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 Southern Forest

Research Note

SO-31 8

Experiment Station November 1985

The Decline and Mortality of Cottonwood Clone

Stoneville 124 on a Clay Soil

John K. Francis and Francis I. McCracken

A decline sequence involving multiple factors was proposed as the cause of death and diminished crowns of

12-year-old cottonwood planted on a clay site. Stoneville

clone 124, of which the plantation was formed, has

proved to be poorly adapted to clay soils. Rates of death

and weakened crowns were shown to be related to

minor elevation differences within the plantation, the

higher, drier areas being the most affected. Finally, several weak pathogens, including Phomopsis macrospora,

apparently participated in weakening and ultimately

killing the trees.

Additional keywords: Populus deltoides, Phomopsis macrospora, twig canker.

INTRODUCTION

Cottonwood (Populus deltoides Bartr. ex Marsh.)

grows naturally on clay soils in the South when disturbances allow its establishment. Those few cottonwood

trees that survive early competition can outpace other

local species and often attain heights of 100 feet or

more. Stoneville select clone 124 (ST-l 24) observed in

this study, had received favorable review, its growth being similar to 13 other superior clones on Sharkey clay at

5 years old (Mohn and others 1970). However, Krinard

and Kennedy (1983) found ST-1 24 inferior to ST-66 and

ST-67 in both growth and survival at 10 years and on the

same soil type. This paper features observations of tree

growth and decline of a cottonwood plantation of clone

ST-124 on a clay site-the same Sharkey seriesthrough age 12. Also reported here are the principal

biological and edaphic factors which we believe contributed to the decline.

THE PLANTATION

In January 1973, a 15acre area on the Delta Experimental Forest, Stoneville, Mississippi, was planted with

20-inch cuttings of cottonwood select clone Stoneville

124. The site had been cleared of an elm-ashsugarberry stand (SAF type 93) and the slash was piled

and burned. The site was disked prior to planting and

disk cultivated three times during the first growing, season to control weeds. The soil was a Sharkey clay, a

member of the montmorillonitic, thermic family of the

Vertic Haplaquepts. The initial spacing was 10 by

10 feet. At the end of the third growing season, every

other row was removed, increasing the spacing to 10 by

20 feet. A selective thinning after the 8th growing season

removed weak or dying trees and reduced the stand to

128 trees per acre.

A 4.4-acre portion of the plantation was chosen for

study. Measurements of diameter (dbh) and height were

made after 1, 2, 3, 4, 8, and 12 growing seasons. The

progression of average heights and diameters is illustrated in figure 1. Cottonwood of ST-1 24 growing on

Sharkey clay in a clonal trial’ averaged 44 feet high and

6.1 inches dbh at 14 years old. On Commerce soil (silty

clay loam texture) a few miles away, it averaged 96 feet

and 15.5 inches dbh at the same age. The cottonwood

in the study reported in this paper grew rapidly for the

first 4 years, then grew much slower, especially in

height. During the latter part of the 12th growing season,

it was recognized that the plantation was in serious trouble; more than 40 percent of the trees were dead, dying,

lunpublished data on file at the Southern Hardwoods Laboratory,

Southern Forest Experiment Station, Stoneville, Mississippi.

Southern Forest Experiment Statlonn-102lO U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La. 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mlsslsslppl, E. Oklahoma, Tennessee, E. Texas, Puerto Rico, U.S. Vlrgln Islands

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AGE (YEARS)

Figure 1 .-Average diameter and height of a cottonwood plantation of

clone Stoneville 124 at ages 1 through 12.

or seriously weakened. Each tree was rated as healthy,

thin crown (many twigs and limbs dead), top dead (at

least the upper 3 feet), or standing dead.

The first symptoms of decline were decreased crown

vigor and size. Closer inspection revealed numerous

twig cankers that resulted in twig dieback. The dieback

progressed to involve larger limbs. The entire top sometimes died and broke off. Stem and branch cross sections showed dark stained zones of wood associated

with cankers. Epicormic branches sometimes developed

on the lower bole and died in turn.

Because weak and dying trees seemed less common

in the lower-lying areas of the plantation, the area was

surveyed and the health groups compared to elevation.

Elevations are relative to a benchmark at the southwest

corner of the plantation and varied about 6 feet from the

high to low areas. The effect of elevation is illustrated in

table 1 where the trees are separated by health categories and divided into four convenient elevation groups.

Note how the proportion of weakened and dead trees

drops off as elevation decreases. Percent of the trees

that were healthy at each elevation (&foot interval) was

regressed on change in elevation below the benchmark.

The following model was used:

where

Y = % in health class, Arcsin-transformed and

X = feet elevation relative to benchmark.

Elevation significantly (a = .05) predicted the proportion

of healthy trees. The coefficient of multiple determination

for percent in the “healthy” class was .82 with a coefficient of variation (CV) of 14.47%.

Soil cores were collected from a high elevation, high

mortality area and a low elevation, mostly healthy area.

There was no discernible difference between the two

profiles in color, mottling, structure or texture (feel

method). The same pH (5.9) was found at 6 inches and

almost the same pH at 18 inches depth (high = 6.3;

low = 6.1) in both profiles.

Pieces of tissue, about 0.1 cubic inch, were removed

aseptically from root, stem, arId branch samples of affected trees in a high elevation area of the plantation and

cultured in the laboratory at room temperature on potato

dextrose agar. Cultures were examined microscopically

and identified. Phomopsis macrospora Kobayshi &

Chiba was isolated from all the twig cankers sampled.

fusarium solani (Mart) Snyder and Hans. and a Penicillium sp. were also isolated from twig samples, but they

occurred less frequently (5-20%) than Phomopsis.

Botryodiplodia theobromae Pat. was recovered from

root and stem tissues. An unidentified basidiomycete

and Bacillus sp. were isolated from root tissues showing

necrosis and decay. All cottonwood trees in the area are

slightly to moderately affected annually by one or more

common leaf diseases caused by Melampsora medusae

Thum, Septoria mu&a Peck, and Phylosticta sp.

Table 1.-Numbers of 12-year-old cottonwood trees per acre in four

health categories across an elevational gradient on a 4.4-

acre tract

Health category

Healthy

Thin crown

Top dead

Standing dead

Feet drop below benchmark

Cl.0 1.0 1.5-2.0 >2.0 Total

--------- numberoftreesperacre ---------

15.7 16.8 15.7 17.5 65.7

7.3 7.0 8.4 2.7 25.4

6.4 3.0 .9 .9 11.2

4.8 2.5 2.0 .7 10.0

John K. Francis is principal soil scientist and Francis I. McCracken is principal plant pathologist 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.

2
The only substantial environmental difference, identified across the gradient from the healthy to poor areas

was elevation. Elevation is the determinant of flooding

depth after winter and spring rains and presumably determines water table depth during the early to midgrowing season. Clay soils can hold a large percentage

of water, but they hold it tightly and release it slowly.

Root absorption of moisture is especially difficult in the

subsoil where roots only penetrate between the large

soil peds. A few extra days of root contact with free

water-rather than having to draw water from the large

subsoil peds- may give a slight advantage in growth to

the lower elevation trees.

Mortality was first noticed in year 8. Although casual

organisms were not diagnosed at that time, twig cankers

were present and P. macrospora was later isolated from

similar cankers, When the plantation was thinned after

growing season 8, all dead and most seriously weakened trees were removed. The current standing dead

trees have died since thinning. Because some of these

trees appeared to be in their second year after mortality,

it would seem that trees can progress from relatively

good health to death in 2 years or less.

Studies by Filer (1967) show that P. macrospa, F.

solani, and other fungi can infect cottonwood trees and

cause cankers and mortality. However, the size of the

cankers and mortality depend upon the quality of the site

on which the tree is growing and upon environmental

conditions during the attack. Above normal temperature

and rainfall during the fall were believed to encourage

disease development on poor sites.

A single cause could not be established for the decline

and mortality of ST-124 on the clay site in this report.

Numerous theories for tree declines have been proposed; however, the decline syndrome (Manion 1981),

which involves several factors acting together, appears

to be the most appropriate approach to an understanding of the decline and mortality of cottonwood on these

sites.

A combination of factors is believed to account for this

example of decline and mortality of ST-124 on a clay

site. The principal factors appear to be the unsuitability

of this cottonwood clone to the clay soil site; the unavailability of water for a part of each year related to

minor differences in elevation on the site, stress each

year from leaf disease and insects, a drought during the

summers of 1980 and 1982, and attack by one or more

canker fungi. The results of this planting suggest that

ST-1 24 is at risk to develop decline symptoms and high

mortality when these clones are planted on clay soils,

especially better drained ridges. No doubt many other

clones would also fail for the same reasons if planted on

clay. One assurance of acceptable growth and survival

on clay soils might be obtained by testing clones through

the chosen rotation age.

LITERATURE CITED

Filer, T. H., Jr. Pathogenicity of Cflospora, Phomopsis,

and Hy~omyces on Populus deltoides. Phytopathology 57(9): 978-980; 1967.

Krinard, Roger M.; Kennedy, Harvey E., Jr. Growth, thinning treatments, and soil properties in a lo-year-old

cottonwood plantation on a clay site. Res. Note SO302. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station; 1983. 4 p.

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.

Manion, P. D. Tree disease concepts. Englewood Cliffs,

NJ: Prentice-Hall, Inc.; 1981. 399 p.

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