Effects of Uneven-Aged and 

Diameter-Limit Management 

on West Virginia Tree and 

Wood Quality 

Michael C. Wiemann 

Thomas M. Schuler 

John E. Baumgras 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

Research 

Paper 

FPL−RP−621 
Abstract 

Uneven-aged and diameter-limit management were compared with an unmanaged control on the Fernow Experimental Forest near Parsons, West Virginia, to determine how 

treatment affects the quality of red oak (Quercus rubra L.), 

sugar maple (Acer saccharum Marsh.), and yellow-poplar 

(Liriodendron tulipifera L.). Periodic harvests slightly increased stem lean, which often causes tension wood. The 

grade of red oak was lower under the diameter-limit treatment compared with that of the control, but this was due 

primarily to tree size; in contrast, uneven-aged management 

improved red oak grade irrespective of tree size. Sugar 

maple grade was poorest in the control but similar in the two 

treatments, regardless of tree size. Yellow-poplar grade was 

best in the control, even when tree size was taken into 

account. Sapwood thickness range was small among all red 

oaks, although the sapwood of the control trees was narrower than that of the treated trees. For yellow-poplar, sapwood thickness increased with tree diameter but was independent of treatment. Sapwood thickness was extremely 

variable in sugar maple. It increased with diameter in both 

treatment sites but not in the control, and it was not significantly correlated with tree age. Young, vigorously growing 

sugar maples produce wide sapwood, but heartwood discoloration begins to affect the trees disproportionately as they 

reach maturity. 

Keywords: growth rate, heartwood, red oak, sapwood, sugar 

maple, tree grade, yellow-poplar 

June 2004 

Wiemann, Michael C.; Schuler, Thomas M.; Baumgras, John E. 2004. 

Effects of uneven-aged and diameter-limit management on West Virginia 

tree and wood quality. Res. Pap. FPL-RP-621. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 16 p. 

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Contents 

 Page 

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

Methods ................................................................................ 2

Study Area, Treatments, and Species................................ 2

Study Sites, Tree Selection, and Tree Measurements ....... 3

Tree Grading ..................................................................... 3

Increment Core Extraction and Measurement................... 3

Computations and Statistical Analyses ............................. 3

Results................................................................................... 3

Number of Trees and Basal Area...................................... 3

Lean .................................................................................. 4

Tree Grade ........................................................................ 4

DBH, Age, and Sapwood Thickness................................. 5

Discussion............................................................................. 9

Grade................................................................................. 9

Age.................................................................................. 10

Growth Rate.................................................................... 11

Sapwood Thickness ........................................................ 13

Conclusions......................................................................... 15

Acknowledgments............................................................... 16

Literature Cited ................................................................... 16
Effects of Uneven-Aged and Diameter-Limit 

Management on West Virginia Tree 

and Wood Quality 

Michael C. Wiemann, Research Scientist 

Forest Products Laboratory, Madison, Wisconsin

Thomas M. Schuler, Research Forester 

Northeast Research Station, Parsons, West Virginia 

John E. Baumgras, Project Leader 

Northeast Research Station, Princeton, West Virginia

Introduction 

The quality of sawlogs is influenced by the silvicultural 

practices that precede their harvest. In addition to external 

characteristics like stem size, shape, and defects (such as 

surface irregularities, bird peck, and epicormic branches), 

internal characteristics are important. Many of these 

characteristics can be predicted from external evaluation but 

some cannot, such as the amount of sapwood and heartwood. 

Because wood color is not apparent in standing trees, its 

effect on value is not usually reflected in stumpage prices. In 

some hardwood species, such as red oak (Quercus rubra L.), 

the dark-colored heartwood is the most valuable portion of a 

log; in others, such as sugar maple (Acer saccharum Marsh.) 

and yellow-poplar (Liriodendron tulipifera L.), the most 

valuable part is the light-colored sapwood. Color is 

especially important in sugar maple lumber, with premiums 

paid for ìwhiteî sugar maple (Barrett and others 1999). 

Shigo (1986) distinguished heartwood (age-altered) from 

discolored wood (injury-altered), but we shall use the term 

heartwood for any dark-colored wood found in the tree 

center, since it is the color of the wood that determines its 

economic value. The heartwood in red oak and yellowpoplar is typical (age-altered), whereas that in sugar maple is 

injury-altered. Therefore, processes that cause injury to 

standing trees might be expected to affect heartwood 

formation in sugar maple but not in red oak or yellowpoplar, although wound-induced heartwood may also form 

in species that produce normal heartwood (Shigo and 

Hillis 1973). 

The sapwood of red oak is typically less than 5 cm wide in 

mature trees (Forest Products Laboratory 1987), whereas 

that of yellow-poplar is often up to 15 cm wide (Lutz 1972). 

The sapwood of sugar maple may be very narrow or it may 

constitute the entire stem cross-section. Unlike the sapwood 

of red oak and yellow-poplar, the sapwood of sugar maple is 

extremely variable in size and shape. The reasons for these 

differences lie in the physiology of the trees and the 

mechanisms of heartwood formation. In species that form 

typical heartwood, a series of physiological changes takes 

place in the wood over time. These changes vary widely 

according to species, as extraneous materials diffuse from 

the dead parenchyma cells into the surrounding wood. In 

species that form injury-altered heartwood, such as sugar 

maple, the extraneous materials are deposited only within 

parenchyma cell cavities because their precursors polymerize to a large size before the parenchyma cell membranes 

break down (Bosshard 1968). Good and others (1955) 

contended that the number of living parenchyma cells in 

sugar maple decreases gradually with age and that the wood 

gradually darkens because of the deposition of colored 

material as the parenchyma cells die. Although the heartwood in sugar maple is wound-induced, not all wounds 

induce heartwood (Shigo 1986). The amount and location of 

discoloration are affected by the cause and location of the 

damage as well as by tree vigor and the ability of the tree to 

compartmentalize wounds (Shigo and Hillis 1973, Shortle 

and others 1996). 

Genetics, site factors, and silvicultural treatments may be 

important in determining the type and amount of heartwood. 

Site factors include climate, previous human and natural 

disturbances, type of regeneration that follows disturbance, 

soil characteristics, and geographic features such as 

elevation, latitude, and topography. Silvicultural treatments 

include pruning, thinning, and harvesting regimes and 

methods. 

In this paper, we compare the quality of trees subjected to 

uneven-aged management, diameter-limit management, and 

no management. Three common and commercially important 

species are examined: red oak, sugar maple, and yellowpoplar. The aim of this study was to determine if these 

management regimes improve tree and wood quality. 
2 

Methods 

Study Area, Treatments, and Species 

This research was part of a long-term silvicultural study 

implemented in 1950 on the Fernow Experimental Forest 

near Parsons, West Virginia. It was carried out in Study 

Area 2, which includes excellent growing sites; for example, 

northern red oak has a site index (SI50) of 24 m. We 

compared two experimental treatments, uneven-aged 

management and diameter-limit cutting, with an unmanaged 

control. The choice of study species was based on shade 

tolerance ratings and heartwood characteristics. Sugar maple 

is very shade-tolerant, and it often produces injury-altered 

heartwood that is much less valuable than its sapwood. 

Red oak is intermediate in shade tolerance, producing typical 

heartwood that is much more valuable than its sapwood. 

Yellow-poplar is shade intolerant, and it produces typical 

heartwood that is less valuable than the sapwood 

(Trimble 1973). 

The first logging in what became the Fernow Experimental 

Forest occurred between 1903 and 1911 (Trimble 1977) 

(Fig. 1). Our control site (Watershed 4A, 28 ha, SI50 = 25 m) 

(Fig. 2) was originally logged between 1905 and 1910 (Pan 

1995), but it has not been disturbed since except for the 

removal of dead American chestnuts (Castanea dentata

(Marsh.) Borkh.) around the time of World War II. In the 

diameter-limit site (Compartment 9B, 33 ha, SI50 = 23 m, 

established 1954), all trees greater than 43.2 cm (17 inches) 

diameter at breast height (DBH) are removed on a 15-year 

cutting cycle. No quality selection criteria are considered, 

except that cull trees are felled and left on site. Prior to our 

study, this site had been cut three times, most recently in 

1986. The trees on the uneven-aged site (Compartment 20A, 

10 ha, SI50 = 24 m, established 1952) are marked and cut to 

maintain a basal area of 15 m2

/ha for trees >27.9 cm 

(11 inches) DBH, with a planned number of trees in every 

diameter class up to 81.3 cm (32 inches). The poorest quality 

trees are selected for removal at each harvest, leaving behind 

the better trees to grow in the additional space. Compartment 

20A has been cut five times, most recently in 1997 (USDA 

Forest Service, Timber and Watershed Laboratory, Figure 1óFernow Experimental Forest, West Virginia. 

 Figure 2óUnmanaged control site. Logged between 

 1905 and 1910. 
3

unpublished data). Although the sites are similar in quality 

and differ primarily in treatment, some site factors could not 

be controlled. These include percentage of slope, slope 

direction, and site aspect. 

Study Sites, Tree Selection, and Tree 

Measurements 

A 40-m-wide transect was set up in each silvicultural 

treatment site, with the starting point and direction of each 

transect depending on the site. Each starting point was at 

least 25 m from the nearest access road. The transect 

direction was chosen so that a transect of at least 300 m 

would stay within the site. The centerline of each transect 

was marked with string; the transect consisted of the area 

20 m on each side of this centerline. In this transect, every 

sugar maple, yellow-poplar, and red oak with a DBH of at 

least 25 cm was tagged. When at least 20 trees each of two 

species were tagged, the transect was considered complete. 

Additional trees of the third species were then tagged from 

trees along both sides of the transect to give a total of at least 

20 trees per species per treatment area. 

In each treatment area, 20 trees of each species were selected 

using a random number table; these were the study trees. 

Maximum percentage of slope was measured at 25-m 

intervals along each transect, and the average steepest slope 

in each transect was calculated as the arithmetic mean of 

these measurements. In addition, the direction of maximum 

slope was measured with a compass at each 25-m interval, 

and average direction of maximum slope was calculated 

from these measurements. No corrections were applied for 

magnetic declination. 

The DBH of each study tree was measured with a diameter 

tape, and the direction of maximum lean of the lower bole 

was determined using a compass (with no correction for 

declination). The angle of lean was measured using a 2-mlong aluminum rod with a plumb bob suspended from the 

top; the horizontal departure of the plumb bob was recorded, 

and the percentage of lean was calculated from the length of 

the rod (hypotenuse) and the horizontal departure. Lean is 

important because tension wood, which has inferior working 

properties, can form on the upper side of a leaning stem. We 

expected that gradual ìsurface slippageî caused by gravity 

might force the lower tree stems to lean downhill on the 

relatively steep slopes. The hypothesis that trees tend to lean 

downhill was tested non-parametrically using Tukeyís studentized range based on absolute differences. Only trees 

with ≥5% lean were included in the test. 

Tree Grading 

Each tree was graded by USDA Forest Service tree graders 

using the criteria summarized in Hanks (1976). In some 

cases the re-measurement of DBH by the graders resulted in 

a tree being considered too small for Forest Service tree 

grades; in these instances, the potential grade was 

determined. Grading took into account attributes such as 

shape of cross section, amount of taper, extent of sweep or 

crook, and presence of lateral and epicormic branches, 

decay, splits, catface, or other damage. 

Increment Core Extraction and 

Measurement 

Two increment borings were taken at breast height from 

each tree. In most cases these borings were taken from the 

north and south side of the tree. Rarely, a core could not be 

taken from one of these directions because of bole damage; 

that core was then taken from the east or west side. Cores 

were mounted with glue in core holders so that transverse 

surfaces faced upwards. The tops of the cores were cut with 

razor blades or sanded to produce surfaces clean enough that 

growth rings could be counted and heartwood could be 

distinguished from sapwood. The criterion for separating 

heartwood from sapwood was wood color as observed with 

the naked eye. The amount of sapwood (lineal distance and 

number of growth rings) was measured in each core and was 

analyzed for each species to determine treatment effects. The 

total number of growth rings was also counted to estimate 

tree age. Radius as a function of age was plotted for the 

cores. 

Computations and Statistical Analyses 

The number of trees per hectare, basal area per hectare, and 

mean DBH were calculated, for each species and treatment, 

from the trees contained within the transects. The DBH, tree 

age, and sapwood thickness (in centimeters and growth 

rings) were compared among sites for each species. 

The data were examined for normality and homogeneity of 

variances. The SAS GLM program, with Tukey comparisons, was used to find differences among site means for 

DBH, age, and sapwood thickness for each species. Pairwise 

t-tests were used to determine equality of variances. 

Results

Number of Trees and Basal Area 

Transect length was 275 m in the control site and 250 m in 

the diameter-limit and uneven-aged sites. Red oak was 

dominant in both number of trees and basal area per hectare 

in the control site, whereas sugar maple was dominant in the 

two treatment sites; red oak was more than twice as frequent 

in the control site as in either treatment site, whereas sugar 

maple was about one-tenth as frequent. Although yellowpoplar was equally common in the two managed sites, it was 

50% more frequent in the control than in either treatment site 

(Table 1). 
4 

Lean 

Within each transect, maximum downhill slope varied by 

50° or less in azimuth and by 22% (12°) or less in 

inclination, and the downhill direction in the control was 

opposite that in the two treatment sites (Table 2). Trees 

had a tendency to lean downhill, although there were many 

exceptions. In general, red oak leaned the most and yellowpoplar the least. Red oak had the greatest percentage of trees 

with at least 5% lean and yellow-poplar had the lowest 

percentage. In the control and diameter-limit sites, fewer 

than half the yellow-poplars had at least 5% lean. 

At all three sites, the species with the greatest percentage of 

ìstraight treesî (≤10% lean) was yellow-poplar (85% to 

95%) and the species with the lowest percentage of straight 

trees was red oak (35% to 50%); sugar maple was intermediate (65% to 75%) (Fig. 3). Thus it seems that the tendency to 

lean is a species characteristic, at least in part. However, 

treatment may also affect lean, since the individual trees 

with the greatest lean in each species were found in the 

treatment sites: red oak and sugar maple in the diameterlimit site and yellow poplar in the uneven-aged site. Overall, 

red oak had the greatest lean in the diameter-limit site, 

sugar maple in the control site, and yellow-poplar in the 

uneven-aged site. 

For all sites combined, there was no difference in lean direction among species. For all species combined, the lean direction, relative to the greatest downhill slope, was different for 

the control than it was for the two treatment sites, which had 

the same lean direction; trees in the treatment sites were 

more apt to lean downhill than were trees in the control site. 

Because the downhill azimuth of the control site (105°) was 

opposite the downhill azimuths of the two treatment sites 

(285° and 290°, Table 2), the direction of prevailing sunlight 

may account for the different effects. 

Tree Grade 

The largest red oaks and sugar maples were found in the 

control site and the largest yellow-poplars in the unevenaged site. Because grade is a function of both bole quality 

and DBH (Miller and others 1986), large trees would tend to 

have higher grades for similar bole evaluations. For this 

reason, Table 3 (percentage of trees in each grade) is divided 

into two categories: the grade distribution of all sample trees 

and the distribution of only those sample trees large enough 

to qualify as Grade 1 (DBH ≥ 40.6 cm). 

Table 1óFrequency, basal area per hectare, and mean DBH of study species 

Number of trees 

per hectare 

Basal area per hectare 

(m2

) 

Mean tree DBHa 

(cm) 

Site 

Red 

oak 

Sugar 

maple 

Yellowpoplar Red 

oak 

Sugar 

maple 

Yellowpoplar Red oak Sugar 

maple 

Yellowpoplar All species 

Control 51 6 18 15.25 2.21 3.37 59.3 (56) 65.3 (7) 47.5 (20) 57.0 (83) 

Diameter-limit 22 74 12 3.87 8.45 1.58 46.4 (22) 37.0 (74) 39.9 (12) 39.2 (108) 

Uneven-aged 20 59 12 5.32 6.55 3.14 55.0 (20) 36.5 (59) 55.1 (12) 43.0 (91) 

a

Number of trees used in calculations given in parentheses. 

Table 2óTransect slopes, percentage of tree lean, and tree lean azimuth at each site 

Transect slopea Tree lean (%) b Tree lean azimuth (°)

c

Site 

Slope 

(%) 

Downhill 

azimuth (°) 

Red 

oak 

Sugar 

maple 

Yellowpoplar All 

species 

Red 

oak 

Sugar 

maple 

Yellowpoplar All 

species 

Control 26 (14ñ36) 105 (70ñ120) 11 (7.0) 11 (9.4) 3 (4.0) 9 (8.0) 160 (17) 125 (14) 175 (3) 145 (34) 

Diameterlimit 31 (27ñ47) 285 (250ñ295) 13 (6.2) 9 (8.3) 3 (3.3) 8 (7.5) 280 (20) 280 (13) 255 (4) 275 (37) 

Unevenaged 30 (23ñ36) 290 (280ñ300) 11 (5.9) 7 (4.6) 7 (7.9) 9 (6.5) 310 (16) 290 (13) 315 (11) 305 (40) 

a

Transect slope includes mean percentage of greatest slope, with measurements taken every 25 m along transect center 

 line, and mean azimuth of downhill slope. Ranges are given in parentheses. b

Tree lean is mean percentage of lean at breast height for all sample trees at each site (standard deviations given in 

 parentheses). 

c

Tree lean azimuth is mean direction of lean for trees with ≥5% lean (number of trees given in parentheses). 
5

DBH, Age, and Sapwood Thickness 

The distributions of tree DBH, age, and sapwood thickness 

data were non-normal, and pairwise t-tests showed that 

variances were not equal. General linear models with 

assumptions of unequal variances were therefore used to 

distinguish differences among control and treatments. Age 

estimates were not used for trees that were hollow or had 

significant heart rot. The trees without age estimates were as 

follows: control site, two red oaks and two sugar maples; 

diameter-limit site, two sugar maples and three yellowpoplars; and uneven-aged site, one red oak. 

Age was estimated for 56 control site trees; of these, 14 were 

greater than 100 years old. Of the four control site trees with 

hollow centers, three trees were large (>85 cm DBH) and 

can also be assumed to have been at least 100 years old. Six 

uneven-aged site trees and one (possibly two) diameter-limit 

site trees were at least 100 years old. The oldest red oak and 

sugar maple trees (166 and 202 years, respectively) were in 

the control site, whereas the oldest yellow-poplar (94 years) 

was in the uneven-aged site (Table 4). For the trees whose 

ages could be estimated, Figure 4 shows tree DBH as a 

function of tree age for each species at each site. 

Red oak mean ages were not statistically different among the 

three sites, although the coefficient of variability (CV) was 

highest in the control site and lowest in the diameter-limit 

site (Table 4). Control sugar maple was both older and larger 

than sugar maple in either treatment site, and the CV of 

sugar maple age was greater in the control than in the 

treatment sites (Table 4). Control yellow-poplar was older 

but not larger than yellow-poplar in the treatments sites 

(Table 4). This is because yellow-poplar, a shade-intolerant 

species, has a large variance in its growth rate, which 

depends on degree of suppression. The mean age for 

yellow-poplar was for a single cohort in the control 

(CV = 5%), the uneven-aged site had two cohorts 

(CV = 35%), and the diameter-limit site had three 

(CV = 30%) (Table 4, Fig. 4). 

Red oak DBH was significantly greater in the control site 

than in the diameter-limit site, but not in the uneven-aged 

site (Table 4). The uneven-aged and diameter-limit sites 

were not significantly different from each other in DBH 

(Table 4). This apparent contradiction is probably 

attributable to the high DBH variability (CV) in the unevenaged site, which did not permit the SAS GLM program to 

distinguish it from either the control or diameter-limit site. 

Sugar maple DBH was greater in the control site than in the 

uneven-aged and diameter-limit sites, in which DBH was 

equal. Yellow-poplar DBH was the same in all three sites. 

DBH variability (CV) was lowest in the diameter-limit site 

for red oak, about equal among sites for sugar maple, and 

highest in the uneven-aged site for yellow-poplar. Diameterlimit management removed all of the largest oaks, which 

accounts for the low CV. The DBH CV for yellow-poplar 

was high in the uneven-aged site because this site has been 

subjected to partial harvests five times, each time engendering a new cohort of trees. The diameter-limit site has 

also been subjected to partial harvests but the largest trees 

have been selectively removed, reducing the DBH CV for 

yellow-poplar to about equal that of the control. Interestingly, the DBH CV for sugar maple was approximately 

equal among sites. In the control, both standard deviation 

(SD) and mean were larger than those values in either 

treatment, where they were about equal (Table 4). 

Table 5 gives the mean sapwood thickness for each 

species/treatment/grade category. In general, sapwood was 

narrower in lower grade trees. Sapwood thickness values of 

each species at each site are also compared in Figure 5. For 

red oak, mean sapwood thickness in the control site was 

somewhat narrower than that in either treatment site (Fig. 5). 

Although there is a great deal of overlap, this difference is 

statistically significant (p = 0.05) (Table 4). Because 

sapwood is considered a defect in red oak, treatment reduced 

the color quality of the wood. For sugar maple, mean and 

median values of sapwood thickness were similar among the 

three sites, although the control had a wider range and 

included one outlier (Fig. 5)óa 54-cm-DBH, 135-year-old, 

Grade 1 tree with no heartwood. For yellow-poplar, mean 

sapwood thickness was narrowest in the control site 

compared with the treatment sites, again with much overlap 

(Fig. 5), so that the differences were not statistically 

significant (Table 4). 

Red oak sapwood thickness, expressed in number of growth 

rings, was not statistically different in either treatment site 

compared with the control, although the two treatments 

were statistically different from each other (Table 4). 

Figure 3óPercentage of trees of each species in each 

lean class at study sites. RO is red oak, SM sugar maple, 

and YP yellow-poplar. 

0

10

20

30

40

50

60

70

80

90

100

RO SM YP RO SM YP RO SM YP

 ≤10

11-20

21-30

31-40

Percentage of trees

Control Diameter-limit Uneven-aged

Percent lean
6 

Table 3óPercentage of trees in each grade (including potential grade) for each treatment and speciesa

 Grade 1 Grade 2 Grade 3 Below-grade 

Sample Site RO SM YP All RO SM YP All RO SM YP All RO SM YP All 

All trees Control 50 5 75 43 20 15 10 15 20 40 10 23 10 40 5 18 

 Diameter-limit 30 20 40 23 10 15 15 13 50 50 45 50 10 15 0 13 

 Uneven-aged 60 20 50 43 10 10 20 13 30 50 30 37 0 20 0 7 

Trees ≥ 40.6 cm DBHb 

 Control 

(19,19,15,53) 

53 5 87 45 16 11 13 13 21 42 0 23 11 42 0 19 

 Diameter-limit 

(12,6,11,29) 

50 33 64 52 8 33 9 14 42 33 27 34 0 0 0 0 

 Uneven-aged 

(15,9,11,35) 

80 44 91 74 7 11 0 6 13 33 9 17 0 11 0 3 

a

RO is red oak; SM, sugar maple; YP, yellow-poplar; All, all three species combined. Trees at least 40.6 cm DBH 

 were large enough to be Grade 1. 

b

Numbers in parentheses are number of red oak, sugar maple, yellow poplar, and all species combined, respectively, 

 with ≥40.6 cm DBH. 

Table 4óDiameter at breast height, age, and sapwood thickness of test species at control and treatment sitesa 

 DBH (cm) Tree age (years) Sapwood thickness (cm) Sapwood thickness (rings) 

Site 

Red 

oak 

Sugar 

maple 

Yellowpoplar Red 

oak 

Sugar 

maple 

Yellowpoplar Red 

oak 

Sugar 

maple 

Yellowpoplar Red 

oak 

Sugar 

maple 

Yellowpoplar 

Control Mean 66.4 A 62.0 A 47.5 A 92.6 A 114.2 A 84.2 A 2.0 A 14.2 A 6.0 A 7.8 AB 71.9 A 29.0 A 

 SD 20.0 12.1 10.5 28.3 36.3 4.1 0.5 5.5 2.4 1.6 19.8 5.6 

 CV 30 20 22 31 32 5 26 39 40 21 28 10 

 Range 35ñ109 39ñ88 28ñ62 58ñ166 66ñ202 75ñ89 1.0ñ3.2 4.4ñ26.9 1.8ñ10.0 5.5ñ10.5 30.5ñ122.5 19.0ñ39.0

 

Diam.- 

limit 

Mean 46.3 B 35.1 B 40.2 A 83.3 A 74.4 B 52.9 B 2.7 B 12.9 A 7.1 A 6.6 B 54.2 B 17.4 B 

 SD 10.1 8.0 8.2 6.1 14.2 15.8 0.7 4.1 1.9 1.0 13.5 4.2 

 CV 22 23 20 7 19 30 26 32 27 15 25 24 

 Range 28ñ60 25ñ49 27ñ56 73ñ93 54ñ111 36ñ83 1.6ñ4.1 5.0ñ19.0 4.8ñ11.2 5.0ñ9.0 29.0ñ76.5 9.5ñ24.0 

 

Unevenaged Mean 55.0 AB 36.6 B 49.7 A 85.1 A 82.8 B 63.2 B 2.6 B 12.8 A 6.9 A 8.2 A 51.8 B 20.7 B 

 SD 19.4 8.0 18.5 11.7 16.8 22.4 0.8 4.4 2.5 1.6 16.5 7.6 

 CV 35 22 37 14 20 35 31 34 36 20 32 37 

 Range 29ñ109 25ñ53 26ñ83 64ñ112 55ñ113 41ñ94 1.5ñ4.2 4.4ñ21.0 3.4ñ11.1 5.0ñ11.0 18.5ñ80.5 12.5ñ37.5

a

 Results of nonparametric tests for differences in means among treatments and species. For each column, treatment means followed 

 by the same letter are not significantly different at the 0.05 level. 
7

Figure 4óDiameter at breast height (DBH) as a function of tree age for each species at each site. 

10 

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200 220

10 

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200 220

10 

20

30

40

50

60

70

80

90

100

0 20 40 60 80 100 120 140 160 180 200 220

Control 

Red Oak 

Control

Sugar Maple 

Control 

Yellow-Poplar 

0 

0 20 40 60 80 100 120 

10 

20 

30 

40 

50 

60 

0 20 40 60 80 100 120

Diameter-limit

Sugar Maple 

Diameter-limit 

Yellow-Poplar 

20 40 60 80 100 120 0 20 40 60 80 100 120 0 20 40 60 80 100 120

Tree age (years) 

10 

20

30

40 

50

60 

70

80

90 

10

20 

30 

40

50

60 

70

80 

90 

10 

20 

30

40

50

60 

70 

80 

90 

100 100 100

Uneven-aged 

Yellow-Poplar 

Uneven-aged

Sugar Maple 

Uneven-aged 

Red Oak 

10

20

30

40

50

60

70 

0 20 40 60 80 100 120

DBH (cm) 

Diameter-limit 

Red Oak 

80

90

100 

10

20 

30 

40 

50

70 

80

90

100 

70 

80

90

100 

60 
8 

Figure 5óDistribution of sapwood thickness. Crosses indicate mean values. Each box depicts middle half 

of data between 25th and 75th percentiles; the horizontal line across the box marks the median value. 

Vertical extensions (whiskers) indicate values greater than the median − 1.5 quartile range but less than 

the median + 1.5 quartile range. Circle indicates an outlier (more than two standard deviations from mean). 

The number of sapwood growth rings was greater in the 

control than in either treatment site for sugar maple and 

yellow-poplar. In yellow-poplar, growth rate (DBH/age) 

was 0.57 cm/year in the control site, but 0.92 and 

0.80 cm/year in the diameter-limit and uneven-aged sites, 

respectively. This greater vigor in the treatment sites resulted 

in fewer rings of sapwood but not a statistically significant 

difference in centimeters of sapwood because the rings were 

wider (Table 4). 

Sugar maple sapwood thickness is compared with diameter 

growth rate in Figure 6, in which sapwood thickness in 

centimeters (a) and number of growth rings (b) is plotted 

against growth rate. Diameter growth rate, equal to tree 

DBH divided by age, includes both the wood and the bark. 

For all trees combined, it is apparent that sapwood thickness 

was unrelated to growth rate; correlations between sapwood 

thickness and growth rate were non-significant for both 

centimeters (r = 0.24) and number of rings (r = ñ0.04). 

Considering each site separately, sapwood thickness in 

centimeters was significantly and positively correlated with 

growth rate for the diameter-limit treatment (r = 0.50) and 

the uneven-aged treatment (r = 0.53). All other correlations 

were non-significant. 

The correlation coefficients among measured variables for 

each species at each site are presented in Table 6. No 

significant relationships hold for all species at all sites. The 

DBH was significantly correlated with tree age for red oak at 

the control site but not at either treatment site; DBH was 

significantly correlated with tree age at only the uneven-aged 

site for sugar maple and at the two treatment sites but not at 

the control site for yellow-poplar. For red oak and yellowpoplar, the significant correlations between DBH and 

tree age at the control and treatment sites, respectively, can 

be attributed to the presence of young and old cohorts within 

the sites, as is evident from Figure 4. For the sugar maple in 

the uneven-aged site, the age and DBH ranges were wide 

Table 5óSapwood thickness for each species and treatment by grade 

 Mean sapwood thickness (cm) a

 Red oak Sugar maple Yellow-poplar 

Grade Control 

Diameterlimit Unevenaged Control Diameterlimit Unevenaged Control Diameterlimit Unevenaged 

Grade 1 2.3 (10) 3.2 (6) 2.9 (12) 26.9 (1) 14.5 (4) 16.4 (4) 6.6 (15) 8.1 (8) 8.2 (10)

Grade 2 1.9 (4) 2.8 (2) 2.2 (2) 16.2 (3) 17.1 (3) 17.6 (2) 5.9 (2) 6.5 (3) 6.4 (4) 

Grade 3 1.8 (4) 2.4 (10) 2.2 (6) 13.7 (8) 11.6 (10) 11.3 (10) 3.5 (2) 6.5 (9) 5.1 (6) 

Below grade 1.2 (2) 2.3 (2) ó 12.2 (8) 11.0 (3) 10.6 (4) 1.8 (1) ó ó 

a

 Numbers of trees given in parentheses. 
9

enough to register a significant (but weak) correlation 

(Table 6, Fig. 4). 

For red oak, sapwood thickness in centimeters was 

significantly (positively) correlated with DBH only at the 

diameter-limit site; for sugar maple it was correlated at the 

two treatment sites but not the control site; and for yellowpoplar it was correlated at all three sites. Sapwood thickness 

in centimeters was significantly correlated with tree age only 

for yellow-poplar at the uneven-aged site, as a result of the 

presence of two very distinct age cohorts (Table 6, Fig. 4). 

Discussion 

Grade 

Considering all trees regardless of DBH, the three sites 

showed species-related differences in grade distributions. 

The uneven-aged site had the largest proportion of Grade 1 

red oak trees (60%) and the diameter-limit site the lowest 

proportion (30%). The control site had the largest proportion 

of Grade 1 yellow-poplar trees (75%) and the diameter-limit 

site the lowest proportion (40%). Grade 1 sugar maple was 

rare (5%) in the control site and constituted only 20% of 

trees in the uneven-aged and diameter-limit sites. Overall the 

diameter-limit site had a low proportion of Grade 1 trees 

(23%) and a high proportion of Grade 3 trees (50%) because 

large trees have been periodically removed from this site. 

The uneven-aged site had no below-grade red oak or 

yellow-poplar and the diameter-limit site had no belowgrade yellow-poplar, but the control site had below-grade 

trees of all three species, especially sugar maple (40%) 

(Table 3). 

In the comparison of the trees large enough to be Grade 1 

(≥40.6 cm DBH), little change was evident in the control site 

because most of those trees (53 of 60) were large enough to 

be Grade 1; of these, 53% red oak, 5% sugar maple, and 

87% yellow-poplar were Grade 1 (Table 3). Compared with 

the control, the diameter-limit site (29 trees) showed little 

change in grade for red oak (50% Grade 1), improved 

quality for sugar maple (33% Grade 1), and lower quality for 

yellow-poplar (64% Grade 1). The uneven-aged site 

(35 trees) showed great improvement in grade: 80%, 44%, 

and 91% of red oak, sugar maple, and yellow-poplar, 

respectively, were Grade 1. Considering all species 

combined, 45% trees at the control site, 52% at the 

diameter-limit site, and 74% at the uneven-aged site were 

Grade 1 (Table 3). 

Our data indicate that compared with no management, 

uneven-aged management can greatly increase the 

proportion of high grade red oak and sugar maple. 

Compared with no management, diameter-limit management 

does not increase the proportion of high grade red oak, 

increases the proportion of high grade sugar maple, and 

decreases the proportion of high grade yellow-poplar. For 

large DBH (≥40.6 cm) trees, the diameter-limit site had no 

below-grade trees, unlike the uneven-aged site, which had 

11% below-grade sugar maple, and the control, which had 

11% below-grade red oak and 42% below-grade sugar maple 

(Table 3). This is the result of periodic felling of all cull 

trees in the diameter-limit site. 

The interpretation of the effect of management on grade is 

confounded by the presence of residual (pre-1910) red oaks 

and sugar maples on the control site. For example, the 

largest oak (109 cm DBH) and the largest maple (88 cm 

DBH) were both culls, and they may represent poor quality 

trees left when the Fernow Experimental Forest was first 

logged. 

Why the mean DBH of trees in the diameter-limit site was 

not significantly smaller than that of trees in the unevenaged site (Table 4) is not clear, but it may be due to growth 

during the interval since the last treatment, which occurred 

in 1997 in the uneven-aged site but in 1986 in the diameterlimit site. Thus, the diameter-limit trees have had an 

Figure 6óSapwood thickness in sugar maple as a 

function of growth rate: (a) thickness in centimeters; 

(b) thickness in number of growth rings. 

(a)

5

10

15

20

25

30

Control

Uneven-aged

Diameter-limit

(b)

20

40

60

80

100

120

140

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8

0

Sapwood thickness (cm)

Diameter growth rate (cm/year)

Sapwood thickness (rings)
10 

additional 11 years of growth compared with the unevenaged trees, reducing the effect of the selective removal of 

large-diameter trees. Note that the largest tree in the 

uneven-aged site was 109 cm DBH, but the largest tree in 

the diameter-limit site was only 60 cm DBH (Table 4). Thus, 

the largest trees had in fact been removed from the diameterlimit site even though their mean DBH measurements were 

not significantly different. 

Age 

As Table 4 indicates, the mean age of control site trees was 

greater than that of the trees in the two treatments, as 

expected, although the differences were not statistically 

significant for red oak because of its high variability. We 

emphasize that the ages obtained are not maximums, since 

the increment borer did not always hit the pith. Nevertheless, 

the ages of the oldest red oak and sugar maple trees exceed 

the elapsed time since the earliest timber harvesting at all 

three sites, indicating that old-growth species composition 

(primarily from the old-growth understory) is still a factor in 

current composition and structure. The ages of the oldest 

yellow-poplars, on the other hand, correspond to the elapsed 

time since the earliest timber harvesting at all three sites, 

indicating the relictual importance of that harvesting. 

Table 6óCorrelation coefficients among measured variables for individual sites and species. 

Italics indicate correlations significant at 0.05 level 

Site Species Variable 

Tree age 

(years) 

Sapwood 

(cm) 

Sapwood 

(rings) 

Control Red oak DBH 0.60 ñ0.32 0.62 

 Tree age ó ñ0.30 0.56 

 Sapwood (cm) ñ0.30 ó ñ0.30 

 Sugar maple DBH 0.46 0.09 0.11 

 Tree age ó 0.41 0.52 

 Sapwood (cm) 0.41 ó 0.89 

 Yellow-poplar DBH 0.05 0.80 0.32 

 Tree age ó ñ0.27 0.22 

 Sapwood (cm) ñ0.27 ó 0.49 

Diameterñlimit Red oak DBH ñ0.24 0.69 ñ0.18 

 Tree age ó ñ0.22 ñ0.66 

 Sapwood (cm) ñ0.22 ó ñ0.02 

 Sugar maple DBH 0.27 0.72 0.03 

 Tree age ó 0.25 0.49 

 Sapwood (cm) 0.25 ó 0.63 

 Yellow-poplar DBH 0.72 0.74 0.52 

 Tree age ó 0.45 0.65 

 Sapwood (cm) 0.45 ó 0.53 

Uneven-aged Red oak DBH ñ0.29 0.40 ñ0.11 

 Tree age ó 0.02 0.00 

 Sapwood (cm) 0.02 ó 0.61 

 Sugar maple DBH 0.46 0.81 0.40 

 Tree age ó 0.23 0.40 

 Sapwood (cm) 0.23 ó 0.72 

 Yellow-poplar DBH 0.83 0.68 0.54 

 Tree age ó 0.57 0.78 

 Sapwood (cm) 0.57 ó 0.70 
11

Interestingly, the age distributions showed low variability 

(SD = 4.1 years) for yellow-poplar in the control site and 

high variability (SD = 15.8 and 22.4 years) for both 

treatments of yellow-poplar (Table 4). Because yellowpoplar is shade intolerant, the population of trees in the 

control primarily consisted of individuals that originated 

after the logging of the early 1900s. In contrast, new yellowpoplar trees originated after treatments in the uneven-aged 

and diameter-limit sites. 

The variability (range, SD, and CV) in age of red oak and 

sugar maple was highest in the control site and lowest in the 

diameter-limit site (Table 4). The control site contained oldgrowth oaks and maples as well as young trees of these 

species. Uneven-aged and diameter-limit management 

periodically removed some of the largest trees of these 

species, reducing the range and variability. 

Several different patterns are evident from Figure 4. Two 

distinct age classes are present for red oak in the control site 

(58 to 94 years and >128 years, corresponding to the periods 

1907ñ1943 and prior to 1872, respectively) and yellowpoplar in the uneven-aged site (41 to 47 years and 77 to 

94 years, corresponding to the periods 1954ñ1960 and 

1907ñ1924, respectively). In contrast, some species and sites 

showed very uniform age, especially yellow-poplar in the 

control site (75 to 89 years, 1912ñ1926) and, to a lesser 

extent, the red oaks in the diameter-limit site (73 to 93 years, 

1918ñ1929). Obviously, the yellow-poplar trees in the 

control site all originated over a short interval after logging 

in the beginning of the 20th century. Some yellow-poplars in 

the uneven-aged site also originated during this period, but 

another cohort followed the first experimental harvest in 

1952. The age distributions of the other species and sites are 

less clear. A cohort of 12 yellow-poplar trees originated on 

the diameter-limit site (initiated 1954) between 1954 and 

1965, but this site also contains yellow-poplars that 

originated between 1918 and 1950. Sugar maple age seemed 

to be fairly evenly distributed at all three sites, although the 

control site contained older sugar maples than did the 

uneven-aged or diameter-limit site (Fig. 4, Table 4). 

Growth Rate 

Growth patterns were affected by treatments as well as 

natural events, as shown by the comparison of inside-bark 

radius as a function of tree age for trees with cores that hit 

pith (Figs. 7 to 9). At the control site (Fig. 7), three treesóa 

166-year-old red oak and 202- and 116-year-old sugar 

maplesówere growing on the site prior to the harvest of the 

early 1900s. At that time, DBH would have been about 

30 cm for red oak and 25 cm for the older sugar maple, 

based on measurements from the cores. The increase in 

growth rate subsequent to the harvest is clearly shown by 

the inflection points corresponding to 1908. Growth rate 

increased at that time but has gradually been slowing, 

especially for sugar maple. The growth rate of the two 

smaller red oaks of Figure 7 has been constant, but that of 

the smaller sugar maple has decreased with age. The red 

oaks in the control are still vigorous, whereas the sugar 

maples have entered a slow growth stage. 

Figure 7óGrowth patterns of selected trees in control 

site. Tree radius is radius inside bark, determined by 

measurement of core that reached pith. 

1900

Sugar Maple

0

5

10

15

20

25

30

35

40

1800 1850 1900 1950 2000

72.9 cm DBH; 202 years

77.5 cm DBH; 116 years

42.4 cm DBH; 66 years

Yellow-Poplar

0

5

10

15

20

25

30

35

40

1800 1850 1950 2000

45.2 cm DBH; 89 years

60.2 cm DBH; 87 years 

27.8 cm DBH; 89 years 

Red Oak

0

5

10

15

20

25

30

35

40

1800 1850 1900 1950 2000

97.5 cm DBH; 166 years

57.2 cm DBH; 87 years

43.5 cm DBH; 58 years

Tree radius (cm)

Year 
12 

The yellow-poplars in the control site (75 to 89 years old) 

originated subsequent to the harvest of the early 1900s. One 

tree depicted in Figure 7 has been growing at a uniform rate, 

whereas the growth rates of the other two have been 

slowing. The smaller of these two trees grew slowly under 

suppressed conditions, whereas the larger tree grew rapidly. 

Surprisingly, the diameter-limit site contained some old 

trees. Figure 8 includes the growth pattern of a 111-year-old 

sugar maple, which was slow and uniform until the 

compartment was established in 1954, after which the 

growth rate increased. In 1954, the DBH of this tree would 

have been about 14 cm. Figure 8 also depicts a 93-year-old 

Figure 8óGrowth patterns of selected trees in diameterlimit site. Tree radius is radius inside bark, determined 

by measurement of core that reached pith. 

Figure 9óGrowth patterns of selected trees in unevenaged site. Tree radius is radius inside bark, determined 

by measurement of core that reached pith. 

Tree radius (cm) 

Red Oak 

0

5

10

15

20

25

30

1880 1900 1920 1940 1960 1980 2000

30.9 cm DBH; 93 years 

28.5 cm DBH; 80 years

55.9 cm DBH; 76 years

Sugar Maple

0

5

10

15

20

25

30 

1880 1900 1920 1940 1960 1980 2000

44.4 cm DBH; 111 years

27.9 cm DBH; 93 years

26.0 cm DBH; 57 years

Yellow-Poplar

0

5

10

15

20

25

30

1880 1900 1920 1940 1960 1980 2000

46.2 cm DBH; 78 years 

45.7 cm DBH; 60 years 

27.7 cm DBH; 41 years 

Year 

Red Oak

0

5

10

15

20

25

30

1880 1900 1920 1940 1960 1980 2000

49.2 cm DBH; 112 years

54.8 cm DBH; 90 years

29.4 cm DBH; 83 years

60.0 cm DBH; 69 years

20

25

Yellow-Poplar

0

5

10

15

30

1880 1900 1920 1940 1960 1980 2000

49.7 cm DBH; 94 years

42.8 cm DBH; 47 years

33.1 cm DBH; 46 years

Sugar Maple

0

5

10

15

20

25

30

1880 1900 1920 1940 1960 1980 2000

53.4 cm DBH; 113 years

25.2 cm DBH; 92 years

34.4 cm DBH; 64 years

28.0 cm DBH; 55 years

Tree radius (cm) 

Year 
13

red oak that grew relatively rapidly after the initial harvest 

but gradually decreased in growth rate until establishment of 

the compartment. Growth rate then increased, slowed, and 

increased once again, coinciding with a partial harvest in 

1985. In addition, Figure 8 depicts two red oaks that are 

similar in age (80 and 76 years) but have different diameters 

(28.5 and 55.9 cm DBH). Both trees grew at a relatively 

uniform rate, although the smaller tree grew much more 

slowly until the partial harvest of 1985. 

Of the two younger sugar maples in Figure 8, the 93-yearold tree originated after the initial cut and the 57-year-old 

tree originated 10 years prior to the establishment of the 

compartment in 1954. The older of these trees responded to 

the establishment of the compartment with increased growth 

rate, whereas the younger was unaffected by this event. 

However, the younger tree responded to the treatment in 

1985, whereas the older one did not. 

The growth rate of the oldest of the three yellow-poplars in 

Figure 8 (78 years) was relatively uniform and then increased after the establishment of the compartment in 1954. 

The growth rate of the 60-year-old tree increased after 

treatment in 1970 but not in 1986, whereas the growth rate 

of the 41-year-old tree increased after the 1986 treatment. 

The uneven-aged site also contained trees that were present 

prior to the initial harvest. The growth patterns of two of 

these trees, a 112-year-old red oak and a 113-year-old sugar 

maple, are shown in Figure 9. Both of these trees showed 

slow growth until the compartment was established in 1952, 

at which time their growth rate increased. These trees would 

have been about 14 cm and 12 cm DBH, respectively, in 

1952. 

Figure 9 also shows growth rates for three additional red 

oaks, three additional sugar maples, and three yellowpoplars. One yellow-poplar originated immediately after the 

initial harvest and two after compartment establishment. 

Some of these trees had relatively uniform growth rates, but 

the 47-year-old yellow-poplar and 55-year-old sugar maple 

obviously responded to 1973 and 1977 thinnings, 

respectively. 

Sapwood Thickness 

An a posteriori comparison of sapwood thickness in sugar 

maple trees in the control site indicated a general trend 

toward narrower sapwood in lower grade trees. The mean 

sapwood thickness was 27 cm for the single Grade 1 tree 

(outlier in Fig. 5), 16 cm for the three Grade 2 trees, 14 cm 

for the eight Grade 3 trees, and 12 cm for the eight belowgrade trees (Table 5). If this trend can be substantiated, it 

indicates that the external indicators of grade are reflected in 

the quality of wood color in sugar maple. Table 7 extends 

this comparison to the treatments, comparing only sugar 

maple trees large enough to be Grade 1. We emphasize that 

these are unplanned comparisons and should only be used to 

define areas of future research. In the control site, the trend 

for sapwood thickness for Grades 1, 2, 3, and below-grade 

trees (27, 18, 14, and 12 cm, respectively) was essentially 

the same as that for all trees because only one tree 

(a Grade 2) was too small to make Grade 1. In the treatment 

sites, in which many trees were too small to be Grade 1, 

Grade 2 trees had the widest sapwood and Grade 3 the 

narrowest (Table 7). Although no statistically valid 

inferences can be made from these comparisons, they do 

suggest that management can improve the color quality of 

large sugar maple trees, in spite of the possibility that 

logging damage in the treatment sites might cause heartwood 

formation. 

As tree diameter increases, sapwood can decrease in 

thickness yet maintain a constant cross-sectional area. This is 

a possible explanation for the narrower sapwood in red oak 

in the control site compared with red oak in the treatment 

sites. The red oaks in the control site were larger than those 

in the diameter-limit site, but their mean sapwood thickness 

was smaller (Table 4). Figure 10 shows sapwood thickness 

Table 7óMean tree DBH and sapwood thickness (SWT) in large (≥40.6-cm DBH) sugar maple trees in each gradea

Mean DBH and sapwood thickness (cm) 

Grade 1 Grade 2 Grade 3 Below-grade All grades 

Siteb DBH SWT DBH SWT DBH SWT DBH SWT DBH SWT 

Control 

(1,2,8,8,19) 

54 27 74 18 62 14 63 12 63 14 

Diameter-limit 

(2,2,2,0,6) 

47 17 43 18 48 16 ó ó 46 17 

Uneven-aged 

(4,1,3,1,9) 

44 16 53 21 41 15 43 16 44 17 

a

Trees at least 40.6 cm DBH were considered large enough to be Grade 1. b

Numbers in parentheses are number of trees in each grade category. 
14 

in centimeters as a function of DBH. Examination of the 

points corresponding to the control shows that, in red oak, 

sapwood thickness may be constant until the trees reach a 

large size (in this case, about 85 cm DBH), then becomes 

narrower. Clearly, more data are needed to establish the 

effect of tree size on sapwood thickness in red oak. A 

comparison of sapwood cross-sectional area with DBH 

might have revealed a trend, but because the stems of the 

large trees were sometimes extremely irregular and sapwood 

thickness was based on only two measurements, the 

computation of area would be subject to large errors (see 

Wiemann and others 2002). A significant correlation 

between red oak DBH and number of sapwood rings in the 

control, and the lack of such correlation in the treatments 

(Table 6), is apparent in Figure 11, which shows sapwood 

thickness in number of growth rings as a function of DBH. 

Figure 10óSapwood thickness, in centimeters, as a 

function of tree DBH. 

Figure 11óSapwood thickness, in growth rings, as 

a function of tree DBH. 

1

2

3

4

5

0 20 40 60 80 100 120

Control

Uneven-aged

Diameter-limit

5

10

15

20

25

30 

0 10 20 30 40 50 60 70 80 90 100

Sapwood thickness (cm) 

0

2

4

6

8

10

12

10 20 30 40 50 60 70 80 90

DBH (cm)

Yellow-Poplar 

Sugar Maple 

Red Oak Red Oak

2

4

6

8

10

12

0 20 40 60 80 100 120

Control

Uneven-aged

Diameter-limit

Sugar Maple

0

20

40

60

80

100

120

140

10 20 30 40 50 60 70 80 90 100

Sapwood thickness (rings)

Yellow-Poplar

5

10

15

20

25

30

35

40

45

0 10 20 30 40 50 60 70 80 90

DBH (cm) 
15

The sugar maples at the control site were larger than those at 

either treatment site, but sapwood thickness, in centimeters, 

did not differ among sites (Table 4, Fig. 10). Sapwood 

thickness in rings, however, was greater at the control site 

than at either treatment site (Table 4, Fig. 11). The 

combination of older, larger trees with more numerous (but 

narrower) sapwood rings at the control site, compared with 

the trees at the two treatment sites, resulted in similar lineal 

sapwood thickness values among the three sites. 

Because sugar maple does not form normal heartwood, the 

amount of sapwood is not directly related to the sap transport 

requirements of the tree and the explanation used for red oak 

does not apply. We thought that the partial harvests in the 

two treatment sites might have resulted in residual stand 

damage, which would have resulted in more frequent and 

more extensive heartwood formation in the remaining sugar 

maples. Apparently this did not occur. Greater heartwood 

would be manifested as narrower sapwood in trees of equal 

diameter. The control site sugar maples were larger than the 

maples at the treatment sites, but their mean sapwood 

thickness was not; therefore heartwood in the control site 

was larger than that of either treatment. 

Old sugar maples, such as those found in the control site, 

may be less able to fend off the effects of damage. The 

effects of age and treatment can be separated by comparing 

only trees within an age cohort. Comparing sapwood of only 

trees within the 50-year age range of 65 to 115 years (control 

site, 13 trees, 12 cm DBH, 64 rings; diameter-limit site, 

15 trees, 14 cm DBH, 58 rings; uneven-aged site, 16 trees, 

13 cm DBH, 54 rings) does not suggest that treatment 

reduces sapwood thickness, either in centimeters or number 

of growth rings, although we emphasize that these are 

a posteriori comparisons. 

Sapwood may be wider in vigorously growing sugar maple 

trees at least until they reach senescence and DBH might be 

useful as a predictor of sapwood thickness if the trees are 

growing vigorously, as they were in the two treatment sites, 

but not after trees have reached senescence, as was 

frequently the case in the control. Tree age seems to be 

useless as a predictor of sapwood thickness in sugar maple 

regardless of treatment (Table 6). Perhaps this is because 

heartwood formation in sugar maple is a stochastic event 

with the causal agents, crown or root damage, periodically 

affecting young and old trees alike. Nonetheless, it is 

somewhat surprising that the stand interventions of the two 

treatments did not produce more injury-altered heartwood, 

with a concomitant reduction in sapwood thickness. As in 

red oak, cross-sectional area might provide a more 

meaningful evaluation of sapwood because it more directly 

affects tree physiology. However, since sapwood thickness 

is based on only two radii and many sugar maple stems are 

irregular in cross section, the errors in such an analysis are 

likely to be large. 

Diameter at breast height is a predictor of sapwood thickness 

in yellow-poplar regardless of treatment; larger trees require 

wider sapwood. Because yellow-poplar produces typical 

heartwood, stand history would not be expected to affect 

sapwood thickness except to the extent that it affects overall 

tree size, as evident in Figure 4. 

Conclusions 

Silvicultural treatments affected species frequency distributions and tree size and age. Periodic cuttings favored sugar 

maple. Tree diameter range was dependent on species and 

treatment, with tree size distributed into one, two, or three 

cohorts; these were related to longevity, periodicity of harvests, and light requirements of each species. As a result of 

the opening of canopy gaps, periodic harvests increased the 

probability that some stems would exhibit severe lean 

(>30%), which would increase the likelihood of tension 

wood in these stems. For some species, treatment also affected tree grade. Overall grade of red oak was lower under 

the diameter-limit treatment compared with uneven-aged 

treatment, and sugar maple grade was lowest in the control 

site. This was true even when the effects of tree DBH were 

removed. 

In red oak, where wide sapwood is a defect, the range of 

sapwood thickness among all 60 trees was only 1.0 to 

4.2 cm, with the treatments producing wider sapwood than 

did the control. In yellow-poplar, where wide sapwood is 

desirable, sapwood thickness increased with tree diameter 

but was independent of treatment. 

Sapwood thickness was extremely variable (4.4 to 26.9 cm) 

in sugar maple. Sapwood thickness was significantly correlated with DBH and growth rate in the two treatments but 

not in the control, and surprisingly it was not significantly 

correlated with tree age at any site. Vigorously growing 

sugar maples produce wide sapwood, but heartwood discoloration begins to disproportionately affect the trees as they 

reach maturity. Whereas the largest maples in the control 

may have included poor quality residuals, the largest maples 

in the two treatment sites were products of vigorous growth. 

Therefore, to maximize the yield of ìwhiteî maple, it is 

important to harvest the trees before they enter senescence; 

this means that both age and DBH must be taken into 

account to ensure high color quality. 

In conclusion, for the three species studied, we found that 

managing stocking to increase individual tree growth was 

consistent with producing desirable heartwood/sapwood 

characteristics. Concerns that repeated stand interventions 

might increase the production of wound-induced heartwood 

in sugar maple were unfounded. Periodic reductions in 

stocking did increase growth rates as expected, but this did 

not alter sapwood width in either sugar maple or yellowpoplar, and the effects in red oak were small. However, we 

expect the long-term use of uneven-aged management will 
16 

eventually lead to dominance by shade-tolerant species, 

effectively excluding both yellow-poplar and northern red 

oak. Alternatively, if even-aged management is used, our 

results clearly suggest that thinning to enhance growth and 

manage stem quality would not have a detrimental impact on 

desirable heartwood/sapwood characteristics. 

Acknowledgments 

Neal Bennett assisted with tree measurements and Bob 

Rosier and Rick Hovatter graded the trees. Help with core 

extraction was provided by Bob Rosier, Rick Hovatter, and 

Jane Rodrigue. Cores were measured by Jane Rodrigue and 

Deborah Butler. Cherilyn A. Hatfield and James W. Evans 

performed the statistical analyses. Daniel Yaussy gave an 

excellent review of the manuscript that included many 

helpful suggestions for the statistical analyses and 

presentation of results. Regis Miller, David McKeever, and 

two anonymous reviewers also commented on the 

manuscript, and we thank them for their suggestions. The 

production team for the final report consisted of 

JoAnn Benisch, Mary Collet, and Noreen Esser. 

Literature Cited 

Barrett, G.; Barrett, R.; Johnson, A.; Warfield, G. eds. 

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