles smaller 

compared with tracheids in the much wider growth rings. 

The differences in the wood produced at extremely wide and 

narrow initial spacings is less a matter of quality than quantity. As emphasized previously, juvenile wood quality characteristics are inherent to the species examined. They can be 

modified only to a limited extent. Thus, narrow spacing 

simply confines the juvenile growth rings to a smaller central 

core. But, as we will discuss later, it is the size of the core 

that is important during conversion to a final product. For 

example, Clark and others (1994) found that loblolly pines 

planted at 6- by 6-ft (1.8- by 1.8-m) spacing and thinned to 

100 ft2

 (9.3 m2) basal area at age 18 yielded 60% No. 2 and 

better lumber when harvested at age 38. A stand planted at 

12- by 12-ft (3.7- by 3.7-m) spacing, thinned to the same 

basal area, yielded 42% No. 2 and better lumber. The lumber 

value for trees at the narrower spacing was about 10% 

higher than those at the wider spacing. 

In most spacing studies of loblolly pine, the close-spaced 

stands have been thinned because of the excessive per-tree 

volume reduction caused by carrying such stands through 

a short rotation. If thinning is not conducted on time, 

nonuniform wood and additional wood quality problems can 

develop. 

Site 

Site quality, which causes variations in overall growth and 

wood formation, is next in importance to stand density. Site 

quality varies greatly within a species range, but in every 

case, wood quality can be related to the growth response. 

That is, good sites will produce trees with wood quality 

characteristics associated with fast growth and poor sites 

with slow growth. Poor sites are usually those with either 

nutrient deficiencies or poor soil moisture conditions. Like 

the effects of stand density, which can be modified by thinning, the effects of site can be ameliorated to some extent by 

fertilization, irrigation, and drainage. 

Most commercial plantations are established on moderate to 

good sites, and differences in wood quality due to the site are 

in most cases insignificant. This does not mean, however, 

that site differences are inconsequential. Zobel and others 

(1960), for example, found highly significant site differences 

in all wood characteristics studied in an extensive investigation of loblolly pine. Lantz and Hofmann (1969) and Zobel 

and others (1972) also found that local site and environment 

had a greater effect on wood quality than the source of seed 

in several progeny tests. 

Geographic Location 

Geographic location refers to the differences in tree growth 

and wood quality throughout a species range. Geographic 

location differs from site. Site differences are due to local 

environmental effects, whereas geographic location differences are due primarily to broad climatic effects, although 

edaphic and other regional factors cannot be ruled out. 

Several studies have demonstrated a general trend for wood 

specific gravity values to decrease from south to north and 

east to west within the species range of loblolly pine. This 

south–north trend is particularly evident in stands in the 

western part of the range and along the Atlantic Coast, but it 

is not present in the Piedmont region. These regional differences strongly coincide with seasonal rainfall patterns and 

length of the growing season. Regional climatic influences 

are presumably responsible for the finding of Clark and 

Saucier (1989). They reported that the period of juvenile 

wood formation in loblolly and slash pines increased from 

6 years in the Gulf Coastal Plain to 14 years in the Piedmont. 

Juvenile wood is apparently influenced to a lesser degree 

than mature wood by geographic location of the planting 

site. For example, Talbert and Jett (1981) concluded that the 

range in specific gravity values for loblolly pine juvenile 

wood was smaller than that of mature wood, and geographic 

trends in the former were not evident. In an earlier study, 

Zobel and others (1959) could detect no trends in the specific gravity of corewood due to geographic location.
16 

Effects of Silviculture 

Thinning 

The effect of stand thinning on wood quality is variable. It 

depends on initial stocking, tree age, time of year, site, and 

many other growing conditions. The main purpose of thinning at any age is to enhance growth rate by promoting 

crown expansion. To maximize wood quality characteristics 

in a young stand, an optimal balance must be struck between 

stem growth rate and a degree of crown expansion sufficient 

to promote competition and self-pruning. Thus, heavy or 

frequent early thinnings will promote lower branch growth, 

delay self-pruning, increase stem taper, increase the proportion of springwood in the growth ring, increase the tendency 

for compression wood formation, as well as other characteristics associated with rapid juvenile growth. Light or delayed 

early thinnings of closely stocked stands will produce essentially opposite growth and wood quality responses. From the 

wood quality standpoint, some of these responses are beneficial but at the expense of volume growth. 

The response to thinnings conducted at older ages, such as 

the pole stage, are less predictable because of the many 

interrelated variables. Thinning cannot revive decadent 

lower-crown branches, but it can rejuvenate living branches 

thereby increasing their size and longevity. Most thinnings 

tend to favor early season crown development. Thus, as the 

crown expands, it not only promotes wider growth rings but 

also the proportion of springwood and transition tracheids in 

the growth rings. In some situations, thinning can also favor 

late-season growth processes. That is, in addition to increasing crown foliage mass, thinning can also increase foliage 

efficiency and extend the seasonal duration of wood formation. These conditions would enhance summerwood production, and the growth rings produced after thinning, although 

wider, would not show any appreciable decrease in the 

percentage of summerwood or wood specific gravity. 

A good example of the latter condition would be closely 

stocked stands in which reduced root competition alleviated 

late-season soil moisture stress (Bassett 1969, Smith 1968). 

This, again, would be an indirect effect with the greater 

availability of water promoting late-season foliage 

efficiency. 

The duration of thinning response depends on initial stocking and stand conditions, intensity of thinning, and response 

of the trees to thinning. The response as measured by enhanced growth ring widths can be short-lived, usually lasting 

for 2 or 3 years (Szymanski and Tauer 1991), but sometimes 

longer. It will continue until either crown or root competition, whichever becomes limiting, is reestablished. 

In general, judicious thinning schedules have a negligible 

effect on wood specific gravity. The response is usually 

short-lived, and a reduction in summerwood production for a 

few years is minimized when averaged across all rings in a 

juvenile core or across a rotation. For example, Burton and 

Shoulders (1974a,b) demonstrated that it was possible to 

grow 18- to 20-in. (457.2- to 508-mm) diameter loblolly 

pines averaging 3 rings per inch (1.2 rings/cm) by periodic 

heavy thinning. However, the trees had large, persistent 

branches requiring pruning to produce merchantable sawlogs. Although wood specific gravity at DBH averaged 0.53 

for all 27 growth rings, specific gravity for the juvenile core 

was presumably much below this level. Several additional 

examples of thinning studies have been described by 

MeGraw (1986). 

The benefits of thinning in terms of growth promotion are 

many and obvious. However, the negative effects must also 

be recognized and balanced against the positive in keeping 

with the product objective. 

Pruning 

Pruning involves the artificial removal of branches from a 

tree. Dead branch pruning simulates natural self-pruning by 

removing dead branches or branch stubs that would otherwise extend outward in the juvenile core. Green or live 

branch pruning eliminates branches that would otherwise 

continue growing. Their removal ensures a smaller knot size 

and a smaller knotty core. 

The effect of green pruning is to reduce the crown of an 

open-grown tree to that of a simulated stand-grown condition. Severe green pruning, in which many lower-stem 

branches are removed at one time, causes pronounced readjustments in tree growth. Because of the smaller residual 

crown, height growth might be temporarily reduced. Meanwhile the lower branches at the new crown base become 

larger and more vigorous. Radial growth at the stem base is 

reduced in heavily pruned trees, and the height level in the 

stem at which maximum ring width occurs shifts upward to 

the new crown base. Concomitant with these changes in ring 

width, the percentage of summerwood and the specific gravity values increase in the lower stem. All these responses can 

be associated with a smaller, less vigorous crown and a long, 

branch-free stem. In young trees, pruning tends to accelerate 

the transition from juvenile to mature wood characteristics in 

growth rings below the new crown base. In many respects, 

the growth responses after pruning are opposite those caused 

by stand thinning. But, as in thinning, the effects are usually 

short-lived. Depending on the degree of live branch removal, 

the growth pattern returns to normal within a few years. 

The aforementioned growth responses are typical of what 

might be anticipated with moderate to severe green pruning. 

Light green pruning might elicit either a negligible or insignificant response. Green pruning is labor-intensive and 

relatively costly, although it is routinely performed in the 

fast-growing pine plantations of New Zealand and South 

Africa and in some loblolly pine plantations in the southern 

United States. 
17 

The benefits of green pruning are to produce lower-stem 

bolts or logs with small, tight knots and short branch-free 

stubs confined to a small knotty core. Ancillary benefits are 

reduced stem taper and increased percentage of summerwood and specific gravity in the lower stem, depending on 

the growth response. In addition to economic considerations, 

another negative effect of pruning is the increased growth of 

branches at the new crown base, which often drastically 

reduces the grade of the lumber from upper logs. 

Fertilization 

The purpose of fertilization is to increase tree growth by 

artificially supplying one or more mineral nutrients that are 

limiting to growth in the natural environment. In one sense, 

fertilization provides a temporary boost in site quality. 

It is difficult to generalize regarding the effect of fertilization 

on wood quality because of the large number of influencing 

variables and the fact that no two studies were conducted 

under similar conditions. General statements can be made, 

however, as to the anticipated growth responses of tree stem 

and crown. The effects of fertilization are somewhat akin to 

those observed after thinning. If height growth and overall 

crown development are promoted, increased wood growth 

will usually be accompanied by a increase in springwood 

and transition tracheid formation, hence a decrease in 

summerwood percentage and specific gravity. If, on the 

other hand, foliage mass and photosynthetic efficiency are 

promoted or the duration of seasonal growth prolonged, then 

the percentage of summerwood might be maintained despite 

the increase in growth ring width. Under some circumstances, increased photosynthetic efficiency can significantly 

increase cell wall thickness of the summerwood tracheids. 

Tree age at the time of fertilizer application apparently has a 

pronounced effect on the nature of the response. Fertilization 

either at the time of planting or during the first few years of 

growth, especially if combined with cultivation, increases 

both height growth and crown development. Decreases in 

summerwood percentage and specific gravity usually accompany these growth responses. In older trees, particularly 

beyond the juvenile stage, the response is less dramatic. 

Although a modest decrease in the percentage of summerwood often occurs during the first few years after fertilization, it is usually short-lived. A curve of summerwood percentage compared with age will therefore show a severalyear decline followed by a return to normal values. This 

temporary decline in summerwood percentage has a negligible effect on specific gravity. In fact, most studies conducted 

on southern pines growing on reasonably good sites indicate 

that summerwood percentage and wood specific gravity are 

not adversely affected by site fertilization (MeGraw 1986, 

Blanche and others 1992, Jokela and Stearns-Smith 1993). 

If, however, fertilizer treatments are either heavy or frequently repeated, as in Posey’s (1964) studies on loblolly 

pine, then significant reductions can occur in both summerwood percentage and specific gravity. These values return to 

normal gradually over a period of years. Posey (1964) and 

Rockwood and others (1985) noted tree to tree variation, 

suggesting a genetic response to fertilization. 

Irrigation and Drainage 

The growth responses due to irrigation are similar to those 

brought about by fertilization. That is, the response depends 

on the time of year in which water is artificially applied. 

Consequently, early-season irrigation will favor height 

growth and overall crown development, which promotes 

springwood formation, whereas late-season irrigation will 

prolong seasonal cambial activity, which promotes summerwood formation. In most irrigation studies, water is supplied 

throughout the growing season resulting in greater growth 

and wider growth rings. Because both springwood and 

summerwood formation are promoted under this irrigation 

schedule, the effect on wood specific gravity is usually 

negligible. 

In practice, water might more realistically be supplied when 

needed. Because soil moisture is most commonly limiting 

during late-season growth, irrigation at this time of year 

would promote summerwood formation and increase specific gravity. 

Cultivation 

Cultivation involves the removal of competition by herbaceous weeds, grasses, and woody undergrowth. In newly 

planted stands, cultivation removes plants that not only 

overtop and “smother” small seedlings but also compete for 

soil moisture and nutrients. Cultivation is often continued in 

young sapling stands as a growth enhancement practice. 

Schmidtling (1973) reported that cultivation of a loblolly 

pine plantation during the first 3 years of growth resulted in 

a 6-ft (1.9-m) growth advantage compared with uncultivated 

controls by the 9th year. In addition to a much greater 

growth rate by trees in the cultivated stand, the size distribution among trees was more uniform. Despite the increase in 

growth rate, specific gravity values were not appreciably less 

than that of uncultivated controls. Again, one of the anticipated effects of cultivation is to prolong summerwood formation by increasing the late-season availability of soil 

moisture. 

Clark and others (1991) examined the effect of cultivation 

on wood formation of slash pine when growing on moderately well-drained and poorly drained soils in the lower 

Coastal Plain of Georgia. On study plots that received no 

cultivation, the length of juvenility was 8 years on both the 

moderately well-drained and poorly drained sites. On intensively cultivated plots, juvenile wood was produced 2 years 

longer on moderately well-drained soil than on poorly 

drained soil. However, the specific gravity of the juvenile 

wood from the trees on the cultivated, moderately 
18 

well-drained site was 6% higher than that of the trees on the 

control sites or poorly drained cultivated sites. 

Mechanical and Strength 

Properties 

Shrinkage 

Longitudinal shrinkage is the defect most frequently associated with juvenile wood. Although wood sometimes expands 

during the early stages of drying, most wood shrinks longitudinally to some degree as moisture is removed from within 

the cells and cellular matrix. If compression wood is present, 

longitudinal shrinkage will be greatly accentuated (Harris 

1977). Differential shrinkage also contributes to warp, which 

compounds the effect of the defect (Beard and others 1993). 

Shrinkage of juvenile wood is closely correlated with specific gravity. The lower the specific gravity, the greater the 

longitudinal shrinkage, and the higher the specific gravity, 

the greater the radial, tangential, and volumetric shrinkage 

(Yao 1969). Low density springwood shrinks to a far greater 

degree than high density summerwood in juvenile wood. 

The lower density of the springwood can be attributed to 

shorter tracheids with larger radial diameters and thinner 

walls. As moisture is removed from the interstices between 

microfibrils and finally from within the cellulose matrix, 

anisotropic shrinkage progressively increases. Fibril angle, 

in turn, is negatively correlated with both tracheid length and 

wall thickness. McAlister and Clark (1992) have pointed out 

that there is no single, easily measurable property related to 

longitudinal shrinkage. Similarly, Beard and others (1993) 

concluded that there are no readily observable growth characteristics to identify lumber with a proclivity to warp. However, available evidence suggests that shrinkage might be 

most closely related to fibril angle (Ying and others 1994). 

MOR and MOE 

Modulus of rupture (MOR) and modulus of elasticity (MOE) 

are mechanical properties of wood that are highly correlated 

with specific gravity. Both properties are therefore strongly 

influenced by the age patterns of specific gravity typically 

found in the juvenile core. The relatively few studies that 

have compared the strength properties of juvenile and mature wood have consistently shown lower values for juvenile 

wood. Data from a study by Pearson and Ross (1984) based 

on wood from a 15-year-old loblolly pine progeny test (six 

4-ft (1.2-m) logs) and a 25-year-old commercial plantation 

(three 4-ft (1.2-m) logs) are given in Table 6. 

Data from another study by Bentdsen and Senft (1986) based 

on a 30-year-old loblolly pine plantation (six 6-ft (1.8-m) 

logs) are given in Table 7. 

Table 6—Average value of specific gravity, modulus of elasticity (MOE), and modulus of rupture (MOR) at 

average number of rings from pith for two different age trees 

Specific gravity MOE (×106

 lb/in2)

a MOR (lb/in2

)

a

Number of rings 

from pith 25-yr-old tree 15-yr-old tree 25-yr-old tree 15-yr-old tree 25-yr-old tree 15-yr-old tree 

0+ 0.4 0.38 0.88 0.64 9,080 7,260 

2+ 0.43 0.39 1.31 1.04 10,600 8,980 

5+ 0.47 0.44 1.53 1.36 13,100 11,400 

10+ 0.5 0.517 2.08 1.64 16,700 13,900 

a

1 lb/in2 = 6.9 kPa. 

Table 7—Average properties by age for loblolly pine 

Age (years) 

Specific 

gravity 

MOR 

(lb/in2

)

a MOE 

(×106 lb/in2)

a

Maximum 

crush 

(lb/in2

)

a Tracheid 

length (mm) 

Fibril angle 

(deg) 

Ring width 

(in.)b

1 0.412 4,200 0.289 2,020 1.57 36.5 0.394 

2 0.384 4,240 0.294 1,880 1.73 39.0 0.508 

3 0.400 3,800 0.293 1,620 1.95 39.3 0.360 

4 0.400 4,400 0.349 1,730 2.14 37.0 0.367 

5 0.436 5,470 0.498 2,160 2.37 31.0 0.348 

6 0.423 5,490 0.514 2,100 2.53 33.7 0.312 

7 0.467 6,470 0.642 2,550 2.68 33.2 0.260 

8 0.502 6,848 0.710 2,960 2.82 29.5 0.223 

9 0.514 8,160 0.904 3,190 3.03 24.5 0.181 

10 0.531 9,820 1.120 3,430 3.16 27.3 0.164 

15 0.582 11,570 1.541 4,140 3.51 22.0 0.138 

a

1 lb/in2 = 6.9 kPa. b

1 in. = 25.4 mm. 
19 

In the latter study, there was a fivefold increase in the average MOE (0.3 to 1.6 ×106

 lb/in2 (2.1 to 11 GPa)) and about a 

threefold increase in MOR (4,000 to 12,000 lb/in2

 (27.6 to 

82.7 MPa)) from early juvenile wood to late mature wood 

(23+ years). Pearson (1988) found that maximum crushing 

strength and MOE of clear loblolly pine nominal 2- by 4-in. 

(standard 38- by 89-mm) lumber (2 by 4’s) cut from juvenile 

wood, on average, were only 52% and 37%, respectively, of 

the corresponding means for mature wood. To appreciate the 

significance of these differences in both wood quality characteristics and physical properties, imagine a 6-in. (15.2-cm) 

radially cut board extending inward to the pith. Even at a 

growth rate of 3 rings per inch (1.2 rings/cm), such a board 

would encompass 18 growth rings. 

Although these data are revealing, it must be recognized that 

the sampling base in all such studies is small and rarely are 

comparisons made for juvenile and mature wood obtained 

from the same tree. Moreover, in relatively few studies did 

the authors relate strength properties to wood characteristics 

other than specific gravity. Yet, available data suggest that 

the differences in strength properties between juvenile and 

mature wood cannot be accounted for solely by differences 

in specific gravity (Bendtsen 1978). The actual volume of 

springwood and the large fibril angles of the springwood 

tracheids in the early juvenile growth rings might be far 

more important than previously realized. In support of this 

suggestion, Cave and Walker (1994) concluded that fibril 

angle was the only factor that alone could account for the 

pronounced decrease in stiffness (MOE) of radiata pine 

wood. 

Tensile Strength 

Tensile strength of juvenile wood has been of increasing 

concern in recent years because of its effect when used in 

laminated beams and finger joints in lumber. In the latter 

case, finger joints in nominal 2- by 6-in. (standard 38- by 

140-mm) lumber containing juvenile wood from southern 

pines were 34% lower in tensile strength than those without 

juvenile wood (Moody 1970). Tensile strength values of 

2 by 4’s composed entirely of loblolly pine juvenile wood 

were from 45% to 59%, depending on lumber grade, of 

those composed entirely of mature wood (Kretschmann and 

Bendtsen 1992). As in the case of other strength properties, 

the large fibril angles of juvenile wood tracheids appear to 

strongly influence the tensile strength values. 

Shear Parallel to Grain and 

Compression and Tension 

Perpendicular to Grain 

Most information developed on juvenile wood to date has 

concentrated on ultimate tensile stress, MOR, and MOE. 

Little work has been done looking at the effect of juvenile 

wood content on less important properties. In one study, the 

effect of ring orientation and percentage of juvenile wood 

was investigated on shear parallel to grain and compression 

and tension perpendicular to grain strength (D.E. Kretschmann, unpublished report). The data indicate that the average of all three properties decreased with increasing amounts 

of juvenile wood in the cross section. Shear strength was 

insensitive to annual ring orientation and followed the expected shear strength density relationship. Compression and 

tension perpendicular to grain strength was very sensitive to 

annual ring orientation. Also, tension and compression 

perpendicular to grain, with loads applied to the radial face, 

were more sensitive to changes in juvenile wood content 

than expected. 

Conclusion 

Two main conclusions can be drawn from a review of the 

extensive literature on juvenile wood and wood quality 

characteristics in loblolly pine and related species: 

1. Wood formation and the interrelations among various 

wood quality characteristics are exceedingly complex. 

2. The existing literature provides few identifiable clues 

as to how to deal with this complexity. 

Discussion 

We consider the second conclusion first. The literature on 

juvenile wood, although extensive and filled with valuable 

information and data, has never been synthesized from the 

standpoint of solid wood products and structural wood-based 

composites. That is, each published report focused on a 

particular objective and addressed an isolated part of the 

juvenile wood problem. In addition, the variables in the 

studies, such as tree growth and stand conditions, differed 

so widely that few data yielded valid comparisons. 

Most investigations provided average values for the selected 

characteristics based on either several to many growth rings 

or the entire juvenile core. Average values are perhaps legitimate for analyzing wood quality characteristics for pulpwood, and pulpwood has been the main objective of juvenile 

wood research over the years. When pulped, juvenile wood 

has good paper properties except for significantly low tear 

strength because of short tracheids. When juvenile wood is 

processed in the mill, it is mixed with mature wood and the 

low tear properties become less critical. That is, wood quality is averaged out. 

Average values for juvenile wood characteristics are essentially meaningless for solid wood products and structural 

wood-based composites. For example, summerwood percentage and wood specific gravity are often used to define 

the size of the juvenile core. Yet, the average specific gravity 

of a board containing wide juvenile growth rings provides 

little or no information as to how the board will respond to 

drying. A board cut through the juvenile core might have a 
20 

perfectly acceptable average specific gravity, but within that 

board, one to several substandard growth rings would be 

sufficient to cause unacceptable shrinkage or warp. That is, 

individual boards do not shrink on the basis of average 

values but only on the characteristics of the annual rings that 

comprise them. Although present grading rules based on 

growth ring width and summerwood percentage would 

perhaps downgrade such boards, the rules are admittedly 

subjective. The main point of this discussion is not to criticize grading rules. Rather, it is to emphasize that average 

juvenile wood quality characteristics derived from investigations with pulpwood as an objective are not directly applicable to solid wood products. 

For the same reasons cited above, we might argue against a 

juvenile wood zone of 10-year duration because it has been 

reported to vary with geographic location. Again, this value 

was established for pulpwood and it, too, is based on an 

average tree, growing in an average stand, on an average site 

for loblolly pine. Criteria for identifying a juvenile core are 

needed that are more appropriate for solid wood products. 

However, since we do not at present have such a model, we 

will continue to refer to the 10-year juvenile core in this 

discussion. 

Juvenile wood quality is indeed exceedingly complex. In the 

main body of this report, we have briefly summarized how 

juvenile wood is formed, the important wood characteristics 

associated with juvenile wood, and how these wood characteristics vary with environmental conditions and silvicultural 

practices. Like all previous reports on the subject, this review provides few clues as to how to deal with this complexity. Admittedly, there is no simple solution to the problems 

confronting the utilization of juvenile wood, but it is possible to narrow the scope of the problem and confine the 

extent of future investigations. 

We know what characteristics of juvenile wood contribute to 

undesirable solid wood properties. Above all are the inherent 

changes in wood characteristics that occur with increasing 

growth ring age within the juvenile core. These changes are 

greatly accentuated in the extremely wide growth rings 

found in rapidly grown plantation trees. Wide juvenile 

growth rings have relatively low summerwood percentages 

and low wood specific gravity values compared with those 

of mature wood. However, both summerwood percentage 

and specific gravity are simply indices that reflect anatomical differences of the individual tracheids such as radial 

diameter and wall thickness. Although these indices provide 

valuable rules of thumb, for example, grading rules, the 

indices by themselves do not provide an answer to the juvenile wood problem. 

We also know that within a growth ring, springwood differs 

greatly from summerwood. In juvenile wood of loblolly 

pine, springwood specific gravity averages about 0.29 and 

that of summerwood about 0.63. Again, these differences are 

due to the larger radial diameters and thinner walls of the 

springwood tracheids relative to those of summerwood. The 

specific gravity of juvenile springwood is not significantly 

different from that of mature springwood, both of which fall 

within the range of 0.29 to 0.40. However, the specific 

gravity of juvenile summerwood is significantly different 

from that of mature summerwood, which might range from 

0.65 to 0.85 (Koch 1972). One might therefore conclude that 

efforts should be made to increase juvenile summerwood 

specific gravity. However, summerwood with a specific 

gravity of 0.50 to 0.55 or higher does not shrink or warp 

excessively. In fact, growth rings consisting entirely of 

juvenile summerwood would undoubtedly be acceptable 

from the strength standpoint for most solid wood products. 

On the basis of the foregoing analysis, one might argue that 

a high proportion of springwood is the major problem in 

juvenile wood. Wide juvenile growth rings that contain a 

high proportion of springwood and transition tracheids have 

springwood tracheids that are shorter with larger fibril angles than summerwood tracheids and have larger radial 

diameters and thinner cell walls. It would appear that a high 

proportion of juvenile springwood is the characteristic of 

greatest impact, which is more specifically the thickness of 

the walls and the fibril angles of the tracheids that comprise 

the springwood. 

Two possibilities exist for rectifying this imbalance between 

juvenile springwood and summerwood: silvicultural and 

genetic practices. 

A first step in an evaluation program would be to establish 

meaningful parameters for juvenile wood characteristics and 

physical properties applicable to solid wood products. A 

suggested procedure would be to analyze individual growth 

rings throughout the stem of planted loblolly pine growing 

under a wide range of silvicultural practices across the geographic range of the species. Minimal data to be obtained 

from each growth ring would be ring width, springwood 

specific gravity, summerwood specific gravity, summerwood 

percentage, springwood and summerwood tracheid radial 

diameters, tracheid lengths, double wall thickness, and fibril 

angles. Additional data might include springwood and 

summerwood MOE and longitudinal shrinkage where feasible on small samples. 

From these data, it should be possible to estimate at what 

ages physical properties attain acceptable values for different 

growth ring widths. It should also be possible to determine 

which wood characteristics, alone or in combination, contribute most strongly to the physical properties of juvenile 

wood and which characteristics might be susceptible to 

genetic improvement. 

With the above database, if based on a sufficiently large and 

diverse sample, it should be possible to develop models for 

predicting ring widths, specific gravity, tracheid lengths, 
21 

microfibrillar angle of springwood and summerwood, and 

ring MOE based on ring age, height in stem, geographic 

location, site productivity, and silvicultural practice. These 

models would then be used to determine the wood properties 

for specific silvicultural practices applied to specific sites in 

various geographic regions of the South. Knowing the wood 

properties would facilitate processing of timber into its 

optimum product application. 

To test for the effect of growth rate on physical properties, 

analyses could be confined to juvenile growth ring numbers 

four through eight. The rational is as follows. The first three 

rings are truly juvenile, with wood quality characteristics 

well below acceptable values. Any improvement of rings 

four through eight might also, but not necessarily, benefit 

these rings. Any improvement in wood quality characteristics of rings four through eight would naturally benefit rings 

nine and older because of the inherent increase in wood 

quality characteristics with age. Confining analyses to rings 

four through eight would not only simplify sampling but also 

minimize any effect of averaging. 

This exercise should provide information as to whether or 

not, and to what extent, wood quality characteristics and 

physical properties can be modified by silvicultural practices 

that, in turn, modify growth rate. It would provide information not now available, such as whether a reduction in juvenile ring width would reduce springwood percentage, and if 

so, whether it would result in an improvement in physical 

wood properties. This exercise would not provide information as to the practical and economic feasibility of silvicultural control of juvenile wood formation. 

Another possibility for using the foregoing database and 

prediction models is manipulating the growth rate of genetically improved trees by silvicultural practices such as stand 

density control. For example, modifying growth rate by 

stand density alone might be uneconomical because of reduced volume production. However, the combination of 

genetically improved trees and judicious stand density regulation might result in higher physical properties that would 

offset any reduction in volume growth. 

A second suggestion that might warrant consideration relates 

to site and geographic location. We know that wood specific 

gravity of loblolly pine varies from site to site and also 

regionally within the species range. It might be feasible to 

harvest from predetermined regions for solid wood products 

with specific strength and stiffness requirements. 

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25 

Appendix—References 

Extensive literature exists on the anatomical characteristics 

of juvenile wood and the effects of juvenile wood on wood 

properties. This reference list is confined to the southern 

pines, primarily to loblolly and slash pines. Numerous references to radiata pine, grown mainly in Australia and New 

Zealand, have also been included because of its close resemblance to the southern pines and the extensive research 

conducted on this species. Not all listed references are cited 

in the report.

Key Words 

Species 

General overview 

Wood characteristics 

Ring width (includes ring per inch and growth rate) 

Ring age (includes growth ring age from pith, length of 

juvenile period, and juvenile–mature comparisons) 

Specific gravity (includes wood density, basic density, and 

dry weight yields) 

Uniformity (applies to growth ring width and specific 

gravity values) 

Summerwood percentage 

Springwood vs. summerwood (Springwood–summerwood 

comparison of wood characteristics) 

Tracheid length 

Tracheid diameter (includes radial and tangential lumen 

diameter) 

Wall thickness (refers to radial and tangential tracheid 

wall thickness) 

Fibril angle (also microfibrillar angle and micellar angle) 

Position in stem (refers to variation in wood characteristics 

at different stem heights) 

Other wood-related properties 

Branchiness (includes branch size, angle, and position) 

Knots (includes associated knotwood) 

Compression wood (includes reaction wood) 

Extractives (includes pitch, resin, mineral deposits, and 

lignification) 

Heartwood 

Spiral grain (includes twisted grain) 

Bark (bark thickness and volume) 

Tree characteristics 

Crown size (includes crown length and width and tree 

height) 

Foliage efficiency (includes needle mass, net assimilation, 

and contribution of different-aged needles) 

Tree age (includes juvenile compared with mature trees) 

Tree diameter (includes tree class — suppressed compared 

with dominant) 

Stem form (twist, torsion, crook, sweep, etc.) 

Stem taper 

Stand characteristics 

Stand density (initial tree spacing trials as opposed to thinning; includes stocking based on basal area and trees per 

acre) 

Site (site quality, site index, local environment) 

Geographic location (includes climatic differences) 

Silvicultural modification 

Thinning (includes release cutting) 

Pruning (includes partial defoliation — natural and artificial) 

Fertilization 

Irrigation 

Drainage 

Cultivation (postplanting disking, weeding, mowing, other 

than fertilization) 

Inheritance 

General heredity 

Provenance tests 

Clonal tests 

Progeny tests 

Heritability estimates 

Parental specific gravity (evaluation or selection for trees 

with high and low specific gravity or identification of 

such trees) 

Structural properties 

Shrinkage (longitudinal, radial, tangential, and volumetric) 

Warp (includes twist, bow, and other distortions) 

Brashness 

Modulus of rupture (parallel and perpendicular to grain) 

Modulus of elasticity (parallel and perpendicular to grain) 

Compressive strength (parallel and perpendicular to grain) 

Tensile strength (parallel and perpendicular to grain) 

Shear strength 

Sawlog yield (refers also to lumber yield and sawtimber 

quality) 

Other structural (structural mechanical properties other 

than above) 
26 

References Read in Preparing 

This Report

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research. Tech. Note 199. FORPRIDECOM. 2 p. 

(general overview, specific gravity, tracheid length) 

Bannister, M.H. 1959. Artificial selection and Pinus 

radiata. New Zealand Journal of Forestry. 8: 69–90. 

(P. radiata, specific gravity, branching, general heredity, 

progeny tests) 

Bannister, M.H.; Vine, M.H. 1981. An early progeny trial 

in Pinus radiata 4. Wood density. New Zealand Journal of 

Forest Science. 11: 221–243. 

(P. Radiata, ring width, ring age, specific gravity, branchiness, tree diameter, stem form, progeny tests, heritability 

estimates)

Bassett, J.R. 1969. Growth in widely spaced loblolly pine. 

Journal of Forestry. 67: 634–636. 

(P. taeda, specific gravity, crown size, tree diameter, stand 

density, sawlog yield) 

Beard, J.S.; Wagner, F.G.; Taylor, F.W.; Seale, R.D.

1993. The influence of growth characteristics on warp in two 

structural grades of Southern Pine lumber. Forest Products 

Journal. 43(6): 51–56. 

(southern pines, ring width, knots, compression wood, warp) 

Beckwith, J.R.; Reines, M. 1978. Aerial fertilization increases volume and weight of planted loblolly pine. 

Southern Journal of Applied Forestry. 2: 118–120. 

(P. taeda, ring width, specific gravity, summerwood 

percentage, site, fertilization) 

Bendtsen, B.A. 1978. Properties of wood from improved 

and intensively managed trees. Forest Products Journal. 

28(10): 61–72. 

(general overview, southern pines, specific gravity, tracheid 

length, fibril angle, general heredity, shrinkage, other 

structural) 

Bendtsen, B.A.; Senft, J. 1986. Mechanical and anatomical 

properties in individual growth rings of plantation-grown 

eastern cottonwood and loblolly pine. Wood and Fiber 

Science. 18(1): 23–38. 

(P. taeda, ring width, ring age, specific gravity, tracheid 

length, fibril angle, compression wood, modulus of rupture, 

modulus of elasticity, compressive strength, general 

heredity) 

Bendtsen, B.A.; Ethington, R.L.; Galligan, W.L. 1972. 

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U.S. Department of Agriculture, Forest Service, Forest 

Products Laboratory. 61–76. 

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gravity, geographic location, modulus of rupture, modulus of 

elasticity, compressive strength, other structural)

Berkley, E.E. 1934. Certain physical and structural properties of three species of southern yellow pine correlated with 

the compression strength of their wood. Annals of the 

Missouri Botanical Garden. 21: 241–338. 

(P. taeda, P. palustris, P. echinata, ring width, ring age, 

specific gravity, summerwood percentage, tracheid length, 

wall thickness, extractives, compressive strength)

Bethel, J.S. 1941. The effect of position within the bole 

upon fiber length of loblolly pine (Pinus taeda L.) 

(P. taeda, ring age, tracheid length, position in stem) 

Bethel, J.S. 1950. The influence of wood structure on the 

strength of loblolly pine wood (Pinus taeda L). Sch. For. 

Tech. Rep. 3. Raleigh, NC: North Carolina State University. 

6 p. 

(P. taeda, specific gravity, summerwood percentage, compressive strength) 

Biblis E.J. 1969. Transitional variation and relationships 

among properties within loblolly pine growth rings. Wood 

Science and Technology. 3: 14–24. 

(P. taeda, specific gravity, springwood vs. summerwood, 

modulus of elasticity, tensile strength) 

Blair, R.L.; Zobel, B.J.; Barker, J.A. 1975. Predictions of 

gain in pulp yield and tear strength in young loblolly pine 

through genetic increases in wood density. TAPPI Journal. 

58: 89–91. 

(P. taeda, specific gravity, general heredity) 

Blanche, C.A.; Lorio, P.L.; Sommers, R.A.; Hodges, J.D; 

Nebeker, T.E. 1992. Seasonal cambial growth and development of loblolly pine: xylem formation, inner bark chemistry, resin ducts, and resin flow. Forest Ecology and Management. 49: 151–165. 

(P. taeda, xylem formation, inner bark chemistry, 

fertilization) 

Boone, R.S.; Chudnoff, M. 1972. Compression wood formation and other characteristics of plantation grown Pinus 

caribaea. Res. Pap. ITF–13. U.S. Department of Agriculture, Forest Service. 16 p. 

(P. caribaea, specific gravity, compression wood, site, 

shrinkage, modulus of rupture, modulus of elasticity, compressive strength) 

Boyd, J.D. 1974. Anisotropic shrinkage of wood: Identification of dominant determinants. Mokuzai Gakkaishi. 

20: 473–482. 

(wall thickness, fibril angle, extractives, shrinkage) 
27 

Boyd, J.D. 1980. Relationships between fibre morphology, 

growth strains and physical properties of wood. Australian 

Forest Research. 10: 337–360. 

(P. radiata, ring width, specific gravity, wall thickness, fibril 

angle, modulus of elasticity, compressive strength) 

Brazier, J.D. 1985. Juvenile wood. In: Kucera, L.J. (ed). 

Xylorama. Bassel, Switzerland: Birkhauser Verlag: 25–3.2. 

(general overview) 

Bridgwater, F.E. 1984. The impact of genetic improvement 

of stem straightness on yield and value of lumber. In: Proceedings, Symposium on utilization of the changing wood 

resource in the South; 1984 June 12–14. Sch. For. Resources. Raleigh, NC: North Carolina State University: 

80–87. 

(P. taeda, tree form, general heredity, sawlog yield) 

Brown, C.L; Klein, J. 1961. Observations on inheritance of 

wood specific gravity in seedling progeny of loblolly pine. 

Journal of Forestry. 59: 898–899. 

(P. taeda, specific gravity, progeny tests, parental specific 

gravity) 

Burdon, R.D.; Harris, J.M. 1973. Wood density in radiata 

pine clones on four different sites. New Zealand Journal of 

Forestry Science. 3: 286–303. 

(P. radiata, ring width, position in stem, tree diameter, site, 

clonal tests) 

Burley, J. 1982. Genetic variation in wood properties. In: 

Baas, P., ed. New perspectives in wood anatomy, 

Nijhoff/Junk. The Hague. 151–169. 

(general overview, general heredity) 

Burton, J.D.; Shoulders, E. 1974a. Wide rings, short rotations, and dense wood in loblolly pine plantations. 

In: Proceedings, TAPPI forest biology conference; 1974 

September 18–20; Seattle, WA: 81–84. 

(P. taeda, stem taper, stand density, thinning, sawlog yield) 

Burton, J.D.; Shoulders, E. 1974b. Fast-grown, dense 

loblolly pine sawlogs: a reality. Journal of Forestry. 

72: 637–641. 

(P. taeda, ring width, specific gravity, branchiness, tree 

diameter, stem taper, thinning, pruning, cultivation, sawlog 

yield) 

Cave, I.D. 1968. Anistropic elasticity of the plant cell wall. 

Wood Science Technology. 2: 268–278. 

(P. radiata, fibril angle, modulus of elasticity) 

Cave, I.D. 1976. Modelling the structure of the softwood 

cell wall for computation of mechanical properties. Wood 

Science Technology. 10: 19–28. 

(P. radiata, specific gravity, wall thickness, fibril angle, 

extractives, shrinkage) 

Cave, I.D.; Walker, J.C.F. 1994. Stiffness of wood in fastgrown plantation softwoods: the influence of microfibril 

angle. Forest Products Journal. 44(5): 43–48. 

(P. radiata, fibril angle, modulus of elasticity) 

Choong, E.T.; Chang, B.Y. 1974. Effect of cultural treatments on density and growth in a loblolly pine plantation. 

LSU Wood Util. Notes 25. Baton Rouge, LA: Louisiana 

State University. 4 p. 

(P. taeda, ring width, ring age, specific gravity, stand density, thinning, pruning) 

Choong, E.T.; Box, B.H.; Fogg, P.J. 1970. Effects of intensive cultural management on growth and certain wood 

properties of young loblolly pine. Wood and Fiber. 

2: 105–112. 

(P. taeda, ring age, specific gravity, tracheid length, extractives, tree diameter, fertilization, irrigation cultivation) 

Clark, A., III. 1994. Heartwood formation in loblolly and 

longleaf pines for red-cockaded woodpecker nesting cavities. In: Jones, Edwin J. ed. Proceedings of the 46th annual 

conference of southeastern associations of fish and wildlife 

agencies; 1992 October 25–28; Corpus Christi, TX: 79–87. 

(P. taeda, P. elliottii, red-cockaded woodpecker, heartwood 

formation) 

Clark, A., III; Saucier, J.R. 1989. Influence of initial 

planting density, geographic location, and species on juvenile wood formation in Southern Pine. Forest Products Journal. 39(7/8): 42–48. 

(P. taeda, P. elliottii, ring age, specific gravity, summerwood percentage, wall thickness, tree diameter, stand density, geographic location, shrinkage) 

Clark, A., III; Saucier, J.R. 1991. Effects of silvicultural 

treatments and environmental factors on wood properties of 

southern pines. In: Proceedings of the 1991 Society of 

American Foresters national convention; San Francisco: 

92–98. 

(P. taeda, P. elliottii, stand density, thinning, sawlog yield) 

Clark, A., III; Schmidtling, R.C. 1989. Effect of intensive 

culture on juvenile wood formation and wood properties of 

loblolly, slash and longleaf pine. Gen. Tech. Rep SO–74. 

Athens, GA: U.S. Department of Agriculture, Forest Service, Southern Research Station. 211–217. 

(P. taeda, P. elliottii, P. palustris, ring age, specific gravity, 

tree diameter, fertilization, cultivation, progeny tests, parental specific gravity) 

Clark, A., III; Saucier, J.R.; Sarigumba, T.I. 1991. Effect 

of site preparation, planting density, and soil drainage on 

juvenile wood formation of slash pine. Gen. Tech. Rep. SE–

70. Athens, GA: U.S. Department of Agriculture, Forest 

Service, Southern Research Station. 757–768. 

(P. elliottii, specific gravity, stand density, drainage) 
28 

Clark, A., III; Saucier, J.R.; Baldwin, V.C.; Bower, D.R. 

1994. Effect of initial spacing and thinning on lumber grade, 

yield, and strength of loblolly pine. Forest Products Journal. 

44(11/12): 14–20. 

(P. taeda, stand density, thinning, sawlog yield) 

Cleaveland, M.K.; Wooten, T.E.; Saucier, J.R. 1974. 

Annotated bibliography of the effects of fertilization on 

wood quality. For. Res. Series 29. Clemson, University, 

College of Forestry and Recreation Resources. 53 p. 

(fertilization) 

Cockrell, R.A. 1949. Further observations on longitudinal 

shrinkage of softwoods. In: Proceedings, Madison, WI: 

Forest Products Research Society. 3: 455–459. 

(P. taeda, P. palustris, P. echinata, ring width, shrinkage) 

Cole, D.E.; Zobel, B.J.; Roberds, J.H. 1966. Slash, 

loblolly, and longleaf pine in a mixed natural stand; a 

comparison of their wood properties, pulp yields, and paper 

properties. TAPPI Journal. 49: 161–166. 

(P. taeda, P. elliottii, P. palustris, specific gravity, tracheid 

length, extractives) 

Collicott, L.V.; Strickland, J.R.; Stonecypher, R.W.

1968. Dry-weight yields of slash pine plantations. Tech. 

Note 27. Bainbridge, GA: Southlands Experiment Forest 

International Paper Company. 17 p. 

(P. elliottii, ring width, specific gravity, position in stem, 

branchiness, tree age, tree diameter, thinning) 

Cown, D.J. 1973. Effects of severe thinning and pruning 

treatments on the intrinsic wood properties of young radiata 

pine. New Zealand Journal of Forestry Science. 3: 379–389. 

(P. radiata, ring width, ring age, specific gravity, summerwood percentage, springwood vs. summerwood, tracheid 

length, position in stem, thinning, pruning) 

Cown, D.J. 1974a. Wood density of radiata pine: Its variation and manipulation. New Zealand Journal of Forestry 

Science. 4: 84–92. 

(P. radiata, general overview, ring age, specific gravity, 

tracheid length, fibril angle, position in stem, tree diameter, 

stand density, site) 

Cown, D.J. 1974b. Comparison of the effects of two thinning regimes on some wood properties of radiata pine. New 

Zealand Journal of Forestry Science. 4: 540–551. 

(P. radiata, ring width, ring age, specific gravity, tracheid 

length, position in stem, compression wood, heartwood, 

stem form, thinning, pruning) 

Cown, D.J. 1977. Partial defoliation and wood properties of 

5-year-old Pinus radiata. New Zealand Journal of Forestry 

Science. 7: 192–198. 

(P. radiata, ring width, ring age, specific gravity, summerwood percentage, springwood vs. summerwood, tracheid 

length, foliage efficiency, pruning) 

Cown, D.J. 1989. Wood characteristics of New Zealand 

radiata pine and Douglas fir: Suitability for processing. New 

Zealand Forest Research Institute Rep. Commissioned by 

New Zealand Forestry Coop. Ltd. 85 p. 

(P. radiata, general overview, ring width, ring age, specific 

gravity, summerwood percentage, springwood vs. summerwood, tracheid length, position in stem, branchiness, compression wood, extractives, heartwood, spiral grain, thinning, 

pruning, fertilization, shrinkage) 

Cown, D.J.; McConchie, D.L. 1983. Radiata pine wood 

properties survey (1977–1982). FRI Rep. 50. New Zealand 

Forest Service. 42 p. 

(P. radiata, ring width, ring age, specific gravity, tracheid 

length, position in stem, extractives, heartwood, tree age, 

site, geographic location, shrinkage, sawlog yield) 

Cown, D.J.; Love, J.G.; McConchie, D.L.; Colbert, C.

1984. Wood properties of radiata pine in some forests of the 

Bay of Plenty/Taupo region. FRI Rep. 81. New Zealand 

Forest Service. 23 p. 

(P. radiata, ring age, specific gravity, position in stem, 

heartwood, site, geographic location, sawlog yield) 

Cregg, B.M.; Dougherty, P.M.; Hennessey, T.C. 1988. 

Growth and wood quality of young loblolly pine trees in 

relation to stand density and climatic factors. Canadian 

Journal of Forest Research. 18: 851–858. 

(P. taeda, specific gravity, summerwood percentage, tracheid diameter, wall thickness, foliage efficiency, thinning) 

Cromer, R.N.; Barr, N.J.; Williams, E.R.; McNaught, 

A.M. 1985. Response to fertilizer in a Pinus radiata plantation. New Zealand Journal of Forestry Science. 15: 59–70. 

(P. radiata, specific gravity, branchiness, bark, crown size, 

foliage efficiency, stem taper, fertilization) 

Cubbage, F.W. 1990. Economic impacts of southern pine 

wood quality changes. Gen. Tech. Rep. SE–63. Asheville, 

NC: U.S. Department of Agriculture, Forest Service, Southeastern Station. 70: 57. 

(general overview, southern pines, sawlog yield) 

Dadswell, H.E.; Nicholls, J.W.P. 1959. Assessment of 

wood qualities for tree breeding. I. In: Pinus elliottii var. 

Elliottii from Queensland, Australia. For. Prod. Tech. Pap. 

CSIRO Division Forest Products Laboratory. 4: 1–16. 

(P. elliottii, ring width, specific gravity, summerwood percentage, tracheid length, fibril angle, compression wood, 

spiral grain, general heredity, shrinkage) 

Dadswell, H.E.; Fielding, J.M.; Nicholls, J.P.; Brown, 

A.G. 1961. Tree-to-tree variations and the gross heritability 

of wood characteristics of Pinus radiata. TAPPI Journal. 

44(3): 174–179. 

(P. radiata, ring width, ring age, summerwood percentage, 

springwood vs. summerwood, compression wood, spiral 

grain, clonal tests, heritability estimates, shrinkage) 
29 

de Villiers, A.M. 1965. Silvicultural, exploitation and conversion methods that affect timber quality. Pt. 1. South 

African Forestry Journal. 55: 21–31. 

(P. taeda, P. elliottii, P. patula, ring width, ring age, specific 

gravity, tracheid length, branchiness, compression wood, 

extractives, spiral grain, stand density, thinning, pruning, 

other structural, sawlog yield) 

de Villiers, A.M. 1966. Silvicultural, exploitation and conversion methods that affect timber quality. Pt. 2. South 

African Forestry Journal. 56: 5–10. 

(P. taeda, P. elliottii, P. patula, ring width, ring age, specific 

gravity, tracheid length, branchiness, compression wood, 

extractives, spiral grain, stand density, thinning, pruning, 

other structural, sawlog yield) 

Dinwoodie, J.M. 1975. Timber—a review of the structuremechanical property relationship. Journal of Microbiology. 

104: 3–32. 

(general overview) 

Echols, R.M. 1960. Effects of growing space on wood 

specific gravity in loblolly pine. In: Proceedings, Society of 

American Forestry; 1959: 140–143. 

(P. taeda, specific gravity, tree diameter, stand density, 

thinning) 

Einspahr, D.W.; Goddard, R.E.; Gardner, H.S. 1964. 

Slash pine, wood and fiber property heritability study. Silvae 

Genetica. 13: 103–109. 

(P. elliottii, specific gravity, summerwood percentage, tracheid length, compression wood, extractives, clonal tests, 

heritability estimates) 

Elliott, G.K. 1970. Wood density in conifers. Commonwealth Forestry Bureau of Technical Communications 8. 

44 p. 

(general overview, ring width, ring age, specific gravity, 

summerwood percentage, springwood vs. summerwood, 

tracheid length, tracheid diameter, wall thickness, position in 

tree, stand density, site, geographic location, fertilization, 

progeny tests) 

Fenton, R.I. 1973. Profitability of second log pruning. New 

Zealand Journal of Forestry Science. 3: 313–322. 

(P. radiata, pruning, sawlog yield) 

Fielding, J.M. 1967. Influence of silvicultural practices on 

wood properties. International Review of Forest Research. 

2: 95–126. 

(general overview, ring age, specific gravity, tracheid length, 

compression wood, spiral grain, stand density, thinning, 

pruning, fertilization, general heredity) 

Fielding, J.M.; Brown, A.G. 1961. Tree-to-tree variations 

in the health and some effect of superphosphate on the 

growth and development of Monterey pine on a low quality 

site. Forest Timber Bureau Australia Leaflet 79. 19 p. 

(P. radiata, ring width, specific gravity, crown size, fertilization, clonal tests) 

Frampton, L.J., Jr.; Jett, J.B. 1989. Juvenile wood specific gravity of loblolly pine tissue culture plantlets and 

seedlings. Canadian Journal of Forest Research. 

19: 1347–1350. 

(P. taeda, specific gravity, uniformity, site, clonal tests, 

progeny tests) 

Franklin, E.C. 1987 Economics of forest management 

options: influence on wood properties. In: TAPPI Research 

and Development conference; 1987 April; Atlanta, GA: 

43–48. 

(P. taeda, tree age, stand density, site, thinning, sawlog 

yield) 

Franklin, E.C.; Bridgwater, F.E. 1981. Genetics of fast 

growth and wood properties. In: Proceedings, TAPPI annual 

meeting; 1981 March 2–5; Chicago IL: 445–448. 

(P. taeda, P. elliottii, specific gravity, tracheid length, tree 

form, general heredity) 

Geary, T.F.; Sanabria, Macia, F.R. 1973. Density of 

juvenile wood of Pinus caribaea var. hondurensis grown in 

subtropical moist and wet life zones in Puerto Rico. 

Turrialba. 23: 477–480. 

(P. caribaea var. hondurensis, ring width, ring age, specific 

gravity, position in stem, extractives, site) 

Gentle, S.W.; Bamber, R.K.; Humphreys, F.R. 1968. 

Effect of two phosphate fertilizers on yield, financial yield, 

and wood quality of radiata pine. Forest Science. 

14: 282–286. 

(P. radiata, specific gravity, summerwood percentage, tracheid length, fertilization, sawlog yield) 

Gerry, E. 1916. Fiber measurement studies: A comparison 

of tracheid dimensions in longleaf pine and Douglas fir, with 

data on the strength and length, mean diameter and thickness 

of wall of the tracheids. Science. 43 (1106): 360. 

(P. palustris, ring age, springwood vs. summerwood, 

tracheid length, tracheid diameter, wall thickness) 

Geyer, W.A.; Gilmore, A.R. 1965. Effect of spacing on 

wood specific gravity in loblolly pine in southern Illinois. 

Forest Note 113. Urbana, IL: University of Illinois Agricultural Experiment Station. 5 p. 

(P. taeda, ring width, ring age, specific gravity, summerwood percentage, tree diameter, stand density) 

Gilmore, A.R.; Metcalf, G.E.; Bogess, W.R. 1961. Specific gravity of shortleaf pine and loblolly pine in southern 

Illinois. Journal of Forestry. 59: 894–896. 

(P. taeda, P. echinata, specific gravity, geographic location) 

Gilmore, A.R.; Boyce, S.G.; Ryker, R.A. 1966. The relationship of specific gravity of loblolly pine to environmental 

factors in southern Illinois. Forest Science. 12: 399–405. 

(P. taeda, specific gravity, summerwood percentage, site, 

geographic location) 
30 

Goddard, R.E.; Cole, D.E. 1966. Variation in wood production of six-year-old progenies of select slash pine. 

TAPPI Journal. 49: 359–362. 

(P. elliottii, specific gravity, extractives, geographic 

location, progeny tests, parental specific gravity) 

Goddard, R.E.; Strickland, R.K. 1962. Geographic variation in wood specific gravity of slash pine. 

TAPPI Journal. 45: 606–608. 

(P. elliottii, specific gravity, site, geographic location) 

Goggans, J.F. 1961. The interplay of environment and 

heredity as factors controlling wood properties in conifers 

with special emphasis on their effects on specific gravity. 

Sch. For. Tech. Rep. 11. Raleigh, NC: University of North 

Carolina. 56 p. 

(P. taeda, general overview, ring width, ring age, specific 

gravity, summerwood percentage, springwood vs. 

summerwood, tracheid length, tracheid diameter, wall thickness, extractives, site, general heredity) 

Goggans, J.F. 1964. Correlation and heritability of certain 

wood properties in loblolly pine (Pinus taeda.) TAPPI Journal. 47: 318–322. 

(P. taeda, ring width, specific gravity, summerwood percentage, springwood vs. summerwood, tracheid length, 

tracheid diameter, wall thickness, site, progeny tests, 

heritability estimates) 

Gordon, J.C.; Larson, P.R. 1970. Redistribution of reserve 

food in young red pines during shoot elongation. Forest 

Science. 16: 14–20. 

(foliage efficiency) 

Gorman, T.M. 1985. Juvenile wood as a cause of seasonal 

arching in trusses. Forest Products Journal. 35: 35–40. 

(P. taeda, shrinkage) 

Grant, R.K. 1978. Predicting the impact of silvicultural 

treatment on wood characteristics of Pinus radiata. New 

Zealand Journal of Forestry Science. 8: 277–287. 

(P. radiata, tree diameter, tree age, stand density, thinning, 

sawlog yield) 

Greene, J.T. 1966. Selection for tracheid length in loblolly 

pine (Pinus taeda L.). Georgia Forest Research Council. 

Rep. 18. 30 p. 

(P. taeda, ring age, tracheid length, position in stem, progeny tests, heritability estimates) 

Greene, J.T.; Carmon, J.L. 1962. Variation of 

tracheid length in clonal lines of shortleaf pine. Georgia 

Forest Research Council. Res. Pap. 13. 6 p. 

(P. echinata, tracheid length, clonal tests) 

Hallock, H. 1968. Observations on form of juvenile core in 

loblolly pine. Res. Note FPL–0188. Madison, WI: U.S. 

Department of Agriculture, Forest Service, Forest Products 

Laboratory. 6 p. 

(P. taeda, ring width, ring age, compression wood, warp) 

Hamilton, J.R.; Harris, J.B. 1965. Influence of site on 

specific gravity and dimensions of tracheids in clones of 

Pinus elliottii Engelm. and Pinus taeda L. TAPPI Journal. 

48: 330–333. 

(P. taeda, P. elliottii, specific gravity, tracheid length, 

tracheid diameter, wall thickness, site, clonal tests) 

Hamilton, J.R.; Matthew, R.M. 1965. Wood characteristics of planted loblolly and shortleaf pine. Res. Pap. 27. 

Georgia Forest Research Council. 5 p. 

(P. taeda, P. echinata, ring width, ring age, specific gravity, 

summerwood percentage, crown size, tree diameter, stand 

density) 

Harris, J.M. 1965. A survey of the wood density, tracheid 

length and latewood characteristics of radiata pine grown in 

New Zealand. For. Serv. Tech. Pap. 47. New Zealand Forest 

Research Institute. 31 p. 

(P. radiata, ring width, ring age, specific gravity, uniformity, summerwood percentage, springwood vs. summerwood, 

tracheid length, branchiness, extractives, heartwood, stem 

form, site, geographic location, general heredity, parental 

specific gravity) 

Harris, J.M. 1977. Shrinkage and density of radiata pine 

compression wood in relation to its anatomy and mode of 

formation. New Zealand Journal of Forestry Science. 

7: 91–106. 

(P. radiata, ring age, specific gravity, tracheid length, wall 

thickness, fibril angle, compression wood, stem form, general heredity, provenance tests, shrinkage) 

Harris, J.M. 1981. Wood quality of radiata pine. Appita. 

35: 211–215. 

(P. radiata, ring age, specific gravity, tracheid length, tracheid diameter, wall thickness, site, general heredity) 

Harris, J.M.; Meylan, B.A. 1965. The influence of microfibril angle on longitudinal and tangential shrinkage in 

Pinus radiata. Holzforschung. 19: 144–153. 

(P. radiata, springwood vs. summerwood, fibril angle, compression wood, clonal tests, shrinkage) 

Harris, J.M.; James, R.N.; Collins, M.J. 1976. Case for 

improving wood density in radiata pine. New Zealand Journal of Forestry Science. 5: 347–354. 

(P. radiata, ring width, specific gravity, branchiness, thinning, general heredity, parental specific gravity, modulus of 

rupture, modulus of elasticity) 

Hiller, C.H. 1954. Variations in fibril angles in slash pine. 

FPL Rep. 2003. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 6 p. 

(P. elliottii, ring width, ring age, fibril angle, crown size, tree 

diameter, general heredity) 
31 

Hiller, C.H. 1964a. Correlation of fibril angle with wall 

thickness of tracheids in summerwood of slash and loblolly 

pine. TAPPI Journal. 47: 125–128. 

(P. taeda, P. elliottii, ring age, wall thickness, fibril angle, 

position in stem) 

Hiller, C.H. 1964b. Estimating size of the fibril angle in 

latewood tracheids of slash pine. Journal of Forestry. 

62: 249–252. 

(P. elliottii, ring width, ring age, summerwood percentage, 

tracheid length, wall thickness, fibril angle, crown size) 

Hiller, C.; Brown, R.S. 1967. Comparison of dimensions 

and fibril angle of loblolly pine tracheids formed in wet or 

dry growing seasons. American Journal of Botany. 

54: 453–460. 

(P. taeda, ring width, summerwood percentage, springwood 

vs. summerwood, tangential diameter, wall thickness, fibril 

angle, position in stem) 

Hodge, G.R.; Purnell, R.C. 1993. Genetic parameter estimates for wood density, transition age, and radial growth in 

slash pine. Canadian Journal of Forest Research. 

23: 1881–1891. 

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Ifju, G. 1969 Within-growth-ring variation in some physical 

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strength, other structural) 

Ifju, G.; Labosky, P. 1972. A study of loblolly pine growth 

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springwood vs. summerwood) 

Jackson, L.W.R. 1959. Loblolly pine tracheid length in 

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Jackson, L.W.R. 1962. Effects of size of forest openings on 

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foliage efficiency, tree diameter, thinning) 

Jackson, L.W.R.; Greene, J.T. 1957. Hereditary variations 

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length, position in stem, branchiness, progeny tests) 

Jackson, L.W.R.; Greene, J.T. 1958a. Tracheid length 

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Jackson, L.W.R.; Greene, J.T. 1958b. Slash pine tracheid 

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Jackson, L.W.R.; Morse, W.E. 1965a. Tracheid length 

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summerwood, tracheid length) 

Jackson, L.W.R.; Morse, W.E. 1965b. Variation in fibril 

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tests) 

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springwood vs. summerwood, position in stem, geographic 

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32 

Jurbergs, K.A. 1963 Determining fiber length, fibrillar 

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Jurbergs, K.A. 1968. Transverse dimensions of slash pine 

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(P. elliottii, tracheid diameter, wall thickness, springwood 

vs. summerwood) 

Kellison, R.C. 1981. Characteristics affecting quality of 

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grain, general heredity) 

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Kelsey, K.E. 1963. A critical review of the relationship 

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(P. taeda, specific gravity, modulus of rupture, modulus of 

elasticity, other structural) 

Kerr, J. 1931. Summerwood formation in southern pines 

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Kirk, D.G.; Breeman, L.G.; Zobel, B.J. 1972. A pulping 

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(southern pines, ring width, specific gravity, summerwood 

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Koch, P. 1972b. Utilization of the southern pines. Vol. I. 

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Koehler, A. 1938. Rapid growth hazards usefulness of 

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(P. taeda, P. elliottii, ring width, specific gravity, uniformity, fibril angle, compression wood, shrinkage, warp, 

compressive strength, other structural) 

Koehler, A. 1939. Heredity versus environment in improving wood in forest trees. Journal of Forestry. 37: 683–687. 

(general overview, general heredity) 

Kramer, P.R. 1957. Tracheid length variation in loblolly 

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length, springwood vs. summerwood, general heredity) 

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strength and modulus of elasticity of fast-grown plantation 

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Kromhout, C.P.; Basman, D.L. 1981. The influence of 

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Lantz, C.W.; Hofmann, J.G. 1969. Geographic variation in 

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In: Proceedings, 10th Southern forest tree improvement 

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(P. taeda, P. elliottii, ring width, specific gravity, geographic 

location, provenance tests) 

Larson, P.R. 1956. Discontinuous growth rings in suppressed slash pine. Tropical Woods. 104: 80–99. 

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Larson, P.R. 1957. Effect of environment on the percentage 

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(P. elliottii, ring width, ring age, specific gravity, summerwood percentage, tree diameter, stand density, site, geographic location) 

Larson, P.R. 1960. A physiological consideration of the 

springwood-summerwood transition in red pine. Forest 

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Larson, P.R. 1962a. A biological approach to wood quality. 

TAPPI Journal. 45: 443–448. 

(ring width, ring age, specific gravity, summerwood percentage, crown size, tree diameter, site, geographic location, 

thinning, pruning) 

Larson, P.R., ed. 1962b. The influence of environment and 

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tracheid diameter, wall thickness, fibril angle, compression 

wood, extractives, heartwood, spiral grain, tree diameter, 

stand density, site, geographic location, thinning, pruning, 

fertilization, irrigation, general heredity) 

Larson, P.R. 1963a. Evaluating the environment for studies 

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(summerwood percentage, crown size, stand density, general 

heredity) 

Larson, P.R. 1963b. Microscopic wood characteristics and 

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(summerwood percentage, springwood vs. summerwood, 

tracheid length, tracheid diameter, wall thickness, crown 

size, foliage efficiency) 

Larson, P.R. 1963c. Stem form development of forest trees. 

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thinning, pruning, general heredity) 

Larson, P.R. 1964. Contribution of different-aged needles 

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(ring width, specific gravity, tracheid diameter, wall thickness, foliage efficiency) 

Larson, P.R. 1968. Assessing wood quality of fertilized 

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(specific gravity, summerwood percentage, springwood vs. 

summerwood, wall thickness, branchiness, crown size, 

foliage efficiency, site, fertilization) 

Larson, P.R. 1969 Wood formation and the concept of 

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(specific gravity, summerwood percentage, uniformity, 

tracheid diameter, wall thickness, compression wood, crown 

size, foliage efficiency, stem taper, stand density, thinning, 

pruning, general heredity) 

Larson, P.R. 1972. Evaluating the quality of fast-grown 

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crown size, stand density, thinning , fertilization, irrigation) 

Larson, P.R. 1973. The physiological basis for wood specific gravity in conifers. In: Proceedings. IUFRO Division 5, 

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(specific gravity, summerwood percentage, tracheid length, 

tracheid diameter, wall thickness, crown size, foliage efficiency, stand density) 

Larson, P.R. 1994. The vascular cambium: Development 

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(general overview) 

Lindgren, R.M. 1949. Density and moisture relations in 

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Department of Agriculture, Forest Service. 2 p. 

(P. elliottii, ring width, specific gravity, position in stem) 

Lodewick, J.E. 1933. Some summerwood percentage relationships in the southern pines. Journal of Agricultural 

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(P. taeda, P. palustris, ring width, specific gravity, summerwood percentage, springwood vs. summerwood, wall 

thickness, position in stem, stand density) 

Loo, J.A.; Tauer, C.G.; van Buijtenen, J.P. 1984. 

Juvenile–mature relationships and heritability estimates of 

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diameter, progeny tests, heritability estimates, parental 

specific gravity) 

Loo, J.A.; Tauer, C.G.; McNew, R.W. 1985. Genetic 

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(P. taeda, ring age, specific gravity, tracheid length, site, 

progeny tests, heritability estimates, parental specific 

gravity) 

Lulay, R.; Galligan, W.L. 1981. The impact of juvenile and 

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modulus of elasticity) 

Manwiller, F.G. 1966. Southern pine cell walls and shrinkage. Southern Lumberman. 213(2656): 184–186. 

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warp) 

Manwiller, F.G. 1972. Wood and bark properties of spruce 

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(P. glabra, ring width, ring age, specific gravity, summerwood percentage, springwood vs. summerwood, tracheid 

length, tracheid diameter, wall thickness, fibril angle. 

Martin, J.W. 1984. Forest management practices that will 

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(P. taeda, specific gravity, knots, tree form, stand density, 

general heredity) 

Marts, R.O. 1949. Effect of crown reduction on taper and 

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(P. palustris, specific gravity, springwood vs. summerwood, 

crown size, stem taper, pruning) 

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(P. palustris, specific gravity, summerwood percentage, 

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stem, crown size, tree taper, pruning) 

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(ring width, sawlog yield) 

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(P. taeda, ring age, specific gravity, tracheid length, bark, 

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(P. taeda, ring age, specific gravity, geographic location, 

provenance tests, modulus of rupture, modulus of elasticity) 

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McKinnell, F.H.; Rudman, P. 1972. Potassium fertilizer 

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(P. radiata, ring width, ring age, specific gravity, tree diameter, stand density, thinning, fertilization) 

McMillan, C.W. 1968. Morphological characteristics of 

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(P. taeda, ring width, ring age, specific gravity, springwood 

vs. summerwood, tracheid length, tracheid diameter, wall 

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Megraw, R.A. 1985. Wood quality factors in loblolly pine. 

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(P. taeda, general overview) 

Megraw, R.A. 1986. Effect of silvicultural practices on 

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(P. taeda, general overview, ring width, specific gravity, 

fibril angle, position in stem, compression wood, stand 

density, site, thinning, pruning, fertilization) 

Meier, R.J.; Goggans, J.F. 1977. Heritabilities of height, 

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(P. virginiana, specific gravity, crown size, site, progeny 

tests, heritability estimates) 

Meylan, B.A. 1968. Cause of high longitudinal shrinkage in 

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Meylan, B.A. 1972. The influence of microfibril angle on 

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(P. radiata, specific gravity, tracheid diameter, wall thickness, fibril angle, compression wood, shrinkage) 

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(P. elliottii, specific gravity, position in stem, bark, tree 

diameter, site) 

Mitchell, H.L. 1964. Patterns of variation in specific gravity 

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(general overview, southern pines, ring width, ring age, 

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(P. taeda, specific gravity, tree diameter, fertilization, irrigation) 

Moody, R.C. 1970. Tensile strength of fingerjoints in pithassociated and non-pith-associated Southern Pine lumber. 

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(southern pines, ring width, specific gravity, modulus of 

elasticity, tensile strength) 

Moschler, W.W., Jr.; Woods, F.W.; Vincent, L.W. 1985. 

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(P. caribaea, ring age, tracheid length, position in stem, 

crown size) 

Namkoong, G.; Barefoot, A.C.; Hitchings, R.G. 1969. 

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(P. taeda, specific gravity, tracheid length, heritability estimates) 

Nicholls, J.W.P. 1967. Preliminary observations on the 

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(P. radiata, ring width, ring age, specific gravity, summerwood percentage, tracheid length, spiral grain, clonal tests, 

heritability estimates) 

Nicholls, J.W.P. 1971. The effect of environmental factors 

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(P. radiata, ring width, ring age, specific gravity, summerwood percentage, springwood vs. summerwood, 

tracheid length, site, fertilization, irrigation) 

Nicholls, J.W.P. 1984. Tracheid cell dimensions and density 

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Nicholls, J.W.P.; Dadswell, H.E. 1962. Tracheid length in 

Pinus radiata D. Don. For. Prod. Tech. Pap. 24. Australian 

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(P. radiata, tracheid length, springwood vs. summerwood, 

position in stem) 

Nicholls, J.W.P.; Fielding, J.M. 1965. The effect of growth 

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(P. radiata, ring width, ring age, specific gravity, summerwood percentage, tracheid length, position in stem, spiral 

grain, clonal tests, shrinkage) 

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(P. radiata, ring width, ring age, specific gravity, summerwood percentage, spiral grain, irrigation) 

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(P. radiata, ring width, ring age, specific gravity, summerwood percentage, tracheid length, spiral grain, clonal tests, 

heritability estimates, shrinkage) 

Nicholls, J.W.P.; Morris, J.D.; Pederick, L.A. 1980. 

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(P. radiata, ring width, specific gravity, summerwood percentage, springwood vs. summerwood, site, progeny tests, 

heritability estimates) 

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(black and white spruce, fibril angle, pulp, tensile strength, 

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Paul, B.H. 1913. Variation in weight of slash pine wood and 

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tree age) 

Paul, B.H. 1929. Relation of growth factors to wood quality 

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(P. taeda, P. elliottii, P. palustris, P. echinata, ring width, 

ring age, specific gravity, crown size, stand density, site, 

geographic location, thinning) 

Paul, B.H. 1932a. Quality versus size as an index of a profitable tree: loblolly pine. Journal of Forestry. 30: 831–833. 

(P. Taeda, stand density, thinning) 

Paul, B.H. 1932b. Some properties of slash pine. Pulp & 

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(P. elliottii, ring age, specific gravity, position in stem, 

heartwood, stand density) 

Paul, B.H. 1938. Reducing bowing and crooking of lumber 

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(P. taeda, P. elliottii, ring width, uniformity, shrinkage, 

warp) 

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(P. taeda, P. elliottii, P. palustris, P. echinata, specific 

gravity, springwood vs. summerwood, position in stem) 

Paul, B.H. 1952. Variability of wood of southern pines as 

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U.S. Department of Agriculture, Forest Service, Forest 

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(general overview, ring width, specific gravity, springwood 

vs. summerwood, compression wood, heartwood, site, pruning, shrinkage) 

Paul, B.H. 1955. Importance of wood quality in tree breeding. Journal of Forestry. 53: 659–661. 

(southern pines, ring width, ring age, fibril angle, general 

heredity, shrinkage, other structural) 

Paul, B.H. 1957. Juvenile wood in conifers. FPL Rep. 2094. 

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(southern pines, ring width, ring age, specific gravity, crown 

size) 

Paul, B.H. 1958. Specific gravity changes in southern pines 

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(P. taeda, P. palustris, P. echinada, specific gravity, summerwood percentage, position in stem, crown size, stand 

density, site, thinning) 

Paul, B.H. 1960. The juvenile core in conifers. TAPPI 

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(P. elliottii, P. palustris, ring width, ring age, stand density, 

shrinkage, warp) 

Paul, B.H.; Marts, R.O. 1931. Controlling the proportion 

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(P. palustris, ring width, springwood vs. summerwood, 

foliage efficiency, fertilization, irrigation) 

Pawsey, C.K.; Brown, A.G. 1970. Variation in properties 

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Australian Forest Research. 4: 15–25. 

(P. radiata, specific gravity, tracheid length, compression 

wood, tree form, site, clonal tests) 

Pearson, R.G. 1984. Characteristics of structural importance 

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(P. taeda, ring age, specific gravity, position in stem, knots, 

modulus of rupture, modulus of elasticity) 

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(general overview, ring age, specific gravity, modulus of 

rupture, modulus of elasticity, compressive strength) 

Pearson, R.G. 1988. Compressive properties of clear and 

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(P. taeda, ring age, specific gravity, knots, site, progeny 

tests, modulus of elasticity, compressive strength) 

Pearson, R.G.; Gilmore, R.C. 1971. Characterization of the 

strength of juvenile wood of loblolly pine (Pinus taeda L.) 

Forest Products Journal. 21(1): 23–31. 

(P. taeda, ring age, specific gravity, position in stem, shrinkage, modulus of rupture, modulus of elasticity) 

Pearson, R.G.; Gilmore, R.C. 1980. Effect of fast growth 

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shrinkage, warp, modulus of rupture, modulus of elasticity, 

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Squillace, A.E.; Echols, R.M.; Dorman, K.W. 1962. 

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Talbert, J.T.; Bridgwater, F.E.; Jett, J.B.; Jabromi, S.

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TAPPI. 1970. Fifth forest biology conference; 1970 May 

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diameter, stand density, site, geographic location) 

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general heredity) 

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(P. taeda, P. elliottii, ring age, specific gravity, position in 

stem, extractives, heartwood, geographic location, 

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fertilization) 

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geographic location) 

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(P. taeda, specific gravity, tracheid length, site, progeny 

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Zobel, B.J.; Kellison, R.C.; Matthias, M.F.; Hatcher, 

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(P. taeda, P. elliottii, P. palustris, P. virginiana, ring age, 

specific gravity, position in stem, extractives, bark, tree age, 

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(P. taeda, specific gravity, compression wood, site, thinning, 

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