@ e. United States 

Department of 

Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

Stem-Quality Changes on 

Young, Mixed Upland 

Hardwoods After Crop-Tree 

Release 

David L. Sonderman 
1 

'1 Abstract 

Relative change of several types of stem defects was studied over an &year 

period to determine the effects of crop-tree thinning on the development of tree 

quality. Special interest was given to changes in relative quality associated with 

defect indicators of crop trees compared to trees in unthinned plots. The relative 

quality classes of the crop trees went from "poor" to "medium" for red maple 

and "poor" to "good" for aspen. The oaks stayed in the poor classification and 

yellow-poplar remained unchanged in the medium classification. Results showed 

a decrease in the number of epicormic branches on the crop trees, and an 

increase in the size of live limbs. 

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 located at 

Delaware, Ohio, with the Station's project on management and utilization alternatives for nonindustrial private forests. 

Manuscript received for publication 2 June 1986 

Northeastern Forest Experiment Station 

370 Reed Road, room all, PA 19008 

April 1987 
Introduction Methods 

Forest managers need information on stem quality to better 

assess young hardwood trees. Quantifying limb-related 

defects is one method of evaluating how young growing 

stock stands should be thinned to grow the best possible 

defect-free stems. Little work has been done on developing 

the methodology for relating limb-defect changes over time 

to different thinning practices, particularly crop-tree release. 

However, one study showed that thinning young white oaks 

to low density levels resulted in severe epicormic branching 

(Dale 1968). It was found that quality losses more than 

offset gains from increased volume when stocking was 

reduced below 50 percent. In a more recent study of a 

young mixed-oak stand, the number of live and dead limbs 

increased substantially more in the heavily thinned plots 

than in the unthinned plots (Sonderman 1985). This confirms the common belief that stand density affects stem 

quality after only a few years. Additional research has 

shown that heavy thinning in young white oak stands has 

delayed, if not substantially reduced, the potential to 

develop high-quality stems. 

In this study, various types of limb-related defects were 

examined on a 17-year-old mixed upland hardwood stand 

that had been thinned by a crop-tree release. The potential 

crop trees were selected on the basis of tree form, crown 

position, and spacing. The stands were thinned to free the 

crowns of the selected crop trees on all sides without leaving large gaps in the canopy. These data, combined with 

other hardwood quality information (Dale and Sonderman 

1984; Sonderman l984a, b; Sonderman 1985, 1986), comprise an important data base for future reference and analysis of limb-related defects. 

The Stand 

The 3-acre stand in this study is located on the Vinton 

Furnance Experimental Forest in southern Ohio. The original stand, which was clearcut in 1959, contained mature, 

even-aged, fully stocked, mixed-oak species on a good site. 

In 1977, the young stand was divided into two treatment 

areas-one thinned as a crop-tree release and the other 

left as a control. The crop-tree release contained seven 

1110-acre plots and the control eight 1110-acre plots. A 

112-chain-wide isolation strip was left around each treatment. All plots were about the same in density, age, site 

class, species, and quality. Species composition consisted 

of aspen, red maple, sugar maple, mixed oaks, yellowpoplar, black cherry, blackgum, butternut, beech, red elm, 

and hickory. From these plots, 259 study trees were 

selected and measured. Potential crop-tree selection was 

based on crown position, vigor, spacing, size, and apparent 

quality. Six groups were used in the analysis: oak, yellowpoplar, red maple, aspen, miscellaneous, and "all" species. Red maple was the most common species, accounting for 38 percent of the total trees in the stand. 

All trees 3.6 inches or larger in diameter at breast height,, 

(d.b.h.) were graded by the quality classification system 

developed by Sonderman and Brisbin (1978). This system 

measures limb-related external defects on both the first and 

second &foot section of the butt 16-foot log on each tree. 

Measurements were made before thinning in 1977 and 

again in 1985. Limb.s are branches 0.3 inch or larger in 

diameter. Branches smaller than 0.3 inch are classed as 

epicormic branches. Various stem characteristics and 

limb-related defects were identified and classified on each 

selected tree. The following tree characteristics were measured: 

total height 

crown class 

crown ratio 

sweep and crook 

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

section of the butt 16-foot log 

size of the largest live limb on the first and second 

8-foot section of the butt 16-foot log 

number of dead limbs on the first and second &foot 

section of the butt 16-foot log 

size of the largest dead limb on the first and second 

8-foot section of the butt 16-foot log 

number of epicormic branches on first and second 

8-foot section of the butt 16-foot log 

Epicormic branches were grouped into three categories to 

make counting easier: (1) trees with no epicormic 

branches, (2) trees with one to six epicormic branches, and 

(3) trees with seven or more epicormic branches. 

As part of the quality classification system, a relative quality index was used to measure gross quality changes. This 

was done by assigning a numerical value to selected tree 

characteristics to be used as indexes: 
Crown Class 

Dominant 

Codominant 

Intermediate 

Suppressed 

Sweep and Crook 

(Deviation in inches) 

1 

2-4 

5-6 

7-8 

9+ 

Fork, Rot, or Seam 

Limb Count (Limb 2 

0.3 inch) 

1-2 

3-4 

5-8 

9-1 6 

17+ 

Value 

4 

3 

2 

1 

Value 

4 

3 

2 

1 

0 

0 

Value 

By adding the individual values, the relative quality class of 

a tree was determined as follows: 

Sum of individual Relative quality class 

values 

1-7 Poor 

8-9 Medium 

10-12 Good 

Determining relative quality was the first step in quantifying 

tree characteristics that are important for growing quality 

trees. In-dept analyses and comparison of individual tree 

characteristics by species groups are included in this 

report. Additional information on the measurement of individual tree characteristics was published by Sonderman 

(1979). Computations were made using weighted averages. 

Results and Discussion 

Relative Quality Index 

The relative indexes (Fig. 1) showed that aspen increased 

most in quality in the crop-tree release, going from the 

"poor" to "good" classification. However, in the control, 

aspen stayed in the "poor" quality class. Yellow-poplar's 

performance showed the least change, remaining as a 

"medium"-quality tree in both treatments. Figure I shows 

that crop-tree thinning had a positive effect on red maple 

and aspen, but little effect on yellow-poplar or oak. 

Diameter and Height Growth 

Crop-tree release had a greater effect on diameter growth 

than the control. Table 1 shows an overall increase in 

average tree diameter of 2.6 inches for "all" species combined in the crop-tree plots versus only 1.4 inches in the 

control plots for the 8-year period. Yellow-poplar in the 

crop-tree release was the fastest growing, increasing 4.3 

inches in diameter from 7977 to 1985. The oak group had 

the slowest diameter growth of all the species. 

Height growth (Table 1) was best for yellow-poplar in the 

crop-treeltreatment, but second to aspen in the control 

plots. Height growth for the oak group, as with diameter, 

was slowest of all the species measured. There were virtually no differences between the oak trees in the control 

plots and those in the crop-tree release plots. Comparing 

the data for "all" species, the crop-tree treatment outgrew 

the control in height by 2.7 feet. 

Crown Ratio 

Crown ratio is the ratio of live crown length to total tree 

height (Table 1). Thinning around a tree in a crop-tree 

release provides additional light, which can cause an 

increase-in limb growth. This results in a downward extension of the crown and an increase in crown ratio. This was 

true in the crop-tree treatment which increased by 1.2 

percent when analysed by "all" species. When individual 

species were analyzed, the crown ratios for aspen and 

yellow-poplar increased by about 15 percent in the croptree plots, but only by about 2 percent in the control plots. 

Similar crown-ratio results were found in relation to thinning 

in an earlier study by Sonderman (1984b). 

Limb Defects per Square Foot of Surface Area 

As a tree grows, the surface expands, causing an increase 

in surface area. If there are no changes in the number of 

defects on the surface, then the number of defects per 

square foot of surface area will decrease. Changes in limb 

defects per square foot of surface area are shown in Table 

1. There was an overall reduction in the number of defects 

per square foot of surface area between 1977 and 1985 in 

both the crop-tree treatment and control on the butt 16-foot 

log of the study trees. Neither the crop-tree treatment nor 

the control appeared to vary much when analyzed for "all" 

species, but because the crop trees had greater diameter 

growth than the control trees, they had more surface area 

and developed more limb-related defects. 
OAK YELLOW- RED ASPEN MISC ALL 

POPLAR MAPLE 

Figure 1.-Average relative quality index by species and treatment, 1977-85. 

Live Limbs Dead Limbs 

Generally, there were more live limbs (Table 2) on the The average number of dead limbs for "all" trees (Table 2) 

second &foot section of the butt log of the tree than on the 

first. There also was a reduction in the number of live limbs 

on the second 8-foot section for both the crop-tree release 

and control from 1977 to 1985. However, on the second 

8-foot section in 1985, oak showed an increase in live limb 

frequency for both the crop-tree and control treatments. By 

contrast, the number of live limbs on red maple decreased 

dramatically for both treatments. Red maple live limbs 

stayed on the tree longer and reached a size of 3 to 4 

inches in diameter before dying. Few new live limbs developed during that time. The result was a decrease in the 

number of live limbs and an increase in the size of dead 

limbs (Table 3). 

was reduced substantially from 1977 to 1985, but the difference between treatments was small. The full stocking of 

the control plots caused some natural pruning, resulting in 

fewer but larger dead limbs remaining on the stems over 

the 8-year growth period. Size was the reason for dead 

limbs hanging on, because large limbs usually do not 

prune off easily or quickly. The average diameter (Table 3) 

of the dead limbs in the secnd 8-foot section for "all" 

species in 1985 was 2.92 inches for the crop-tree treatment 

and 3.03 inches for the control. 
Table 1.-Summary of average tree characteristics in 1977 and 1985, by 

species group and treatment 

Species 

group 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Crop-tree release Control 

1977 1985 1977 1985 

D.B.H. (inches) 

5.1 6.5 4.8 5.6 

5.1 9.4 4.9 7.6 

5.3 8.1 5.4 6.8 

5.0 7.8 4.3 6.8 

5.4 7.4 4.9 6.0 

5.3 7.9 5.1 6.5 

HEIGHT (feet) 

44.0 46.2 43.0 46.3 

47.5 63.8 47.9 60.7 

47.6 59.3 46.5 54.3 

51 .O 64.5 49.2 71.1 

44.1 52.4 44.8 50.5 

46.2 56.8 46.0 53.9 

CROWN RATIO (percent) 

35.0 26.0 30.0 22.1 

26.8 41.4 25.7 28.1 

49.1 48.2 38.3 35.6 

30.0 45.0 26.4 28.6 

37.8 37.6 27.5 25.4 

41 .O 42.2 31.4 29.4 

DEFECTS/FT2 SURFACE AREAb (number) 

0.270 0.165 0.452 0.191 

.I00 .ti6 .I47 .060 

,387 .07b .396 .092 

.812 .I79 .836 .608 

.447 .I30 ,411 .lo7 

,373 .lo4 .383 .I20 

alncludes sugar maple, black cherry, blackgum, hickory, butternut, beech, and red 

elm. 

bLive and dead limbs, butt 16-foot section. 
Table 2.-Average number of live and dead limbs in butt and second 

8-foot sections, 1977-85, by species group 

Crop-tree release Control 

Species 1977 1985 1977 1985 

group Live Dead Live Dead Live Dead Live Dead 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

BUTT 8-FOOT SECTION 

2.23 0.39 - 4.08 

- 1.82 - 1.02 

0.03 .29 0.19 2.65 

- - - 6.57 - 1.55 .09 2.39 

.17 .94 .09 2.57 

SECOND 8-FOOT SECTION 

3.57 1.68 0.93 11.61 

0.20 6.34 .63 3.90 

1.41 2.74 3.21 10.33 

- 11.27 1.28 19.98 

1.08 4.73 1 .O6 12.21 

All 1.28 4.03 1 .71 10.57 .98 3.89 

aln~ludesugar maple, black cherry, blackgum, hickory, butternut, beech, and red 

elm. 

Table 3.-Average diameter, in inches, of largest live and dead limbs in 

butt and second 8-foot sections, 1977-85, by species group 

Crop-tree release Control 

Species 1977 1985 1977 1985 

group Live Dead Live Dead Live Dead Live Dead 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

All 

Oaks 

Yellow-poplar 

Red maple 

Aspen 

Miscellaneousa 

BUTT 8-FOOT SECTION 

0.50 2.50 - 0.55 

- 1.35 - 1 .03 

2.00 1.55 0.95 .62 

- - - 50 

- 1.80 1.00 .59 

1.25 1.62 .96 .62 

SECOND 8-FOOT SECTION 

1.00 5.41 0.91 0.82 

5.00 2.20 .75 .64 

4.00 3.27 .98 .75 

- 2.00 .75 .53 

3.41 2.46 1.25 .69 

All 1.04 .77 3.71 2.92 1.00 .71 2.41 3.03 

alncludes sugar maple, black cherry, blackgum, hickory, butternut, beech, and red 

elm. 
Yellow-poplar was the only species to increase in the number of dead limbs in both &foot sections of the crop-tree 

treatment, while aspen was the only species~ to increase in 

the number of dead limbs in both 8-foot sections of the 

control. The oak group had the largest dead limbs, averaging 5.4 inches in diameter in the second &foot section of 

the croptree treatment. Aspen and yellow-poplar had the 

smallest dead limbs in that same 8-foot section. 

Epicormic Branches 

Study results show that the percentage of epicormic 

branches increased the most in the control plots (Table 4). 

An increase in light around the crop trees caused the 

existing limbs on the stem to continue to grow larger. This 

resulted in little new epicormic branch activity. Natural 

variation in sprouting ability among species also was a 

factor. When the data were analyzed by individual species, 

red maple and oak were the most prolific sprouters, while 

yellow-poplar and aspen barely sprouted. Smith (1977) 

found similar effects on 60-year-old yellow-poplars following 

thinning. Another study (Brinkman 1955) showed that dominant and codominant trees had a tendency to "feather out" 

less with epicormic branches than intermediate or suppressed trees. Since this way a crop-tree release that 

favors dominant and codominant trees in the residual 

stand, one would anticipate less epicormic branching. 

Although some epicormic branching may be species 

related, a large amount of branching was influenced by the 

degree of thinning and the residual stocking of the stand. 

Table 4.-Percentage of trees with epicormic branches, 1977-85, by species group - - 

I Species Crop-tree release Control 

group 1977 1985 1977 1985 

BUTT 8-FOOT SECTION 

Oaks 0.0 40.0 7.1 71.9 

Yellow-poplar 0.0 0.0 0.0 3.7 

Red maple 5.8 38.0 0.0 45.2 

Aspen 0.0 0.0 0.0 0.0 

Miscellaneousa 3.7 7.4 0.0 26.0 

All 3.7 22.5 0.5 32.3 

SECOND 8-FOOT SECTION 

Oaks 0.0 40.0 7.1 85.6 

Yellow-poplar 0.0 18.1 7.4 18.5 

Red maple 11.6 44.0 3.0 49.9 

Aspen 0.0 0.0 0.0 0.0 

Miscellaneousa 3.7 7.4 0.0 39.9 

All 6.2 32.3 2.7 42.4 

alncludes sugar maple, black cherry, blackgum, hickory, 

butternut, beech, and red elm. 

Results of a previous study showed that heavily thinned 

stands with low residual stocking and open canopys 

resulted in heavy epicormic sprouting (Dale and Sonderman 1984). 

Summary and Conclusion 

Tree quality is not markedly affected by residual standdensity levels that are maintained above C-level stocking. 

The crop-tree release in this study resulted in many 

changes in stem-quality and growth characteristics. The 

average diameters (d.b.h.), heights, and crown ratios 

increased in the crop-tree treatment, as did the number of 

limb defects per square foot of surface area. This study 

showed an increase in live and dead limbs in the crop 

trees, and a decrease in epicormic branches. The additional live and dead limbs occurred because the expanded 

growing space around each tree that resulted from thinning 

allowed existing live lirnbs to develop (grow) and curtailed 

natural pruning of the dead limbs. For this reason, fewer 

epicormic branches formed. 

In some instances, opening the canopy around crop trees 

may be agreater stimulus to the growth.gf already established branches than to the formation of new epicormics. 

Fewer ebicormics would, over time, mean a reduction in 

the number of new stem defects on the prime grading 

section (butt 16-foot log) and result in improved tree quality 

in the future. The fact that dominant trees, which were left 

for the final crop trees, were known to sprout less than 

codominants and intermediates may have contributed to 

fewer epicormic branches. All of this information will help 

evaluate the quality of young growing-stock trees and serve 

as a basis for selecting silvicultural treatments. Other 

important findings were: 

Epicormic branches increased most on the second 

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

The oaks had the most epicormic branches of all the 

species. 

The number and size of the live and dead limbs were 

greatest on the second 8-foot section of the butt 

16-foot log. 

The oak species in the crop-tree release plots had the 

largest number of live limbs in both the first and 

second 8-foot sections of the butt 16-foot log. They 

averaged more than 3.5 limbs per tree in the second 

8-foot section. 

Yellow-poplar was the only species to increase in the 

number of dead lirnbs in the crop-tree release plots 

during the &year growth period. 
The oak trees in the crop-tree release plots had the 

largest dead limbs. The average number of these 

large dead limbs was fewer than 2 per tree. 

Because this study was limited to a crop-tree thinning, a 

single site class, and one age group, caution should be 

used when applying these data to other trees and stands. 

Acknowledgment 

I thank forest technicians John Beaton and Deloris Weiss 

for assistance in collecting the data. 

Literature Cited 

Brinkman, K. A. 1955. Epicormic branching on oaks in 

sprout stands. Tech. Pap. 146. Washington, DC: U.S. 

Department of Agriculture. 8 p. 

Dale, Martin E. 1968. Growth response from thinning 

young even-aged white oak stands. Res. Pap. NE-223. 

Upper Darby, PA: U.S. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 9 p. 

Dale, Martin E.; Sonderman, David L. 1984. 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. 12 p. 

Smith, H. Clay. 1977. Changes in tree density do not 

influence epicormic branching of yellow-poplar. Res. 

Note NE-239. Upper Darby, PA: US. Department of 

Agriculture, Forest Service, Northeastern Forest Experiment Station. 3 p. 

Sonderman, David L. 1979. 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. 12 p. 

Sonderman, David L. 1984a. Quality response of evenaged 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. 6 p. 

Sonderman, David L. 1984b. Quality response of 29-yearold, even-aged central hardwoods after thinning. Res. 

Pap. NE-546. Broomall, PA: U.S. Department of Agriculture, Forest Service, Northeastern Forest Experiment 

Station. 9 p. 

Sonderman, David L. 1986. Changes in stem quality on 

young thinned hardwoods. Res. Pap. NE-576. 

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

Service, Northeastern Forest Experiment Station. 9 p. 

Sonderman, David L. 1985. 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. 

8 P. 

Sonderman, David L.; Brisbin, Robert L. 1978. A quality 

classification system for young hardwood trees-the 

first step in predicting future products. Res. Pap. 

NE-419. Broomall, PA: US. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment Station. 

7 P. 
Sonderman, David L. 1987. Stem-quality changes on young, mixed 

upland hardwoods after crop-tree release. RP-NE 597. Broomall, 

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

Experiment Station. 7 p. 

Relative change of several types of stem defects was studied over an 

8-year period to determine the effects of crop-tree thinning on the 

development of tree quality. Special interest was given to changes in 

relative quality associated with defect indicators of crop trees compared to 

trees in unthinned plots. The relative quality classes of the crop trees went 

from "poor" to "medium" for red maple and "poor" to "good" for aspen. 

The oaks stayed in the poor classification and yellow-poplar remained 

unchanged in the medium classification. Results showed a decrease in the 

number of epicormic branches on the crop trees, and an increase in the 

size of live limbs. 

ODC 228.1 :242:851:852:11 

Keywords: Stand density; thinning; stem quality 
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