United States Changes in Stem Quality 

Forest Service on Young Thinned Hardwoods 

Northeastern Forest 

Experiment Station David L. Sonderman 

Research Paper 

N E-576 
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 Station's project on management and utilization alternatives for nonindustrial private forests. 

Manuscript received for publication 6 June 1985. 

Abstract 

Describes changes in limb-related defects on 18-year-old, even-aged 

hardwoods 6 years after thinning. Stocking levels of 30, 45, and 60 percent 

were studied. There were fewer defects per square foot of surface area in 

the higher stocking plots than in the lower stocking plots. The average 

number of live limbs decreased by 83 percent in the unthinned plots and 

increased slightly in the heavily thinned plots. The results show that the 

frequency and size of limb-related defects are affected by stand density 

over a short period of time. 
Introduction 

Manipulating stand density is one way to improve 

the quality of young hardwood stems. Various thinning 

schemes have successfully improved the quality of 

some hardwood stems by reducing the number of 

defects that normally occur. Although some trees 

inherently develop fewer defects than others, the 

majority of the commercial species do not fall into this 

category. Sometimes, trees develop poor stem quantity 

when extensive thinning methods are used to improve 

volume growth. However, moderate stand density 

reduces the adverse effects. For example, Godman and 

Brooks (1971) found that northern hardwood stem quality of pole-size trees improved after 15 years of treatment at 85 square feet of basal area per acre. This 

provided a compromise between good quality 

improvement and a substantial growth rate. In a more 

recent study on young white oak crop trees by Dale 

and Sonderman (1984), similar effects were found on 

thinning methods above C-level stocking where tree 

quality was not markedly affected, and in some instances, did improve with increased stand density. 

Sonderman (1984) found that in mixed central hardwoods, the number of limb-related defects per square 

foot of surface area increased by 6 percent over the 

control in plots thinned to 30 percent in only 6 years. 

Limb-related defects are one of the greatest deterrents 

to stem quality and should be an important consideration in the management of a stand. 

In this study, changes in limb-related characteristics were analyzed over a 6-year period after initial thinning. Species, age, site, and stocking levels are the 

most important factors that affect potential stem 

quality. Limb-related defects that are measured on 

each tree, such as live limbs, dead limbs, and epicormic branches, should be considered simultaneously 

when interpreting the results because a progression of 

biological events is taking place. That is, epicormic 

branches grow into live limbs that die and become 

dead limbs. After dropping-off, the dead limbs form 

overgrowths. The length of the cycle depends on the 

stocking levels and ages of the trees. 

The Stand 

The study plots are located on the Vinton Furnace 

Experimental Forest in southern Ohio. The 18-year-old 

even-aged stand had its origin as a result of a circular 

clearcut made as part of a "size of opening" study 

established in 1959. It is 5 acres in size, a good cove 

hardwood site, a northeast facing slope, and approximately a 75 to 80 site index for northern red oak. 

The study consisted of twenty 1110-acre plots, representing three thinning treatments of 30, 45, and 60 

percent stocking. A control was established plus a 112- 

chain-wide isolation strip that surrounded each treatment boundary. Stocking was determined by the tree 

area ratio equation for mixed oaks developed by Gingrich (1967). A stratified sample of 154 trees, randomly 

selected, came from four species groups: oaks, yellowpoplar, red maple, and a miscellaneous group. The last 

group consisted of hickory, ash, black cherry, blackgum, and red elm. An aspen group was eliminated from 

the analysis because of an inadequate number of sample trees. 

Methods 

External tree characteristics were systematically 

measured by the quality classification system (Sonderman 1979) on sample trees 3.6 inches or larger in 

diameter at breast height (d.b.h.). The measurements of 

limb-related surface characteristics were recorded from 

the first and second 8-foot section of the butt 16-foot 

log on each tree at initial thinning in 1977 and again in 

1983. These surface characteristics include: 

0 d.b.h. 

0 total height 

0 crown ratio 

0 number of live limbs on the first and second 8-foot 

section of the butt 16-foot log 

0 number of dead limbs on the first and second 8-foot 

section of the butt 16-foot log 

e diameter of the largest live limb on the first and 

second 8-foot section of the butt 16-foot log 

0 diameter of the largest dead limb on the first and 

second 8-foot section of the butt 16-foot log 

0 number of epicormic branches on the first and 

second &foot section of the butt 16-foot log 

In this study, epicormic branches were grouped to 

facilitate counting: 0 = No epicormic branches, 1 = 1 

to 6 epicormic branches, and 2 = 7 or more epicormic 

branches. 

The branch had to be 0.3 inch or more diameter at 

the base to qualify as a measurable live or dead limb; 

otherwise, it was considered an epicormic branch. All 

stem defects were summarized by species, plot, and 

stocking level. Covariance analysis was used to test 

the limb-related variables; the value of the variable at 

initial time was used as the covariate. 
Results and Discussion 

Diameter Growth 

Thinning hardwood stands to different density 

levels affects the diameter growth of the residual trees. 

The data in Figure 1 show a decrease in the average 

diameter growth as the stocking increases. When analyzed for all species combined, the change from 1977 

to 1983 in average diameter growth was: 3.5 inches in 

the 30 percent stocking, 2.5 inches in the 45 percent 

stocking, 2.3 inches in the 60 percent stocking, and 

only 2.0 inches in the control. Yellow-poplar was the 

single fastest growing species, increasing 3.8 inches in 

diameter in the 30 percent stocking plots and only 2.8 

inches in the control. The next fastest growing species 

was red maple, followed last by the oak group. 

Dbh (Inches) 

Height Growth 

After thinning, the average total height for all species combined decreased as the stocking level 

increased (Fig. 2). From 61.5 feet in the 30 percent 

stocking, average height decreased to 61.0 feet in the 

45 percent stocking, 57.5 feet in the 60 percent stocking, and 55.2 feet in the control. The largest change in 

height growth for all species combined from 1977 to 

1983 was in the 45 percent stocking plots, averaging 

over 3 feet per year. The trend was similar for individual species. One of these, yellow-poplar, outgrew all 

other species, in the 45 percent stocking plots. Other 

studies on tree quality (Sonderman 1985) involving tree 

heights in relation to stocking have shown similar 

trends resulting in maximum height growth change in 

the 45 to 70 percent stocking. 

30 45 60 Control. 

TREATMENT 

Figure ?.-Average d.b.h. for all species combined by treatment-1977-83. 
HEIGHT (Feet) 

TREATMENT 

Figure 2.-Average height for all species combined by treatment-1977-83. 

60 Control 

Crown Ratio 

Crown ratio is the ratio of live crown length to 

total height of the tree. It is usually one of the best 

indicators of the effects of stand density on stem quality. For all species combined, the average crown ratio 

increased slightly in the plots with 30 and 45 percent 

stocking from 1977 to 1983, and remained about the 

same in the 60 percent and control plots (Fig. 3). During those 6 years, the heavily thinned plots with open 

crown canopies and much light from above influenced 

the crown ratios of many study trees. In many 

instances, there was a downard extension of the crown 

that resulted in an increase in epicormic branching and 

live limb development. 

Live and Dead Limb Defects per Square Foot of 

Surface Area 

As tree d.b.h. expands, so does the surface area. 

Live and dead limb defects per square foot of surface 

area generally decrease as the tree grows and the surface area expands-if no new defects develop. In this 

study, the heavily thinned plots showed an increase in 

the number of defects per square foot of surface area 

even though surface area greatly increased. Therefore, 

these plots developed many new limb-related stem 

defects in only 6 years. 
PERCENT 

TREATMENT 

Figure 3.-Average crown ratio, in percent, for all species 

combined by treatment-1977-83. 

The analysis showed that surface area increases 

for all species combined between 1977 and 1983 from 

lowest to highest stocking levels were 64, 45, 47, and 

39 percent, respectively. In comparison, the number of 

defects per square foot of surface area for all species 

combined between 1977 and 1983 is: 

Stocking Treatment (%) 

Year 30 45 60 Control 

Comparison of live and dead limb defects per 

square foot of surface area (butt 16-foot section) for all 

species combined after 6 years showed that the 30 percent stocking plots had a significantly greater number 

of defects than the other stocking plots (P<0.12) when 

tested by covariance analysis. 

Control 

Epicormic Branches 

Thinning a stand heavily often opens the crown 

canopy to ligh'i which stimulates suppressed buds that 

may develop into epicormic branches on some tree 

species. In many instances, these branches will continue to grow into small live limbs so long as light is 

abundant. 

In this study, few of the trees had epicormic 

branches when first measured in 1977. Six years after 

thinning, however, the percentage of trees with epicomic branches had increased in all stocking plots 

(Fig. 4). The 60 percent stocking level had the largest 

increase in the number of epicormic branches found in 

the butt 16-foot log. This large change resulted partially from a high proportion of red maple trees in this 

stocking level. Red maples are prolific sprouters, and 

almost half of them in the plots with 60 percent stocking had seven or more epicormic branches when meas- 
PERCENT 

Control 

ured in 1983 (Table 1). Similarly, more than one-half of 

the red maples in the control plots had seven or more 

epicormic branches in the same amount of time. In 

comparison, yellow-poplar in the 60 percent stocking 

plots made up less than 10 percent of the trees having 

seven or more epicormic branches and had none in the 

control. 

Live Limbs 

None of the trees in any of the stocking plots had 

live limbs in 1977 when the butt &foot section was 

analyzed. However, by 1983 many trees in the 30 

percent stocking plots had grown new live limbs, but 

the control plots remained free. 

TREATMENT 

Figure 4.-Percentage of trees with epicormic branches for all species combined 

(butt 16-foot section) by treatment-1977-83. 

1 11-6 Epicormics 

m7-t Epicormics 

For all species combined, the average number of 

live limbs (Table 2) in the second 8-foot section 

increased the most in the 30 percent stocking plots 

and decreased by 83 percent in the control plots. The 

size of the live limbs (Table 3) for all species combined 

in the 30 percent stocking plots decreased by 23 percent from 1977 to 1983, but increased only 1 percent in 

the control. As a rule, the second 8-foot section of the 

butt 16-foot log usually will contain more and larger 

live limbs than the butt &foot section. 

Treatment differences for live limbs in the butt 16- 

foot section for all species were significant (P<0.01). In 

the butt 16-foot section, the 30 percent stocking plots 

had an increase of 0.7 live limbs, and the control plots 

had a loss of 0.6 live limbs. 
Table 1.-Percent of trees with epicormic branches in the butt 16-foot 

section, 1977-83, by species 

Stocking level (%) 

Number of 

epicormic 30 45 60 Control 

branches 

1977 1983 1977 1983 1977 1983 1977 1983 

OAK 

100.0 - (NoTrees) 

- - - - - 100.0 - - 

Y ELLOW-POPLAR 

100.0 40.0 100.0 9.2 - 60.0 - 81.8 

- - - 9.0 

RED MAPLE 

80.0 20.0 100.0 15.9 

- 60.0 - 36.8 

20.0 20.0 - 47.3 

MISCELLANEOUSa 

100.0 33.4 100.0 70.6 

- 55.5 - 29.4 

- 11.1 - - 

ALL 

96.0 32.0 100.0 29.4 

- 56.0 - 51.7 

4.0 12.0 - 18.9 - 

aMiscellaneous group includes hickory, ash, black cherry, blackgum, and red elm. 

Table 2.-Average number of live limbs in the butt and second 8-foot 

sections, 1977-83, by species group 

Stocking level (%) 

Species 30 45 60 Control 

group 

1977 1983 1977 1983 1977 1983 1977 1983 

Oaks 

Yellow-poplar 

Red maple 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Miscellaneousa 

All 

BUTT 8-FOOT SECTION 

- - (No trees) - - 0.21 - 0.09 - - - - .14 - - .29 - - - - 20 - .08 - 

SECOND 8-FOOT SECTION 

- - (No trees) 6.93 

0.99 0.57 1.95 0.23 .86 

.87 2.06 2.51 1.67 4.90 

.83 .74 .40 .60 1.63 

.87 1.03 1.75 .87 2.52 

aMisce1laneou.s group includes hickory, ash, black cherry, blackgum, and red elm. 
Table 3.-Average diameter, in inches, of the largest live limbs in the 

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

group 

Species 

group 

Dead Limbs 

Stocking level (%) 

30 45 60 Control 

BUTT 8-FOOT SECTION 

Oak - 0.75 - - (No trees) - - Yellow-poplar - .55 - 1.25 - 3.00 - - Red maple - 1.00 - - - .50 - - Miscellaneousa - - - .50 - - - - 

All - .64 - .87 - 1.75 - - 

SECOND 8-FOOT SECTION 

Oak - 0.75 - - (No trees) 1.00 - Yellow-poplar 1.00 .64 0.87 1.00 0.92 1.00 1.91 2.00 

Red maple 1.37 1.62 2.00 1.16 1.05 1.09 .87 - 

Miscellaneousa 1.75 2.50 .87 .62 1.41 .50 1.35 1.06 

All 1.15 .89 1.10 .95 1.06 .97 1.23 1.25 

aMiscellaneous group includes hickory, ash, black cherry, blackgum, and red elm. 

The average number of dead limbs (Table 4) for all 

species combined in the second 8-foot section 

decreased in all stocking plots from 1977 to 1983. However, the numbers of dead limbs in the control plots 

did not decrease as much as those in the other stocking plots. This was due partially to the larger average 

size of the dead limbs in the control plots. In fact, the 

average size of the largest dead limbs for all species 

combined (Table 5) occurred in the control plots where 

they increased by 49 percent as opposed to a 22 percent decrease in size in the 30 percent stocking plots. 

Large dead limbs, when they reach a certain size, do 

not prune-off easily even in the unthinned plots. 

Summary and Conclusion 

Limb-related defects are the major cause of 

degrading stem quality in young hardwood trees. It is 

improbable that all defects can be prevented; so, the 

results of this study may provide the land manager 

with enough information on stand density choices to 

reduce stem-defect occurrence and numbers. To do 

this, forest management decisions should be based on 

the best residual stand densities needed to grow highquality trees at fast volume growth. The results of 

these data show that the heavily thinned stands 

usually have good diameter growth, large numbers of 

stem defects, and big crowns. Therefore, stand densities should be held above C-level stocking to maintain 

tree quality. 
Table 4.-Average number of dead limbs in the butt and second 8-foot 

sections, 1977-83, by species group 

Stocking level (%) 

Species 

QrOUD 30 45 60 Control 

BUTT 8-FOOT SECTION 

Oak - - - - (No trees) 3.60 0.94 

Yellow-poplar 0.12 0.94 - 0.36 0.85 0.09 .28 .19 

Red maple 4.01 - 1.22 - 1.27 .28 1.28 - 

Miscellaneousa 1.28 .84 .66 - 2.03 1.19 2.06 50 

All .53 .a1 .55 .11 1.31 .48 1.39 .34 

SECOND 8-FOOT SECTION 

Oak 18.41 6.79 2.26 - (No trees) 6.55 4.54 

Yellow-poplar 4.34 2.75 4.05 2.98 2.61 1.49 2.16 1.91 

Red maple 9.09 2.74 6.88 .83 10.16 2.42 7.40 5.98 

Miscellaneousa 11.34 5.73 7.37 3.10 10.67 5.75 10.29 7.75 

All 5.84 3.32 5.99 2.48 7.36 3.12 6.60 5.32 

aMiscellaneous group includes hickory, ash, black cherry, blackgum, and red elm. 

Table 5.-Average diameter in inches of the largest dead limbs in the 

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

group 

Species 

group 

Stocking level (%) 

30 45 60 Control 

BUTT 8-FOOT SECTION 

Oak - - - - (No trees) 0.75 0.50 

Yellow-poplar 0.62 0.50 - 0.50 0.95 0.50 1.00 1.00 

Red maple 1.00 - 0.75 - .68 1.00 .62 - 

Miscellaneousa 1.00 .87 .75 - .85 .92 1.00 .66 

All .89 .55 .75 50 .81 .90 .85 .70 

SECOND 8-FOOT SECTION 

Oak 1.00 0.75 0.75 - (No trees) 1.25 1.25 

Yellow-poplar .72 .61 .84 0.82 0.82 0.86 .91 1.66 

Red maple 1.25 .87 .62 1.37 .81 1.02 .85 1.10 

Miscellaneousa 1.41 .95 .78 1.18 1.08 1.35 .77 1.15 

All .92 .72 -77 1.01 .91 1.11 .85 1.27 

aMiscellaneous group includes hickory, ash, black cherry, blackgum, and red elm. 
Other important results are: 

Diameter (d.b.h) growth increased as the growing 

space increased. 

Average crown ratio for all species combined 

increased only in the 30 and 45 percent stocking 

plots. 

Limb defects per square foot of surface area 

increased the most in the 30 and 45 percent stocking plots when average surface area was 

considered. 

The average number of live limbs in the second 

8-foot section of the butt 16-foot log decreased as 

the percent stocking increased. 

Average size of live limbs in the second 8-foot section of the butt 16-foot log was smaller in the lower 

stocking plots and increased as stocking increased. 

The number of dead limbs in the second 8-foot section of the butt 16-foot log of the control plots did 

not decrease as much as the dead limbs in the 

same section of the other stocking plots. 

0 Average size of dead limbs in the second &foot 

section of the butt 16-foot log decreased in the 30 

percent stocking plots and increased in all other 

stocking plots. 

a The unthinned plots had the lowest percentage of 

trees with epicormic branches in the butt 16-foot 

section. 

Yellow-poplar increased the most in diameter 

growth, height growth, and crown ratio of all the 

species. 

For all trees combined, all stocking levels had some 

epicormic branches after thinning. The majority of 

the trees had 1 to 6 epicormic branches. 

Acknowledgments 

The author wishes to thank the following forest 

technicians for assistance in collecting the data: John 

Beaton, William Pierce, and Deloris Weiss. 

Literature Cited 

Dale, Martin E.; Sonderman, David L. Effect of thinning 

on growth and potential quality of young white oak 

crop 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. 

Godman, Richard M.; Books, David J. Influence of 

stand density on stem quality in pole-size northern 

hardwoods. Res. Pap. NC-54. St. Paul, MN: US. 

Department of Agriculture, Forest Service, North 

Central Forest Experiment Station; 1971. 7 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: US. Department of Agriculture, Forest Service, Northeastern Forest Experiment 

Station; 1979. 12 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; 1984. 9 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 Ex~eriment Station; 

Sonderman, David L. Changes in stem quality of young 

thinned hardwoods. Res. Pap. NE-576, Broomall, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station; 1986. 9 p. 

Describes changes in limb-related defects on 18-year-old, 

even-aged hardwoods 6 years after thinning. Stocking levels 

of 30, 45, and 60 percent were studied. There were fewer 

defects per square foot of surface area in the higher stocking 

plots than in the lower stocking plots. The average number of 

live limbs decreased 83 percent in the unthinned plots and 

increased slightly in the heavily thinned plots. The results 

showed that frequency and size of limb-related defects are 

affected by stand density over a short period of time. 

ODC 228.1 :242:851:852.11 

Keywords: Stand density, thinning, stem quality 

2U.S. GOVERNMENT PRINTING OFFICE:1986-602-026:20042 
Headquarters of the Northeastern Forest Experiment Station are in 

Broomall, Pa. Field laboratories are maintained at: 

Amherst, Massachusetts, in cmperation 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. 

0 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. 

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

New York College of Environmental Sciences and Forestry at 

Syracuse University, Syracuse. 

0 University Park, Pennsylvania, in cooperation with the 

Pennsylvania State University. 

Warren, Pennsylvania.