United States 

Department of 

Agriculture 

Forest Service 

Northeastern Forest 

Experiment Station 

Research Paper NE-620 

Applying a Crop-Tree Release 

in Small-sawtimber 

White Oak Stands 

Jeffrey W. Stringer Gark W. Miller 

Robert F. Wittwer 
Abstract 

Small-sawtimber white oak crop trees in Kentucky were released by a 

crown-touching technique. In two cutting treatments, 20 and 34 crop trees were 

released per acre at a total cost of $35 and $42, respectively. Both treatments 

yielded commercial volumes of cut material. Total mean merchantable volume (> 

5.0 inches d.b.h.) in cut trees was 693 cubic feetlacre, with approximately 2,400 

board feetiacre in sawtimber (2 11.0 inches d.b.h.). On the basis of early crop-tree 

stem response, the released trees are growing 0.16 inchlyear compared with 0.13 

inch/year for the unreleased trees. 

The Authors 

JEFFREY W. STRINGER is a research specialist in silviculture with the Department 

of Forestry, University of Kentucky, Lexington. 

GARY W. MILLER is an economist with the Timber Management Research Project, 

Timber and Watershed Laboratory, Northeastern Forest Experiment Station, 

Parsons, WV. 

ROBERT F. WlTTWER is an associate professor with the Department of Forestry, 

Oklahoma State University, Stillwater. 

Manuscript received for publication 18 May 1988 

Northeastern Forest Experiment Station 

370 Reed Road, Broomall, PA 19008 

October 1988 

Kentucky Agriculture Experiment Station 

Journal Article #88.8.76 
Introduction 

Since upland oaks are a significant component of eastern 

forests, there has been considerable research on their 

management. Much effort has been focused on the 

manipulation of stand density (Roach and Gingrich 1968) and 

its effect on growth and yield following intermediate cutting 

treatments in upland oak forests (Dale and Hilt 1986). 

Resulting management guides recommend 'maintenance of 

growing stock (stand density) at certain minimum levels. In 

general, poorer quality trees are removed and higher quality 

trees are retained. However, in many caseslthis approach 

has not resulted in the highest quality trees being cultured 

adequately in the residual stand. The importance of 

emphasizing individual trees in identifying silvicultural 

alternatives is discussed in DeBald and Mendel (1 976). 

This study tested the concept of maximizing timber-value 

production per unit area by applying crown-tbuching release 

to individual crop trees with the potential for yielding 

high-quality, high-value sawtimber and venepr logs. In this 

approach, stands with low stocking by some; standards may 

have potential for continued management. Also, potentially 

high-value trees in adequately stocked stands will receive 

more attention than would normally be afforOed by area-wide 

treatments. Concentration on release of on19 potentially 

high-value trees can simplify and reduce costs of cultural 

work. The crop-tree approach concentrates treatment 

benefits from intermediate cutting treatmenti on trees with 

the highest potential value increase. With area-wide 

thinnings, trees are more likely removed witdout considering 

the benefits to the residual stand. 

In this paper we present initial results of a crpp-tree release, 

including treatment costs, volume of removals, and 

preliminary, 3-year growth data. This information can be used 

to help determine costs of treatments designled to release 

individual trees as well as felling costs for predetermined 

volumes in intermediate cuts. Cost data coubled with 

yield-response data will enable managers to formulate guides 

for selecting crop trees and determine the cdst effectiveness 

of intermediate treatments. 

Study Description 

The study was conducted at the University of Kentucky's 

Robinson Forest located in Breathitt, Knott, dnd Perry 

Counties in eastern Kentucky. Two cutting trjatments, 

releasing 20 and 34 crop trees per acre, and a control 

treatment were replicated 4 times and randomly distributed 

among 12 stands selected for study. The nu&ber of crop 

trees released per acre was determined by r4alistic goals for 

the merchantable stand at final harvest. Our goal was to have 

a fully stocked stand in which codominant trebs averaged 22 

1 to 24 inches d.b.h. at final harvest and occupled 

approximately 80 percent of full stand stockidg (Gingrich 

1967). The remaining 20 percent stocking is hccupied by 

understory trees. In managed stands, 80 percent stocking in 

24-inch trees is achieved with 22 crop trees per acre. In 

unmanaged stands, where tree crowns are smaller, 80 

percent stocking in 24-inch trees is achieved with 34 crop 

trees per acre. Thus, the two release treatments bracket the 

minimum number of crop trees needed to promote a stand at 

final harvest made up of 24-inch codominant trees. Our 

objective was to give crop trees enough canopy space to 

allow unhindered growth throughout the remainder of the 

rotation. No additional treatments are planned before final 

harvest. 

Crop trees were released using a crown-touching treatment; 

that is, any tree touching or overlapping the outer edge of the 

crop tree crown was eliminated unless the competing tree 

was another crop tree. It is important to note that only trees in 

direct competition with crop trees are removed. Some canopy 

trees not competing directly with the crop trees are retained 

and also benefit from the release treatment. 

Stand Description 

The 12 stands in this study consisted primarily of white oak, 

which occupied an average of 58 percent of the total 11 1 ft2 

of basal arealacre (stems 2 1.0 inch) in each stand (Fig. 1). 

Figure 1 .-Small-sawtimber white oak stand, 70 to 75 years 

old, in eastern Kentucky. 
These stands averaged 67 dominant and codominant 

treesiacre and could be considered large poles or small 

sawtimber with an average d.b.h. of 13 inches. Canopy trees 

consisted primarily of white oak with scattered black oak, 

yellow-poplar, American beech, and hickories. White oak site 

index (base age = 50 years) of the stands ranged from 65 to 

83 feet, averaging 73 feet, with an average age of 73 years. 

The average stem diameter and the number of stems per 

acre for all stems 2 1.0 inch before treatment were 5.2 

inches d.b.h. and 760, respectively (Table 1). It should be 

noted that acccording to Gingrich's upland oak stocking chart, 

these stands are overstocked. When eliminating trees < 3.0 

inches, as suggested by Roach and Gingrich (1 968), the 

stands are understocked. 

Methods 

In each of the 12 stands selected for study, a 2-acre 

treatment area was established with a 112-acre growth and 

yield plot located within each treatment area. All trees 2 1.0 

inch d.b.h. in the growth and yield plots were tagged 

according to Lamson and Rosier (1 984). The entire 2-acre 

treatment area was used to obtain time data for determining 

treatment costs and the merchantable volume of cut trees, 

and to provide a buffer area for the growth and yield plot. The 

growth and yield plot was used to monitor quantity and quality 

changes of individual trees and to determine crop-tree 

volume and damage to the residual stand from the release 

treatments. Pretreatment data recorded in the growth and 

yield plots included species. d.b.h., crown class, and remarks 

on stem condition for each plot. Crop tree selections were 

made on both the treated and control plots according to the 

following criteria: 

1. Crown class--only dominant or codominant tress. 

2. Species--white oak preferred. 

3. Quality--trees with potential butt log grade 1 or 2. 

4. Spacing--even distribution where possible. 

5. All things equal, trees with larger d.b.h. 

Crop trees were released by felling competing trees with a 

chain saw. To determine costs associated with each 

treatment, time-study data were collected during felling 

operations. Time data were recorded according to productive 

and nonproductive activities. Productive activities included 

felling unwanted stems and walking from tree togtree. 

Nonproductive activities included refueling, routine saw 

maintenance, personal breaks, and machine downtime. 

These data were summarized to determine average total time 

per crop tree and average total time per acre for each 

treatment. Immediately after the treatments, merchantable 

volume cut in the treatment areas was measured. In the 

grcwth and yield plots, crop-tree butt-log grade, crown 

dimensions, and distances to crown of nearest neighbor were 

recorded. After three growing seasons, the d.b.h. and butt-log 

grades of the crop trees were remeasured. 

Table 1.-Stand per-acre characteristics for two crop-tree release treatments in pole 

and small sawtimber white oak stands 

- 

Crop tree No. of Percent Basal Ave. stem Merchantable volumea 

treatment Stand stems stocking area diameter Cubic feet Board feet 

ftZ Inches 

34 Initial 786 110 111.5 5.1 2,114 6,187 

Cut 56 33.7 10.5 764 2,360 

Damage 18 1.5 3.9 19 74 

Residual 712 80 77.1 4.5 1,331 3,753 

Crop trees 34 20 25.2 11.7 584 2,407 

20 Initial 735 104 107.9 5.2 2,122 6,799 

Cut 38 27.1 11.4 622 2,462 

Damage 18 2.5 5.0 50 189 

Residual 679 79 78.3 4.6 1,450 4,148 

Crop trees 20 15 20.1 13.3 505 2,311 

Control Initial 451 104 112.6 5.7 2,356 10,154 

Crop trees 28 25 31.4 14.1 777 4,187 

alnternational 114-inch rule, form class 78. 
Results 

Time and Cost Data 

Both of these factors are a function of the number of crop 

trees released per acre. Under normal circumstances, the 

trees with high crop-tree potential tended to be the largest 

trees in the plots. The selection of crop trees tended to The average time required to select and mark crop trees prior proceed in descending order of size as is evident from the to actual felling operation averaged 0.P hourlacre for the 

20-tree plots and 1.0 hourlacre for th< 34-tree plots, average crop-tree sizes in Table 1. As additional crop trees 

were selected per acre, the average size of both crop trees increasing as more crop trees were selected per acre (Table and cut trees decreased. Also, as the number of crop trees 2). The felling operation required an aberage of 3.7 per acre increases, the likelihood that cutting one tree may for 20 trees and 4'7 hburslacre for 34 crop lead to the release of more than one crop tree also increases. Marking and productive times +re both greater per Thus, the number of trees cut per crop tree decreases as the crop tree for the 20-tree versus the 34ltree plots. number of crop trees increases. 

primary factors, the number and the size trees being The total treatment cost, including marking crop trees and the removed, influenced the amount of tide needed to release an 

individual crop tree. Total felling time generally increases as actual release operation, was $35 for 20 crop trees and $42 

d.b.h. increases. Cut trees in the 20-trbe areas were an 

for 34 crop treeslacre (Table 2). Releasing additional crop 

average of 1 inch larger in d.b.h. than in the 34-tree areas 

trees lowered the average cost per crop tree. The average 

treatment cost decreased from $1.77 to $1.24/crop tree as (Table 3)' The 20-tree plots also had a( greater number Of cut the number of crop trees increased from 20 to 34tacre. trees per crop tree, 1.9 cut treeslcrop tree compared with 1.6 

cut treeslcrop tree in the 34-tree plots. 

Table 2.-Estimated cost per acre for two crop-tree release treatments in 

70-year-old white oak stands in Kentuckv 

Crop tree ~eledse Marking Total Labof Machineb Total Total cost/ 

treatment time time cost cost crop tree 

------------ /-/ours/acre ------------ ---------- Dollars/acre---------- Dollars 

a Wage rate = $5.0iD/hour plus 31 percent mandatory fringe benefits including Social 

Security, workmen's compensation insurance, and unemployment compensation - 

$6.55/hour. 

Machine cost = $$.12/operating hour; operating hours = 50 percent of release time 

(Miyata 1980). 

Table 3.-Summary of time-study data for two ccop-tree release treatments in 

70-year-old white dak stands in Kentucky 

Time study Ave. total time per: 

Crop tree Crop trees Trees Average d.b.h. Productive Delay Total Crop Cut 

treatment observed cut of cut trees time time time tree tree 

-----Number ----- Inches ....................... Minutes ----------------------, 

alncludes refueling, Saw maintenance, personal time, and repairs. 
Volume of Removals Discussion 

Crown release of 20 crop treeslacre resulted in removing 

about 27 percent of the initial basal area (1.0 inch d.b.h. and 

larger). The residual stand stocking was 70 percent of full 

stocking defined by the upland oaks stocking guide (Gingrich 

1967). Merchantable volume included in the cut averaged 

2,462 board feetlacre in 14 sawtimber trees (1 1.0 inches 

d.b.h. and larger) per acre. Total merchantable volume in cut 

trees (5.0 inches d.b.h. and larger)-averaged 622 ft3/acre 

(Table 1). Crown width of crop trees averaged 23.7 feet. 

Following release, selected crop trees were free-to-grow with 

an average crown growing space of 10.1 feet, as defined by 

the average distance from the edge of the crop tree crowns to 

the closest adjacent tree crown (Table 4). 

Releasing 34 crop trees per acre resulted in removing 31 

percent of the initial stand basal area. Residual stocking 

averaged 68 percent of full stocking (Gingrich 1967). 

Merchantable volume included in the cut averaged 2,360 

board feetiacre in 17 sawtimber trees per acre. Total 

merchantable volume in cut trees averaged 764 ft3/acre 

(Table 1). Average crown width of residual crop trees was 

21.5 feet. Following release, selected crop trees were 

free-to-grow with an average crown space of 12.4 feet (Table 

4). 

Three-Year Growth Response 

Diameter-growth response for all released trees was pooled 

for comparison with unreleased potential crop trees. The 

d.b.h. growth of released trees after three growing seasons 

averaged 0.1 6 inchlyear; significantly higher than that of 

unreleased trees (0.13 inchiyear (p = 0.01)). The d.b.h. 

growth for released trees ranged from 0.14 to 0.21 inchlyear 

and for unreleased trees ranged from 0.1 1 to 0.17 inchiyear. 

In earlier studies, white oak poletimber occupying a 

codominant crown position responded to crown release. 

Minckler (1 967) found that a partial crown release increased 

diameter growth of white oak crop trees for at least 10 years 

after treatment. In another study, white oak crop trees 

released on one or two sides of the crown grew faster than 

their unreleased counterparts for 20 years following treatment 

(Schlesinger 1978). Research results indicate that the d.b.h. 

of codominant white oak poletimber trees can be increased 

by 1.5 to 2.0 inches in about 10 years following one partial 

crown release. In this study, crop trees received a full 

crown-touching release. On the basis of the success of 

previous studies involving partial crown release of white oak 

poletimber, we expect the crown-touching release in this 

study to maximize potential diameter growth. Beyond the 

period of faster growth, released trees are expected to be at 

least 2 inches larger and have higher stumpage values than 

unreleased trees. 

The d.b.h. growth of unreleased crop trees averaged 0.13 

inchlyear. Released trees, however, did show a significant 

difference between crown sizes. Released crop trees with 

relatively large and medium-size crowns maintained a higher 

growth rate (0.1 7 inchlyear) than trees with relatively small 

crowns (0.13 inchlyear). Thus, trees with the largest crowns 

exhibited the greatest growth differential, 0.04 inchlyear, 

between released and unreleased trees. 

The potential quality of white oak crop trees can be reduced 

by heavy thinning. Moderate or light area-wide thinnings, 

where residual basal area is above 50 ft2, do not result in 

significant losses in crop-tree stem quality (Dale and 

Sonderman 1984; Sonderman 1984). In this study, average 

basal area was reduced to about 77 ft2/acre in both release 

treatments. This could be considered a light thinning, though 

cut trees were concentrated around the crop trees. Changes 

in stem quality will have to be monitored to determine if the 

crown-touching release has the same detrimental effects as 

heavy, area-wide thinnings. 

Table 4.-Data summary for crop-tree release treatments 

Average Average Ave. crown No. of 

Crop-tree Trees Trees Trees crop-tree crop-tree growing space trees cut Average 

treatment selected destroved released d.b.h. crown width after release per acre d.b.h. - - -- - - - - 

---------- Number/acre ----------- Inches ------------------ Feet --------------- Inches 
In precommercial operations, the cost per cropltree increases 

as fewer trees are released. In addition, crop-tree selection 

will influence the composition of the stand at fi4al harvest. It 

is important to focus investment dollars on the best available 

trees. We select the trees we want from the redjdual stand. 

The more we select, the fewer nature selects fcjr us. Also, 

selecting fewer trees allows more of the final hqrvest to be 

determined by chance. In this study, cut volumds were similar 

for both 20 and 34 residual crop trees per acre. iln the latter 

treatment, however, we were able to culture a larger 

proportion of trees that will develop into final hahest trees. 

Literature Cited 

Dale, M. E.; Hilt, D. E. 1986. Thinning pole and small 

sawtimber mixed oak stands. In: Smith, H. Clay; Eye, 

Maxine C.; eds. Guidelines for managing immature 

Appalachian hardwood stands: Workshop proceedings; 

1986 May 28-30; Morgantown, WV. SAF Publ. 86-02. 

Morgantown, WV: West Virginia University Books: 99-1 17. 

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. 

DeBald, P. S.; Mendel, J. J. 1976. An individual-tree 

approach to make stand evaluations. Res. Pap. 

NE-336. Upper Darby, PA: U.S. Department of Agriculture, 

Forest Service, Northeastern Forest Experiment Station. 

13 p. 

Gingrich, S. F. 1967. Measuring and evaluating stocking 

and stand density in upland hardwood forests in the 

central states. Forest Science. 13(1): 38-53. 

Lamson, N. I.; Rosier, R. L. 1984. Wires for long-term 

identification of trees. Journal of Forestry. 82: 110. 

Minckler, L. S. 1967. Release and pruning can improve 

growth and quality of white oak. Journal of Forestry. 65: 

654-655. 

Miyata, Edwin S. 1980. Determining fixed and operating 

costs of logging equipment. Gen. Tech. Rep. NC-55. St. 

Paul, MN: U.S. Department of Agriculture, Forest Service, 

North Central Forest Experiment Station. 16 p. 

Roach, 6. A.; Gingrich, S. F. 1968. Even-aged silviculture 

for upland central hardwoods. Agric. Handb. 355. 

Washington, DC: U.S. Department of Agriculture. 39 p. 

Schlesinger, Richard C. 1978. Increased growth of 

released white oak poles continues through two 

decades. Journal of Forestry. 76: 726-727. 

Sonderman, David L. 1984. 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. 6 

P. 
Stringer, Jeffrey W.; Miller, Gary W.; Wittwer, Robert F. 1988. Applying a 

crop-tree rblease in small-sawtimber white oak stands. 

Res. Pap. NE-620. Broomall, PA: U.S.Department of Agriculture, 

Forest ~erdce, Northeastern Forest Experiment Station. 5 p. 

Small-sawtimber white oak crop trees in Kentucky were released by a 

crown-touchins technique. In two cutting treatments, 20 and 34 crop trees 

were released ber acre at a total cost of $35 and $42, respectively. Both 

treatments yielhed commercial volumes of cut material. Total mean 

merchantable {olume (> 5.0 inches d.b.h.) in cut trees was 693 cubic 

feet/acre, with approximately 2,400 board feetiacre in sawtimber (m 11.0 

inches d.b.h.). Qn the basis of early crop-tree stem response, the released 

trees are growihg 0.16 inchtyear compared with 0.13 inchtyear for the 

unreleased treds. 

ODC 242:176.1 

Keywords: white oak; crown touching; felling cost; three-year growth; 

Kentucky