United States

Department of

Agriculture

Forest Service

Southern 

Research Station

Research Paper

SRS–53 

Early Pruning Affects 15-Year 

Growth of Cottonwood Planted 

at 40- by 40-Foot Spacing

James S. Meadows and Roger M. Krinard
Authors:

James S. Meadows, Principal Silviculturist, and 

Roger M. Krinard, Mensurationist (deceased), 

U.S. Department of Agriculture Forest Service, 

Southern Research Station, Stoneville, MS 38776. 

January 2013

Southern Research Station

200 W.T. Weaver Blvd.

Asheville, NC 28804

www.srs.fs.usda.gov
Early Pruning Affects 15-Year 

Growth of Cottonwood Planted 

at 40- by 40-Foot Spacing

James S. Meadows and Roger M. Krinard

Abstract

We compared the growth of eastern cottonwood (Populus deltoides Bartr. 

ex Marsh.) trees planted at 40- by 40-foot spacing and subjected to four 

pruning treatments from the 2nd through the 8th year of growth. Treatments 

were (1) no pruning, (2) prune to one-third of total height annually, (3) 

prune to one-half of total height annually, and (4) prune to 17 feet when 

diameter at breast height (d.b.h.) exceeded 8.5 inches, which occurred in 

the 4th year. Diameter and height measurements were taken annually for 15 

years. By age 15, average diameters differed significantly among all four 

treatments and ranged from 16.8 inches (half-height pruning) to 19.8 inches 

(no pruning). Pruning had no effect on total height, which averaged 110 feet 

across all treatments. Total sawtimber volume differed significantly among 

treatments and ranged from 3,921 board feet (Doyle) per acre (half-height 

pruning) to 6,919 board feet (Doyle) per acre (no pruning). In widely 

spaced cottonwood plantations, pruning is not recommended if pulpwood 

production is the sole objective of management, but is necessary if quality 

sawtimber production is the primary objective of management. The mean 

d.b.h. of unpruned trees planted at 40- by 40-foot spacing represents the 

maximum potential diameter achievable for cottonwood and can serve as a 

benchmark for comparison to diameters observed at narrower spacings.

Keywords: Bole quality, eastern cottonwood, growth, plantation 

management, pruning, wide spacing.

INTRODUCTION

Diameter growth of eastern cottonwood (Populus deltoides

Bartr. ex Marsh.) in plantations is restricted by competition 

from other cottonwood trees. The age at which competition 

begins and the intensity of competition depend on the initial 

spacing of the plantation, site characteristics, moisture 

availability, and the genetics of the planting stock. At initial 

spacings ranging from 4 by 9 feet to 16 by 18 feet, maximum 

diameter growth of cottonwood occurred in the first 4 years 

after plantation establishment (Krinard and Johnson 1975). 

Initial spacing is thus an important consideration in plantation 

management of cottonwood because it ultimately influences 

both tree size and rotation length, whether pulpwood or 

sawtimber production is desired.

However, the influence of competition on crown 

development and diameter growth of cottonwood 

established at a very wide spacing may be minimal. 

Diameter growth under conditions of minimal competition 

may identify the maximum potential diameter increment 

achievable for cottonwood and could serve as an upper 

limit for comparison to diameter growth observed at other 

spacings. A very wide initial spacing also may identify 

the minimum rotation length required for production 

of sawtimber or veneer logs, or both. Widely planted 

cottonwood trees would need to be pruned, however, to 

maintain clear boles and improve stem quality.

This study was initiated to compare growth of cottonwood 

trees planted at 40- by 40-foot spacing and to evaluate the 

effects of different pruning treatments on growth. Early 

results were reported by Krinard (1979, 1985).

METHODS

The study was established on batture land (unprotected by 

levees) at Huntington Point in western Bolivar County, MS. 

The land is within the floodplain of the Mississippi River 

and was owned by Chicago Mill and Lumber Company at 

the time of plantation establishment. Soil type is Commerce 

silt loam (fine-silty, mixed, superactive, nonacid, thermic 

Fluvaquentic Endoaquept). Site index for cottonwood 

was estimated to range from 105 to 125 feet at 30 years 

(Broadfoot 1976).

The 9-acre study site was cleared in 1971, fallowed in 1972, 

and planted in 1973. However, the Mississippi River flood 

of 1973 destroyed the plantation and it was replanted in 

January 1974. A matrix of 16 rows by 16 columns provided 

256 planting spots. Spacing between planting spots was 40 

by 40 feet. Three 18-inch cuttings of select Stoneville clone 

66 (Land 1974) were planted at each spot and thinned to one 

tree per spot in June 1974.

Study design was a randomized complete block with four 

replications of four treatments. Each treatment plot per 

replication consisted of 4 rows by 4 columns, for a total of 

16 trees. This 16-tree plot (0.588 acres) was considered to be 

the experimental unit.

Disking was performed several times each year to control 

weeds during the first five growing seasons. The site was 

tilled in July of the sixth growing season to help eliminate 

ruts. Annual weed control thereafter was by mowing.

Pruning treatments were applied from the 2nd through the 

8th years: (1) no pruning (control), (2) prune to one-third 

of total height annually (third-height pruning), (3) prune to 
 2

one-half of total height annually (half-height pruning), and 

(4) prune to 17 feet when diameter at breast height (d.b.h.) 

exceeded 8.5 inches, which first occurred in the 4th year (17-

foot pruning).

Trees were pruned by hand from a boom-mounted ladder 

attached to a small bulldozer. Pruning was completed 

during the dormant season after the 2nd through the 5th years, 

delayed until early July due to flooding after the 6th year, and 

completed in early May after the 7th and 8th years. Epicormic 

sprouts were removed monthly from the 2nd through the 

5th years, but were removed only at the time of pruning in 

subsequent years.

Total height and d.b.h. of each tree were measured annually 

for 15 years. Maximum crown diameter in the north-south 

and east-west directions for all trees and diameters outside 

bark at 9, 13, and 17 feet on four trees per treatment plot were 

measured after the 5th and 10th years. Crown diameter and 

upper-stem diameter data were reported by Krinard (1985).

Board-foot volume estimations were obtained from 

dendrometer measurements taken on two trees per treatment 

plot during the 9th growing season and after the 14th growing 

season. Data were combined to produce the following volume 

equation for trees ≥ 12.5 inches d.b.h. to a minimum top 

diameter of 10 inches:

VDOYLE = -85.1 + 0.008090D2H r2 = 0.98 sy,x = 11.9

where

VDOYLE = volume, in board feet (Doyle scale)

D = d.b.h., in inches

H = total height, in feet

Analysis of variance for a randomized complete block 

design was used to detect differences among treatments 

in d.b.h., annual diameter increment, total height, and 

annual height increment for each of the 15 years of the 

study. Sawtimber volume and annual sawtimber volume 

increment were analyzed for the 10th through the 15th years 

only. Significance tests were conducted at the 0.05 level of 

probability. Treatment effects were considered fixed; block 

effects were considered random. Duncan’s New Multiple 

Range Test was used to separate treatment means. Plot 

averages used in the analyses included all trees except 4 

trees that were replanted after the 1st year and 22 trees that 

suffered broken tops during the first 6 years.

RESULTS AND DISCUSSION

Effects of Pruning on Growth

Mean d.b.h. was significantly affected by pruning treatments 

from the 3rd through the 15th years (table 1). Throughout 

most of this period, all treatments were significantly 

different from each other. Significant differences among 

pruning treatments in mean annual diameter increment 

actually began in the 2nd year and continued through the 

6th year, with significant differences also found in the 8th

and 15th years (table 2). These early reductions in diameter 

growth as a result of pruning were maintained throughout 

the remainder of the study (fig. 1). Annual diameter 

increment generally declined from the 2nd and 3rd years 

through the 8th year, but was nearly constant thereafter (fig. 

2). Mean annual diameter increment of unpruned trees 

(control) and trees not yet pruned (17-foot pruning) peaked 

during the 3rd year, whereas mean annual diameter increment 

of trees pruned at the end of the 2nd year (third-height 

Table 1—Mean d.b.h., by year and pruning treatment, of cottonwood planted at 40- by 40-foot spacing; means within a 

column followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

inches

Control 1.1 a 4.0 a 7.2 a 9.6 a 11.4 a 13.0 a 14.0 a 14.8 a 15.5 a 16.4 a 17.1 a 17.8 a 18.4 a 18.9 a 19.8 a

Third-height pruning 1.1 a 4.1 a 6.9 b 8.9 b 10.3 c 11.6 c 12.5 c 13.2 c 13.9 c 14.7 c 15.4 c 16.0 c 16.5 c 17.2 b 17.9 c

Half-height pruning 1.1 a 3.8 a 6.3 c 8.1 c 9.2 d 10.4 d 11.4 d 12.0 d 12.6 d 13.4 d 14.2 d 14.8 d 15.4 d 16.1 c 16.8 d

17-foot pruning 1.1 a 4.1 a 7.3 a 9.6 a 10.9 b 12.2 b 13.2 b 14.0 b 14.7 b 15.5 b 16.3 b 17.0 b 17.6 b 18.2 a 18.9 b

Overall average 1.1 4.0 6.9 9.1 10.5 11.8 12.8 13.5 14.2 15.0 15.7 16.4 17.0 17.6 18.4

Table 2—Mean annual diameter increment, by year and pruning treatment, of cottonwood planted at 40- by 40-foot spacing;

means within a column followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 2 3 4 5 6 7 8 9 10 11 12 13 14 15

inches

Control 2.9 a 3.2 a 2.4 a 1.7 a 1.5 a 1.0 a 0.9 a 0.7 a 0.8 a 0.7 a 0.7 a 0.6 a 0.6 a 0.9 a

Third-height pruning 3.0 a 2.8 b 2.0 b 1.4 b 1.2 b 0.9 a 0.7 b 0.7 a 0.8 a 0.7 a 0.6 a 0.6 a 0.6 a 0.8 b

Half-height pruning 2.7 b 2.4 c 1.8 b 1.1 d 1.2 b 0.9 a 0.6 b 0.6 a 0.8 a 0.8 a 0.7 a 0.6 a 0.7 a 0.7 b

17-foot pruning 3.0 a 3.2 a 2.4 a 1.3 c 1.2 b 1.0 a 0.8 a 0.7 a 0.8 a 0.8 a 0.7 a 0.6 a 0.6 a 0.8 b

Overall average 2.9 2.9 2.2 1.4 1.3 1.0 0.8 0.7 0.8 0.7 0.7 0.6 0.6 0.8
 3

Figure 1—Mean d.b.h., by year and pruning treatment, of cottonwood planted at 40- by 40-foot spacing.

Figure 2—Mean annual diameter increment, by year and pruning treatment, of cottonwood planted at 

40- by 40-foot spacing.
 4

pruning and half-height pruning) peaked during the 2nd year 

and declined thereafter.

Pruning had no effect on either total height (table 3) or mean 

annual height increment (table 4) at any time during the 

course of the study. Consequently, data for both variables 

were averaged across all treatments. Height growth was 

very rapid and mean total height reached 100 feet by age 11 

(fig. 3). Mean annual height increment actually peaked in 

the 4th year, but remained high through the 5th year (fig. 4). 

It gradually declined from the 5th through the 12th years and 

was nearly constant thereafter.

Sawtimber volume differed significantly among treatments 

from the 10th through the 15th years (table 5). Early 

differences among treatments in diameter growth as a 

result of pruning eventually translated into differences in 

sawtimber volume, and these differences were maintained 

through later years (fig. 5). Mean annual sawtimber volume 

increment also differed significantly among treatments in 

most years (table 6). Annual volume growth fluctuated from 

year to year and among treatments, but generally averaged 

from 500 to 900 board feet (Doyle) per acre (fig. 6).

The cottonwood clone used in this study was classified as a 

select clone primarily because of rapid early growth when 

planted at close spacings (Mohn and others 1970). Other 

cottonwood clones with different rates of growth and crown 

development may respond differently at wide spacings, but 

similar data for other clones are not available.

During the period of maximum diameter growth (within 

the first 5 years), pruning treatments had a negative effect 

on diameter growth. Because pruning reduced the length 

of the crown and therefore reduced the amount of foliage 

on the tree, total photosynthate production by the tree 

also was reduced and diameter growth was diminished. 

When pruning was discontinued, mean annual diameter 

increment recovered, but the early effects of pruning on tree 

diameter persisted for the remainder of the study. In other 

words, trees that had smaller diameters as a result of early 

pruning continued to have smaller diameters many years 

after pruning was discontinued, even though mean annual 

diameter increment no longer was affected.

Unpruned cottonwood trees in this study were larger and 

contained more sawtimber volume than pruned trees, 

but logs in the unpruned trees exhibited very low quality 

because of the large number of limbs retained on the bole. 

In fact, logs in the unpruned trees likely will be marketed as 

pulpwood rather than as sawtimber due to the large number 

of defects on the bole.

The decision to prune or to not prune cottonwood trees 

planted at very wide spacings depends on the goals of 

management. If the sole objective of management is 

pulpwood production, pruning is not recommended. The 

unpruned trees in this study were significantly larger and 

contained more volume than the pruned trees. Thus, pruning 

is not necessary to achieve the management objective 

of maximum fiber production in the shortest period of 

time. However, if the primary objective of management is 

sawtimber production, pruning of trees planted at very wide 

spacings is necessary to produce quality sawlogs.

However, annual pruning over several years probably is 

not economically feasible. In this study, a one-time pruning 

to a height of 17 feet when d.b.h. exceeded 8.5 inches 

Table 3—Mean total height, by year and pruning treatment, of cottonwood planted at 40- by 40-foot spacing; means within a 

column followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15

feet

Control 10 a 24 a 37 a 50 a 62 a 72 a 81 a 84 a 91 a 95 a 101 a 103 a 105 a 107 a 109 a

Third-height pruning 11 a 24 a 36 a 50 a 62 a 72 a 80 a 84 a 92 a 96 a 102 a 104 a 106 a 110 a 112 a

Half-height pruning 11 a 23 a 35 a 48 a 60 a 67 a 77 a 81 a 88 a 92 a 99 a 100 a 102 a 106 a 108 a

17-foot pruning 11 a 24 a 36 a 50 a 62 a 70 a 80 a 82 a 91 a 96 a 102 a 104 a 106 a 108 a 111 a

Overall average 11 24 36 50 62 70 80 83 90 94 101 103 105 108 110

Table 4—Mean annual height increment, by year and pruning treatment, of cottonwood planted at 40- by 40-foot spacing;

means within a column followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 2 3 4 5 6 7 8 9 10 11 12 13 14 15

feet

Control 13.2 a 13.2 a 12.8 a 12.6 a 9.1 a 9.4 a 3.0 a 7.0 a 4.0 a 6.1 a 2.0 a 2.0 a 2.0 a 2.1 a

Third-height pruning 12.9 a 12.4 a 13.9 a 12.3 a 9.4 a 8.8 a 3.9 a 7.7 a 3.6 a 6.3 a 2.0 a 2.1 a 3.5 a 2.0 a

Half-height pruning 12.4 a 11.8 a 13.3 a 11.6 a 7.6 a 9.6 a 3.8 a 7.4 a 3.7 a 6.9 a 1.7 a 2.0 a 4.0 a 1.9 a

17-foot pruning 13.4 a 12.2 a 13.3 a 12.4 a 8.2 a 9.7 a 3.0 a 7.9 a 4.5 a 6.4 a 1.8 a 2.3 a 2.3 a 2.3 a

Overall average 13.0 12.4 13.3 12.2 8.6 9.4 3.4 7.5 4.0 6.4 1.9 2.1 3.0 2.1
 5

Figure 4—Mean annual height increment, by year, of cottonwood planted at 40- by 40-foot spacing.

Figure 3—Mean total height, by year, of cottonwood planted at 40- by 40-foot spacing.
 6

Table 5—Mean sawtimber volume, in board feet (Doyle) per acre, for the 10th through the 15th years, by 

pruning treatment, of cottonwood trees ≥12.5 inches d.b.h. to a 10-inch top; means within a column

followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 10 11 12 13 14 15

Control 3172 a 4048 a 4744 a 5338 a 5970 a 6919 a

Third-height pruning 2142 b 2915 b 3450 b 3990 b 4686 b 5406 b

Half-height pruning 1075 c 1736 c 2192 c 2749 c 3426 c 3921 c

17-foot pruning 2716 ab 3632 ab 4241 ab 4840 ab 5554 ab 6362 ab

Overall average 2276 3083 3657 4229 4909 5652

Figure 5—Mean sawtimber volume (Doyle) for the 10th through the 15th years, by pruning treatment, of 

cottonwood planted at 40- by 40-foot spacing.

(which occurred during the 4th year) resulted in the least 

adverse effect on mean d.b.h. by age 15 years. This pruning 

treatment did not significantly reduce mean sawtimber 

volume per acre, when compared to the unpruned control. 

However, numerous epicormic branches were produced 

along the lower bole of trees subjected to this one-time 

pruning at the end of the 4th year. Because the spacing 

between trees was very wide, most of the epicormic 

branches persisted and were still on the lower bole at 

the end of the 15th year. Consequently, the quality of the 

butt log on trees that received this pruning treatment was 

low. Additional pruning operations subsequent to the one 

performed at the end of the 4th year would be necessary to 

maintain a clear butt log.

A potentially attractive silvicultural option to optimize 

diameter growth, sawtimber volume growth, and the 

production of clear sawlogs may be to prescribe a series of 

two or more pruning operations designed to produce a clear 

bole to a height of 33 feet at the end of the second pruning. 

The first operation prunes the lower 17 feet of the bole when 

mean d.b.h. of the trees exceeds 8.5 inches. In our study, this 

threshold was reached by the end of the 4th year. Pruning to 

a height of 17 feet created a clear bole length that accounted 

for 34 percent of total tree height. The second operation 

prunes the lower 33 feet of the bole when the proportion of 

clear bole length to total tree height again would be about 

35 percent after pruning. In our study, this threshold would 

have been reached by the end of the 10th year. At this point, 

total tree height averaged 94 feet. Pruning to a height of 

33 feet would create a clear bole length that accounts for 

35 percent of total tree height. A third pruning operation to 

remove epicormic branches produced on the lower 33 feet 

of the bole may or may not be necessary.

Maximum Potential Diameter and its Relation 

to Other Initial Spacings

A second objective of this study was to identify the 

maximum potential diameter achievable for cottonwood on 

a good site under conditions of minimal competition. The 
 7

cottonwood trees established at the 40- by 40-foot spacing 

experienced little competition from adjacent trees, such 

that crown development and diameter growth essentially 

were unimpeded over the course of the first 15 years after 

plantation establishment. In this sense, the mean d.b.h. of 

the unpruned trees in this study represents the maximum 

potential diameter achievable for cottonwood on similar 

sites, and can serve as a benchmark for comparison to 

diameters observed at narrower spacings.

Krinard and Johnson (1984) compared diameter growth 

over a 20-year period of cottonwood trees planted at four 

different initial spacings: 4 by 9 feet, 8 by 9 feet, 12 by 12 

feet, and 16 by 18 feet. The plantation was established on a 

bottomland site on Commerce silt loam soil (the same soil 

series found in our study) near Fitler in Issaquena County, 

MS. Although site index was not measured directly in our 

study or in the Krinard and Johnson (1984) study, Broadfoot 

(1976) estimated site index for cottonwood on Commerce 

silt loam to range from 105 to 125 feet at 30 years. Because 

Commerce silt loam is the dominant soil series at both 

locations, we believe that the two sites are similar in site 

quality for cottonwood.

We used data from the unthinned plots in the Krinard 

and Johnson (1984) study to calculate mean d.b.h. of the 

cottonwood trees planted at each of the four initial spacings 

at the end of the 4th through the 15th years after plantation 

establishment. The mean d.b.h. values for each of the four 

initial spacings in that study then were compared to the 

mean d.b.h. values observed for the unpruned cottonwood 

trees at corresponding ages in our study. These comparisons 

are expressed as percentages of the maximum potential 

diameters achievable for cottonwood at ages 4 through 15 

years and are presented in figure 7.

Initial spacing clearly has a strong and persistent effect on 

growth and development of cottonwood plantations on good 

sites (fig. 7), a consequence that has been reported many 

times for a wide variety of species (Clark and others 2010, 

DeBell and Harrington 2002, Kennedy 1993, Reukema and 

Smith 1987). Our intention, however, was not only to verify 

Figure 6—Mean annual sawtimber volume (Doyle) increment for the 10th through the 15th years, by 

pruning treatment, of cottonwood planted at 40- by 40-foot spacing.

Table 6—Mean annual sawtimber volume increment, in board feet (Doyle) per acre, for the 10th through 

the 15th years, by pruning treatment, of cottonwood trees ≥12.5 inches d.b.h. to a 10-inch top; means

within a column followed by the same letter are not significantly different at the 0.05 level of probability

Year

Pruning treatment 10 11 12 13 14 15

Control 759 a 876 a 696 a 594 a 632 a 949 a

Third-height pruning 620 b 773 b 535 b 540 a 696 a 720 b

Half-height pruning 559 b 661 c 456 c 557 a 677 a 495 c

17-foot pruning 718 a 916 a 609 ab 599 a 714 a 808 ab

Overall average 664 806 574 572 680 743
 8

this effect, but also to quantify the degree to which initial 

spacing limits growth and development of cottonwood 

plantations. We express the influence of initial spacing as 

the percentage of maximum potential diameter achieved 

by cottonwood planted at the four initial spacings reported 

by Krinard and Johnson (1984). To illustrate, mean d.b.h. 

of cottonwood trees planted at the two narrow spacings 

(4 by 9 feet and 8 by 9 feet) ranges from 31 to 37 percent 

and from 41 to 46 percent, respectively, of the maximum 

potential diameter achievable for cottonwood at ages 4 

through 15 years on good sites (fig. 7). Development of 

these cottonwood plantations is limited greatly by the 

narrow initial spacings. The influence of initial spacing 

on plantation development is somewhat less severe for 

cottonwood trees planted at the two wider spacings (12 by 

12 feet and 16 by 18 feet), where mean d.b.h. ranges from 

51 to 55 percent and from 58 to 63 percent, respectively, of 

maximum potential diameter (fig. 7).

The extent to which initial spacing limits growth and 

development of cottonwood plantations established at the 

four spacings evaluated by Krinard and Johnson (1984) 

remains relatively constant over time, at least through the 

first 15 years after plantation establishment (fig. 7). The lack 

of fluctuation within each of the lines depicted in figure 7 

gives the illusion that plantation development is a stable and 

steady process. On the contrary, plantation development is 

a very dynamic and volatile process that results in many 

changes in stand density and structure over time.

The rapidity of these changes is especially pronounced in 

young cottonwood plantations. Because cottonwood is an 

inherently fast-growing species (Putnam and others 1960), 

individual trees in a plantation, except those established at 

very wide spacings, begin to experience severe competition 

from adjacent trees during the early stages of plantation 

development. Because cottonwood is a very shade-intolerant 

species (Baker 1949), individual cottonwood trees are not 

able to withstand severe competition for a long period of 

time. In general, small trees succumb quickly to severe 

competition and die in a short period of time. As severe 

competition becomes more widespread across the plantation, 

more and more trees die and the mortality rate increases 

sharply. When the majority of the trees that die have 

diameters smaller than the mean d.b.h. of the plantation 

as a whole, there is an immediate jump in the mean d.b.h. 

of the surviving trees. This process of self-thinning and 

the associated jump in mean d.b.h. likely contribute to the 

apparent ability of a cottonwood plantation to maintain a 

relatively stable relationship over time between its mean 

d.b.h. and the maximum potential diameter.

The onset of severe competition in cottonwood plantations 

established at narrow initial spacings occurs at a younger 

age and has a more detrimental effect than in plantations 

established at wide initial spacings. For example, the 

cottonwood plantation established at an initial spacing 

of 4 by 9 feet in the Krinard and Johnson (1984) study 

experienced a sharp increase in mortality rate during the 7th

year and exceeded 50 percent cumulative mortality during 

the 11th year. By the end of the 15th year after establishment, 

cumulative mortality was 75 percent, mean d.b.h. of the 

plantation was 7.4 inches, and mean sawtimber volume 

was only 890 board feet (Doyle) per acre. In contrast, the 

cottonwood plantation established at an initial spacing of 16 

by 18 feet in the Krinard and Johnson (1984) study did not 

Figure 7—Percentage of maximum potential diameter, by year, achieved by cottonwood planted at four 

different initial spacings. (Spacing data source: Krinard and Johnson 1984)
 9

suffer a large increase in mortality rate until the 14th year. By 

the end of the 15th year, cumulative mortality was only 24 

percent, mean d.b.h. was 12.1 inches, and mean sawtimber 

volume was 5,534 board feet (Doyle) per acre. If we use the 

unpruned portion of our cottonwood plantation established 

at an initial spacing of 40 by 40 feet as a benchmark for 

maximum production of cottonwood plantations on good 

sites, then maximum potential diameter at age 15 years 

is 19.8 inches and maximum potential sawtimber volume 

at the same age is 6,919 board feet (Doyle) per acre. 

Clearly, selection of the most appropriate initial spacing 

for management objectives is one of the most important 

decisions to be made prior to plantation establishment.

ACKNOWLEDGMENTS

We thank Chicago Mill and Lumber Company for providing 

the study site and for cooperation in all phases of the study. 

We specifically thank Robert C. Horton, of Chicago Mill 

and Lumber Company, for his assistance throughout this 

study. We also thank Tracy S. Hawkins and Michael G. 

Shelton for providing helpful suggestions on earlier drafts of 

this manuscript.

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and inventory of southern hardwoods. Agric. Handb. 181. 

Washington, DC: U.S. Department of Agriculture. 102 p.

Reukema, D.L.; Smith, J.H.G. 1987. Development over 25 years 

of Douglas-fir, western hemlock, and western redcedar planted 

at various spacings on a very good site in British Columbia. Res. 

Pap. PNW-RP-381. Portland, OR: U.S. Department of Agriculture 

Forest Service, Pacific Northwest Research Station. 46 p.
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Meadows, James S.; Krinard, Roger M. 2013. Early pruning affects 15-year growth 

of cottonwood planted at 40- by 40-foot spacing. Res. Pap. SRS–53. Asheville, NC: 

U.S. Department of Agriculture Forest Service, Southern Research Station. 9 p.

We compared the growth of eastern cottonwood (Populus deltoides Bartr. ex Marsh.) 

trees planted at 40- by 40-foot spacing and subjected to four pruning treatments from 

the 2nd through the 8th year of growth. Treatments were (1) no pruning, (2) prune 

to one-third of total height annually, (3) prune to one-half of total height annually, 

and (4) prune to 17 feet when diameter at breast height (d.b.h.) exceeded 8.5 inches, 

which occurred in the 4th year. Diameter and height measurements were taken 

annually for 15 years. By age 15, average diameters differed significantly among 

all four treatments and ranged from 16.8 inches (half-height pruning) to 19.8 inches 

(no pruning). Pruning had no effect on total height, which averaged 110 feet across 

all treatments. Total sawtimber volume differed significantly among treatments and 

ranged from 3,921 board feet (Doyle) per acre (half-height pruning) to 6,919 board 

feet (Doyle) per acre (no pruning). In widely spaced cottonwood plantations, pruning 

is not recommended if pulpwood production is the sole objective of management, but 

is necessary if quality sawtimber production is the primary objective of management. 

The mean d.b.h. of unpruned trees planted at 40- by 40-foot spacing represents the 

maximum potential diameter achievable for cottonwood and can serve as a benchmark 

for comparison to diameters observed at narrower spacings.

Keywords: Bole quality, eastern cottonwood, growth, plantation management, 

pruning, wide spacing.

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