United States

Department of 

Agriculture

Forest Service

Northern 

Research Station

General Technical

Report NRS-83

Coopers Rock Crop Tree 

Demonstration Area—

20-Year Results

Arlyn W. Perkey

Gary W. Miller

David L. Feicht
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Manuscript received for publication 7 January 2011

Abstract

During the 1988/1989 dormant season, the Coopers Rock Crop Tree Demonstration Area 

was established in a 55-year-old central Appalachian hardwood forest in north-central 

West Virginia. After treatment, 89 northern red oak (Quercus rubra L.) and 147 yellowpoplar (Liriodentron tulipifera L.) crop trees were monitored for 20 years. This report 

summarizes the growth in diameter at breast height (d.b.h.) and crown development 

of crop trees from age 55 to 75 after they received various degrees of crown release 

resulting from crop tree management and traditional area-wide thinning. Annual d.b.h. 

growth response is presented to illustrate the year-to-year fl uctuations in growth that 

occurred throughout the demonstration area. In general, d.b.h. growth response and 

crown expansion were related to the degree of crown release. Northern red oak exhibited 

a greater response in d.b.h. growth and crown expansion than did yellow-poplar over the 

20-year study period.

Cover photo

The Coopers Rock Crop Tree Demonstration Area was established at Coopers Rock State 

Forest through cooperation of the West Virginia Division of Forestry and the U.S. Forest 

Service’s Northeastern Forest Experiment Station (now the Northern Research Station) 

and Northeastern Area State and Private Forestry. Clay Smith (left) and Arlyn Perkey 

welcome visitors at the entrance sign in 1990. Photo by U.S. Forest Service.
1

INTRODUCTION

During the 1988/1989 dormant season, the Coopers Rock Crop Tree Demonstration 

Area was established at Coopers Rock State Forest near Exit 15, U.S. Interstate 68 

in eastern Monongalia County, West Virginia. Th e project is a cooperative eff ort 

of the state of West Virginia, Division of Forestry, and the U.S. Forest Service’s 

Northeastern Area State and Private Forestry, and Northern Research Station 

(previously Northeastern Forest Experiment Station). Th e easily accessible location 

was chosen to encourage use by foresters, landowners, and others interested in the 

stewardship of family forests in the eastern hardwood region. Providing assistance to 

these clients was and is a goal for both of the supporting public agencies.

As this demonstration area was installed, the publication “Crop Tree Management 

in Eastern Hardwoods” had not yet been published, but its foundations were being 

developed (Perkey et al. 1994). Consequently, many of the terms and descriptive 

phrases used here are described in that publication. Th e concept of crop tree 

management (CTM) was emerging as an eff ective tool for improving communication 

between natural resource professionals and family forest landowners. Th e Coopers 

Rock Crop Tree Demonstration Area was the fi rst of several demonstration areas 

established to provide on-the-ground examples of how CTM could be implemented 

to help accomplish the goals of family forest owners. It was also a means of 

transferring technology that was developed through many years of crop tree release 

research done by the U.S. Forest Service and universities.

DEMONSTRATION AREA

Th e approximately 10-acre demonstration area is subdivided into fi ve plots, consisting 

of four treatment plots and a Control plot. Th ree separate CTM treatment plots 

and an Area-wide Th inning plot were oriented so four corners and sides adjoined. 

Th is layout provided a common viewpoint for visitors to observe each treatment 

from the four-corners location (Fig. 1). Because of limited space, the Control plot 

is not contiguous with the four treatment plots. It is located in the vicinity, with 

similar species composition, but on a more fertile growing site. Consequently, when 

treatment growth rates are contrasted with Control growth rates, any acceleration in 

growth evident on the treated plots is conservative. Furthermore, any acceleration of 

growth in treatment areas is clearly not because of more favorable site conditions. Th e 

four treatment plots are located on an upper, south-facing slope. Th e Control plot 

is located on a somewhat steeper mid-slope with a north-facing aspect. Th e Control 

plot is on a cooler, moister site, described as mesic Site Class 2 in “Using Diagnostic 

Plants To Evaluate Site Class” (Carvell and Perkey 1997). In contrast, the treatment 

plots are located on Site Class 4 and 5. In more traditional terms, the treated plots are 

located on site index 70 for northern red oak(Quercus rubra L.) (base age 50), and 

the Control plot is located on site index 80.

Th e Authors

ARLYN W. PERKEY is 

retired from the U.S. Forest 

Service’s Northeastern Area 

State and Private Forestry at 

Morgantown, WV.

GARY W. MILLER is 

a research forester with 

the U.S. Forest Service’s 

Northern Research Station at 

Morgantown, WV.

DAVID L. FEICHT is 

a retired forester from 

the U.S. Forest Service’s 

Northern Research Station at 

Morgantown, WV.
2

Th e lower third of the Control plot includes old pits that indicate disturbance by mining 

activity during the iron industry era described below. However, the height of the trees and the 

species composition of understory plants do not indicate any diff erence in site productivity 

from the rest of the Control plot. Basal area on the treated plots averaged 136 ft2/ac, compared 

to 157 ft2/ac on the Control plot (Table 1).

Coopers Rock State Forest, including this demonstration area, has a long history of humancaused disturbance (Rodd 1994). Five iron furnaces were established between 1798 and 

1842. Iron ore, limestone, and charcoal were all obtained locally to make the industry viable. 

Supplying charcoal to the furnaces required heavy timber cutting, and subsequent wildfi res were a 

common occurrence . Th e last of the fi ve furnaces ceased operation in 1868. From 1912 to 1939, 

the area was heavily logged using railroads to transport timber to support sawmills. In 1936 the 

area was purchased by the state of West Virginia, and Coopers Rock State Forest was established. 

At that time, wildfi res were controlled and the infl uence of periodic fi res was greatly reduced.

Th e forest in the vicinity of the demonstration area is largely even-aged, with 1934 as the 

estimated stand-year-of-origin. Th e most common exception to the even-age status of the stand 

is the presence of a few scattered older, large white oaks. Some of them have fi re scars at their 

base, affi rming their presence dates back to the era when wildfi res were common. However, 

there was no evidence of wildfi res in the even-age stands on the demonstration area plots. 

Th e species composition in the overstory basal area is approximately 37 percent yellow-poplar 

(Liriodentron tulipifera L.) and 22 percent northern red oak with another 10 percent of other 

oak species (Table 2). Th e somewhat higher percentage of yellow-poplar in the Control plot 

refl ects the better site conditions.

Figure 1.—This group of visitors in 1989 saw all four treatment plots from a single location. This 

perspective helps show the contrasting appearance of area-wide thinning with three different 

applications of crop tree management.

Photo by U.S. Forest Service
3

Table 1.—Changes in stand basal area and relative density as a result of the treatments and 

subsequent 20-year growth, where BA = basal area, RD = relative density, and CT = Crop Tree

Initial Post-harvest After 20 Years

Treatment 

Objective Plot BA RD BA RD BA

BA

growth RD

RD

growth

ft2/ac % ft2/ac % ft2/ac ft2/ac/yr % %/yr

CTM Timber only

(32 CT/ac ) 2 130 84 43 35 105 3.1 66 1.6

CTM Timber and 

Wildlife

(25 CT/ac) 1 132 78 60 48 147 4.4 91 2.2

CTM Timber, Wildlife, 

and Aesthetics

(21 CT/ac) 4 148 106 83 68 145 3.1 81 0.7

Area-wide Thinning 3 133 99 83 68 147 3.2 88 1.0

Control 5 157 88 157 88 205 2.4 102 0.7

Table 2.—Species composition by basal area in each plot in 2008

Treatment Objective Plot YP NRO BC RM CO Other Total

-------------------------------- percent -------------------------------- ft2/ac

CTM Timber Only

(32 CT/ac ) 2 36 28 16 10 8 2 105

CTM Timber and 

Wildlife

(25 CT/ac) 1 39 22 9 11 8 11 147

CTM Timber, Wildlife, 

and Aesthetics

(21 CT/ac) 4 33 14 2 26 8 17 145

Area-wide Thinning 3 31 27 1 14 14 13 147

Control 5 47 19 7 15 7 5 205

Demo area average All 37 22 7 15 9 10 150

YP=yellow-poplar; NRO=northern red oak; BC=black cherry (Prunus serotina Ehrh.); RM=red maple (Acer 

rubrum L.); CO=chestnut oak (Quercus montana Willd.)
4

METHODS

Th e CTM system focuses on favoring trees that promise to yield future forest benefi ts desired 

by the landowner. Crop trees are those that the landowner wishes to retain for many years 

because they can provide outstanding wildlife benefi ts, rapid increases in timber value, or 

intrinsic natural beauty. In many cases, the landowner is interested in producing multiple 

benefi ts, so crop trees may vary in terms of species or other attributes depending on how they 

meet the landowner’s goals. Once the goals of the landowner are clear, the trees that help meet 

those goals can be identifi ed as crop trees.

Clarifying the landowner’s goals and identifying the crop trees are just initial steps in the CTM 

system. Most crop trees then receive a “crown-touching release,” whereby adjacent trees whose 

crowns touch those of the crop trees are removed. After release, each crop tree is assigned a 

free-to-grow (FTG) rating of 0,1,2,3, or 4 based on the number of sides that are not touching 

the crowns of adjacent trees (Perkey and Wilkins 2001). Such a release treatment reduces 

competition for sunlight and soil nutrients around the crop tree (Fig. 2). Th e free-growing 

space around the crop tree allows it to grow faster and become more vigorous. Th e crop tree 

develops more foliage and a denser crown, thus enhancing its ability to gather sunlight and 

produce carbohydrates through photosynthesis. Belowground, the crop tree develops a larger 

root system so it can gather more moisture and nutrients from the soil. Released crop trees also 

become more resistant to insects, pathogens, and severe weather conditions than do their less 

vigorous neighbors.

Figure 2.—The crop tree crown in the center of this illustration has been separated into four 

quadrants, or sides. A free-to-grow (FTG) rating is determined by the number of sides that are 

not touching the crowns of neighboring trees. The FTG rating for this tree equals 3 because 

competing trees on three sides have been removed.
5

Although the crown-touching release is a vital step in the CTM system, the two concepts are 

not synonymous. Th e crown-touching release is a specifi c treatment applied to most individual 

crop trees. (For exceptions, see defi nition of wildlife and aesthetic crop trees below). CTM is a 

much broader philosophy of forest management that takes into account the landowner’s desires, 

the current and future condition of the forest, the quality of the growing site, the market for 

forest products, and possible eff ects of factors in the surrounding landscape. Additional details 

on applying the CTM system are available in three earlier references (Perkey et al. 1994, Perkey 

and Wilkins 2001, Miller et al. 2007). At this demonstration area, crop trees were selected 

based on three landowner goals: timber, wildlife, and aesthetics.

Timber Crop Trees

Timber crop trees were those of better form and grade and with higher market value. Th ey were 

also at low risk for being damaged in weather events. Timber crop trees had a minimum initial 

diameter at breast height (d.b.h.) of 9 inches, with relatively large, vigorous crowns in dominant 

or codominant crown classes. Ideal timber crop trees were free of epicormic branches on the 

lower 17 feet of the bole, contained less than 5 percent decay, and were free of low forks and 

severe sweep or crook. If there were not enough trees in the CTM plots to meet those standards, 

additional trees with the highest potential timber quality were selected from the remaining trees.

A key guideline used in the CTM plots was that no more than two crop tree crowns could be 

touching. Th e fi rst preference was that every crop tree would be released from competing trees 

on all four sides of its crown. If two crop trees were adjoining, however, it was acceptable to 

select both as crop trees and remove competitors from around the perimeter of the two crop 

tree crowns. As a result, those two crop trees would have a crown-touching release on only three 

sides.

Wildlife Crop Trees

Wildlife crop trees were those that produce preferred hard or soft mast or those that had 

existing dens or evidence of cavities that had the potential to develop dens for wildlife 

shelter. Trees with dominant and codominant crown classes were preferred. For wildlife food 

production, wildlife crop trees greater than 10 inches d.b.h. with large vigorous crowns were 

released. An attempt was made to fi nd at least two crop trees per acre that provided shelter 

for wildlife. Wildlife crop trees that could produce both food and shelter were also released. 

Wildlife crop trees that were selected only to produce shelter were not released because the 

release treatment would not enhance their ability to provide wildlife shelter.

Aesthetic Crop Trees

Aesthetic crop trees were those having either attractive fl owers in the spring or brilliantly 

colored foliage in the fall. Crop trees were selected if they were unique or distinctive because of 

size, shape, form, or species. Aesthetic crop trees that were selected for their ability to produce 

attractive fl owers or colorful foliage received a crown-touching release. Crop trees that were 

selected only because of their unique or distinctive size, shape, form, or species were not released 

because the release treatment would not enhance these attributes.
6

In the three CTM plots, basal area and relative stand density were not used as guidelines to 

infl uence the selection of trees or the intensity of harvesting. However, these parameters were 

measured for comparative purposes since they are traditional measures of stand density for the 

professional forestry community. Six permanent point locations were established in each of 

the fi ve plots, and fortunately, all points remained throughout the 20 years. Th ese permanent 

variable-radius sample points provided continuity for measuring how the basal area and relative 

stand density changed over the 20 years.

Th e intensity of harvesting in the CTM plots was adjusted by changing the number of crop 

trees selected, but each crop tree was still released on three or four sides of the crown. Reducing 

the number of crop trees released reduces the intensity of cutting on a given area. Conversely, 

increasing the number of crop trees released increases the number of trees that are harvested 

and results in a more open-appearing residual stand. It is better to have fewer crop trees, fully 

released, than more crop trees, partially released.

Th e treatments in each plot were:

CTM timber only. Enhancing the growth of timber crop trees was the only objective recognized 

in this plot. Northern red oak and yellow-poplar accounted for 94 percent of the crop trees. Th e 

treatment involved releasing 32 crop trees per acre on three or four sides of the crown. Th is plot 

received the heaviest harvest and had the most drastic change in appearance (Fig. 3).

CTM timber and wildlife. Th e intensity of cutting in this plot was adjusted downward by 

releasing only 25 crop trees per acre on three or four sides of the crown. Th is reduction in 

intensity of harvesting demonstrated a less abrupt change from the previously existing forest 

Photo by Arlyn Perkey, U.S. Forest Service (retired)

Figure 3.—Clearing a walking trail and publishing an accompanying Trail Guide helped explain 

contrasting treatments. In the CTM Timber Only plot, many visitors commented on the open 

appearance of the area, especially immediately after the release of crop trees.
7

conditions. In addition, the species composition of selected crop trees was broadened to 

refl ect wildlife as well as timber objectives. Species like northern red oak that could produce 

both timber and wildlife benefi ts were high priority candidates for selection as crop trees. 

Northern red oak and yellow-poplar made up 87 percent of the crop trees. Since there were 

more potential crop trees available than were selected for release, these additional trees (mostly 

yellow-poplar) were numbered and their growth was monitored, even though they were not 

intentionally released. Any release they did receive was incidental as a result of releasing the 25 

crop trees per acre.

CTM timber, wildlife, and aesthetics. Th e intensity of cutting in this plot was likewise adjusted 

downward by releasing only 21 crop trees per acre on three or four sides of the crown (Fig. 4). 

Th e species composition of selected crop trees was additionally broadened to refl ect aesthetic 

as well as wildlife and timber objectives. Northern red oak and yellow-poplar constituted 58 

percent of the crop trees. Similar to the CTM Timber and Wildlife plot, there were more 

potential crop trees available than were selected for release. Th ese additional trees (mostly 

yellow-poplar) were numbered and their growth was monitored, even though they were not 

intentionally released.

Area-wide thinning. Th e treatment in this plot was an area-wide thinning to 83 ft2/ac of basal 

area and 68 percent relative stand density. To achieve that reduction in basal area from the 

initial 133 ft2/ac, one of every two pole-sized trees was cut and removed and one of every eight 

small sawtimber-size trees was cut and removed as recommended by Marquis et al. (1992). Th e 

selection of trees to cut was based solely on timber as an objective; the poorest-quality timber 

trees were the highest priority for removal.

Figure 4.—Directional felling was used to minimize damage to residual trees. In the CTM Timber, 

Wildlife, and Aesthetics plot, the lowest-intensity crop tree management treatment, avoiding residual 

trees while felling required specially trained personnel.

Photo by Arlyn Perkey, U.S. Forest Service (retired)
8

Although crop trees were not intentionally selected and released in this plot, potential timber 

crop trees were identifi ed using the same criteria applied in the CTM plots. Th eir growth was 

then monitored so it could be compared to growth of trees that received crown-touching release 

treatments in the CTM plots and unreleased trees in the Control plot.

Control. Th e Control plot received no treatment, but crop trees were selected using the timber 

objective and their growth was monitored for comparison with crop trees in the four treated 

plots.

All crop trees and comparison trees (more than 300 trees in all) were wired and tagged with 

numbers using a technique developed on the Fernow Experimental Forest near Parsons, WV, 

to accurately monitor tree growth (Lamson and Rosier 1984). Under this protocol, d.b.h. was 

measured annually in the dormant season and tree growth was monitored over a 20-year period.

A random sample of 10 northern red oak and 10 yellow-poplar crop trees or comparison trees 

was established in the Control, Area-wide Th inning, and a combination of the three CTM 

plots. Th ese sample trees (30 northern red oaks and 30 yellow-poplars) provided data for 

interim reporting on how growth was progressing. All 60 of these sample trees survived the 

20-year period. Th e growth of the sample subset was compared to the larger population of crop 

trees in the demonstration area, i.e., 236 crop trees.

Initial crown measurements were made on a random sample of 40 northern red oaks and 40 

yellow-poplars in the treatment plots (10 of each species in each treated plot). Crown dimensions 

were measured in the four cardinal directions from the bole of the tree with a measurement 

taken at the drip edge of the crop or comparison tree crown, and a second measurement at the 

drip edge of the adjoining tree crown as a measure of the free-to-grow (FTG) distance. Th e 

average distance between the crop tree crown and the crowns of the adjacent trees measured in 

the four cardinal directions is the FTG distance. Th e same trees were measured 20 years later to 

provide a measure of crown expansion and reduction in FTG distance.

Th e harvesting was done by the U.S. Forest Service logging crew from the Fernow Experimental 

Forest during March and April 1989. Th is crew had experience doing crown-touching release 

treatments with the crop trees marked to leave. Cut trees in the CTM plots were not marked 

before harvest operations began, thus the logging crew felled and removed competing trees 

whose crowns were touching those of the crop trees. In the Area-wide Th inning plot, cut 

trees were marked as is customary for that practice. Skid roads were constructed around the 

perimeter of each treated plot. A Cat® D4 (Caterpillar, Inc., Peoria, IL) and an arch were used 

for skidding (Fig. 5). Th e crew “pulled cable” out to the felled trees from the skid roads to avoid 

equipment traffi c in the interior of the treatment plots and to minimize damage to residual 

trees. When conditions were wet, logging was halted to avoid damage to roots and minimize 

soil compaction.

Th e corners of all plots and the six variable-radius points in each plot were marked with steel 

rebar. Th ese points also served as camera points for before and after photographs. Numerous 

photos were taken throughout the area during the 20-year period.
9

DATA ANALYSIS

With only one plot assigned to each treatment, data from the demonstration area took the 

form of a case study whereby routine statistical analysis was not appropriate (Hurlbert 1984). 

Descriptive statistics, including means and standard errors, are provided to compare d.b.h. 

growth, crown radius growth, and reduction in FTG distance associated with crop trees in the 

various treatment plots over the 20-year period. Th e initial three comparisons focused on the 

response of crop trees among the treatments while keeping the species separate. First, the d.b.h. 

growth of crop trees in the three CTM plots was compared to that observed in the Control 

plots. Second, the d.b.h. growth of the 10 sample crop trees was compared to that of all crop 

trees in the CTM plots, Area-wide Th inning plot, and Control plot. A third within-species 

result compared the d.b.h. growth associated with diff erent degrees of release, i.e., four-sided 

versus three-sided versus two-sided release. Th e fi nal two comparisons focused on the response 

of northern red oak relative to that of yellow-poplar. First, d.b.h. growth of the two species was 

compared for diff erent degrees of release in the treated plots. Second, crown measurements and 

FTG distances associated with the two species were compared in the CTM plots; only those 

crop trees that received a three- or four-sided release were analyzed.

RESULTS

Th e variable-radius sample points in each plot were measured before and after the harvest 

treatments and then again after 20 years to measure changes in stand density. In general, the 

basal area harvested in the CTM plots increased as the number of crop trees increased (Table 1). 

In the CTM Timber, Wildlife, and Aesthetics plot, where 21 crop trees per acre were released, 

the harvest removed 44 percent of the basal area. In the CTM Timber Only plot, where 32 

crop trees per acre were released, the harvest removed 67 percent of the basal area. Similar 

trends were observed for reductions in relative density. Th e harvest in the Area-wide Th inning 

Photo by Arlyn Perkey, U.S. Forest Service (retired)

Figure 5.—Harvested trees were pulled from the treatment plots with cable, and skidded out with a 

Cat® D4 and arch using perimeter roads to minimize damage to residual trees.
10

plot was prescribed to leave a residual relative density of 68 percent. Note that the CTM 

Timber, Wildlife, and Aesthetics plot, which had the lightest harvest of the CTM treatments, 

had the same residual relative density as that observed in the Area-wide Th inning treatment 

(Table 1). Although these treatments had similar eff ects on residual stand density, they diff ered 

in the degree of release around individual crop trees after treatment.

After treatment, the maximum basal area and relative density growth occurred in the CTM 

Timber and Wildlife plot, where 25 crop trees per acre were released (Table 1). Th e Control 

plot exhibited the lowest rate of basal area growth among the fi ve plots, and lower relative 

density growth than all the treatment plots except the CTM Timber, Wildlife, and Aesthetics 

plot. Relative density calculations diff er by species, whereas basal area calculations do not. Based 

on 20-year basal area growth, stand growth on all of the treated plots exceeded that observed in 

the Control plot. 

In the CTM treatment plots, an eff ort was made to provide the crop trees with a three- or 

four-sided release, and the average FTG rating was 3.7 (SE=0.1) for northern red oak and 3.6 

(SE=0.1) for yellow-poplar immediately after release (Tables 3 and 4). In some cases, two crop 

trees were located adjacent to each other, so they were released on only three sides. In most 

cases, however, crop trees were released on all four sides after the harvest operations. After 

20 years, crop trees in the CTM plots were still free to grow on at least one side. In the Areawide Th inning plot, the average FTG rating for both northern red oak (mean=2.4; SE=0.2) 

and yellow-poplar (mean=2.3; SE=0.2) indicated that crop trees in the CTM plots had about 

50 percent more growing space around their crowns after treatment. Th e canopy in the Areawide Th inning plot was nearly closed after 20 years, and the comparison crop trees had FTG 

ratings near zero in 2008. Comparison crop trees in the Control plot had FTG ratings near zero 

throughout the 20-year study period.

Th e degree of release provided to individual trees had a strong infl uence on d.b.h. growth 

response. Northern red oak crop trees in the CTM plots grew 6.5 (SE=0.2) inches in d.b.h. in 

20 years, compared to only 4.1 inches (SE=0.3) for comparison trees in the Control plot (Table 

3). Similarly, yellow-poplar crop trees in the CTM plots grew 5.0 (SE=0.1) inches in d.b.h. in 20 

years, compared to only 3.3 (SE=0.1) inches for comparison trees in the Control plot (Table 4).

After a four-sided release to a northern red oak (crop tree no. 111) and a three-sided release 

to a black cherry (crop tree no. 106), the CTM Timber and Wildlife plot had a more open 

appearance than before treatment (Figs. 6 and 7). After 20 years, the northern red oak grew 

from 17.6 inches to 24.0 inches d.b.h., the black cherry grew from 14.6 inches to 16.9 inches 

d.b.h., and the plot once again had a closed appearance (Fig. 8).

A “random sample” of 10 northern red oak and yellow-poplar crop trees in the CTM, Areawide Th inning, and Control plots was monitored to see how growth of a subset of trees would 

compare to the larger population of all trees in the study. Th e purpose was to determine 

whether a landowner could accurately monitor growth on a large number of crop trees by 

following a few sample trees. Th e growth of the sample trees was comparable to the larger 

population of crop trees for both species. For northern red oak, d.b.h. growth of the 10 sample 
11

Table 3.—Mean changes in free-to-grow (FTG) ratings and d.b.h. growth for northern red oak crop 

trees over a 20-year period. Standard errors are in parentheses.

Treatment Objective Plot N

1988 

FTG

2008 

FTG

1988 

d.b.h.

2008 

d.b.h.

20-yr 

d.b.h. 

Growth

------------------- inches -------------------

CTM Timber Only

(32 CT/ac ) 2 22 3.6 (0.1) 1.8 (0.2) 14.4 (0.5) 20.9 (0.7) 6.5 (0.3)

CTM Timber and 

Wildlife

(25 CT/ac) 1 15 3.8 (0.1) 1.3 (0.2) 14.9 (0.7) 21.5 (0.9) 6.6 (0.3)

CTM Timber, Wildlife, 

and Aesthetics

(21 CT/ac) 4 12 3.8 (0.1) 0.6 (0.2) 14.0 (0.7) 20.2 (1.0) 6.2 (0.4)

All CTM combined 2,1,& 4 49 3.7 (0.1) 1.4 (0.1) 14.4 (0.3) 20.9 (0.5) 6.5 (0.2)

CTM sample 2,1,& 4 10 3.8 (0.1) 1.6 (0.3) 15.2 (0.6) 22.0 (0.9) 6.8 (0.3)

Area-wide Thinning 3 20 2.4 (0.2) 0 (0.0) 14.2 (0.6) 19.4 (0.6) 5.2 (0.3)

Area-wide Thinning 

sample 3 10 2.9 (0.3) 0 (0.0) 15.1 (0.8) 19.9 (1.0) 4.8 (0.3)

Control 5 20 0.1 (0.1) 0 (0.0) 15.4 (0.5) 19.5 (0.8) 4.1 (0.3)

Control sample 5 10 0.1 (0.1) 0 (0.0) 15.2 (0.7) 19.2 (1.0) 4.0 (0.4)

Table 4.—Mean changes in free-to-grow (FTG) ratings and d.b.h. growth for yellow-poplar crop 

trees over a 20-year period. Standard errors are in parentheses.

Treatment Objective Plot N

1988 

FTG

2008 

FTG

1988 

d.b.h.

2008 

d.b.h.

20-yr 

d.b.h. 

Growth

------------------- inches -------------------

CTM Timber Only

(32 CT/ac ) 2 41 3.7 (0.1) 2.1 (0.1) 14.5 (0.4) 19.5 (0.4) 5.0 (0.1)

CTM Timber and 

Wildlife

(25 CT/ac) 1 23 3.5 (0.1) 1.4 (0.2) 15.9 (0.5) 20.8 (0.6) 4.9 (0.2)

CTM Timber, Wildlife, 

and Aesthetics

(21 CT/ac) 4 13 3.5 (0.1) 0.4 (0.1) 14.2 (0.4) 19.6 (0.5) 5.4 (0.2)

All CTM combined 2,1,& 4 77 3.6 (0.1) 1.6 (0.1) 14.9 (0.3) 19.9 (0.3) 5.0 (0.1)

CTM sample 2,1,& 4 10 3.8 (0.1) 2.1 (0.3) 15.4 (0.8) 20.5 (0.7) 5.1 (0.2)

Area-wide Thinning 3 25 2.3 (0.2) 0.3 (0.1) 14.2 (0.5) 17.8 (0.5) 3.6 (0.2)

Area-wide Thinning 

sample 3 10 3.0 (0.3) 0.2 (0.1) 15.6 (0.8) 19.5 (0.9) 3.9 (0.3)

Control 5 45 0.2 (0.1) 0 (0.0) 16.9 (0.4) 20.2 (0.4) 3.3 (0.1)

Control sample 5 10 0.5 (0.2) 0 (0.0) 15.3 (0.5) 18.4 (0.5) 3.1 (0.2)
12

Photo by Arlyn Perkey, U.S. Forest Service (retired) Photo by Arlyn Perkey, U.S. Forest Service (retired)

Figure 6.—In the CTM Timber and Wildlife plot in 1988, prior to release, the d.b.h. of northern red 

oak crop tree no. 111 (being measured) was 17.6 inches d.b.h.

Figure 7.—After a four-sided crown-touching release to tree no. 111, and a three-sided release to 

a 14.6-inch-d.b.h. black cherry crop tree (no. 106, fl agged on right), the stand has a more “open” 

appearance.

trees diff ered from that of the larger population by 5, 8, and 3 percent for the CTM plots 

(n=49), Area-wide Th inning plots (n=20), and Control plots (n=20), respectively (Table 3). 

For yellow-poplar, the diff erence in d.b.h. growth between the 10 sample trees and the larger 

population was 2, 8, and 6 percent for the CTM plots (n=77), Area-wide Th inning plots 

(n=25), and Control plots (n=45), respectively (Table 4). Th e largest diff erence in growth 
13

occurred in the Area-wide Th inning plot, where there was also a notable diff erence in the 

average FTG rating between the sample trees and the larger population.

Th e annual d.b.h. measurements on the crop trees and comparison trees clarifi ed how d.b.h. 

growth varied from year to year within a treatment plot and how d.b.h. growth was aff ected 

by the various treatments (Figs. 9 and 10). In general, northern red oak crop trees in the CTM 

plots grew faster than those in the Area-wide Th inning plot, and crop trees in all of the treated 

plots exhibited faster growth than that observed in the Control plot for most of the study period 

(Fig. 9). For yellow-poplar, d.b.h. growth was greatest from year to year in the CTM plots, 

but there were smaller diff erences between growth in the Area-wide Th inning and Control 

plots, particularly from year 10 to 20 (1998-2008) (Fig. 10). For both species, relatively faster 

d.b.h. growth was observed in 1993, 1995, 1998, and 2001, followed by relatively slower 

growth in 1994, 1996, 1999, and 2002. Such changes in annual d.b.h. growth, both positive 

and negative, appeared to be related to precipitation and unusual events because variations 

in growth exhibited similar year-to-year trends on all of the plots (Figs. 9 and 10). For 

example, the sharp decline in growth in 1994 and 1999 followed winter ice storms that caused 

signifi cant damage to tree crowns, and precipitation in 1999 was well below normal. Although 

precipitation in 1994, 1996, and 2003 appears to be greater than normal, most of the growingseason rainfall occurred in heavy storms in late July and August. Much of the rainfall was lost 

to runoff and had little impact on tree growth in otherwise relatively dry years. Moreover, the 

Presidents’ Day snowstorm in 2003 caused signifi cant crown damage that further reduced 

growth that year. A similar decline in growth occurred in 2007. A wet snow in October 2006 

occurred before the trees had dropped their leaves, and signifi cant crown damage led to slower 

tree growth the following summer.

Photo by Arlyn Perkey, U.S. Forest Service (retired)

Figure 8.—After 20 years, northern red oak crop tree no. 111 has grown 6.4 inches to 24.0 inches 

d.b.h.. Black cherry tree no. 106 has grown 2.3 inches to 16.9 inches d.b.h. Crown expansion has 

reduced the free-to-grow rating on both trees to 1. Mid-story crowns have expanded and the stand 

has a more “closed” appearance.
14

Figure 9.—Average annual d.b.h. growth for northern red oak and precipitation during the 

growing season from April through September.

Figure 10.—Average annual d.b.h. growth for yellow-poplar and precipitation during the growing 

season from April through September.

10

20

30

40

50

60

70

80

90

100

110

120

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Inches of precipitation

Inches d.b.h.

Year

Precipitation Timber Only

Timber and Wildlife Area

-

wide Thinning

Timber,Wildlife and Aesthetics Control

10

20

30

40

50

60

70

80

90

100

110

120

-0.1

-0.05

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0.4

0.45

Inches of precipitation

Inches d.b.h.

Year

Precipitation Timber Only

Timber & Wildlife Area-wide Thinning

Timber,Wildlife & Aesthetics Control
15

Faster growth in the treated plots was apparent in the fi rst year after treatment, while the 

maximum increase in growth occurred 3 or 4 years later. Faster d.b.h. growth on the treated 

plots continued for many years, followed by a general decline in d.b.h. growth on the treated 

plots after 2004 (the 16th year after treatment) as crown expansion of the crop trees and other 

residual trees led to signifi cant canopy closure. While crop trees on the CTM Timber Only 

plot had the highest FTG rating after 20 years, their d.b.h. growth declined in the last 5 years 

and appeared to be returning to pretreatment rates. In contrast, d.b.h. growth in the Control 

plot was consistent throughout the study period, averaging 0.21 (SE=0.02) inches per year for 

northern red oak and 0.17 (SE=0.01) inches per year for yellow-poplar. 

Th e diff erences in d.b.h. growth between the CTM plots and the Area-wide Th inning plot can 

be explained by diff erences in the degree of crown release these treatments provided to the crop 

trees. For both northern red oak and yellow-poplar, faster d.b.h. growth in the CTM plots was 

associated with a greater FTG rating after treatment compared to the Area-wide Th inning plot 

(Tables 3 and 4). In the CTM plots, all of the crop trees received a three- or four-sided release. 

In the Area-wide Th inning plot, the majority of comparison crop trees received a two-sided 

release and only a few received a three-sided release. When the growth response of crop trees 

is stratifi ed by degree of release, it is clear why growth was faster in the CTM plots (Fig. 11). 

For yellow-poplar, growth after a four-sided release exceeded that after a three-sided release and 

growth after a three-sided release exceeded that after a two-sided release. For northern red oak, 

growth after a four-sided release exceeded that observed after a three-sided release. Only 10 oaks 

received a two-sided release, and their growth was about the same as crop trees with a threesided release. Note that for each FTG rating, d.b.h. growth of northern red oak exceeded that of 

yellow-poplar (Fig. 11).

Th roughout the 55-year-old stand, yellow-poplar had grown faster than northern red oak for at 

least some of the time before the demonstration area was installed. Th is diff erence is refl ected 

in the larger initial average d.b.h. of yellow-poplar compared to northern red oak in 1988 

(Table 5) and was most pronounced on the Control plot. Th ese results are consistent with the 

more cool and moist conditions on this north-facing slope. Th ese more mesic conditions are 

0

1

2

3

4

5

6

7

8

43210

Inches

Free-to-grow rating

Northern red oak Yellow-poplar

N=49N=36N=22N=38N=10N=23

N=5

N=14N=18N=38

Figure 11.—Average 20-year d.b.h. growth by free-to-grow rating, with one standard error bar 

shown above each mean.
16

expected to favor yellow-poplar growth. However, the growth trend was reversed on all of the 

plots during the 20-year period from age 55 to 75. Northern red oak grew faster than yellowpoplar during our observation period. On the Control plot, yellow-poplar average d.b.h. still 

exceeded northern red oak average d.b.h. in 2008, but the diff erence had decreased from 1.5 

inches in 1988 to 0.7 inches in 2008 (an 0.8-inch shift in favor of northern red oak). On the 

CTM plots, the size advantage shifted from yellow-poplar to northern red oak: yellow-poplar 

was 0.5 inches larger than northern red oak in 1988 but 0.9 inches smaller in 2008 (a 1.4-inch 

shift in favor of northern red oak). Similarly, on the Area-wide Th inning plots, northern red 

oak and yellow-poplar had identical average diameters in 1988, but northern red oak averaged 

1.6 inches larger than yellow-poplar by 2008.

Crown measurements taken on 30 northern red oaks and 27 yellow-poplars in the CTM 

treatment plots provided information on crown radius growth of crop trees and changes in 

their degree of release. Initially, all of these crop trees were released on three or four sides. 

Immediately after the release treatment, the FTG distance around the crop tree crowns was 

larger for northern red oak, even though the oaks had a slightly larger crown radius compared 

to yellow-poplar (Table 5). Th e FTG distance declined faster around the northern red oak crop 

trees. Th e reduction in FTG distance over the 20-year study resulted from expansion of the 

crop tree crowns as well as expansion of the adjacent trees. About one-third of the reduction 

in FTG distance was due to expansion of the crop tree crowns. After release, both d.b.h. and 

crown radius of northern red oak crop trees grew approximately 23 percent and 50 percent 

faster, respectively, than those of yellow-poplar (Table 5).

Another result of the faster growth of northern red oak is a shift in species composition of 

the largest trees in the demonstration area (Table 6). Th e 1988 species mix of the largest 20 

percent of the trees by d.b.h. was compared to the 2008 species mix of the same number 

of trees. In the CTM and Area-wide Th inning plots, the species mix of the largest trees has 

shifted in favor of northern red oak (Table 6). In the Control plot, it has remained the same. 

Table 5.—D.b.h. growth, crown radius growth, and changes in free-to-grow (FTG) distance for 

crop trees released on three or four sides in the CTM plots. Standard errors are in parentheses.

Species N

d.b.h.

1988

d.b.h.

2008

d.b.h. 

Growth 

Crown

radius

1988

Crown

radius

2008

Crown 

radius 

growth

FTG 

distance

1988

FTG 

distance

2008

FTG 

distance

reduction

------- in. ------- in./yr ------- ft ------- ft/yr ------- ft ------- ft/yr

NRO 30 14.7 

(0.5)

21.0 

(0.7)

0.32 

(0.01)

11.5 

(0.5)

17.7 

(0.7)

0.3 

(0.02)

22.4 

(1.8)

3.3 

(0.6)

- 1.0 

(0.1)

YP 27 15.0 

(0.5)

20.1 

(0.4)

0.26 

(0.01)

10.6 

(0.5)

14.6 

(0.5)

0.2 

(0.02)

21.2 

(1.4)

4.8 

(0.7)

- 0.8 

(0.1)

Table 6.—Species composition of the largest 20 percent of trees by d.b.h. within each 

treatment plot

Treatment Plot(s) N 1988 species mix 2008 species mix

All CTM combined 2,1,& 4 24 13 YP 11 RO 10 YP 14 RO

Area-wide Thinning 3 7 4 YP 3 RO 2 YP 5 RO

Control 5 17 13 YP 4 RO 13 YP 4 RO
17

Changes in both the average tree size and the number of trees of each species indicate that the 

treatments have accelerated this shift in size dominance from yellow-poplar to northern red 

oak. It is also interesting to note that in 1988 the two largest trees on the demonstration area 

were yellow-poplars that measured 22.5 inches d.b.h.. One was located in the Control plot 

and one was located on the CTM Timber and Wildlife plot. By 2008, the two largest trees on 

the demonstration area were northern red oaks, one measuring 30.3 inches d.b.h. in the CTM 

Timber and Wildlife plot, and the other measuring 29.0 inches d.b.h. in the CTM Timber 

Only plot.

While it was not an objective of this demonstration area to compare the dynamic relationship 

between yellow-poplar and northern red oak during the 20-year period, the growth 

measurements provide an opportunity to observe what has happened during this late-rotation 

stage of stand development (age 55 to 75). Annual basal area growth acceleration ratios were 

compared for northern red oak and yellow-poplar (Fig. 12). Average basal area growth rates for 

crop trees released on three or four sides in the CTM plots were divided by the average basal 

area growth rates in the Control plot for each year during the study period. An acceleration 

growth ratio greater than 1 indicates that the released crop trees grew faster than the unreleased 

comparison trees. Yellow-poplar growth acceleration ratios exceeded or matched those of 

northern red oak during the fi rst 10 years after treatment. Th e reverse was true during the 

second 10 years. Note that the growth acceleration ratios of both species declined to equal 

nearly 1 at the end of the 20 years. A comparison of d.b.h. growth between northern red 

oak and yellow-poplar also illustrates how the oaks grew faster for the latter part of the study 

(Fig. 13).

Th e eff ect of maintaining crown release to accelerate the development of large trees in a shorter 

time is exemplifi ed by two northern red oaks on the CTM Timber Only plot (Fig. 14). At age 

55, one was 18.0 inches d.b.h. while an adjoining crop tree was 18.4 inches d.b.h.. In the fi rst 

55 years, they had attained almost the same size. In 1989, the larger tree was released on four 

0.0

0.5

1.0

1.5

2.0

2.5

3.0

Ratio

Year

Northern red oak Yellow-poplar

Figure 12.—Average basal area growth acceleration ratio.
18

0

0.1

0.2

0.3

0.4

0.5

Inches

Year

Northern red oak Yellow-poplar

Figure 13.—Comparison of average annual d.b.h. growth of northern red oak (n=49) and 

yellow-poplar (n=77) for crop trees released on three or four sides in the CTM plots.

Figure 14.—Landowners interested 

in growing big trees in less time 

should maintain a high FTG rating 

around crop trees. The northern 

red oak in the foreground grew 

10.6 inches d.b.h. as its FTG 

rating declined from 4 to 3 in 20 

years. The northern red oak in the 

background grew only 6.9 inches 

d.b.h. as its FTG rating declined 

from 3 to 1 in 20 years. The two 

trees were nearly the same size 

in the CTM Timber Only plot when 

they were released in 1989.

Photo by Arlyn Perkey, U.S. Forest Service (retired)
19

sides and was still free to grow on three sides 20 years later. Th e smaller tree was released on 

three sides, but it was free to grow on one side after 20 years. Th e tree with more release grew 

10.6 inches in d.b.h. in 20 years, while the tree with less release grew only 6.9 inches.

No crown ratio measurements were taken before or after release. However, photographs taken 

immediately after release and about 6 years later reveal the change in crown ratio following 

crown-touching release on northern red oak crop trees (Figs. 15 and 16). Two northern red 

oaks (tree nos. 59 and 60) began with a relatively small crown ratio immediately after treatment 

(Fig. 15) and then developed wider and deeper crowns by the sixth year after treatment (Fig. 

16).

Damage to crop trees from logging wounds was measured in terms of area of exposed sapwood. 

Approximately 20 percent of the crop trees had some visible wounds, but most of those wounds 

were less than 50 in2 in size. Such small wounds tend to form callous tissue and grow closed 

rapidly, especially on trees that have been released and are growing vigorously (Smith et al. 

1994).

Assessing regeneration was not a goal for the demonstration area, so no regeneration 

measurements were taken at the beginning of the 20-year period. Th e approximately 8 acres 

of treatment area were surrounded by forest that had not experienced recent canopy-opening 

disturbance. Consequently, when sunlight penetrated the canopy of the treatment area, 

stimulating understory growth, it became an exceptional food source for deer. Th is disturbed 

“island” off ered far more opportunity for deer browsing than did the surrounding closedcanopy woods.
20

Figure 16.—At the end of six additional growing seasons (October 1995), the live crowns of these 

same two trees were deeper, presumably producing more food and, consequently, more growth.

Photo by Arlyn Perkey, U.S. Forest Service (retired)

Figure 15.—This photo of northern red oak trees nos. 59 and 60 was taken in October 1989 at the 

end of the fi rst growing season following release.

Photo by Arlyn Perkey, U.S. Forest Service (retired)
21

DISCUSSION

After 20 years of measuring trees, monitoring tree growth, and showing the area to visitors, 

what has been learned?

In the fi rst few years after the demonstration area was installed, some visitors to the CTM 

Timber Only plot commented that the harvest seemed too heavy to be considered a form 

of thinning (Perkey and Onken 2000). Th e plot contained 32 crop trees per acre that had 

been released on three or four sides and the residual basal area was only 43 ft2/ac (Table 1). 

Indeed, the residual relative density was only 35 percent, somewhat more characteristic of a 

heavy shelterwood harvest to promote rapid growth of advanced reproduction or even a heavy 

diameter-limit harvest where all the merchantable trees were removed. However, the CTM 

Timber Only plot diff ered from other traditional harvests because the residual stand contained 

the largest and best quality trees available. Th e residual stand after traditional harvests would 

not have had as many high quality trees ready to expand their crowns and increase their growth. 

After 20 years, basal area had reached 105 ft2/ac, and the basal area growth was 3.1 ft2/ac/yr, 

similar to that of the Area-wide Th inning plot (Table 1). Th e most notable result in the CTM 

Timber Only plot was that it exhibited faster d.b.h. growth on a greater number of timber crop 

trees than any other plot on the demonstration area. Th e treatment in the CTM Timber Only 

plot may not have looked like a traditional thinning immediately after harvest, but it was indeed 

a “thinning”: it concentrated growth on the best timber trees in the stand and it promoted a 

future stand that is now fully stocked with large, high quality northern red oak and yellowpoplar crop trees ready for fi nal harvest.

Although the initial focus in applying CTM principles is on retaining crop trees for the future, 

some crop trees will eventually be harvested and some crop trees may be retained indefi nitely. 

Crop trees in the demonstration area were retained for 20 years for the benefi t of students and 

visitors, but in real-world applications of CTM, many of those crop trees can now be harvested 

to provide revenue for the landowner. Similar to other investments, timber crop trees eventually 

reach a fi nancial maturity when it becomes advisable to harvest those trees and allow other trees 

with greater earning power to replace them. Even wildlife and/or aesthetic crop trees may be 

harvested in the future if their removal is necessary to enhance the growth of a new generation 

of crop trees for the future. Applying CTM principles involves both short-term and long-term 

planning; thus it is important to remember that many, if not all, crop trees may eventually be 

removed in later harvests.

In 1988, the 55-year-old forest in the demonstration area had just entered the commercially 

operable stage of development. Average potential crop tree size was 14 inches, with some 

trees as large as 22 inches d.b.h.. In stands like the demonstration area, the harvests in the 

Area-wide Th inning and the CTM Timber, Wildlife, and Aesthetics plots would not have 

been commercially operable because the harvested trees were too small and the total harvested 

volume was too low to attract a buyer. Instead of waiting until the stand grows more volume 

and can be thinned appropriately, the landowner often consents to some form of a diameterlimit harvest whereby all the trees large enough to yield a logging profi t are removed (Fajvan et 

al. 1998). Th e diameter-limit harvest yields immediate revenue, but it also removes all of the 

best growing stock trees such that future stand development is sacrifi ced. A better alternative 
22

would be to apply a harvest based on CTM principles so that modest revenue is possible, while 

retaining the best growing stock for the future. Th e CTM Timber Only and CTM Timber 

and Wildlife treatments produced enough harvest volume to be commercially operable in 

local markets because they removed more than half of the initial basal area. Th e short-term 

income would not be as great as with a traditional diameter-limit harvest, but the treatment 

would promote the largest and highest quality crop trees for a future harvest and provide the 

landowner with other non-timber woodland benefi ts.

Our observations over 20 years confi rmed that the degree of crown release aff ected both the 

magnitude and duration of faster d.b.h. growth exhibited by individual crop trees (Figs. 9 and 

10). Northern red oak and yellow-poplar crop trees were released on three or four sides in 

the CTM plots, while comparison trees in the Area-wide Th inning plots received less release 

and those in the Control plots received no release at all. Crop trees grew fastest on the CTM 

plots, followed by those in the Area-wide Th inning plot; those in the Control plots exhibited 

the slowest d.b.h. growth throughout the 20-year period (Tables 3 and 4). Th e diff erence in 

d.b.h. growth between crop trees in the treated plots and comparison trees in the Control 

plot was greatly reduced during the last 4 years, probably due to a reduction in free growing 

space around the released crop trees. Crown expansion of both crop trees and their neighbors 

gradually led to closure of canopy gaps around the crop trees and a return to growth rates 

similar to unreleased comparison trees (Table 5). A study of 12- to 16-year-old crop trees 

(Miller 2000) showed that those released on three or four sides required 8 years of growth to 

reach crown closure. In this 55-year-old stand, growth reduction associated with crown closure 

did not occur until about 16 years after release. Th is older stand, with larger crop trees and 

larger competitors, required about twice as much time to refl ect growth reduction because of 

crown closure following treatment.

Although the release treatments generally accelerated the growth of crop trees, there were 

periods of lower d.b.h. growth due to abiotic factors such as crown damage from winter storms 

and irregular amounts of precipitation during the growing season (Figs. 9 and 10). Annual 

d.b.h. growth also fl uctuated because of a biotic factor in the form of defoliation of yellowpoplar by the yellow-poplar weevil (Odontopus calceatus [Say] ) in 1993 and 1994. Defoliation 

averaged about 20 percent in those years, as evidenced by a drop in annual d.b.h. growth in 

1994 (Fig. 10). Crop tree crowns recovered from the defoliation in 1995, and d.b.h. growth 

returned to that observed in years before the weevil defoliation. 

Th e ups and downs observed in annual d.b.h. growth were consistent in all treatment plots in 

any given year. Th e average annual d.b.h. growth for northern red oak and yellow-poplar crop 

trees in each treatment plot is also presented in Tables 7 and 8. In general, crop trees with more 

free growing space exhibited greater d.b.h. growth than those with less growing space, even in 

years where annual d.b.h. growth fl uctuated up or down. It was apparent from this observation 

that the crown-touching release was an eff ective means of maintaining faster d.b.h. growth, even 

in years when weather conditions or biotic factors might otherwise have had a more negative 

eff ect on growth.

Yellow-poplar crop trees were larger than northern red oak when the stand was 55 years old 

and the demonstration area was installed. Obviously, yellow-poplar had grown faster than 
23

Table 7.—Average annual d.b.h. growth of northern red oak crop trees by treatment. 

Standard errors are in parentheses.

Year

Timber 

Only

(n=22)

Timber and 

Wildlife

(n=15)

Timber, Wildlife, 

and Aesthetics 

(n=12)

All CTM 

(n=49)

Area-wide 

Thinning

(n=20)

Control

(n=20)

1989 .25 (.02) .28 (.03) .29 (.03) .27 (.01) .25 (.02) .19 (.02)

1990 .24 (.03) .21 (.02) .18 (.03) .21 (.02) .19 (.02) .18 (.02)

1991 .27 (.02) .29 (.03) .37 (.04) .30 (.02) .25 (.02) .21 (.02)

1992 .27 (.02) .35 (.03) .36 (.03) .32 (.02) .27 (.02) .20 (.02)

1993 .40 (.03) .41 (.03) .37 (.03) .39 (.02) .36 (.03) .25 (.03)

1994 .31 (.03) .36 (.04) .28 (.03) .32 (.02) .26 (.02( .13 (.02)

1995 .39 (.03) .40 (.02) .41 (.03) .40 (.02) .31 (.02) .30 (.03)

1996 .41 (.02) .40 (.02) .33 (.03) .39 (.01) .29 (.02) .17 (.02)

1997 .35 (.02) .31 (.02) .37 (.02) .34 (.01) .21 (.02) .21 (.02)

1998 .36 (.03) .37 (.03) .36 (.04) .36 (.02) .32 (.03) .25 (.03)

1999 .27 (.02) .27 (.02) .33 (.02) .28 (.01) .23 (.01) .16 (.02)

2000 .43 (.03) .43 (.03) .34 (.03) .41 (.02) .30 (.02) .26 (.02)

2001 .43 (.03) .42 (.03) .38 (.03) .42 (.02) .31 (.02) .22 (.02)

2002 .36 (.03) .38 (.03) .31 (.03) .35 (.02) .27 (.03) .20 (.02)

2003 .34 (.02) .36 (.01) .31 (.03) .34 (.01) .26 (.02) .18 (.02)

2004 .36 (.03) .36 (.01) .31 (.03) .35 (.02) .26 (.02) .22 (.02)

2005 .26 (.02) .26 (.02) .29 (.03) .27 (.01) .25 (.01) .20 (.02)

2006 .23 (.03) .25 (.03) .22 (.03) .23 (.02) .21 (.02) .15 (.02)

2007 .27 (.03) .28 (.03) .23 (.03) .26 (.02) .20 (.02) .22 (.03)

2008 .25 (.02) .21 (.03) .23 (.02) .23 (.01) .25 (.03) .22 (.02)

Sum 6.45 6.60 6.27 6.44 5.25 4.12

Mean .32 .33 .31 .32 .26 .21

northern red oak for at least some of that time. From age 55 to 75, however, northern red 

oak grew faster than yellow-poplar in both the Control and treated plots (Tables 3 and 4). 

Both species exhibited signifi cantly faster d.b.h. growth after treatments were applied, but the 

increase in growth for northern red oak exceeded that of yellow-poplar (Fig. 13). Observations 

of comparison tree d.b.h. growth in the Control plot indicated that the forest in the general 

vicinity of the demonstration area had reached the stage in stand development described by 

Oliver (1977) during which the oaks begin to dominate neighboring species. Th e crowntouching release treatments, and to some degree the Area-wide Th inning, further enhanced the 

growth of northern red oak compared to yellow-poplar on this growing site. Forest managers 

could apply crown release treatments to the oak crop trees in mixed-species stands as a means of 

sustaining oaks in the upper canopy for many decades (Rentch et al. 2009). In addition, many 

family forest owners enjoy the aesthetic appearance of relatively large trees (Singer and Lorimer 

1997). Family forest owners are likely to understand and accept CTM treatments that result 

in larger trees in a shorter period of time. Promoting large trees of both northern red oak and 

yellow-poplar on the same site further enhances the production of multiple woodland benefi ts 

such as timber value, wildlife food, and species diversity, and reduces the risk from insect and 

disease attack associated with single-species forests.

Slight differences in average 20-year growth also shown in Table 3 are due to rounding.
24

Hard mast production was not monitored during the 20-year period. Consequently, we do 

not have a direct measurement to show an increase in seed production benefi cial to wildlife. 

However, acorns are grown on the perimeter of live crowns where the vegetation is exposed to 

direct sunlight. Th e expansion of live crown area for species like northern red oak indicates that 

released crop trees will be able to produce greater quantities of food for wildlife (Figs. 14 and 

15). During the 20-year period, northern red oak crowns that received a crown-touching release 

on three or four sides, expanded their crown area by 2.4 times while yellow-poplar expanded 

their crowns by 1.9 times (Table 5). Th is greater rate of crown area expansion for the oaks 

means that wildlife species will likely benefi t from greater acorn production in the future.

Some existing wildlife dens in the CTM Timber Only plot and the Area-wide Th inning plot 

were lost when trees containing them were harvested, while existing den trees in the CTM 

Timber and Wildlife plot were retained because they were explicitly marked as crop trees. 

When wildlife shelter is important for meeting landowner goals, the criteria for selecting crop 

trees should include potential den trees so that they are identifi ed and protected during the 

commercial harvest operation. Although den trees may not receive a crown-touching release, as 

is the case for timber crop trees, they should be marked with paint like the other crop trees so 

that loggers can avoid damaging them.

Table 8.—Average annual d.b.h. growth of yellow-poplar crop trees by treatment. Standard 

errors are in parentheses.

Year

Timber 

Only

(n=41)

Timber and 

Wildlife

(n=23)

Timber, Wildlife, 

and Aesthetics 

(n=13)

All CTM 

(n=77)

Area-Wide 

Thinning

(n=25)

Control

(n=45)

1989 .21 (.01) .20 (.02) .22 (.02) .21 (.01) .14 (.01) .15 (.01)

1990 .20 (.02) .17 (.02) .28 (.03) .20 (.01) .14 (.02) .11 (.01)

1991 .32 (.02) .37 (.02) .37 (.02) .34 (.01) .26 (.02) .21 (.01)

1992 .21 (.01) .23 (.02) .30 (.03) .23 (.01) .12 (.02) .11 (.01)

1993 .31 (.01) .27 (.02) .33 (.02) .31 (.01) .20 (.01) .16 (.01)

1994 .23 (.01) .22 (.02) .28 (.02) .23 (.01) .16 (.01) .10 (.01)

1995 .39 (.01) .39 (.02) .41 (.02) .39 (.01) .26 (.02) .28 (.02)

1996 .25 (.01) .23 (.02) .24 (.03) .24 (.01) .14 (.01) .09 (.01)

1997 .28 (.01) .28 (.02) .35 (.02) .29 (.01) .18 (.01) .16 (.02)

1998 .30 (.01) .28 (.02) .32 (.03) .29 (.01) .24 (.01) .21 (.01)

1999 .18 (.01) .18 (.02) .18 (.02) .18 (.01) .13 (.01) .13 (.01)

2000 .26 (.01) .27 (.02) .25 (.02) .26 (.01) .18 (.01) .18 (.01)

2001 .32 (.01) .30 (.02) .35 (.02) .32 (.01) .25 (.02) .24 (.01)

2002 .23 (.01) .24 (.02) .26 (.02) .24 (.01) .19 (.02) .15 (.01)

2003 .24 (.01) .27 (.02) .25 (.02) .25 (.01) .19 (.02) .20 (.01)

2004 .30 (.01) .28 (.02) .27 (.02) .29 (.01) .21 (.01) .21 (.01)

2005 .25 (.01) .26 (.02) .25 (.03) .25 (.01) .18 (.01) .20 (.01)

2006 .18 (.01) .20 (.02) .22 (.02) .19 (.01) .17 (.01) .16 (.01)

2007 .15 (.01) .12 (.02) .15 (.01) .14 (.01) .06 (.01) .13 (.02)

2008 .22 (.01) .18 (.02) .12 (.03) .19 (.01) .18 (.02) .18 (.02)

Sum 5.03 4.94 5.40 5.04 3.58 3.36

Mean .25 .25 .27 .25 .18 .17

Slight differences in average 20-year growth also shown in Table 4 are due to rounding.
25

Some crop trees that exhibited attractive fall foliage were retained and their crowns were 

released to promote crown expansion. Crown expansion was not measured for aesthetic crop 

trees, but subjective visual observations during the fall in the CTM Timber, Wildlife, and 

Aesthetics plot confi rmed that the aesthetic crop trees survived and produced more attractive 

fall foliage than before the CTM treatment. In cases where the forest manager wishes to 

enhance the attractiveness of a landscape viewed from a fi xed observation point, CTM can be 

applied to promote a desired mix of species and their associated fall colors. 

Th e abundance of white-tailed deer (Odocoileus virginianus) in the surrounding area had a 

profound infl uence on the species composition of advanced reproduction that developed in 

the CTM Timber Only and CTM Timber and Wildlife plots. Th e harvests were relatively 

heavy in these plots, with residual basal areas equal to 43 ft2/ac and 60 ft2/ac, respectively. 

Such heavy disturbance to the overstory tends to increase the availability of sunlight on the 

forest fl oor, stimulating the germination of stored seed and enhancing the growth of existing 

seedlings. While establishing or releasing regeneration was not a goal at the demonstration 

area, an important observation was noted. Because browse was more available in the harvested 

plots than in the surrounding forest, browsing pressure by white-tailed deer was heavy. Stump 

sprouts of preferred species like northern red oak, yellow-poplar, and red maple were repeatedly 

nipped back to the stump until it died. Species lower on the browse preference list, like black 

cherry, had favorable conditions to develop advanced reproduction on the forest fl oor. Even 

though black cherry occupied only 7 percent of the initial overstory basal area, the advanced 

reproduction in the understory was eventually dominated by black cherry seedlings and 

saplings. Additional treatments may be needed before the overstory is removed to prepare for 

successful regeneration of other desired species (Brose et al. 2008).

Photo by U.S. Forest Service

Figure 17.—This demonstration area provides an opportunity for family forest owners and 

foresters who serve them to see how alternative treatments might appear.
26

One lesson from the CTM demonstration area was quite valuable: the show-and-tell example 

plots made complex ideas associated with forestry and ecology easy to communicate to visitors 

(Fig. 17). Th e CTM concept was easy for landowners and forest management professionals to 

understand because they could readily grasp the eff ectiveness of identifying and promoting the 

development of individual crop trees. Instead of trying to absorb the complexities of tending 

hundreds of trees per acre, visitors saw fi rsthand how the same job could be accomplished 

by applying a simple crown-touching release to a fairly small number of trees per acre. Th e 

demonstration area also provided visible examples of crop trees that provide specifi c benefi ts 

such as timber value, wildlife food, wildlife shelter, spring fl owers, or beautiful fall colors. 

In some cases, an individual crop tree off ered multiple desired benefi ts. Th e layout of the 

demonstration area further provided an enjoyable, informative “classroom.” Visitors to the 

demonstration area were able to see several variations of CTM and Area-wide Th inning within 

a short walking distance, thus allowing visual reinforcement of key concepts and plenty of 

time for questions and answers within a 1- to 2-hour visit. Many visitors have returned to the 

demonstration area for a self-guided tour using the Trail Guide (Perkey and Wilkins 2005) to 

enhance their understanding of CTM concepts during diff erent seasons of the year. Songbirds 

in spring, lush foliage in summer, brilliant color in autumn, and shining snow in winter add to 

a more complete understanding of how CTM can enhance a family forest.

ACKNOWLEDGMENTS

Th is 22-year project has benefi ted from the eff orts of many individuals. First, the late Clay 

Smith, long-time co-worker and former Northeastern Forest Experiment Station Project 

Leader, was a key partner from the beginning. Much of the success of this project is attributable 

to his wisdom, experience, and way of bringing a variety of people together to accomplish a 

task. Other early participants from the Fernow Experimental Forest include Robert Rosier, 

Richard Hovatter, Brian Simpson, the late Roy Poling, the late Lee Long, and Alan Myers. 

More recent participants from the Northern Research Station include Regis Young, John 

Juracko, Drew Cantis, and Toni Jones. From the Northeastern Area State and Private Forestry, 

we thank Brenda Wilkins (retired), Amy Hill, Roxane Palone (retired), Nancy Lough (retired), 

Helen Wassick, Frank Cromer, and Karen Sykes. From the West Virginia Division of Forestry, 

we thank Andrew Dick, Rodger Ozburn, and Lowell McPherson (retired). From West Virginia 

State Parks, we thank Al Kerns and his staff . From West Virginia University, we thank graduate 

student Jonathan Marden. We also thank Jeff Ward, David Mercker, and John Stanovick for 

helpful review comments.

LITERATURE CITED

Brose, P.H.; Gottschalk, K.W.; Horsley, S.B.; Knopp, P.D.; Kochenderfer, J.N.; McGuinness, 

B.J.; Miller, G.W.; Ristau, T.E.; Stoleson, S.H.; Stout, S.L. 2008. Prescribing regeneration 

treatments for mixed-oak forests in the mid-Atlantic region. Gen. Tech. Rep. NRS-33. 

Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research 

Station. 90 p.

Carvell, K.L.; Perkey, A.W. 1997. Using diagnostic plants to evaluate site class. NA-TP-03-

97. Morgantown, WV: U.S. Department of Agriculture, Forest Service, Northeastern Area, 

State and Private Forestry. 28 p.
27

Fajvan, M.A.; Grushecky, S.T.; Hassler, C.C. 1998. Th e eff ects of harvesting practices on 

West Virginia’s wood supply. Journal of Forestry. 98(5): 33-39.

Hurlbert, S.H. 1984. Pseudoreplication and the design of ecological fi eld experiments. 

Ecological Monographs. 54(2): 187-211.

Lamson, N.I.; Rosier, R.L. 1984. Wires for long-term identifi cation of trees. Journal of 

Forestry. 82: 110-111.

Marquis, D.A.; Ernst, R.L.; Stout, S.L. 1992. Prescribing silvicultural treatments in 

hardwood stands of the Alleghenies (revised). Gen. Tech. Rep. NE-96. Radnor, PA: U.S. 

Department of Agriculture, Forest Service, Northeastern Forest Experiment Station. 101 p.

Miller, G.W. 2000. Eff ect of crown growing space on the development of young hardwood 

crop trees. Northern Journal of Applied Forestry. 17(1): 25-35.

Miller, G.W.; Stringer, J.W.; Mercker, D.C. 2007. Technical guide to crop tree release in 

hardwood forests. Southern Regional Extension Forestry publication SREF-FM-011. [Place 

of publication unknown]: Southern Regional Extension Forestry. Available at http://www.

sref.info/resources/publications/ 24 p. (Accessed June 28, 2011).

Oliver, C.D. 1977. Reconstruction of a mixed-species forest in central New England. 

Ecology. 58(3): 562-572.

Perkey, A.W.; Onken, A. 2000. A decade at a crop tree demonstration area. Forest 

Management Update. 20: 1-13.

Perkey, A.W.; Wilkins, B.L. 2001. Crop tree fi eld guide-selecting and managing crop trees 

in the central Appalachians. NA-TP-10-01, Morgantown, WV: U.S. Department of 

Agriculture, Forest Service, Northeastern Area, State and Private Forestry. 140 p.

Perkey, A.W.; Wilkins, B.L. 2005. Trail guide—Coopers Rock Crop Tree Demonstration 

Area. NA-FR-01-05. Morgantown, WV: U.S. Department of Agriculture, Forest Service, 

Northeastern Area, State and Private Forestry. 36 p.

Perkey, A.W.; Wilkins, B.L.; Smith, H.C. 1994. Crop tree management in eastern 

hardwoods. NA-TP-19-93. Morgantown, WV: Northeastern Area, State and Private 

Forestry. 112 p.

Rentch, J.S.; Miller, G.W.; Gottschalk, K.W. 2009. Crown class dynamics of oaks, yellowpoplar, and red maple after commercial thinning in Appalachian hardwoods: 20-year 

results. Northern Journal of Applied Forestry. 26(4): 156-163.

Rodd, J.S. 1994. A guide to Coopers Rock State Forest-featuring trail guides, area history & 

ecology, & more. Moatsville, WV: Barn Echo Press. 80 p.
28

Singer, M.T.; Lorimer, C.G. 1997. Crown release as a potential old-growth restoration 

approach in northern hardwoods. Canadian Journal of Forest Research. 27: 1222-1232.

Smith, H. C.; Miller, G. W.; Schuler, T. M. 1994. Closure of logging wounds after 10 

years. Res. Pap. NE-692. Radnor, PA: U.S. Department of Agriculture, Forest Service, 

Northeastern Forest Experiment Station. 6 p.
Printed on Recycled Paper

The U.S. Department of Agriculture (USDA) prohibits discrimination in all its programs and activities on 

the basis of race, color, national origin, age, disability, and where applicable, sex, marital status, familial 

status, parental status, religion, sexual orientation, genetic information, political beliefs, reprisal, or because 

all or part of an individual’s income is derived from any public assistance program. (Not all prohibited 

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of program information (Braille, large print, audiotape, etc.) should contact USDA’s TARGET Center at 

(202)720-2600 (voice and TDD). To fi le a complaint of discrimination, write to USDA, Director, Offi ce 

of Civil Rights, 1400 Independence Avenue, S.W., Washington, DC 20250-9410, or call (800)795-3272 

(voice) or (202)720-6382 (TDD). USDA is an equal opportunity provider and employer. 

Perkey, Arlyn W.; Miller, Gary W.; Feicht, David L. 2011. Coopers Rock Crop Tree 

Demonstration Area—20-year results. Gen. Tech. Rep. NRS-83. Newtown 

Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research 

Station. 28 p.

During the 1988/1989 dormant season, the Coopers Rock Crop Tree Demonstration 

Area was established in a 55-year-old central Appalachian hardwood forest in northcentral West Virginia. After treatment, 89 northern red oak (Quercus rubra L.) and 

147 yellow-poplar (Liriodentron tulipifera L.) crop trees were monitored for 20 years. 

This report summarizes the growth in diameter at breast height (d.b.h.) and crown 

development of crop trees from age 55 to 75 after they received various degrees 

of crown release resulting from crop tree management and traditional area-wide 

thinning. Annual d.b.h. growth response is presented to illustrate the year-to-year 

fl uctuations in growth that occurred throughout the demonstration area. In general, 

d.b.h. growth response and crown expansion were related to the degree of crown 

release. Northern red oak exhibited a greater response in d.b.h. growth and crown 

expansion than did yellow-poplar over the 20-year study period.

KEY WORDS: crop tree management, northern red oak, yellow-poplar, crown 

expansion, growth, central Appalachian
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