United States 

Department of 

Agriculture Crop-Tree Release Thinning 

Forest Service In 65-Year-Old Commercial 

Northeastern Forest 

Experiment Station Cherry-Maple Stands 

Research Paper NE-694 (5-Year Results) 

H. Clay Smith 

Gary W. Miller 

Neil I. Lamson 
Abstract 

Crop trees were selected and released in a 65-year-old cherry-maple stand in 

north central West Virginia. Six crop-tree treatments were evaluated. Crop trees 

were selected based on potential for quality sawtimber and veneer products. 

Initially, released crop trees averaged 12.5 inches d.b.h. and 80 feet tall and were 

released an average of 13 feet from the edge of their crown. Five-year stand 

growth, mortality, and ingrowth are discussed for the treatments. Tree quality as 

related to butt-log grade and epicormic branching also are discussed. Detailed 

information is given for d.b.h. growth as related to degree of crown release. In 

general, black cherry, free-to-grow crop trees for the 40 and 60 crop-trees-peracre treatments grew 1.0 inch in 5 years. Similar crop trees in the control areas, 

where tree crowns were not released, grew 0.6 inch during the same period. 

Growth response increased with an increase in number of sides of the tree crowns 

released. After 5 years, less than 2 percent of the released crop trees had a 

reduction in butt-log quality due to epicormic branching. 

The Authors 

H. CLAY SMITH, retired, was principal silviculturalist at the Northeastern Forest 

Experiment Station's Timber and Watershed Laboratory at Parsons, West Virginia. 

He received B.S. and M.S. degrees from West Virginia University and Purdue 

University and joined the Northeastern Forest Experiment Station in 1962. 

GARY W. MILLER is a research forester at the Northeastern Forest Experiment 

Station's Timber and Watershed Laboratory, Parsons, West Virginia. He received 

B.S. and M.S. degrees from West Virginia University and a Ph.D. from Virginia 

Polytechnic Institute and State University and has conducted research in silviculture and forest management since 1981. 

NEIL I. LAMSON is silviculturist with the Northeastern Area State and Private 

Forestry located at Louis C. Wyman Forestry Sciences Laboratory, Durham, New 

Hampshire. He received his B.S. and M.S. in silviculture and forest soils from 

State University of New York College of Environmental Science and Forestry and 

started his U. S. Department of Agriculture, Forest Service career in 1972. 

Manuscript received for publication 5 January 1994 

Acknowledgments 

The authors want to thank personnel from the Greenbrier Ranger District of the 

Monongahela National Forest and the project staff at the Timber and Watershed 

Laboratory for their efforts. All made a major contribution toward the completion of 

this publication. 

USDA FOREST SERVICE 

5 RADNOR CORP CTR STE 200 

PO BOX 6775 

RADNOR PA 19087-8775 

September 1994 
Introduction 

One primary objective in the management of central 

Appalachian hardwood stands is the production of high 

quality sawlogs and veneer products. Practices used to 

achieve this objective include thinning cultural practices in 

precommercial- and commercial-size even-aged stands. 

Common thinning practices in precommercial stands 

include a timber stand improvement approach where 

undesirable trees are removed or individual crop trees are 

released. For commercial stands, stocking guides or.basal 

area techniques often are used in thinning. The overall 

objective in the application of these techniques is to 

provide growing space for the more desirable trees. 

Basically, forest managers want to concentrate future 

growth on the better residual trees to increase stand 

growth and stand value, and improve species composition 

without sacrificing stand productivity. 

Stocking guides generally involve the relationship of crown 

area ratio to basal area and number of trees. These 

guidelines currently indicate that residual basal areas of 50 

to 60 percent full stocking provide the maximum individual 

diameter growth possible for commercial-size stands 

without reducing total per-acre production (Gingrich 1967; 

Marquis et al. 1984). A strict basal area thinning 

application involves leaving a number of the "best" residual 

trees per acre to attain the selected residual basal area 

goal. For both the stocking guide and basal area 

approaches, trees are removed using a low-crown thinning 

approach. Poor-quality and low-vigor trees underneath the 

main overstory canopy (suppressed and intermediate 

crown-class trees) and occasionally some overstory trees 

(codominants) are removed until the desired residual 

percent stocking or stand density is achieved. There are 

several major concerns in these marking concepts. 

Specific desirable trees are not selected for the purpose of 

stimulating growth. Residual tree crowns are' not released 

deliberately to a free-to-grow condition. Thus the choice of 

residual trees as well as their response to thinning is left to 

chance. Also, it is sometimes necessary to leave 

low-quality Or undesirable tree species to attain the desired 

stand density. In most cases, forest managers using these 

approaches usually thin stands without specifically 

providing crown growing space for the desirable individual 

residual trees. 

In addition to stocking guides and basal area thinnings, 

another possible approach to consider when thinning 

commercial stands is the crop-tree crown thinning method. 

As indicated, this crop-tree approach commonly is used in 

precommercial stands. Crop trees are selected based on 

criteria related to both forest management and landowner 

objectives. Usually only trees whose removal benefit the 

crop trees are cut (Smith and Lamson 1986). Depbnding 

on the number of crop trees selected and released per 

acre, crop trees could occupy the entire stand at maturity. 

The principal advantage to the crop-tree method is that 

selected trees based on objectives are released to grow 

and increase in value (not always monetary). Their 

development is not left to chance. 

The purpose of this paper is to provide a 5-year evaluation 

of applying the crop-tree crown thinning approach to a 65- 

year-old black cherry-maple commercial stand. 

Study Methods 

Study Area 

The study area was located on the Monongahela National 

Forest, Loop Road Research Area, on Middle Mountain 

near Thornwood, north central West Virginia. In general, 

these fully stocked, 65-year-old, commercial stands were 

composed primarily of black cherry (Prunus serotina Ehrh.) 

and maples (Acer sp.). Cherry dominated the stand, 

accounting for approximately 56 percent of the stand basal 

area and 79 percent of the board-foot volume (International 

114-inch log rule). Maples (red and sugar) represented 29 

percent of the basal area and 13 percent of the volume. 

White ash (Fraxinus americana L.) and cucumbertree 

(Magnolia acuminata L.) were common associate species. 

Basal areas for trees 1.0 inch d.b.h. and larger range from 

approximately 170 to 190 square feet per acre in these 

large pole-, small sawtimber-size stands. Generally, the 

study areas had very uniform topography with slopes from 0 

to 10 percent. Stand elevations were approximately 3,650 

feet above sea level and the annual precipitation averaged 

59 inches. Soils were moderately deep, weli-drained 

DeKalb soils of sandstone origin. These good growing 

sites had an estimated northern red oak site index in the 

middle 70's. 

Crop Tree Selection and 

Selection criteria. Criteria for selecting crop trees were 

developed with the objective of producing high-quality 

sawlogs and veneer products. The criteria used were as 

foliow: 

@ Dominant or codominant crown class. 

8 Butt-log grade 1 or 2 will become grade 4 or 2 with 

additional diameter growth. 

0 No forks in 16-foot butt log. 

@ No epicormic branches below 33 feet. 

o No dead major branches in the upper crown. 

@ No main-stem forks with evidence of splitting, below 

live crown. 

@ No large holes or open wounds in the second log. 

e No black knot on the main stem or threatening more 

than 50 percent of the crown. 

e No old residuals. 

8 No leaning trees. 

@ No more than two crop trees per sprout clump. 

@ When applying the crown-touching crop-tree release, 

space the crop trees so that crop:tree crowns are 

released on three or four sides. 

I 
When trees were of similar quality, crop-tree selections 

were made based on species. Black cherry was considered 

the most valuable timber and wildlife species. Other 

species of commercial importance were white ash, red 

maple (Acer rubrum L.), and cucumbertree. 

Release method. Crop trees were released using the 

crown touching method. Any tree 7.0 inches d.b.h. and 

larger with a branch touching the crown of a crop tree or 

extending beneath or above- the crown of a crop tree, 

was considered "touching" and was cut. Where two crop 

trees had crown branches that touched, both were 

selected for release. All other adjacent trees touching 

the crown of the two crop trees would be felled. In this 

instance, each crop tree would then have three sides of 

the crown released. 

Merchantable trees were 7.0 inches d.b.h. and larger. Cut 

trees were not marked; instead, a mark-leave tree method 

was used for designating crop trees. High-risk trees that 

were 7.0 inches d.b.h. and larger were cut, too. These 

high-risk trees included black cherry with a black knot on 

the tree bole or at the base of a fork when more than 50 

percent of the crown would be above the knot. Although 

the preferred method to release crop trees was in a free-togrow crown position on all four sides of the crown, many 

trees were released on three and some released on only 

two sides. The two-sided releases were particularly evident 

in the 60 crop-tree-per-acre treatments. 

Treatments 

There were three overstory (trees 7.0 inches d.b.h. and 

larger) crown treatments each combined with one of two 

understory (trees 1.0 to 6.9 inches d.b.h.) treatments, for a 

total of six treatments. 

Plots 

Size of the treatment plots was 2.0 acres. Within each 2-acre 

treatment plot, a 0.5-acre measurement plot was established. 

All data for trees 1.0 inch d.b.h. and larger were collected on 

seventeen 0.5-acre measurement plots. Some additional 

individual crop-tree information was recorded after treatment 

for trees throughout the 2-acre treatment plots. For the four 

commercial stand treatments, the initial cut ranged from 53 to 

69 percent of the basal area (40CT--91.8~ 172.2 = 53.3 

percent to 40CT, cut 17"--121.4e176.4 = 68.8 percent; Table 

1). Cutting understory trees (1.0 to 6.9 inches d.b.h.) in the 

Control, cut <7.0" accounted for approximately 20 percent of 

the basal area (33.0t 173.8 = 19 percent). The amount of 

cubic-foot volume removed during the initial cut ranged from 

55 to 63 percent of the total (40 CT--1888+3440 = 54.9 

percent to 40 CT, cut <7"--2118t3350 = 63.2 percent; Table 

1). For the Control, cut <7" treatment, 6 percent of the 

cubic-foot volume (215s3446) was cut (all small trees less 

than 7 inches d.b.h.). Initially 44 to 52 percent of the 

board-foot volume was removed from the crop-tree treatment 

plots (Table 1). 

Crop tree sample data including d.b.h., average total height, 

crown width, and amount of release were summarized by 

species and overstory crop-tree treatments (Table 2). 

When released, the crop trees for all treatments averaged 

12.5 inches d.b.h., 80 feet tall with an average clear bole of 

42.6 feet. Tree crown widths (diameter) averaged 20.5 feet 

and crop trees were released an average distance of 13 

feet from the edge of the crop tree crown to the adjacent 

tree crown. 

All study data were analyzed using analyses of variance or 

chi-square methods with significance tested at the 

5-percent level. Special interest testing was done using 

Student-Newman Tests. 

The treatments were to: 

Results and Discussion 

Select and release 40 crop trees per acre using the 

crown touching method (40 CT)--Figure 1A. 

Select and release 40 crop trees (CT) per acre using the 

crown touching method. Fell all trees 1.0 to 6.9 inches 

d.b.h.--(40 CT, cut < 7")--Figure 18. 

Select and release 60 crop trees per acre using the 

crown touching method. Fell all trees 1.0 to 6.9 inches 

d.b.h.--(60 CT, cut < 7"). 

Select and release 60 crop trees per acre using the 

crown touching method (60 CT). 

Fell all trees 1 .O to 6.9 inches d.b.h. No trees 7.0 inches 

and larger were cut--(Control, cut < 7")--Figure 2A. 

Cut no trees--(Control)--Figure 2B. 

Each treatment was replicated three times with the 

exception of the 60 CT, cut 17" treatment, which had two 

replications. All cut trees 7.0 inches d.b.h. and larger were 

skidded (tree length) to a log landing and sold. Felled trees 

less than 7.0 inches d.b.h. were not removed from the 

study area. 

Stand Growth 

Basal area growth. Net basal area growth was increased 

by the crop-tree crown thinning treatments when compared 

to the uncut control treatment (Table 3). For the 40 and 60 

crop-tree treatments, where all trees less than 7.0 inches 

d.b.h. were felled, stand basal areas increased an average 

of 11.2 ft2/acre in 5 years. On the 40 and 60 crop-tree 

treatment areas, where trees below 7.0" were not cut (40 

CT, 60 CT), 5-year basal-area increased an average of 13.8 

ft2/acre. Stand basal-area growth for the control plots 

where small trees below 7.0 inches were felled (Control, cut 

<7"), increased 11.1 ft2/acre; and for the control areas 

where no cutting was done, the 5-year basal-area growth 

was 7.2 ft2/acre. 

Periodic mortality varied from 7.4 ft2/acre in the uncut 

control plots to nearly 0 for the 40 crop-tree treatment areas 

where all trees less than 7.0 inches d.b.h. were felled (Table 

3). Since mortality in these stands is concentrated in the 

understory stems, cutting small trees less than 7.0 inches 

Text continues on page 6. 
Figure 1A.--A 65-year-old black cherry-maple stand where 40 crop trees per acre were 

released. Only trees 7.0 inches d.b.h. and larger were cut. 

Figure 16.--A 65-year-old black cherry-maple stand where 40 crop trees per acre were 

released. In addition, all trees 1.0 to 6.9 inches d.b.h. were cut. 
Figure 2A.--A 65-year-old black cherry-maple stand where only trees 1.0 to 6.9 inches 

d.b.h. were cut. 

Figure 2B.--Uncut 65-year-old black cherry-maple stand with a basal area of 180 square 

feet per acre in trees 1.0 inches d.b.h. and larger. 
Table 1.--Per-acre stand data before and after cut, by crop-tree thinning treatments 

Stems 1.0 

Item inch d.b.h.+ 

No. of Basal 

trees area W 

Initial 898 176.4 

Cut 814 121.4 

Residual 84 55.0 

5-year 393 67.4 

Stems 5.0 Stems 11.0 

inches d.b.h.+ inches d.b.h.+ RSDa 

No. of Volume No. of Volume Percent 

trees ft3 trees bd R 

40 CT, CUT < 7" 

31 8 3350 82 8353 111.5 

234 21 18 43 4357 75.3 

84 1232 39 3996 27.6 

83 1511 51 6242 43.8 

40 CT 

Initial 661 172.2 314 3440 85 10107 103.6 

Cut 305 91.8 164 1888 44 4758 52.0 

Residual 357 80.6 150 1552 41 5349 49.7 

5-year 41 2 93.5 159 1853 51 7525 57.7 

60 CT, CUT < 7" 

initial 586 188.7 250 41 31 108 19507 110.2 

Cut 521 117.5 185 2355 50 8996 74.9 

Residual 65 71.2 65 1776 58 10511 27.7 

5-year 249 81 .I 63 2005 59 12777 32.4 

60 CT 

Initial 723 187.8 302 3805 99 13435 111.2 

Cut 367 104.8 174 21 47 46 5945 57.6 

Residual 356 83.0 128 1658 53 7490 47.1 

5-vear 405 97.6 147 201 3 60 10160 54.8 

CONTROL, CUT < 7" 

Initial 772 173.8 272 3446 91 12783 103.2 

Cut 580 33.0 80 21 5 0 0 32.9 

Residual 192 140.8 192 3231 91 12783 69.2 

5-year 188 151.9 188 3578 107 15585 72.8 

CONTROL 

Initial 858 171.5 31 5 3214 72 8918 108.8 

Cut 0 0.0 0 0 0 0 0.0 

Residual 858 171.5 31 5 3214 72 8918 108.8 

5-year 761 178.3 300 3464 83 11219 108.0 

aRSD--Relative stand density trees 1.0 inch d.b.h. and larger. 
Table 2.-Crop-tree release data after treatment 

Clear Crown 

Total boleb Base width CrownC 

Treatment Species Treesa D.b.h. height stem crown (diameter) release 

No. In. Ft. Ft. Ft, Ft. Ff, 

40 CT/A Black cherry 102 12.5 79.2 44.0 52.8 20.2 13.5 

White ash 16 11.3 75.9 36.8 48.3 19.8 12.4 

Basswood 2 13.0 87.0 44.2 53.2 16.5 18.1 

Average 12.3 80.7 41.7 51.4 18.8 14.7 

60 CT/A Black cherry 144 13.6 81.9 45.2 54.1 21.2 10.6 

White ash 2 14.6 81.0 54.8 42.0 26.8 11.6 

Red maple 3 12.0 84.5 39.5 54.0 19.2 13.2 

Average 13.4 82.5 46.5 50.0 22.4 11.8 

Control Black cherry 151 12.8 77.5 42.9 50.8 19.2 0.0 

White ash 24 10.8 76.8 44.2 48.7 18.1 0.0 

Red maple 5 12.0 75.0 32.1 40.8 23.1 0.0 

Averaae ., 11.9 76.4 39.7 46.8 20.1 0.0 

aA sample of crop trees measured throughout the 2-acre treatment plot. 

b~eight to first branch at least 1.0 foot long or merchantable height. 

'Distance between edge of crop-tree crown and adjacent tree. 

had a major influence on mortality regardless of thinning 

treatments done in the overstory. 

The crop-tree crown release treatments concentrated the 

stand growth on fewer, more valuable trees, and where the 

understory was removed, newly established reproduction 

(black cherry, red maple, and striped maple) was readily 

abundant. For example, for the control treatments a net 

basal-area stand growth of 7.2 ft2/acre was distributed 

throughout 665 trees (1 .ON d.b.h. and larger). Where only 

understory trees less than 7.0 inches d.b.h. were cut, a net 

basal-area stand growth of 11 .I ft2/acre was distributed 

over only I85 trees (Table 3). 

Five-year net basal-area survivor growth per tree ranged 

from 0.02 for the control to a maximum of 0.15 ft2/tree for 

the 40CT, cut ~7.0" plots. As expected, all plots where 

trees less than 7.0 inches d.b.h. were removed, had higher 

basal-area survivor growth per tree (Table 3). 

lngrowth into the 1 .O-inch d.b.h. class was strongly related 

to intensity of overstory removal and the felling of all trees 

less than 7.0 inches d.b.h. Generally within the thinning 

treatments, the heavier the cut, the greater the ingrowth. 

However, after 5 years, it is too soon for pole and 

sawtimber ingrowth comparisons among the thinning 

treatments. Due to overhead shading, no ingrowth 

occurred in areas where only the understory was removed. 

Cubic-foot-volume growth. Per acre &year net cubic-footvolume growth of all trees 5.0 inches d.b.h. and larger 

ranged from 229 to 279 ft3, for the 60 and 40 crop-tree 

treatments where trees less than 7.0 inches d.b.h. were 

felled, to 301 to 355 ft3 for similar treatments where trees 

less than 7.0 inches d.b.h. were not felled (Table 3). 

Likewise, survivor growth per tree was highest for the 60 

and 40 crop-tree treatments where trees less than 7.0 

inches were cut (4.0 and 3.4 ft3, respectively). The Control 

and Control, cut c7" treatment areas had the lowest cubicfoot-volume growth per tree when compared to the thinning 

treatments (1.2 and 2.0 ft3/tree). 

Five-year cubic-foot volume mortality for the thinned plots 

was variable but low, averaging from 0 ft3/acre in the control 

plots to 52 ft3/acre in the 40 crop-tree treatment where 

understory trees less than 7.0 inches d.b.h. were not cut. 

Cubic-foot-volume ingrowth was evident only where the 

crop trees were released and the understory was not cut. 

After 5 years, ingrowth into the pole-size stand (5.0 inches 

d.b.h. and larger) averaged 23 and 48 ft3 for the40 CT and 

60 CT areas, respectively. 

Board-foot-volume growth. The 5-year net board-footvolume growth ranged from 2,176 bd Wacre for the 40 

crop-tree treatment (understory not cut) to 2,755 for the 

control areas (understory was cut) (Table 3). Approximately 

24 percent of this volume growth was ingrowth (trees 

crossing the I1 .O-inch d.b.h. threshold for board-footvolume calculations) for all the 40 crop-tree treatments 

while the 60 crop-tree treatments averaged about 7 percent 

ingrowth and the control treatments 14 percent. Boardfoot-volume growth of surviving sawtimber trees averaged 
Table 3.--Five-year growth and mortality, by crop-tree thinning treatment 

Survivor 

Final growth 

Treatment Residual (5-year) lngrowth Mortality Net growtha per treeb 

TREES 1.0 INCH D.B.H. AND LARGER --------------- Basal area @%acre) - - - - - - - - - - - - - - - - - - 

40 CT, cut <7.0" 55.0 67.4 3.1 (309)' 0.2 (I)' 12.4 (391)' 0.11 (83) 

40 CT 80.6 93.5 0.6 (81) 3.4 (25) 12.9 (387) 0.05 (331) 

60 CT, cut <7.0" 71.2 81.1 1.5 (1 86) 1.1 (2) 9.9 (247) 0.1 5 (63) 

60 CT 83.0 97.6 0.6 (74) 2.0 (25) 14.6 (381) 0.05 (331) 

Control, cut e7.0" 140.8 151.9 0.0 1.8 (4) 11.1 (1 85) 0.07 (1 89) 

Control 171.1 178.3 0.1 (1 9) 7.4 (105) 7.2 (665) 0.02 (751) 

TREES 5.0 INCHES D.B.H. AND LARGER --------------- volume(rr/acre) .................... 

40 CT, cut ~7.0" 1232 1511 0 4 (1) 279 (83) 3.4 (83) 

40 CT 1552 1853 23 (91d 52 (10) 301 (149) 2.2 (159) 

60 CT, cut c7.0" 1776 2005 0 24 (2) 229 (61 ) 4.0 (63) 

60 CT 1658 1490 48 (19) 16 (5) 355 (141) 2.5 (147) 

Control, cut c7.0" 3236 3578 3578 36 (4) 342 (185) 2.0 (189) 

Control 3206 3472 0 0 266 (280) 1.2 (300) 

TREES 11.0 INCHES D.B.H. AND LARGER - - - - - - - - - - - - - - - Volume (bd Wacre) - - - - - - - - - - - - - - - - - - 

40 CT, cut <7.0" 3996 6242 528 (12)~ 0 2246 (51) 44.0 (51) 

40 CT 5349 7525 514 (10) 74 (1) 21 76 (50) 44.1 (51) 

60 CT, cut <7.0" 10511 12777 39(1) 91(1) 2266 (59) 39.9 (59) 

60 CT 7490 101 60 315 (7) 0 2670 (60) 44.5 (60) 

Control, cut c7.0" 12783 15538 416(16) 30(1) 2755 (1 07) 26.5 (1 07) 

Control 891 8 11 294 319 (11) 0 2376 (83) 28.6 (83) 

RELATIVE STAND DENSITY 

40 CT, cut <7.0" 27.6 43.8 - - 16.2 (391) 

40 CT 49.7 57.7 - - 8.0 (387) 

60 CT, cut <7.0" 27.7 32.4 - - 4.7 (247) 

60 CT 47.1 54.8 - - 7.7 (381) 

Control, cut <7.0" 69.3 72.8 - - 3.5 (1 85) 

Cqntrol 108.5 108.0 - - -0.5 (665) 

a5-year net growth = survivor growth + ingrowth - mortality. 

b~rowth oftrees that were alive in both the residual stand and 5 years later. 

'Numbers in parentheses are numbers of trees per acre. 

d~umber stems correct, values estimated. 

43 bd Wtree in the release areas and 28 bd ftlacre in the 

control areas. As indicated previously, there was little to no 

mortality of sawlog-size trees during the first 5 years. 

Relative stand density. For the thinned plots, the relative 

density (Stout et al. 1987) increased an average of 

approximately 12 percent for all the 40 crop-tree areas and 

6 percent for the 60 crop-tree areas over the 5-year period 

(Table 3). While relative density for the Control, cut <7" 

treatment, increased 3.5 percent, no increase occurred in 

the uncut stands where basal areas approached 180 sq ftl 

acre. 

D.b.h. response. Crop trees that were released averaged 

1 .O-inch d.b.h. growth during the 5-year period, while crop 

trees in the two control treatments averaged 0.6 inch d.b.h. 

growth (Table 4). This difference was significant at the 

5-percent level of testing. 

Data shown in Table 4 indicate that the crown thinning 

increased individual tree d.b.h. growth. However, 

meaningless conclusions can result in comparing individual 

tree growth data if the number of trees in each treatment 

are not equal or if they change. After 5 years, number of 

trees per acre ranged from 63 to 751, while number of crop 

7 
trees per treatment ranged from 55 to 90 (Table 4). To 

clarify the response of individual trees, d.b.h. growth of the 

40 largest d.b.h. crop treeslacre per treatment plot also was 

compared (Table 4). These data indicate that the thinned 

areas where crop trees were selected and released, had 

significantly more d.b.h. gro h response than any of the 

control plots. Five years after treatment, the average el. 

growth for the 40 largest co-op trees per acie in the thinning 

treatment areas was 1.05 inches, while the 40 largest crop 

trees in the control areas averaged 0.73 inch. 

Number of sides released A majority (71 percent) of the 

crop trees were free-to-grow on three or four sides of the 

crown. Many of the crop trees not released on three or four 

sides were in areas where trees less than 7.0 inches d.b.h. 

were not cut on control areas. Data related to sides of 

crown released were grouped by species for analyses. 

However, too few samples were available for red maple, 

basswood, and white ash to make meaningful statistical 

comparisons. Five-year d.b.h. growth significantly 

increased with the increase in sides released (Table 5). 

Black cherry with no crowns released (254 trees) grew 0.6 

inches d.b.h. in 5 years, while trees free-to-grow on 1 or 2 

sides (81 trees) grew 0.9 inches d.b.h., and trees free-togrow on 3 to 4 sides (160 trees) grew 1.1 inches d.b.h. For 

most situations, the more sides of the crown released, the 

greater the d.b.h. response (Fig. 3). 

Removing trees less than 7.0 inches d. b. h. Growthresponse (d.b.h.) was noi related consistently to removal of 

trees less than 7.0 inches d.b.h. In one case, 40 crop-tree 

treatment, growth ofthe black cherry crop trees was slighily 

higher when cutting the small trees. However, the trend 

was reversed for the 60 crop-tree per-acre treatment. Crop 

trees established where trees less than 7.0 inches d.b.h. 

were not cut, grew about 0.1 inch more compared to similar 

crop trees in areas where all trees were cut less than 7.0 

inches d.b.h. 

Tree-Quality Development 

Epicormic branches result in lumber discoloration primarily 

through ingrown bark and are considered a grade defect for 

factory sawlogs grades 1 to 3. This grade defect can result 

in a significant loss of monetary value to the landowner. 

Crop-tree quality was evaluated by number of epicormic 

Table 4.--Average 5-year d.b.h. growth, by thinning treatments 

Item All treesa Crop trees 40 largest trees 

40 CT, CUT < 7.0" 

No. treeslacre 83.00 55.00~ 40.00 

Initial d.b.h. (inches) 11 .00 1.90 13.54 

5-year growth (inches) 0.93dC 1 .02dC 1 .Ol dc 

40 CT 

No. trees/acre 331 .OO 59.00 40.00 

Initial d.b.h. (inches) 6.54 12.78 14.31 

5-year growth (inches) 0.73e 1.02d 1.06d 

60 CT, CUT c 7.0" 

No. trees/acre 63.00 58.00 40.00 

Initial d.b.h. (inches) 14.22 14.45 16.46 

5-year growth (inches) 1.00d 0.95d 1.02d 

60 CT 

No. treeslacre 331.00 90.00 40.00 

Initial d.b.h. (inches) 6.70 13.09 15.24 

5-year growth (inches) 0.63e 0.98d 1.10d 

CONTROL, CUT < 7.0" 

No. treestacre 189.00 90.00 40.00 

Initial d.b.h. (inches) 11.61 12.82 16.02 

5-year growth (inches) 0.53f 0.58e 0.70e 

CONTROL 

No. treeslacre 751 .OO 90.00 40.00 

Initial d.b.h. (inches) 6.32 12.20 14.66 

5-year growth (inches) 0.289 0.64e 0.75e 

aTrees 1.0 inch d.b.h. and larger that were alive in both the residual stand and 5 years after treatment. 

b~rop trees, not per acre, but total number available after 5 years. 

'Five-year growth means in the same column followed by the same letter are not significantly 

different at 0.05-level of testing. 
Table 5.--Black cherry crop-tree d.b.h. growth response, by sides of 

crowns released and thinning treatmenPb 

Sides crown released 

Treatment 0 1-2 3-4 

40 CT, cut < 7.0"- 

40 GT - 

60 CT, cut < 7.0" - 

60 CT - 

Control, cut c 7.8" 

40 CT 0.59 (55) - 

60 CT 0.52 (78) - 

ControlC 

40 CT 0.64 (47) - - 

60 CT 0.63 (74) - - 

aParentheses = number of trees. 

b~aiues in the same row followed by the same letter are not significantly 

different at 0.05-level of testing. 

'First 40 trees are in the 40 crop-tree treatment and an additional 20 crop 

trees make the 60 crop-tree treatment for the control areas only. 

Figure 3.--Five-year d.b.h. growth of black cherry crop trees as related to sides of crown 

released. Number of trees is shown in boldface. 
branches occurring as a result of the study treatments. 

Due to available samples, black cherry was the only species 

evaluated. 

When released, black cherry trees are susceptible to the 

development of epicormic branches along their tree boles 

(Smith 1966). However, crown class is an important factor 

when considering trees for release. Trees in the dominantcodominant crown classes are not as susceptible to 

epicormic branching as trees in the intermediateovertopped crown classes. In this crop-tree release study, 

all crop trees were dominant-codominant and free of 

epicormic branches along the tree bole before the thinning 

treatment. 

After 5 years, epicormic branching resulting from any of 

the crop-tree-release treatments did not reduce butt-log 

grade for most of the black cherry trees. Only 4 

(2 percent) of the 241 released black cherry crop trees had 

a degraded butt log due to epicormic branches. A total of 

42 trees (17 percent) produced at least one epicormic 

branch on the lower portion of the tree bole (1 to 33 feet). 

However, only 16 (7 percent) had one or more epicormic 

branches on the butt log. For both control treatments, 4 of 

254 (2 percent) trees produced epicormic branches along 

the tree bole (17 to 33 feet). No sprouts occurred on the 

butt log; 

Due to the limited development of epicormic branches, it 

was not necessary statistically to evaluate the results of 

individual treatments. Released trees did produce more 

epicormic branches than trees on the nonreleased (control) 

areas, but the degrade on the butt log was insignificant. 

After 5 years, growth of the understory is developing rapidly 

and shading the butt log. No additional epicormic branches 

as a result of the crop-tree-release treatments should occur. 

Shading will induce natural pruning (the branches will die) 

and any additional butt-log degrade due to epicormic 

branching is not expected to occur. 

Summary 

In this study, six crop-tree treatments were applied to a 65- 

year-old black cherry-maple stand. Three crop-tree crownrelease overstory treatments were used--selecting and 

releasing 40 crop trees per acre, 60 crop trees per acre, 

and no release of crop trees. Three additional treatments 

were similar except all trees less than 7.0 inches d.b.h. 

(saplings and small pole-size trees) were felled. Before 

treatment, stands averaged approximately 180 square feet 

per acre in trees 1.0 inch d.b.h. and larger. The average 

height and d.b.h, of the crop trees at time of release was 80 

feet and 12.5 inches d.b.h. 

A crown-touching technique was used to release crop trees. 

The release provided an average of 13 feet of growing 

space from the edge of the crop-tree crown to the edge of 

adjacent trees. Most trees'(71 percent) were free to &:ow 

on three or four sides of their crowns. Residual stands 

include both crop trees and other trees not selected as crop 

trees. Criteria were developed for choosing crop trees to 

produce high-quality sawlogs and veneer products with key 

points related to crown class, stem quality, and vigor. 

For the released black cherry crop trees, the average d.b.h. 

growth was 1 inch during the &year period after release, 

while d.b.h. growth for the nonreleased crop trees was 

significantly lower, averaging about 0.6 inch. The same 

response was found for the 40 largest trees per acre. Fiveyear data from a nearby study in which 60-year-old stands 

were thinned using SILVAH, indicated a similar response to 

the crop-tree crown-release thinning. The 50 largest d.b.h. 

black cherry trees per acre (not crop trees) in the SILVAH 

thinned stands averaged about 1.2 inches in d.b.h. growth. 

Trees on the control plots averaged 0.8 inches in 5 years 

(Lamson and Smith 1988). 

Removing trees 1.0 to 6.9 inches d.b.h. had no significant 

effect on residual tree d.b.h. growth for any treatment. 

Black cherry crop trees that were free-to-grow on three or 

four sides of their crowns responded more (5-year d.b.h. 

growth 1.1 inches) than similar trees released on one or two 

sides of their crown (0.85 inch). 

Five-year growth for basal area, volumes, and relative 

densities was summarized for each treatment. Data also 

were summarized for mortality and, depending on the 

variable, ingrowth into the 1.0, 5.0, and 11.0 inches d.b.h. 

classes (sapling-, pole-, and sawtimber-size trees). In 

general, for the crop-tree treatments, net basal-area growth 

averaged 12.5 square feet per acre compared to 9.2 square 

feet for the control areas. Net cubic-feet growth averaged 

291 for the crop tree treatments and 304 for the control 

plots. Net board-feet growth for the crop-tree treated plots 

averaged 2,340 per acre while the controls averaged 2,565 

per acre. The control plots had more trees than the 

released plots and, thus, growth by individual trees is more 

meaningful. For example, the 5-year growth per tree for the 

crop-tree plots averaged 43 board feet while the crop trees 

on the control areas averaged 28 board feet of growth per 

tree. Five-year relative density net growth for the crop-tree 

treatment plots averaged 9.2 percent while the control plots 

averaged 1.5 percent. 

When using this crop-tree release method, one-half to twothirds of the basal area was removed from the 65-year-old 

previously unmanaged cherry-maple stands. About 35 

percent of the crop trees had some degree of exposed 

sapwood wounds due to logging. Also, 80 percent of 

damaged crop trees had exposed sapwood wounds that 

were 50 square inches or less in size. It is anticipated that 

wounds of this size will be closed after 10 years and for 

black cherry, little or no degrade will occur in the butt log. 

However, this initial damage to the residual trees was much 

higher than expected. There are several ways to minimize 

the damage such as leaving fender trees along skid roads 

or reducing tree length winching-skidding to a maximum 

length of 32 feet. Loggers also can anticipate where 

damage can occur and try to avoid the problem. Where 

damage is going to occur, the loggers can consider 

damaging the less desirable than more desirable residual 

trees. Of course, paying for residual trees damaged during 
logging or receiving a bonus for little to no damage are 

other ways of minimizing damage. 

Black cherry is susceptible to the development of epicormic 

branching. All crop trees were in the codominant crown 

class and trees in the dominant-codominant crown class are 

less susceptible to branching. After 5 years, only 4 of 244 

(2 percent) black cherry trees had a reduced butt-log grade 

due to epicormic branching. However, the growth of the 

understory reproduction was developing rapidly and shading 

the butt log. We expect all epicorrnic branches resulting 

from the crop-tree treatments to die. Thus, epicormic 

branching was not a serious problem in this study. 

A vigorous commercial stand remains where 40 to 60 crop 

trees per acre were selected. After 5 years, the individual 

trees are responding to release as evident by d.b.h. growth 

and basal area and volume growth. At this point we expect 

the future stands to be of significantly higher quality and of 

average tree size compared to the uncut control areas. As 

a result, released trees will mature faster (based on tree 

size-4.b.h.) and provide wood products in a shorter period. 

A significant amount of black cherry reproduction was 

established for both the 40 and 60 crop-tree-per-acre 

treatments where all trees less than 7.0 inches d.b.h. were 

felled. In most cases, the reproduction will continue to 

respond and develop. After 5 years, ingrowth, or 

reproduction, into the 1.0 inch d.b.h. class averaged about 

250 trees per acre. Thus, the crop-tree treatments were 

setting the stage for a future sheltewood overstory 

removal. In some instances, a form of two-age 

management could be considered too, but black cherry will 

not have the life expectancy compared to species such as 

beech and maples. Where trees less than 7.0 inches d.b.h. 

were not felled, little to no black cherry reproduction was 

established. 

It is important to recognize that crop trees can be selected 

for many purposes. Though the timber resource was the 

primary objective in this study, other objectives such as 

wildlife, esthetics, or combinations easily could be selected. 

In using this crop-tree approach for thinning of forest 

stands, landowners and forest managers have an 

opportunity to become more satisfied with the results. 

Landowners will become more aware of ecological 

concepts, while forest managers will be able to use another 

tool to satisfy landowner desires and gain confidence in 

forest management practices. 

Literature Cited 

Gingrich, Samuel F. 1967. Measuring and evaluating 

stocking and stand density in upland hardwood 

forests in the central states. Forest Science. 13(1): 

38-53. 

Lamson, Neil I.; Smith, H. Clay. 1988. Thinning cherrymaple stands in West Virginia: 5-year results. Res. 

Pap. NE-615. Broomall, PA: US. Department of 

Agriculture, Forest Service, Northeastern Forest 

Experiment Station. 7 p. 

Lamson, Neil 1.; Smith, H. Clay; Perkey, Arlyn W.; Brock, 

Samuel M. 1990. Crown release increases growth of 

crop trees. Res. Pap. NE-635. Radnor, PA: US. 

Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station. 8 p. 

Marquis, David A.; Ernst, Richard L.; Stout, Susan L. 1984. 

Prescribing silvicultural treatments in hardwood 

stands of the Alleghenies. Gen. Tech. Rep. NE-96. 

Broomall, PA: US. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 90 p. 

Rast, Everette D.; Sonderman, David E.; Gammon, Glenn 

L. 1973. A guide for hardwood log grading (revised). 

Gen. Tech. Rep. NE-1. Upper Darby, PA: US. 

Department of Agriculture, Forest Service, Northeastern 

Forest Experiment Station. 32 p. 

Smith, H. Clay. 1966. Epicormic branching on eight 

species of Appalachian hardwoods. Res. Note NE53. Upper Darby, PA: US. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment 

Station. 4 p. 

Smith, H. Clay; Lamson, Neil 1. 1986. Cultural practices 

on Appalachian hardwood sapling stands-if done, 

how to do them. In: H. Clay Smith and Maxine C. Eye, 

eds. Proceedings, guidelines for managing immature 

Appalachian hardwood stands; 1986 May 28-30; 

Morgantown, WV. Morgantown, W. West Virginia 

University: 46-61. 

Stout, Susan L.; Marquis, David A.; Ernst, Richard L. 1987. 

A relative density measure for mixed-species' 

stands. Journal of Forestry. 85(7): 45-47. 
Smith, H. Clay; Miller, Gary W.; Lamson, Neil 1. 1994. Crop-tree release 

thinning in 65-year-old commercial cherry-maple stands (&year results). 

Res. Pap. NE-694. Radnor, PA: US. Department of Agriculture, Forest 

Service, Northeastern Forest Experiment Station. 11 p. 

Crop-tree release was applied to a 65-year-old cherry-maple stand in north 

central West Virginia. Criteria were developed for selecting crop trees for high 

quality sawtimber and veneer products. Five-year stand growth, mortality, and 

ingrowth using basal areas, volume, relative density, and number of trees were 

discussed for the treatments. 

I ODC: 242:Ii'6.l 

Keywords: crop trees, selection criteria, release, thinning, commercial stands, 

growth, yield, quality. 

0 U.S. GOVERNMENT PRINTING OFFICE: 1994-550-112/00004 Printed on Recycled Paper 
Headquarters of the Northeastern Forest Experiment station is in Radnor, 

Pennsylvania. Field laboratories are maintained at: 

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Delaware, Ohio 

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C 

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in cooperation with the University of Maine 

Parsons, West Virginia 

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

ental Sciences and orestry at Syracuse 

cooperation wit The Pennsylvania State 

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