7

United States

/a Department of

w

t Argriculture

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Bs Forest Service Research Note - Southern Forest

Experiment Station

SO-302

December 1983

Growth, Thinning Treatments, and Soil Properties in a

1 O-Year-Old Cottonwood Plantation on a Clay Site

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

SUMMARY

Two of .four Stoneville select cottonwood (Populus deltoides Bartr. ex Marsh.) clones planted at 12- by 12-foot

spacing on old field clay soils had 80+ percent survival

at age 5 and were subjected to three stocking levels.

Plots were left unthinned (approximately 266 trees/acre)

and thinned to half the number of trees (about 126 trees/

acre) and to 60 trees per acre at age 5. Dbh growth the

next 5 years differed significantly but amounted to only

0.3, 0.4, and 0.5 inch annually by treatments. Thinned

plots had 23 and 35 percent less total volume (5th-year

cut plus lOth-year standing) than unthinned plots. Tenthyear soil N, P, K, Ca and Mg values were greater than

5th-year values, but only Ca equalled and Mg exceeded

plantation establishment measurements.

Additional keywords: Populus cfeltoides.

INTRODUCTION

Cottonwood plantation establishment costs, estimated

at $255 per acre in 1980 (Dutrow 1980) where.land clearing was involved, represent a considerable expense.

Consequently, most cottonwood plantations in the Midsouth have been established on medium-textured soils,

where cottonwood grows best, rather than on clay soils,

where growth is considered marginal. The difference in

height of 5-year-old trees of the same select clonal material was 25 feet between cleared Sharkey clay and Commerce silt loam soils (Mohn et al. 1970). In an attempt to

improve growth, select cottonwood clones, planted on an

old field clay soil, were thinned after the 5th year. This

note presents stand and soil characteristics of the plantation 5 years later for both the thinned and unthinned

areas.

METHODS

The study was planted on clay soils of a Sharkey (clay

extends >36 inches)-Tunica (clay cap 20 to 36 inches

thick) complex in lssaquena County, Mississippi, on the

Mahannah Plantation of the Anderson-Tully Company.

The site had been cleared and planted to soybeans for 6

years, then summer-fallowed prior to planting cottonwood. Three tons of lime per acre had been applied to

the area before the last soybean crop in 1970.

Four clones-Stoneville (ST) 66, 67, 92, and 124-

were randomly selected as representative of above-average material (Mohn et al. 1970) and cuttings were

planted in December 1971 at 12- by 12-foot spacing.

Each clone was planted as a unit, with 9 plots per clone

except for ST-92 with only 8 plots. Overall plot size was

17 rows (east-west) by 7 7 columns (north-south) with

measurement plots 10 rows by 10 columns.

ST-66 and ST-67 were thinned in March and April

1977 at the start of the sixth growing season; ST-92 and

ST-124 were not thinned because of poor survival. Thinning treatments were: (1) control or check (CK), equivaSouthern &rest Experiment StationTT-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
lent to approximately 266 trees per acre; (2) thin every

other column, leaving half the trees (TH) or about 126

trees per acre; and (3) thin every other column, then thin

remaining columns to four trees each (20 trees per plot)

or 60 trees per acre (T6).

A randomized complete block design was used to test

thinning treatments at the 0.05 level. Where clonal means

were compared, a t-test at the 0.05 level was used.

Diameters of all measurement plot trees were taken

every year while a sample of heights was taken, using

two columns in CK and TH plots and all trees in T6 plots.

Ten-year standing-tree volumes from Barr and Stroud

dendrometer measurements were combined with 5year

cut-tree volumes for volume determinations in the form:

V = 1.445848 + 0.002063 D*H - 6.117578(1/A);

r* = 0.992, S, x = 0.330

where

V = total stem volume (cubic feet) outside bark from lfoot stump to the top of the tree,

D=dbh,

H = total height, and

A = age (years).

In the 10th year, samples of height to live crown, maximum crown diameter, and, for ST-66 and ST-67, number

of limbs and limb stubs in the first 17 feet of height were

taken. As trees had been pruned to about 5 feet in the

third year, the limb count generally indicated number of

limbs from 5 to 17 feet.

Soil moisture determinations at the surface and 1-, 2-,

3-, and 4-foot depths were made several times during

each growing season using a neutron probe and nine soil

moisture tubes. Measurements taken nearest the middle

of each month from May through September were used

to characterize growing season moisture.

Bulk soil samples from 0 to 6 inches deep were collected at the start of the first growing season and in September of the 5th and 10th year from all plots. Soil chemical analyses, using standard laboratory procedures (Krinard and Kennedy 1980) were made for N, P, K, Ca,

Mg, organic matter (OM), and pH.

RESULTS

Unthinned Plots

After 5 years, considering all 35 plots, survival was 75

percent. Average dbh and height were 5.4 inches and 43

feet. Basal area and volume per acre were 38 square feet

and 681 cubic feet. The mean annual increment (mai) of

volume, 136 cubic feet per acre per year, was equivalent

to 1.5 cords (90 cubic feet = 1 cord).

At age 10, based on clonal averages of unthinned

plots, average dbh and height increased to 6.9 inches

and 60 feet while basal area and volume per acre

reached 60 square feet and 1,594 cubic feet. Volume mai

was 1.8 cords.

At age 5 (and also age lo), ST-66 and ST-67, compared to ST-92 and ST-124, had a third more trees with

approximately 40 percent more basal area and about 60

percent more volume (table 1). Differences were significant by t-tests; thus, ST-66 and ST-67 were regarded as

representative of better surviving select clones and considered separately from the poorer surviving clones.

Thinned Plots

Thinning after the 5th year increased the average dbh

of T6 plots to 5.8 inches compared to 5.5 inches for the

CK and TH plots. After 10 years, average dbh for CK, TH

and T6 plots were 6.9, 7.5, and 8.4 inches, all significantly different from each other. The 5 years’ diameter

growth of 1.3, 2.0, and 2.6 inches were also significantly

different.

Comparing the 20 largest trees per plot after 10 years’

(so that CK and TH plots had the same type “thinning” as

T6 plots, i.e., favor largest trees from alternate columns

and no two trees adjacent in the same “leave” column)

showed no difference at age 5: all treatments averaged

5.8 inches dbh. At age 10, TH and T6 trees were larger

than CK trees. Diameter growth was different between all

treatments. Thinning increased diameter growth, and

larger trees tended to respond slightly more than smaller

trees.

There were no significant differences in total height

between treatments after the 5th or 10th year. Average 5

and 10 years’ heights were 46 and 65 feet.

After 10 years, crown ratios of CK trees were significantly less than the other two thinning treatments-39

(CK) vs. 57 (TH) and 62 (T6) percent-while crown widths

of T6 trees were significantly greater-l 0.6 (CK) and 12.0

(TH) vs. 14.3 (T6) feet. Diameter was more closely related

to crown width (r* range by treatment from 0.42 to 0.59)

than to crown ratio (r* range from 0.02 to 0.29).

Number of branches and stubs on the first 17 feet of

stem did not differ by thinning treatments within clones,

but did differ between clones. Mean number by clones

over all thinning treatments was 28 for ST-66 and 17 for

ST-67. Live branches in the first 17 feet were found on 21

of the 26 observed trees of ST-66, while only 2 of the 23

ST-67 trees had live branches.

Soil Moisture

By months, the general trend was for soil moisture to

decline from May through August, then increase in September. By years, the eighth growing season (1979) was

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.

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Table 1 .-Average tree and stand values at age 5 after thinning treatments applied and at age 10, by clones

Clones Treatment

Age 5 Age 10

Trees/ Basal Basal Crown Crown

A bbh G area Volume Dbh i? area Volume ratio width

ST-66 CK’

TH’

T63

ST67 CK

T H

T 6

ST-92 CK

ST-124 CK

Ei ft282 45.3

ft’/A ft’/A

46.9 871

133 5.5 43.4 22.3 405

6 0 5.7 45.4 10.8 200

250 5.5 48.8 42.1 842

119 5.6 49.2 2l.O 431

6 0 5.8 50.0 11.3 228

209 5.2 38.0 32.4 535

184 5.4 37.9 30.3 489

f t

6t3 65.0

ftYA

73.2

7.5 61.7 41.0

8.3 66.3 22.9

6.9 66.0 64.8

7.7 65.6 38.9

8.5 65.6 24.2

6.4 52.5 47.8

7.3 55.8 53.7

ftYA % f t

2052 40.0 10.8

1091 55.6 11.8

628 63.4 13.7

1851 38.7 10.5

1079 54.3 12.0

656 59.6 15.3

1147 34.0 10.2

1315 53.7 11.6

CK: Check (no thinning).

‘TH: Thin half of trees.

1T6: Thin to 60 trees/acre.

the wettest year at all depths, having both the most rainfall and backwater flooding from the Mississippi River in

April and May that reached 6112 feet deep. The driest year

differed by depths. Regardless, yearly dbh growth

showed little response to soil moisture differences.

Soil Properties

There was a significant increase in soil N, P, K, Ca,

and Mg contents and a significant reduction in soil OM

and pH in the 10th year compared to the 5th year (table

2). Only Mg exceeded and Ca equalled soil values measured prior to planting cottonwood.

DISCUSSION

The main intent of this study was to determine growth

of select cottonwood stock. Indications are that ST-66

and ST-67, with better survival and growth, would be preferred pulpwood clones for clay sites compared to ST-92

and ST-124. At this time, ST-67 appears to have better

sawtimber potential than ST-66 because of fewer limbs in

the first log.

Thinning has improved dbh growth, but the difference

is small. Yearly growth rates for years 6 through 10 were

only 0.3,0.4, and 0.5 inch from least to heaviest thinning.

Site comparisons of volume production of unthinned

cottonwood at 12- by 12-foot spacing may be made

between select clones on clay soils and random, run-ofthe-bar planting stock on medium-textured soils by using

the Mahannah data and Fitler, Mississippi, data (Krinard

and Johnson 1980). The Fitler planting, on old-field and

pasture Commerce silt loam soil, averaged 1,260 cubic

feet per acre after 5 years and 3,052 cubic feet after 10

years. In a best case comparison; with better surviving

Table 2.-Soil property values before the first growing season (year 0)

and after year 5 and year 10

Year N P K Ca Mg pH OM

% fwm pm rv pm %

0 0.188al 81a 465a 5489a 1225b 6.76b 3.84a

5 0.162~ 55c 35oc 3882b 997c 7.15a 3.27b

1 0 0.174b 58b 415b 5439a 1330a 6.01~ 2.94c

‘Values in columns not followed by same letter significantly different at

0.05 level by Duncan’s multiple range test.

clones, medium-textured soils produced IV2 times more

volume after the 5th and 10th years and 2112 times more

volume in a worst case comparison, with poorer surviving

clones. These volume differences represent 4.6 and 8.3

fewer cords on clay sites after 5 years and 12.2 and 20.2

fewer cords after 10 years.

In considering select clones on clay sites for pulpwood

production, total harvesting could start at about age 8 or

9 or the volume could be stored on the stump for several

years, with little difference in yield in a continuous plantation system. Thinning decreased total yields at age 10 by

one-fourth to one-third. For thinned plots to be equivalent

to unthinned plots at age 10, the dollar value of volumes

cut at age 5 would need to appreciate at a 16 percent

compound interest rate.

The measured soil elements appear to be in a continuing state of change. Others have also shown soil property

variation and changes over time where agronomic fields

were planted to trees (Gilmore and Boggess 1976,

Ovington 1956).

This is a continuing study of the survival and growth of

cottonwood on clay sites cleared for soybeans and

replanted to trees. Cottonwood was not a major component of the cleared stand. However, cottonwood can

grow on these marginal sites to at least pulpwood size,

although yields may be only 40 to 60 percent of those

obtainable from medium-textured soils.

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LITERATURE CITED

Dutrow, George F. Economic consideration in, artificial

and natural regeneration of hardwoods. In: Proceedings, Hardwood Regeneration Symposium; 1980

January 29; Atlanta, GA. Forest Park, GA: Southeastern Lumber Manufacturers Assoc.; 1980: 48 - 57.

Gilmore, A. R.; Boggess, W. R. Changes in a reforested

soil associated with tree species and time. I. Soil

organic matter and pH in pine relationships. For. Res.

Note, Urbana-Champaign, IL: University of Illinois,

Department of Forestry: 1976. 5 p.

Krinard, R. M.; Johnson, R. L. Fifteen years of cottonwood plantation growth and yield. South. J. Appl. For.

4(4): 180 - 185; 1980.

Krinard, R. M.; Kennedy, H. E., Jr. Five-year-old cottonwood plantation on a clay site: growth, yield, and soil

properties. South. J. Appl. For. 4(2): 80 - 83; 1980.

Mohn, C. A.; Randall, W. K.; McKnight, J. S. Fourteen

cottonwood clones selected for Midsouth timber production. Res. Pap. SO-62, New Orleans, LA: U.S.

Department of Agriculture, Forest Service, Southern

Forest Experiment Station; 1970. 17 p.

Ovington, J. D. Studies of the development of woodland

conditions under different trees. IV. The ignition loss,

water, carbon, and nitrogen content of the mineral soil.

J. Ecol. 44(l): 171 - 179. 1956.

Soil Test Work Group. Procedures used by state soil testing laboratories in the southern region of the United

States. South. Coop. Serv. Bull. 190; 1974.23 p.

*U.S. GOVERNMENT PRINTING OFFICEt 1983-769-089:5