United States 

Department of 

Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

Research Paper 

N E-561 

Stand Density-A Factor Affecting 

Stem Quality of Young Hardwoods 

David L. Sonderman 
The Author 

David L. Sonderman, research forest product technologist, joined the 

Northeastern Forest Experiment Station in June 1962, and was on the staff 

of the Eastern Softwood Timber Quality project until June 1972. He is currently stationed in Delaware, Ohio, with the Northeastern Station's project 

on management and utilization alternatives for nonindustrial private forests. 

Manuscript received for publication 2 October 1984 

Abstract 

A 14-year-old mixed oak stand was thinned in 1977 to stocking levels 

of 30, 50, and 60 percent and a control. From this stand, 117 trees were. 

selected and their stem-related defects recorded. Six years later these 

same trees were reevaluated. The number of limb defects per square foot 

of surface area increased substantially more in the heavily thinned plots 

than in the unthinned plots. Trends in these data confirm commonly held 

beliefs that stand density affects stem quality after only a few years. 
Introduction 

Growing good quality timber is 

a goal of most foresters and woodlot managers. Although many 

factors affect timber quality, this 

research is aimed at determining 

the stocking level that optimizes 

quality and volume growth. Recent 

thinning studies show that tree 

quality will improve if stocking 

levels are maintained. Dale and 

Sonderman (1984) showed the effect 

of thinning on growth and quality of 

a 33-year-old white oak stand after 

16 years of treatment. We found 

that the number of limb-related 

defects decreased as stand density 

increased. In a similar 6-year study 

of a 29-year-old mixed hardwood 

stand, I found that the number of 

defects per square foot of surface 

area and the number of epicormic 

branches both decreased with an 

increase in stocking'(Sonderman 

1984b). The results of a study on 80- 

year-old white oak trees thinned 18 

years earlier (Sonderman 1984a) suggest that heavy thinning had a detrimental effect on potential stem 

quality by significantly increasing 

treatments established according to 

Gingrich's (1967) guide on stocking 

percentages. The 31 plots, each 

1110-acre in size, were divided into 

treatments of 30, 50, and 60 percent 

stocking and control plots. Each 

treatment was surrounded by a 112- 

chain wide isolation strip, treated 

the same as the plot. From these 

plots, 117 study trees were 

selected. The residual stand 

contained mixed oaks, yellowpoplar, red maple, aspen, black 

walnut, blackgum, red elm, black 

cherry, and hickory. Five species 

groups were used in the analysisoaks, yellow-poplar, red maple, 

aspen and a miscellaneous group. 

Yellow-poplar, the most common 

species, accounted for 45 percent 

of the total number of trees. The 

oak and red maple groups, each 

accounted for 15 percent of the 

total. The aspen group made up 

only 4 percent. The miscellaneous 

group, which included black cherry, 

hickory, black walnut, red elm, and 

blackgum, accounted for 21 percent 

of the total number of trees. 

the number of defects per square 

foot of surface area. In all of the 

studies, limb-related defects and Methods 

epicormic branches were the most 

serious degraders of stem quality A stratified sample of trees 3.6 and were affected the most by inches or larger in diameter at thinning. breast height (d.b.h.) was randomly 

This research is an integral part 

of a long-term study relating time 

and stocking treatments to tree 

quality characteristics in young 

hardwoods. Species, age, crown 

ratio, and stocking density are a few 

of the important factors affecting 

potential stem quality that are 

analyzed in this study. 

The Stand 

selected from plots within 

treatments. The quality classification system (Sonderman and 

Brisbin 1978) was used to measure 

the limb-related external defects on 

both the butt and second &foot 

section of the butt 16-foot log on 

each tree. Live and dead limbs had 

to be at least 0.3 inch in diameter to 

be measured, otherwise they were 

considered epicormic branches. The 

quality classification system was 

applied to the trees in 1977 and 

again in 1983. The quality differThe &acre stand, located on ences between the two measurethe Vinton Furnace Experimental ments provided a quality profile, the 

Forest in southern Ohio, was orig- this paper. 

Tree quality characteristics 

(Sonderman 1979) recorded were: 

dbh 

total height 

crown ratio 

number of live limbs on the first 

and second 8-foot section of the 

butt 16-foot log 

number of dead limbs on the first 

and second 8-foot section of the 

butt 16-foot log 

diameter of the largest live limb 

on the first and second &foot 

section of the butt 16-foot log 

diameter of the largest dead limb 

on the first and second &foot 

section of the butt 16-foot log 

number of epicormic branches on 

the first and second 8-foot section 

of the butt 16-foot log 

Several categories of branches 

were used in the classification 

system. Small live or dead shoots 

less than 0.3 inches in diameter at 

their bases were considered epicormic branches. In this study, 

these branches were grouped and 

coded to facilitate the analysis as 

follows: 

0 = No epicormic branches 

1 = 1 to 6 epicormic branches 

2 = 7 + epicormic branches 

All branches 0.3 inches or more 

in diameter at their bases were 

measured and counted on each tree 

section. 

All measurements were summarized and analyzed by covariance 

analysis, using the value of the 

variable at initial time as the 

covariate. 

inally a fully stocked, even-aged - 

mature mixed oak stand that was 

clearcut in 1963. The average site 

index of the stand was 71. The 

stand was thinned in 1977 and four 
Results and Discussion 

Diameter and height growth 

The effect of different stocking 

treatments on the diameter growth 

of the sample trees is apparent in 

Table 1. The analyses show that the 

largest average diameter growth 

was in the plots with 50 percent 

stocking. The diameter increased 76 

percent in 6 years. The control 

plots, in comparison, had the 

slowest diameter growth-a 56 

percent increase from 1977 to 1983. 

Of all the individual species groups, 

yellow-poplar and aspen increased 

the most in diameter in the 30 

percent treatment. The oak group 

was the slowest growing. Aspen 

continued to show outstanding 

diameter growth in both the 50 and 

60 percent stocking plots. 

Average height growth for all 

trees combined attained a maximum 

in the plots with 50 percent 

stocking. The average growth was 

7.0 feet more than that of the trees 

in the control. Aspen led all other 

species in height growth in the 

plots with 50 percent stocking. It 

grew 22 feet in height there, but 

only 17 feet in the control plots. No 

statistical tests were performed for 

diameter or height growth. However, 

in a similar study of white oak by 

Dale and Sonderman (1984), mean 

height growth was not significantly 

related to treatment differences. Hilt 

(1979) reported similar diametergrowth trends in relation to thinning 

treatments in an earlier study. 

Crown ratio 

Crown ratio is the ratio of live 

crown length to total tree height. 

For all species combined, crown 

ratio was greatest in the plots with 

30 percent stocking (Table 1). From 

1977 to 1983, average crown ratio 

increased from 28 percent to 39 

percent in those plots and from 32 

percent to 38 percent in the control 

plots. The data show that as the 

percentage stocking increased, the 

crown ratio decreased. 

Table 1.-Summary of average tree characteristics in 1977 and 1983, 

by species group and stocking level 

Stocking level (%) -- -- - - 

Species 30 50 60 Control 

group 

Oaks 4.5 

Yellow-poplar 5.3 

Red maple 5.0 

Aspen 4.0 

Miscellaneousa 4.2 

All 4.9 

Oaks 39.5 

Yellow-poplar 42.3 

Red maple 39.2 

Aspen 44.5 

Miscellaneous 36.1 

All 40.0 

Oaks 26.3 

Yellow-poplar 25.0 

Red maple 33.0 

Aspen 32.5 

Miscellaneous 30.3 

All 27.6 

Oaks 0.403 

Yellow-poplar .273 

Red maple .603 

Aspen .923 

Miscellaneous .969 

All .546 

17.b.h. (inches) 

Height (feet) 

Crown ratio (percent) 

Defectslft2 surface area (n~rnber)~ 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 

b Live and dead limbs, butt 16-foot section. 
Live and Dead Limb Defects per 

Square Foot of Surface Area 

Measuring live and deal limb 

defects per square foot of surface 

area provides a relative comparison 

of the effects of stand density on 

stem quality (Table 1). There is an 

expansion in both diameter and 

surface area when a tree grows. 

This expansion of surface area will 

result in a decrease in the number 

of defects per square foot of 

surface area-if no new limb , defects develop. The following 

tabulation shows the number of 

defects per square foot of surface 

area in the butt 16-foot section by 

stocking treatment from 1977 to 

1983 for all species: 

Year Stocking Treatment 

(Percent) 

30 50 60 Control 

All of the treatments show a 

decrease in the average number of 

defects per square foot of surface 

area after 6 years. The 30 and 50 

percent stocking levels were the 

least effective in reducing the 

number of defects per square foot 

of surface area. Although they were 

accompanied by a much larger 

increase in diameter growth (surface 

area), they had the most new 

defects. 

Epicormic branches 

Epicormic branches will 

normally develop when dormant 

buds in the tree stem are exposed 

to full sunlight. They will usually 

persist and grow into live limbs 

where thinning has been heavy. 

In this study, none of the trees 

in the 50 and 60 percent stocking 

plots had epicormic branches when 

first measured in 1977 (Table 2). 

However, by 1983 the percentage of 

trees with epicormic branches had 

increased substantially in all treatments. The plots with 30 percent 

stocking had the smallest increase 

in percentage of trees (all species 

and both 8-foot sections combined) 

with epicormics after 6 years' 

growth. In this treatment, large 

amounts of light from the open 

crown resulted in continued growth 

of existing epicormics and live 

limbs rather than development of 

new ones. Both the number of live 

limbs and the crown ratio increased. 

The fact that the 30 percent 

stocking level contained a large 

number of yellow-poplars and some 

aspen species may account for the 

limited epicormic branch development; these species are not considered prolific epicormic sprouters. 

The oak group increased 

uniformly in the percentage of trees 

with epicormic branches in all treatments. Conversely, the aspen group 

showed little change, except in the 

50 percent treatment where the 

percentage of trees with epicormic 

branches increased in both the butt 

and the second 8-foot sections. 

Live limbs 

The number of live limbs was 

recorded from the butt and second 

8-foot sections of each tree. The 

greastest effect of density on live 

limb development was found on the 

second &foot section (Table 3). The 

number of live limbs on this section 

increased by 5.6 percent on the 

plots with 30 percent stocking and 

decreased as the stand density 

increased. On the control plots, the 

number of live limbs decreased 87.7 

percent from 1977 to 1983. The 

following tabulation shows the 

percentage change in the number of 

live limbs by treatment from 1977 to 

1983, for the second Sfoot section 

for all species combined: 

Stocking Treatment (percent) 

Live limbs 5.6 - 66.0 - 43.7 - 87.8 

Natural pruning, epicormic 

branch development, and rapid live 

limb growth are a few of the 

reasons for the increase in number 

of live limbs in the plots with 30 

percent stocking. However, tests 

comparing the number of live limbs 

for all species combined showed no 

significant differences among 

treatments. 

Summarizing the data by individual species, the number of live 

limbs increased substantially in the 

second &foot section of trees in the 

oak group in both the 30 percent 

and 50 percent stocking plots. In 

contrast, the number of live limbs in 

both Sfoot sections of trees in the 

aspen group decreased in all 

treatments. 

The largest average live limb 

size was found in the second 8-foot 

section of both the oak and the red 

maple groups on the control plots. 

These limbs decreased in size as 

the stocking density decreased 

(Table 4). 

Dead Limbs 

The number of dead limbs on 

the second &foot section for all 

species combined increased only on 

the control plots (Table 5). This 

increase was caused by the lack of 

sunlight under the closed canopy, 

which resulted in live limbs dying 

earlier than in the thinned plots. 

Given enough time, these dead 

limbs would be naturally pruned off. 

Covariance analysis tests of the 

number of dead limbs for all 

species combined in both 8-foot 

sections showed no significant 

difference among treatments. 

The largest average size of 

dead limbs (Table 6) for all species 

combined occurred in the second 8- 

foot section of the control plots. 

There the dead limb size increased 

58 percent from 1977 to 1983. One 

reason for the increase was that the 

larger limbs in the more densely 

stocked plots did not die and prune 

off as quickly as the smaller ones. 

Generally, the average size of the 

largest dead limbs in the second 8- 

foot section decreased with a 

decrease in stocking for all species 

combined. 
Table 2.-Percentage of trees with epicormic branches in butt and 

second 8-foot sections, 1977-83, by species 

Stocking level (%) 

Number of 

epicormic 30 50 60 Control 

branches 

1977 1983 1977 1983 1977 1983 1977 1983 

OAK 

Butt 8-foot section 

Second 8-foot section 

YELLOW-POPLAR 

Butt 8-foot section 

Second &foot section 

RED MAPLE 

Butt &foot section 

Second &foot section 

(table 2-cont.) 
Stocking level (%) 

Number of 

epicormic 30 50 60 Control 

branches 

1977 1983 1977 1983 1977 1983 1977 1983 

ASPEN 

Butt 8-foot section 

Second 8-foot section 

Butt 8-foot section 

Second 8-foot section 

ALL 

Butt 8-foot section 

Second &foot section 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 
Table 3.-Average number of live limbs in the butt and second 8- 

foot sections, 1977-83, by species 

Stocking level (%) 

Species 30 50 60 Control 

group 

Oaks - Yellow-poplar - Red maple 1.1 1 

Aspen - Miscellaneousa .34 

All .21 

Oaks 0.60 

Yellow-poplar 2.87 

Red maple 10.52 

Aspen 4.45 

Miscellaneous 7.86 

All 5.22 

Butt 8-foot section 

Second 8-foot section 

- - - - 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 

Table 4.-Average diameter (in inches) of the largest live limbs in 

the butt and second 8.foot sections, 1977-83, by 

species 

Stocking level (%) 

Species 30 50 60 Control 

group 

1977 1983 1977 1983 1977 1983 1977 1983 

Butt 8-foot section 

Oaks - 0.50 1.50 - 1.50 - 1.25 - 

Yellow-poplar - .60 .75 .50 - - 1.25 - 

Red maple .87 .91 .75 .75 1.66 2.33 - - 

Aspen - - - - - - - - 

Miscellaneousa 1 .OO .62 .75 - - 50 1.12 - 

All .93 .66 .90 .58 1.60 1.87 1.18 - 

Second 8-foot section 

Oaks 1.50 0.50 - 4.00 1.41 1.83 1.41 2.25 

Yellow-poplar 1.07 1.30 1 .OO 1.18 - - 1.06 - 

Red maple 1.30 1.62 1.00 1.75 1..12 1.95 .91 2.1 2 

Aspen 1 .OO - 1.50 - 1.25 - 1.00 - 

Miscellaneous 1.21 1.79 1.00 - 1.00 1.25 1.16 - 

All 1 .I6 1.41 1.02 1.75 1.22 1.79 1.12 2.16 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 
Table 5.-Average number of dead limbs in the butt and second 8- 

foot sections, 1977-83, by species 

Stocking level (%) 

Species 30 50 60 Control 

group 

1977 1983 1977 1983 1977 1983 1977 1983 

Butt 8-foot section 

Oaks 3.32 1.01 7.10 3.56 7.02 '2.52 9.15 11.34 

Yellow-poplar 1.55 1.09 3.21 .77 - - 2.95 .29 

Red maple 5.37 2.12 1.78 1.79 6.75 3.64 8.73 1.14 

Aspen 7.86 6.43 10.64 7.09 12.41 7.10 1.77 1.77 

Miscellaneousa 7.31 2.03 7.10 - 8.64 3.12 7.49 2.38 

All 4.33 1.79 3.96 1.21 7.43 3.23 5.90 3.31 

Second &foot section 

Oaks 10.90 3.49 9.03 2.25 17.06 4.23 9.27 10.62 

Yellow-poplar 6.99 3.97 11.07 6.15 - - 6.83 5.57 

Red maple 5.35 .96 - - 6.36 3.98 5.20 6.17 

Aspen 15.74 22.11 22.59 24.93 4.51 18.14 15.84 15.88 

Miscellaneous 14.99 8.18 2.26 9.07 24.14 14.66 5.10 16.66 

All 10.45 6.12 10.36 6.60 13.24 6.46 7.24 9.68 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 

Table 6.-Average diameter (in inches) of the largest dead limbs in 

the butt and second &foot sections, 1977-82, by species 

Stocking level (%) 

Species 30 50 60 Control 

group 

1977 1983 1977 1983 1977 1983 1977 1983 

Butt 8-foot section 

Oaks 0.75 0.62 0.75 1.50 0.97 1.57 0.83 1.25 

Yellow-poplar .71 .54 .67 .65 - - .96 1.50 

Red maple .55 .62 .75 1.00 .59 .85 .83 .50 

Aspen .75 .62 50 .50 .75 .75 .50 .50 

Miscellaneousa .75 1.40 50 - .66 58 .66 .83 

All .71 .84 .66 .78 .77 1.10 .80 .93 

Second &foot section 

Oaks 0.81 1.06 1.00 0.50 1.00 1.25 0.75 1.83 

Yellpw-poplar .76 .69 .86 .93 - - .70 .91 

Red maple .75 50 - - .60 .83 38 1 .OO 

Aspen .75 1 .OO 1.00 1.75 .75 1.25 .75 1 .OO 

Miscellaneous .79 1.20 .50 1.00 .83 .91 .91 1.16 

All .77 . .91 .86 .95 .82 1.03 .73 1.15 

a Miscellaneous group includes hickory, black cherry, blackgum, black walnut, and 

red elm. 
Summary and Conclusion Literature Cited 

This research is part of a longterm quality study that will be 

merged with similar quality studies 

to determine the best stocking 

density to grow high-value trees 

fast. Trends in these data suggest 

that tree species, age, and stand 

density greatly affect the number 

and size of stem defects. These 

trends should be observed as a 

piogression of biological events 

that take place as the tree grows. 

For example, epicormic branches 

develop and grow into measurable 

live limbs that eventually die. The 

dead limbs, if given enough time, 

will naturally prune off and become 

overgrowths, All of the defects from 

this progression will leave internal 

or external scars on the tree, eventually causing some degrade. 

Trends in these data show that 

the heavier the thinnings, the 

greater the diameter growth and 

greater the chance for defects. Also, 

with the growth rate increase will 

come increases in crown ratio that 

eventually will result in additional 

live limbs. 

Important results in this study 

are: 

Diameter (d.b.h.) growth increased 

with an increase in growing 

space. 

Average crown ratio for all trees 

combined increased the most in 

the lowest stocking level. 

At the 30 percent and 50 percent 

stocking levels, red maple 

increased the most in crown ratio. 

Live and dead limb defects per 

square foot of surface area 

increased as the stocking 

decreased. 

There were more epicormic 

branches in the second 8-foot 

section of the tree than in the 

butt 8-foot section. 

For all species combined, the 

number of live limbs in the 

second &foot section of the tree 

increased only at the 30 percent 

stocking level. 

Live limbs were substantially 

larger and more numerous on the 

second 8-foot section of the tree. 

The average number of dead limbs 

for all species combined in the 

second &foot section of the tree 

increased only in the control 

plots. 

Dead limbs were generally larger 

and more numerous for all 

species combined on the second 

8-foot section of the tree. 

The results of this study have 

limited application because only 

one site class and age group were 

studied. Therefore, caution should 

be exercised when applying this 

information to other trees and 

stands. 

Acknowledgments 

The author thanks these forest 

technicians for assistance in collecting the data: John Beaton, William Pierce, and Deloris Weiss. 

Dale, Martin E.; Sonderman, David L. 

Effect of thinning on growth and 

potential quality of young white 

oak trees. Res. Pap. NE-539. 

Broomall, PA: U.S. Department of 

Agriculture, Forest Service, Northeastern Forest Experiment Station; 1984. 12 p. 

Gingrich, S. F. Measuring and 

evaluating stocking and stand 

density in upland hardwood 

forests in the central states. 

Forest Science 13: 38-52; 1967 

Hilt, Donald E. Diameter growth of 

upland oaks after thinning. Res. 

Pap. NE-437. Broomall, PA: U.S. 

Department of Agriculture, Forest 

Service, Northeastern Forest 

Experiment Station; 1979. 11 p. 

Sonderman, David L. Guide to the 

measurement of tree characteristics important to the quality 

classification system for young 

hardwood trees. Gen. Tech. Rep. 

NE-54. Broomall, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest 

Experiment Station; 1979. 12 p. 

Sonderman, David L. Quality 

response of even-aged 80-year-old 

white oak trees after thinning. 

Res. Pap. NE-543. Broomall, 

PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment 

Station; 1984a. 6 p. 

Sonderman, David L. Quality 

response of 29-year-old, even-aged 

central hardwoods after thinning. 

Res. Pap. NE-546. Broomall, 

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

Northeastern Forest Experiment 

Station; 1984b. 9 p. 

Sonderman, David L.; Brisbin, 

Robert L. A quality classification 

system for young hardwood 

trees-the first step in predicting 

future products. Res. Pap. 

NE-419. Broomall, PA: U.S. 

Department of Agriculture, Forest 

Service, Northeastern Forest 

Experiment Station; 1978.7 p. 
Sonderman, David L. Stand density-a factor affecting stem 

quality of young hardwoods. Res. Pap. NE-561. Broomall, 

PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment Station; 1985. 8 p. 

A 14-year-old mixed oak stand was thinned in 1977 to stocking levels of 30, 50, and 60 percent and a control. From this 

stand, 117 trees were selected and their stem-related defects 

recorded. Six years later these same trees were reevaluated. 

The number of limb defects per square foot of surface area 

increased substantially more in the heavily thinned plots than 

in the unthinned plots. Trends in these data confirm commonly held beliefs that stand density affects stem quality after 

only a few years. 

Keywords: Stand density; thinning; stem quality 

* U. S. GOVERNMENT PRINTING OFFICE: 1985-505-028: 20014 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

Amherst, Massachusetts, in cooperation with the University of 

Massachusetts. 

Berea, Kentucky, in cooperation with Berea College. 

Burlington, Vermont, in cooperation with the University of 

Vermont. 

Delaware, Ohio. 

0 Durham, New Hampshire, in cooperation with the University of 

New Hampshire. 

Hamden, Connecticut, in cooperation with Yale University. 

Morgantown, West Virginia, in cooperation with West Virginia 

University, Morgantown. 

0 Orono, Maine, in cooperation with the University of Maine, 

Orono. 

Parsons, West Virginia. 

Princeton, West Virginia. 

Syracuse, New York, in cooperation with the State University of 

New York College of Environmental Sciences and Forestry at 

Syracuse University, Syracuse. 

University Park, Pennsylvania, in cooperation with the 

Pennsylvania State University. 

Warren, Pennsylvania.