United States

Department of

Agriculture Cottonwood Plantation

Forest Service

Southern Forest

Experiment Station

New Orleans,

Louisiana

Research Paper

so-21 2

December 1984

0

m1.1x11

Growth Through

20 Years

Roger M. Krinard and Robert L. Johnson

. .
._

SUMMARY ‘.‘*,, ‘L‘5,

At age 20 survival of unthinned cottonwood (Populus deltoides Bartr.

ex Marsh.) planted on medium-textured soil at spacings of 4 by 9, 8

by 9, 12 by 12, and 16 by 18 feet was 10, 17, 30, and 62 percent, and

average diameters were 10.6, 11.8, 12.6, and 13.7 inches, respectively.

Depending on spacing and diameter threshold, -cubic volume mean

annual increment peaked at ages 7 to 13. Thinning compared to no

thinning reduced cubic volume production. Thinned or unthinned plots

of 16- by l&foot spacing and heaviest thinning at 12 by 12 spacing

produced from 340 to 400 board feet per acre per year (Doyle) during

the 20 years in trees 2 12.0 inches to a lo-inch top. Other spacingtreatment combinations provided from 110 to 230 board feet per acre

per year.
Cottonwood Plantation Growth Through 20 Years . .

Roger M. Krinard and Robert L. Johnson

INTRODUCTION

Cottonwood is a valuable source of veneer,

lumber and pulp and the fastest growing tree

species in the South. From 1961 through the

mid-1970’s, an estimated 40,000 to 50,000 acres

of eastern cottonwood (Populus deltoides Bartr.

ex Marsh.) were planted in the lower Mississippi

River Valley (Burkhardt and Krinard 1976); however, the subsequent rate of planting has declined. Generally, initial tree spacings were 9 by

9 or 10 by 10 feet to accommodate traditional

farm equipment for first-year mechanical cultivation. At those spacings, trees were expected to

reach pulpwood size by the first thinning, require

no pruning, and provide adequate stocking if

two-thirds of the trees survived.

A study to compare the relationship of diameter and volume growth to initial spacing and

basal area control of stocking in cottonwood

plantations during the first 10 years (Krinard

and Johnson 1975) and the following 5 years

(Krinard and Johnson 1980) has been reported.

This final paper on the study provides a summary of previous work and additional information through age 20.

METHODS

The study was located on Crown Zellerbach

land outside the main Mississippi River levee

near Fitler, Mississippi, on medium textured

soils, mainly Commerce and Convent silt loams

(thermic family of Aeric Fluvaquents). Estimated

site indices of these soils, for natural cottonwood

stands, range from 105 to 125 feet at age 30

(Broadfoot 1976).

Standard 20-inch unselected cuttings obtained

from the Winona State Nursery and the company nursery at Fitler were planted in January

1963 at spacings of 4 by 9, 8 by 9, 12 by 12,

and 16 by 18 feet. Plots were about 250 feet

square, with a 144-foot square measurement plot

centered within each plot. .A randomized complete block design with four replications of four

spacings and four future thinning treatments

were planted; however, losses, primarily to deer,

reduced the planting to eight plots per spacing.

After the foudh year, plots were arrayed according to basal a+a within spacings, and thinning

treatments we&:. randomly assigned to the four

plots with the highest and lowest basal areas.

The study area had been in pasture for many

years and was pan-plowed 14 inches deep before

planting. Plots were disked during the first year

for weed control. After the: first year the plots

were only mowed in late summer through age

10.

Four thinning treatments were planned to reduce basal area per acre to 40, 65, 90, and 115

square feet whenever these levels were exceeded

by 15 square feet. The two plots per spacing to

be thinned to 115 square feet never reached that

level, were never thinned, and thus served as

checks. The two plots each of the 4 by 9 and 8

by 9 spacings were reduced from 105 square feet

to 50 square feet, rather than 90 square feet, because experience had shown lack of response to

thinning 15+ square feet from basal area levels

of 55+ and 80+ square feet.

.After 15 years, plots other than the check

plots were reduced to 46 trees per acre if they

were not already at least to that stocking level.

The reasoning was that after 15 years pulpwood

was not the major consideration, and the creation of sawlog growing conditions was needed.

Thinning was from below with spacing being

the major consideration after removing the obviously weak, poorly formed trees.

For spacings of 4 by 9 and 8 by 9, 55+ to 40

basal area thinnings were initiated at age 4

(average dbh 3.2 and 4.4 inches). The 80+ to 65

basal area thinnings began at age 5 (average

Roger M. Krinard is Mensurationist and Robert L. Johnson is Principal Silviculturist at the Southern Hardwoods Laboratory,

maintained at Stoneville, Mississippi, by the Southern Forest Experiment Station, Forest Service-USDA, in cooperation with

the Mississippi Agricultural and Forestry Experiment Station and the Southern Hardwood Forest Research Group.

1
dbh 3.8 and 5.2 inches). Thinnings were done

at 2- to 3-year intervals. The 105+ to 50 basal

area thinning was done after the 9th year (average dbh 5.4 and 6.0 inches).

For 12 by 12 spacing, 55+ to 40 thinnings began at age 5 (average dbh 7.0 inches), and the

8Ot to 65 thinnings began at age 8 (average dbh

7.9 inches), with from 2 to 4 years between thinnings. The 55t to 40 thinnings at 16-by 18-foot

spacing came at year 7 or 8 (average dbh 9.6

inches) and again at year 10 or 11.

From age 1 through 3, plots were sampled for

survival. From age 4 through 20, diameters of

all trees taller than 4.5 feet were measured with

calipers. Dominant tree heights were randomly

sampled after the 4th, 6th, 8th, lOth, 15th, and

20th years.

Sample tree volumes were obtained from cut

trees and from standing trees using a Barr and

Stroud dendrometer. The tree volumes were then

used in constructing local volume tables, with

l-inch dbh classes, for plot volume estimates. Merchantable cubic-foot volume was calculated for

volume outside bark in trees ~5.0 inches dbh to

a 4-inch top outside bark. Total volume was stem

volume outside bark to a total height for trees

?2.0 inches dbh. Board-foot volumes were obtained for trees >12.0 inches dbh to a lo-inch

upper diameter inside bark.

The study had two replications. Statistical comparisons were made among the unthinned plots

of the four spacings as they suffered no unusual losses through the 20 years. As some thinned

plots were lost to storm damage, no other statistical analyses were made.

RESULTS AND CONCLUSIONS

Figures 1 through 9 show trends over time for

check plots by spacings for survival, dbh, basal

area, and cubic- and board-foot volumes. Tables

1 through 4 provide 20-year average diameters

and total basal areas and volumes by spacings

for residuals, mortality, and thinnings.

Generally, the results show closer spacings lead

to longer planting times and more cuttings, earlier and greater mortality, smaller average

diameters, greater basal area mean annual increment (mai), .earlier and greater total volume

mai, and less board-foot production.

Specifically, the 4 by 9 spacing yielded many

small trees which did not reach merchantability,

whether through thinnings or mortality. This

spacing may be termed more aptly a fiber or

biomass spacing rather than a pulpwood spacing. Utilization of the majority of the trees from

the spacing would probably mean using both

bark and wood because of small tree sizes involved. Maximum total volume mai was produced, but by only 2 percent more than 8 by 9

spacing on 86 percent more trees. Average diameters of 6 and 8 inches were reached in12 and

16 years with survival of 40 and 18 percent. With

the inherent drawbacks in large tree numbers

and small sizes, plus first-year weed control

problems because of close spacing (too close for

cross disking), the 4 by 9 spacing has little to

offer the cottonwood grower.

The 8 by 9 spacing is a pulpwood spacing.

Two-thirds and three-fourths of the trees were 5.0

inches dbh or larger at peak mai for total (7th

year) and merchantable (9th year) volumes.

While maximum merchantable volume mai was

produced, it was only 6 percent more than 12

by 12 spacing ‘& 52 percent more trees ~5.0

inches dbh, plus‘aearly 80 more trees per acre

less than 5.0 inches. Fewer than 50 percent of

the cut trees in the heaviest thinning-to favor

better trees for potential sawtimber developmenthad reached .5.0 inches dbh. Doyle board-foot volume mai through 20 years was less than 235

board feet per acre per year. Average dbh’s of

6, 8, and 10 inches were reached at 8, 13, and

16 years when survival was 70, 44, and 27 percent, respectively.

The 12 by 12 spacing may be the best compromise of the spacings tried, and considered as

either a pulpwood spacing or a pulpwood and

sawtimber combination. The maximum merchantable volume mai was only 0.2-cord per acre per

year less than the 8 by 9 spacing. The heaviest

thinning, where nearly 90 percent of the cut trees

were of merchantable size, provided 350 Doyle

board feet per acre per year over 20 years. Average diameters of 6, 8, 10, and 12 inches were

reached in 5, 9, 14, and 18 years with survival

of 79, 75, 60, and 34 percent, respectively.

The 16 by 18 spacing provides a pulpwoodsawtimber combination, producing lowest maximum cubic volume mai’s but maximum Doyle

board-foot mai (fig. 10). The merchantable volume

peak mai was 8 percent less than 12 by 12

spacing and 14 percent less than 8 by 9 spacing in 56 and 137 percent fewer trees. Thinned

or unthinned plots produced from 340 to 400

board feet per acre per year-residual plus cutduring the 20 years. Average diameters of 6, 8,

10, and 12 inches were reached in 5, 7, 10, and

15 years, respectively, with survival of 90, 90,

88, and 76 percent.

Spacing influence on diameter and volume

growth over time may be analyzed by using the

38 largest trees per acre (to be comparable to

2
------------- ----\

---.-

---..

4x 9

I I

._ I

5 IO $ 15 20

AGE (YEARS) *;‘r

Figure l.-Survival of check plots.

,.;.,

I I I I 1

-4 5 IO 15 20

AGE (YEARS)

Figure 2.-Average dbh of all trees (d) and average dbh of largest 38 trees per acre at

age 20 (0) in check plots.
AGE (YEARS)

Figure 3.-Basal area of check plots. _

4,500

4,000

3,5oc

3,ooc

2 2,5OC

3

k

L

2,ooc

I ,5OC

l.OO(

5oc

/

I6 x 18

.’

/, I I 1

‘4 5 IO 15 2 0

AGE (YEARS)

Figure 4.-Total cubic volume for check plots.
^_

I I I I

‘ii: I

4 5 IO 15 .L. 2 0

AGE (YEARS)

Figure 5.-Mean annual increment of total cubic volume of check plots.

.%

4,00

3,50

3.00

2

::

& 2.50

h:

c

2.00

1.50

I,00

5 0

16 x I8

,--*

/

AGE (YEARS)

Figure 6.-Merchantable cubic volume for check plots.

5
6,00(

5.00(

2 4,OOC

F

s

? 3,OOC

2,OOC

I ,OO(

I I I I

.

I

4 5 IO 15 2 0

AGE (YEARS)

Figure 7.-Mean annual increment of merchantable cubic volume of check plots.

16 x 18

/

/”

:

/

.*

/

/”

:

I

12 x l2/

C .

0 IO I5 2 0

AGE (YEARS)

Figure K-Doyle board foot volume for check plots,

6

350

300 :

I

:

100

5 0

0

0 IO 15 2 0

AGE (YEARS)

Figure 9.-Mean annual increment of Doyle board foot

volume for check plots.
Table l.-Average dbh by spacings and thinning treatments at

age 20

Spacing

Thinning treatments

55+ to 80+ to 105+ to

40ft2/A 65 ft”/A 50 ft2/A 15 Check

feet inches

4x9 14.8 13.5 13.9 . 10.6

8x9 14.6 14.6 14.1 . 11.8

12x12 16.5 14.6 14.3 12.6

16x18 17.4 15.2 13.7

‘Thinned only at age 15 to 46 trees per acre. 155.9 159.1 161.4 163..5

Table 2.-Basal area per acre by spacings and thinning treatments for (1) age 20, (2) thinnings from age 4 through

age 15, and (3) mortality from ages 5 through 20

Thinning treatments

Spacing

55+ to 80+ to 105+ to ”

40 fF/A 65 ft2/A 50 ft’/A 15’ Check

feet

4x9

Age 20

cut

Mortality

8x9

Age 20

cut

Mortality

12x12

Age 20

cut

Mortality

16x18

Age 20

cut

Mortality

46.2 41.3 45.2 76.9

99.3 103.0 95.2

10.4 14.8 21.0 k6:6

46.7 51.4 50.9

78.4 96.4 90.4

13.1 7.0 9.7

-1’ 138.2 154.8 151.0 ‘I_

‘;

‘Yj7.5 50.4

58.3 63.6

13.4 9.5 . .

129.2 _ 123.5

79.2

. .

73.0

152.2

44.7 81.6

51.2

20.3 46.3

116.2 127.9

61.2 57.6 98.2

38.6 49.4

6.4 4.6 20.4

106.2 111.6 118.6

‘Thinned only at age 15 to 46 trees per acre.

Table 3.-Number of trees and volumes by dbh classes and unthinned spacings for age 20 and mortality from ages 5 through 20

Dbh classes (inches)

Spacing

(feet)

<2 2-4 5-11 12+ Total

N/A’ N/A ft3/A2 N/A ft”/A N/A ft3/A N/A ft”/A fbm/A,j

4x9

Age 20

Mortality

8x9

Age 20

Mortality

12x12

Age 20

Mortality

16x18

Age 20

Mortality

. 3.1 8 84.0 1884 32.6 1486 119.7 3378 2168

115.6 437.0 676 234.2 2075 . 786.8 2751 . .

115.6 440.1 684 318.2 3959 32.6 1486 906.5 6129 2168

. 2.1 6 55.6 1363 44.1 2193 101.8 3562 3493

24.2 130.3 226 210.1 2324 1.0 43 365.6 2593 63

24.2 132.4 232 265.7 3687 45.1 2236 467.4 6155 3556

. . . 1.0 3 34.7 951 54.6 2765 90.3 3719 4521

16.8 25.2 41 108.2 1598 4.2 152 154.4 1791 168

16.8 26.2 44 142.9 2549 58.8 2917 244.7 5510 4689

. . ‘4:2 “ 9 21.0 576 72.4 3916 93.4 4492 6832

3.2 27.3 482 8.4 321 43.1 812 430

3.2 4.2 9 48.3 1058 80.8 4237 136.5 5304 7262

‘Trees per acre.

Wubic-foot volume per acre.

3Doyle board-foot volume per acre.
Table 4.-Number of trees and volumes by dbh classes and spacings-by-thinning treatments for (1) age 20, (2)

thinnings from ages 4 through.15, and (3) mortality from ages 5 through 20

$L pacing Dbh classes (inches)

tft) and

thinning - 2 2-4 5-11 12+ Total

(ft”:A)‘ N/A’ N/A ft’/A” N/A ft’/A N/A ft”/A N/A ft”/A fbm/A”

4x9: 55+/40

Age 20

cut

Mortality

4x9: 80+/65

Age 20

cut

Mortality

4x9: 105+/50

Age 20

cut

Mortality

8x9: 55+>,40

Age 20

cut

Mortality

8x9: 80+/65

Age 20

Gut

Mortality

8x9: 105+ ‘50

Age 20

cut

Mortality

12x12: 55+/40

Age 20

cut

Mortality

12x12: 80+/65

Age 20

cut

Mortality

12x12:’

Age 20

cut

Mortality

16x18: 55+/40

Age 20

cut

Mortality

16x18:’

Age 20

cut

Mortality

.., 3.1 99 35.7 2045 38.8 2144 3948

161.8 647.0 687 198.5 1914 1.0 36 1008.3 2637 38

13.6 215 4.2 169 17.8 384 242

161.8 647.0 687 215.2 2228 40.9 2250 1064.9 5165 4228

5&4 $37

3.1 93 37.8 1765 40.9 1858 2566

129.2 230.0 2578 2.1 72 869.7 3287 76

52.5 11.6 23 29.4 345 4.2 150 97.7 518 164

181.7 520.0 660 262.5 3016 44.1 1987 1008.3 5663 2806

255:2 “’

5.2 165 36.8 1906. 42.0 2071 3164

13.6 430 253.2 2664 4.2 150. 526.2 3244 176

79.8 166.0 178 33.6 348 1.0 44 ‘!_ 280.4 570 63

93.4 421.2 608 292.0 3177 42.0 2100 _:> 848.6 5885 3403

28:4 244.8 “’ s;k

3.1 88 36.8 2076 39.9 2164 3803

209.0 1812 1.0 33 483.2 2163 30

10.5 245 7.4 264 17.9 509 313

28.4 244.8 318 222.6 2145 45.2 2373 541.0 4836 4146

. . . . . . 1.0 33 43.1 2360 44.1 2393 4178

23.1 167.0 239 238.4 2703 8.4 315 436.9 3257 405

10.5 3.1 3 14.7 170 2.1 78 30.4 251 95

33.6 170.1 242 254.1 2906 53.6 2753 511.4 5901 4678

2.1 55 44.1 2305 46.2 2360 3915

7.3 139.8 264 251.0 2673 5.2 179 403.3 3116 189

9.4 35.7 43 17.8 217 1.0 35 63.9 295 30

16.7 175.5 307 270.9 2945 50.3 2519 513.4 5771 4134

‘3:l 20.0 “’ “’ 29 151.3 1.0 1470 27 35.7 6.3

2654 36.7 2681 6768

228 180.7 1727 338

6.3 144 9.4 381 15.7 525 561

3.1 20.0 29 158.6 1641 51.4 3263 233.1 4933 7667

“’ 3.1 99 39.9 2201 43.0 2300 4022

3.1 28.4 54 129.2 1909 8.4 356 169.1 2319 594

3.1 5.2 7 12.6 265 2.1 83 23.0 355 120

6.2 33.6 61 144.9 2273 50.4 2640 235.1 4974 4736

2.1 66 37.8 2017 39.9 2083 3341

2.1 2.1 1 105.0 2031 . . 109.2 2032 . . .

10.5 23.1 29 56.7 525 4.2 156 94.5 710 191

12.6 25.2 30 163.8 2622 42.0 2173 243.6 4825 3532

. . . 36.8 2924 36.8 2924 7532

3.1 3.1 6 55.6 846 12.6 409 74.4 1261 458

1.0 2 2.1 33 4.2 221 7.3 256 473

3.1 4.1 8 57.7 879 53.6 3554 118.5 4441 8463

1.0 33 44.1 2611 45.1 2644 5114

1.0 3 41.0 853 27.3 1165 69.3 2021 1900

4.2 4.2 9 9.4 116 1.0 37 18.8 162 38

4.2 5.2 12 51.4 1002 72.4 3813 133.2 4827 7052

‘Trees per acre. ‘Cubic-foot volume per acre. ‘Doyle board-foot volume per acre.

‘Thinned only at age 15 to 46 trees per acre.

8

/’
thinned plots) in each unthinned plot after 20

years and comparing growth by 5-year periods.

The dbh growth differential between spacings

was greatest in the first 5-year period, but the

12 by 12 and 16 by 18 spacings did not differ

and were significantly greater (0.05 level) than

all other spacing-period combinations. During the

second 5-year period, growth of trees at the

widest spacing was greater than at the other

spacings. Spacings did not influence dbh growth

in either the third or fourth 5-year periods. Within spacings, each succeeding 5-year growth period

was less than the previous period except the

second and third period did not differ at 4 by 9

spacing. From 49 to 55 percent of the 20th-year

dbh, depending on spacing, was obtained by year

5.

For the three closer spacings, the upper basal

area limits ranged from about 105 to 115 square

feet per acre while peak cubic volumes per acre,

which occurred from ages 13 to 15, were slightly

better than 4000 cubic feet. Basal area-nearly

100 square feet per acre-and total cubic volumeabout 4500 cubic feet per acre-were maximum

at age 20 for 16 by 18 spacing.

Thinning, as done in this study, tended to reduce mortality if initiated by age 7 and generally gave largest average diameter at age 20 with

heaviest thinning. Compared to not thinning,

total basal area production-residual, cut, and

mortality-was similar or less while cubic volume

production was reduced.

Total heights of dominant/codominant trees at

age 20 averaged 106 feet for both unthinned and

thinned plots. Average height growth over the

last 5 years was only 6 feet. Prior growth of

tallest trees approximated 12 feet annually the

first 4 years, 8 feet annually during the next 4

years, and 3 feet annually for the next 7 years.

This was the first large-scale spacing-thinning

study with cottonwood in the Midsouth with a

management objective to produce veneer and

sawlog size trees along with intermediate products as they occurred on a maximum growth

rate basis. A rotation of 30 years was planned.

However, at the start of the 21st growing season a windstorm destroyed 120 trees, including

some of the largest, and the study was closed.

This was the fourth weather-related tree loss,

starting with flooding from the Mississippi River

in the 11th year and accompanying windthrow

and broken stems. Flooding increased incidence

of stem canker and possibility of future stem

breakage. Although this study may or may not

be representative of average storm-related damages, all cottonwood plantings in the batture

have the potential for flooding and accompanyFigure lo.- Unthinned, 20.year-old cottonwood planted at

16. by la-foot spacing with 58 percent survival,

13.6 inches average diameter, and 6,600 board

feet per acre, Doyle, to a lo-inch top dib.

ing problems. Thus, long-term, i.e., sawtimber,

plantations on these sites have a built-in risk

factor which may decrease yields.

Very rapid early diameter and height growth

characterize cottonwood plantings, with diameter

growth peaking in the third or fourth year regardless of spacing. Cottonwood, if it is to continue rapid growth, cannot tolerate side competition, so wide spacings or early thinnings at

close spacings prior to severe competition are

needed. Thinnings in this test, which removed

too few trees or occurred too late, may have

helped maintain growth of residual trees but did

not increase growth. There was no observable

response of crown growth into created openings.

An estimated 40 percent or more live crown ratio

is needed for good growth, as measured on dominant and codominant cottonwood in natural

stands (Johnson and Burkardt 1976).

The last 5 years of plantation development

added nothing to previous conclusions regarding

spacings for pulpwood production and for both

9
pulpwood and sawtimber production. To reiterate,

8 by 9 and 12 by 12 spacings are recommended

for pulpwood production. Volume mai peaked

from the 7th to 10th years, depending on spacing and merchantability limits. For pulpwood production, no thinnings are needed. The 12 by 12

and 16 by 18 spacings appear feasible for producing both pulpwood and sawtimber. A possible method of treating the spacings would involve one or two pulpwood thinnings, taking half

the trees at each thinning at about 60 square

feet of basal area, to put both spacings at a 24

by 24 spacing. .At least one sawtimber thinning,

when basal area reaches 80 to 100 square feet

per acre, should provide a final crop of about

38 trees with average dbh of 24 inches and 120

square feet of basal area. Rotation age to 24

inches is not precisely known.

In the publication based on the 15year results

of this study (Krinard and Johnson 1980), it was

estimated that thinned plots of the two widest

spacings might produce 23,000 board feet in 30

years, which would be similar to yields on unthinned natural stands found by Johnson and

Burkhardt (1976). The yield prediction assumed

an average dbh of 24 inches, merchantable

length of 3% logs, and 40 trees per acre. The

24-inch dbh figure assumed 15 and 16-inch trees

would grow 8 to 9 inches in 15 years, or 2.7 to

3.0 inches in 5 years. Unless the ever-decreasing

diameter growth rates were reversed-the same

trees surviving after 20 years in the thinned

plots of the two wider spacings grew 7.9, 3.8,

2.6, and 1.4 inches by &year growth intervalsthere would be no way for the trees to average

24 inches in 30 years. Even the two plots of the

16 by 18 spacing, which received the heaviest

thinning and have been stocked with 42 trees

per acre or less since the 12th growing season,

only grew 1.5 inches in the past 5 years. The

trees have room to grow but do not have the

crown development of dominant/codominant trees

of natural stands.

An obvious conclusion is that wider initial

spacings, with pruning for quality, should be

used where a sawtimber rotation of less than

30 years is the objective. Even wider spacing,

though taking advantage of very rapid early diameter growth, may not maintain that growth

for much longer intervals. For example, diameter growth of unpruned trees at 40 by 40 spacing (27 trees per acre) grew 5.0 inches from age

6 through 10 (unpublished data on file at the

Southern Hardwoods Laboratory, Stoneville,

Mississippi), but the 27 largest trees per acre in

the unthinned 16 by 18 spacing grew 4.2 inches

in the same period-less than an inch difference

in 5 years. The big difference, though, occurred

in the first 5 years when diameter growth of the

two spacings was 11.4 (Krinard 1979) and 8.0

inches.

For sawtimber production, is there a spacing

which would produce 24-inch trees with two high

quality logs in 20 years? Maybe, but unpruned

trees in the previously mentioned 40 by 40 spacing which were 16.4 inches in 10 years, were

growing 0.8 inch a year in the 8th through 10th

years. If that growth could be maintained for

10 years, 24-inch trees would be possible, but

limbs would make trees low in stumpage value.

.As pruning reduces diameter growth, 24-inch

trees in 20 years does not appear to be reasonable expectation over large areas. Assumptions,

based on extrapolation of growth of existing plantations and kno-w,n pruning effects on diameter

growth, indicate Z!8 by 28 to 32 by 32 spacing

may produce 20-&h trees and 11,000 to 12,000

board feet in 20 years and nearly 25-inch trees

and 21,000 to 22,000 board feet in 30 years.

Direct comparisons with European methods are

difficult. .Although their culture is much more intensive, an average guide for ‘good sites in the

PO River Valley in Italy showed 12.5-inch trees

in 15 years with 202 trees per acre (about 15-

foot spacing) and 18.2-inch trees in 20 years with

96 trees per acre (about 21-foot spacing) (Food

and Agriculture Organization of the United

Nations 1979).

Wider spacings provide less than full site utilization, require intensive pruning, and the trees

are still subject to flooding, wind damage, cankers, and insects. Because of the costs and risks

involved, cottonwood from planting may not be

suitable for long rotations for some landowners.

Either a change in utilization standards, so that

smaller trees and shorter rotations are feasible,

or higher stumpage values which would justify

higher management costs, or different management practices and/or clones, which would sustain early plantation growth, could change that

outlook.

The main factors favoring cottonwood plantings are the very rapid early growth and early

returns. Negative factors are high plantation establishment costs and, for sawtimber and veneer

logs, long-term weather risks, and lack of data

on alternative cultural methods and superior

clone performance in long rotation management.

LITERATURE CITED

Broadfoot, Walter M. Hardwood suitability for

and properties of important Midsouth soils.

Res. Pap. SO-127. New Orleans, LA: U.S. De10
partment of Agriculture, Forest Service, Southern Forest Experiment Station; 1976. 84 p.

Burkhardt, E. C.; Krinard, R. M. Summary of

the 1976 cottonwood plantation survey. In:

Thielges, Bart A., and Land, Samuel B., Jr.,

eds. and camps. Proc. Symposium on eastern

cottonwood and related species; 1976 September 28October 2; Greenville, MS; 1976:

428-431.

Food and Agriculture Organization of the United

Nations. Poplars and willows in wood production and land use. FAO Forestry Series

No. 10. Rome: International Poplar Commission; 1979. 328 p.

Johnson, R. L.; Burkhardt, E. C. Natural cottonwood stands-past management and implications for plantations. In: Thielges, Bart A.,

and Land, Samuel B., Jr., eds. and camps.

Proc. Symposium on eastern cottonwood and

related species; 1976 September 28-October 2;

Greenville, MS; 1976: 20-30.

Krinard, R. M. Five years’ growth of pruned and

unpruned cottonwood planted at 40- by 40-foot

spacing. Res. Note SO-252. New Orleans, LA:

U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station;

1979. 5 p.

Krinard, R. M.; Johnson, R. L. Ten-year results

in a cottonwood plantation spacing study.

Res. Pap. SO-106. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station; 1975. 10 p.

Krinard, R. M.; Johnson, R. L. Fifteen years of

cottonwood.,plantation growth and yield.

South. J. App& For. 4(4): 180-185; 1980.

IL

11

Krinard, Roger M.; Johnson, Robert L. Cottonwood plantation growth through 20 years. Res. Pap. SO-212.

New Orleans, LA: U.S. Department of Agriculture,

Forest Service, Southern Forest Experiment Station;

1984.11 p.

Twenty-year summary of a cottonwood study that

compares the relationship of diameter and volume

growth to initial spacing and basal area control of

stocking.

Additional keywords: Populus deltoides, stand development, thinning.