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U S Forest Service

 Southern Forest

Research Note

Experiment Station

SO-336

April 1967

Fifteen-Year Growth of Six Planted Hardwood Species

on Sharkey Clay Soil

Roger M. Krinard and Harvey E. Kennedy, Jr.

SUMMARY METHODS

Six hardwood species planted on Sharkey clay soil

that had been disked the first 5 years for weed control

were significantly taller at age 5 when compared to species grown on mowed sites. By age 15, there were no

differences in heights within species except for sweet

pecan. Average heights by species at age 15 were: cottonwood (Populus deltoides Barb. ex Marsh.), 60 feet;

sycamore (Flatanus occidentalis L.), 38 feet; green ash

(Fraxinus pennsylvanica Marsh.), 36 feet; sweetgum

(Liquidambar styracifha L.), 30 feet; Nuttall oak (Quercus nuttallii Palmer), 27 feet; and sweet pecan (Carya

illinoensis (Wangenh.) K. Koch), 19 feet.

The study was located on the Delta Experimental

Forest (DEF) near Stoneville, Mississippi. Planting was

in 1971 after the slackwater area had been cleared of

trees and the site raked and disked. The soil is Sharkey

clay.

Additional keywords: Populus deltoides, Ratanus

occidentalis, Fraxinus pennsylvanica, Liquidambar

styraciflua, Quercus nuttallii, Carya illinoensis.

Species planted were cottonwood (CW-PopuEus deltoides Bartr. ex Marsh.), sycamore (SY-Hatanus occidentalis L.), green ash (GA-Fraxinus pennsylvanica

Marsh.), sweetgum (SG-Liquidambar styraciflua L.),

Nuttall oak (NO-Quercus nuttallii Palmer), and sweet

pecan (SP-Carya illinoensis (Wangenh.) K. Koch). Estimated midrange site indices for these species on

Sharkey clay are 95 feet for CW (30 years); 90 feet for

SY, SG, and NO; 85 feet for GA; and 80 feet for SP (all

at 50 years) (Broadfoot 1976).

INTRODUCTION

Planting hardwood species is an option for clay soils

being withdrawn from agricultural production in the Midsouth. Clearing and planting of slackwater sites can also

be considered as a method for regenerating cutover and

depleted stands and for introducing desired species on

given sites. Yields on clay soils are inherently less than

yields on medium textured soils and therefore provide

poorer economic returns. Cultural treatments that would

increase tree growth would be beneficial. This note provides growth information through 15 years for hardwood

plantings where some weed control by disking or mowing was maintained yearly for 10 years and where selective thinning after 5 years doubled the original planting

spacing for five of the six species in the study.

One-year-old nursery grown seedlings or 20-inch-long

CW cuttings were planted in a split-plot design with six

blocks (replications). Species subplots consisted of a

4-column by 6-row planting (24 trees) on a 1 O-foot spacing. Each CW row contained a separate Stoneville clone,

either clone 66, 67, 78, 82, 213, or 244. Plots were

mowed or disked three to five times annually the first

5 years.

After the 5th year, species subplots with 80 percent or

more survival based on trees >4.5 feet tall,were thinned

to six trees each, or an equivalent 20- by 20-foot spacing. Consequently, SG and I\lO mowed plots and SP

mowed and disked plots were not thinned because of

slow height growth. For thinning, subplots were subdivided into squares of four trees each, and one tree per

square was left to maintain spacing over a subplot. Mowing or disking treatments, one to three times annually, for

years 6 to 10 were randomly assigned to whole blocks to

Southern Forest Experiment Stationfl-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Virgin Islands

1’
compare effects of continued or switched cultural treatments on tree growth. But since there was so little difference between mowing and disking the second 5 years

(Krinard and Kennedy 1983), results are discussed relative to the first 5-year weed control treatments.

Data presented are 5-, lo-, and 15-year measurements of total height and d.b.h. and 15-year survival of

unthinned plots. For comparison with thinned plots, the

six largest trees on unthinned plots were selected after

the 15th year in the same manner as thinning techniques

were applied after 5 years.

RESULTS

At age 15, based on 109 trees per acre and averaged

over all six species, trees on plots disked the first 5 years

were significantly taller and larger in d.b.h. than trees on

plots that had been mowed.’ However, for practical purposes the differences were unimportant as they only

amounted to 1.3 feet in height and 0.6 inch in diameter.

For height, by species, CW > SY = GA > SG > NO

> SP, where CW was 22 feet taller than SY, SY was

8 feet taller than SG, SG was 3 feet taller than NO, and

NO was 8 feet taller than SP. D.b.h. rankings among

species were the same except that SG and NO did not

differ. There was no cultural treatment by species interaction for either height or diameter.

‘Error mean squares for analyses used in this note are given in

Appendix, table 1.

Individual species analyses of variance for treatment

effects were planned a priori regardless of overall F-test

results, and the comparisons are presented in table 1. At

age 5, d.b.h. and height of disked trees were significantly

larger than mowed trees for all species tested. Diameter

comparisons for SG, NO, and SP were not made because 25 to 94 percent of the mowed trees were not tall

enough to have d.b.h. measurements.

At age 10, diameters and heights of both CW and GA

did not differ by disking or mowing treatments, but differences were still detected for the other four species. By

age 15, however, only SG diameters and SP heights and

diameters differed by weed control treatments. Since the

SG diameter comparison was between thinned and unthinned trees, a difference might be expected; however,

diameters of NO trees did not differ even though thinned

and unthinned trees were also compared.

Survival after 15 years on mowed SG and NO plots

and disked SP plots ranged from 76 to 84 percent (table

2) and were within 1 percent of the survival at 5 years.

Through the 5th year and beyond, a number of the

mowed SP trees were dying back and subsequently root

sprouting, so that the actual survival appeared to increase from 48 to 58 to 62 percent after 5, 10, and 15

years, respectively.

The maximum number of CW trees per clone that

could have been selected for either cultural treatment

after the 5th year was 12. In disk plots, the number of

trees per clone selected varied from four (clones 78 and

82) to eight (clones 66 and 244); in mowed plots the

number varied from two (clone 78) to nine (clone 67).

The Friedman rank test did not indicate a difference in

Table 1 .-Average diameter and height by species, age, and first 5 years’ cultural treatment for equivalent 20- by20-foot

spacing (109 trees per acre)

Cottonwood Sycamore Green ash Sweetgum Nuttall oak Sweet pecan

Age D1 M2 D M D M D M D M D M

5 4.3’3 2.V 3.0* 1.4’ 2.4* 1.8’ 1.2 ---4 1.1 --- ---- ----

1 0 8.4 7.6 ’ 5.P 4.4’ 5.1 5.1 3.8* 2.4* 3.3* 2.2* 1.8’ 0.8’

15 11.0 10.2 6.5 8.5 6.5 7.0 5.9” 4.7’ 5.8 5.0 3.4 2.2

_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ - - _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ Height (feet) _______-_-_-________----------------------

5 26.9* 19.9 20.6 13.1* 17.9* 14.7’ 10.4. 5.7* 10.0* 5.3* 4.4’ 2.9

1 0 48.7 46.4 30.4 26.1’ 29.6 27.8 21.8* 18.7’ 19.1* 14.3* 13.0* 8.1*

1 5 60.4 59.6 37.7 38.8 36.3 36.4 30.6 29.6 28.2 26.1 21.7’ 16.5’

lD = Disk.

2M = Mow.

3* = Means within same age and species significantly different at 0.05 level.

4-- = 25 to 94 percent of trees ~4.5 feet in height.

Roger M. Krinard is mensurationist and Harvey E. Kennedy, Jr., 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.
Table 2.-Average 15-year survival, diameter, and height for unthinned plots by species and cultural treatment during first

5 years

Survival (percent)

Diameter (inches)

Height (feet)

Sweetgum Nuttall oak

Mow Mow

7 6 6 3

4.2 4.0

27.6 24.0

Sweet pecan

Disk Mow

6 4 6 2

2.5 1.7

17.6 13.9

the number of trees selected per clone in either treatment. A completely random design was used to compare

d.b.h. and heights of the CW clones at age 15 on disk

and mow plots. Best height growth was by clones 66,

244, and 67, which averaged 66,64, and 61 feet, respectively. The other three clones averaged 51 to 56 feet tall

(table 3).

DISCUSSION

This study provided an example of relative growth

rates among species over a 15year period where there

was some control of competition variables and where

individual species competed only with themselves.

Using average heights of combined mow and disk plots,

and assigning a rating of 100 to CW because it was the

fastest growing tree, other species, in the order SY, GA,

SG, and NO, rated 72, 70, 34, and 33 at age 5; 59, 60,

43, and 35 at age 10; and 64,61,50, and 45 at age 15.

Thus, SY and GA have generally been 60 to 70 percent

as tall as CW, and SG and NO have increased from

one-third to about one-half as tall as CW.

Although disking (when compared to mowing) was

beneficial because of better growth and survival during

the first 5 years of stand establishment, the effects were

lost in the following 5 to 10 years. At least on Sharkey

clay soil, there appear to be no growth benefits that will

be maintained throughout a rotation. Disking provided

better survival at age 5: 91 vs. 80 percent averaged over

the six species. Survival differences between treatments

within species other than SP varied from only 1 percent

for GA to 12 percent for NO. Better survival provides

more possibilities in thinning, but if thinnings have no

commercial value, there appears to be little difference

between disking and mowing at lo- by 1 O-foot spacings.

Better survival would definitely be a factor at wider spacings, however. As the application of either operation requires the use of a tractor, the economics of the treatments appear similar, assuming equal site preparation

requirements.

Where species had significant differences in diameters and heights at age 5 but none at age 15, obvious

growth pattern differences had occurred between trees

starting out under the two weed control systems. The

most striking example was SY, which grew about 13 feet

each 5year period on mowed plots while trees on disked

Table 3.-Average diameters and heights at age 15 by cottonwood

clones and weed control trecitments

Clone

Disk

D.b.h. Height

Inches Feet

6 6 11.3 67al

6 7 10.4 61 bc

7 6 10.3 54d

6 2 10.5 58cd

213 10.3 54d

244 12.2 64ab

Mow

D.b.h.

Inches

Height

Feet

10.4ab

9.6bc

7.6c

.9.3bc

1 O.Obc

11.8a

65a

61a

48b

55b

55b

64a

l Means within the same column followed by the same letter were not

significantly different at the 0.05 level by Duncan’s multiple range

test; where no letters appear, overall test was not significant.

plots grew about 21, 10, and 7 feet over each of the

same three periods. For all species, the height differences between the two treatments was less the last

5-year period than during the first 5-year period. The

reason for the different growth patterns is not known.

One speculation is that mowing, by controlling height of

competing vegetation but not root development, may

force the tree species into an eventual deeper or better

rooting pattern, while disking provides a relatively

competition-free root zone with the trees having a more

shallow, less developed root system just beneath the

disked area.

By thinning CW at age 5, a viable population was

maintained, at least through 15 years. Other unthinned,

or less severely thinned, CW plantings on the DEF have

had high mortality, very weak crowns on the survivors,

and no stems with a chance of becoming future crop

trees. The only obvious advantage in starting with lo- by

lo-foot spacings and thinning at age 5, as opposed to

starting with 20- by 20-foot spacings with no thinning, is

some choice in the selection of leave trees. However,

given the poor utilization market for small trees now

available, a lo- by 1 O-foot spacing with CW on clay soils

appears too close.

Height growth over 15 years of the six CW clones in

this planting showed a separation into two groups, with

one group averaging about 54 feet and the other about

64 feet. Using Broadfoot’s site index curves for natural

stand CW (1960) those heights approximate 30-year

site indices of 77 and 89 feet.

The heights of the tallest one-third of the mowed, unthinned SG and NO trees were within 1 or 2 feet of the

same species in disk plots. But even at age 15, trees in

mowed plots were too small for a commercial thinning.

Height of the planted NO was similar to direct-seeded

NO on another area of the DEF, which at age 15 produced 183 dominant/codominant trees per acre that averaged 26 feet tall.

The growth of SP is very slow on Sharkey clay soil.

One possible reason for planting the species would be

as a mast crop for wildlife, but it would be a very long3
term proposition. A better alternative would be directseeded sawtooth oak (Quercus acutissima Carruth.),

which in an adjoining area on the DEF averaged 4.0

inches in d.b.h. and 28 feet in height at 14 years, with 88

percent of the trees producing acorns (Francis and Johnson 1985).

The following information is available on planted species development on better sites through 15 years for

comparison with the growth on Sharkey clay in this

study. Dominant CW on silt loam soils averaged 96 to

104 feet in 15 years depending on spacing (Krinard and

Johnson 1980); at age 6 dominants averaged approximately 64 feet, which exceeded 15year-old CW growth

on clay soil. Average heights at an equivalent 15foot

spacing, about 195 trees per acre, on medium-textured

soils were 65 feet in 18 years for SG (Krinard and Johnson 1985)-vs. 37 feet in 18 years on the DEF-and 70

feet in 16 years for SY. These data indicate that clay

soils, compared to medium-textured soils, were only

0.55 to 0.60 as productive for hardwood growth.

While all six species may be successfully planted, to

do so only for timber production would not be a good

economic investment because of slow growth (Anderson

and Krinard 1985). Direct seeding of NO (Johnson 1981)

to ensure an oak component, together with natural regeneration, could be the best practical regeneration approach on clay soils.

LITERATURE CITED

Anderson, Walter C.; Krinard, Roger M. 1985. The investment potential of cottonwood sawtimber plantations. In: Shoulders, Eugene, ed. Proceedings of the

3d biennial southern silvicultural research conference;

1984 November 7-8; Atlanta, GA. Gen. Tech. Rep.

SO-54. New Orleans, LA: U.S. Department of Agricul-

, ture, Forest Service, Southern Forest Experiment Station; 190-l 97.

Broadfoot, W. M. 1960. Field guide for evaluating cotton-

&-. wood sites. Occas. Pap. 178. New Orleans, LA; U.S.

Department of Agriculture, Forest Service, Southern

‘Forest Experiment Station; 6 p.

Rroadfoot, Walter M. 1976. Hardwood suitability for and

properties of important Midsouth soils. Res. Pap. SO127. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station; 84 p.

Francis, John K.; Johnson, Robert L. 1985. Directseeded sawtooth oaks (Quercus acufissima Carruth.)

show rapid growth on diverse sites. Tree Planters’

Notes. 36(3): 3-5.

Johnson, R. L. 1981. Oak seeding-it can work. Southern Journal of Applied Forestry. 5(l): 28-33.

Krinard, R. M.; Johnson, R. L. 1980. Fifteen years of

cottonwood plantation growth and yield. Southern

Journal of Applied Forestry. 4(4): 180-185.

Krinard, Roger M.; Johnson, Robert L. 1985. Eighteenyear development of sweetgum (Liquidambar sfyraciflua L.) plantings on two sites. Tree Planters’ Notes.

36(3): 6-8.

Krinard, Roger M.; Kennedy, Harvey E., Jr. 1983. Tenyear growth of five planted hardwood species with

mechanical weed control on Sharkey clay soil. Res.

Note SO-303. New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest Experiment Station; 4 p.

Appendix

Table 1 .-Error mean squares for analyses

-

Df’

Age 15 Age 10 Age 5

Height Diameter Height Diameter Height Diameter

1. Page2

Disk vs. mow

Six species

2. Table 2

Cottonwood

Sycamore

Green ash

Sweetgum

Nuttall oak

Sweet pecan

3. Table 3

Cottonwood

clones, disk

clones, mow

5 3.61 0.35 . . . . . .

50 9.38 0.67 . . . . . .

5 42.29 2.11 32.31

5 3.72 0.35 0.84

5 3.90 0.54 3.04

5 4.17 0.26 3.67

5 6.33 0.43 4.35

5 2.41 0.28 3.30

30 19.91 1.73 ......

29 30.91 2.32 ......

. . . . . . . . . . . . . . . . . .

1.14 6.77 0.46

0.06 2.21 0.09

0.30 2.05 0.10

0.19 2.03 . . . . . . .

0.32 1 .Q6 . . . . . . .

0.14 0.56 . . . . . . .

. ..*... . . . . . . . . . . . .

lError degrees of freedom.

4