1978

Fertilization Increases Growth of Thinned and Nonthinned

Upland Oak Stands in the Boston Mountains of Arkansas

D. L. GRANEY AND P. E. POPE

SUMMARY

Thinning and fertilization tests with pole-sized red

oaks (northern red oak Quercus rubra L. and black

oak Q. velufina Lam.) and white oak (0. alba L.) were

begun in the Boston Mountains of Arkansas in the

spring of 1975. Fertilizer treatments of either (1) no

fertilization, (2) 200 Ibs N + 45 Ibs P per acre, or (3)

400 Ibs N + 45 Ibs P per acre were applied to 288 red

and white oaks that had received thinning or nonthinning treatments. Two-year diameter growth response for thinned red-oaks increased by 52 percent

for the 200-lb treatment and by 97 percent for the

400-lb treatment. Increases for nonthinned red oaks

averaged 40 and 58 percent for the 200- and 400-lb

treatments.

Diameter growth for thinned white oaks increased

by 95 percent for the 200-lb treatment and by 86

percent for the 400-lb treatment. Increases for nonthinned white oaks averaged 48 and 74 percent for

the 200- and 400-lb treatments: Thinning did not

significantly increase response to fertilization for

either red or white oaks.

HELPING ACCELERATE GROWTH

OF HARDWOOD STANDS

Over 200,000 acres of forest land in the Boston

Mountains of Arkansas support overstocked, evenaged, pole-sized stands of oaks and associated

species. Although many stands are on medium to

good sites (height of 60 to 70 ft at 50 years), diameter

growth averages only about 1 inch in 10 years. A lack

of outlets for small diameter hardwoods has prevented intermediate cutting in these stands. But, because demands for sawtimber are increasing and

inventories of large hardwood poletimber and immature sawtimber are small, some land managers

have begun non commercial thinning programs to

accelerate growth in the slow-growing hardwood

stands. Fertilization may further stimulate growth of

crop trees. Positive growth responses of oaks and

other upland hardwoods to fertilization have been

demonstrated (Mitchell and Chandler 1939, Farmer

and others 1970, Ward and Bowersox 1970, Karnig

1972, Watt 1974). Generally, the greatest response

of hardwoods has been associated with nitrogen (N)

and to a lesser degree phosphorus (P) when applied

with N.

Study Area

PROCEDURES

The Boston Mountains are the highest and southernmost member of the Ozark Plateaus physiographic province (fig. 1). They form a band 30 to 40

miles wide and 200 miles long from north central

Arkansas westward into eastern Oklahoma. Elevations range from about 900 ft in the valley bottoms to

2500 ft at the highest point. The plateau is sharply

dissected, and most ridges and spurs are flat to

Southern Forest Experiment Station/T-l0210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans, La, 70113

Forest Service, U.S. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee, Eastern Texas.
gently roiling and generally less than one-half mile

wide. Mountain slopes consist of an alternating

series of steep simple slopes and gently sloping

benches.

Rocks in the area are sedimentary and predominantly of Pennsylvanian age; they consist of alternate

horizontal beds of shales and resistant sandstones.

Annual precipitation averages 46 to 48 inches in

the 2.2 million acre portion within Arkansas. March,

April, and May are the wettest months. Extended

summer dry periods are common, and autumn is

usually dry. The frostfree period is normally 180 to

200 days long.

Three study areas were selected from overstocked

stands on mountain benches that range from 2 to 3

chains wide and are typified by deep, well-drained

soils of the Nella or Leesburg series (Typic

Paleudults). These soils were formed from

sandstone and shale colluvium and are among the

most productive upland soils in the mountains.

Sample Trees

In each study area, 48 red oak and 48 white oak

trees were selected for the thinning and fertilizer

treatments. The trees from each species were arranged into 16 sets of 3 trees each. Individual members of each three-tree set were uniform in diameter,

crown size, and height, and were located on essentially the same site conditions. Consecutive threetree sets were randomly assigned the thin or nonthin

treatments, and three fertilizer treatments were randomly assigned each three-tree thinned or nonthinned set. Thus, 144 red oaks and 144 white oaks at

three locations were used to determine the effects of

thinning and fertilization on diameter growth.

Tree Measurements

For each sample tree, diameter at breast height

(d.b.h.) was measured to the nearest 0.01 inch. The

diameter measurement point was identified by a

painted band on each tree. Increment cores were

MISSOURI

I I I P I I

,:,9”, [;;;;“( CLEBURNE 1

0. L. Graney is Silvicukurist, Southern Forest Experiment Station, Forest Service - USDA, Fayetteville, Ark. P. E. Pope is Assistant

Professor, Department of Forestry and Natural Resources, Purdue University, West Lafayette, Indiana. Study was initiated while Pope was

Assistant Professor, Department of Horticulture and Forestry, University of Arkansas, Fayetteville.

2
extracted from the north, east, south, and west sides

of each tree and were used to determine tree age and

to obtain a measure of past growth, which served as a

covariate in the data analysis. After extraction, cores

for each tree were sealed in plastic soda straws. For

each core, a binocular microscope was used to measure annual radial growth to the nearest 0.01 inch.

Total height was also recorded for each sample tree.

Thinning Treatments

Basal area near each sample tree was determined

with a prism. From this initial value, the basal area

was reduced by removing two major competitors and

several smaller trees until an area of about 70 ft2 per

acre was attained. Thinning treatments were completed in March 1975. Average stand and tree

characteristics for red and white oak thinned and

nonthinned treatments are shown in table 1.

Table l.-Average stand and tree characteristics for red and

white oak plots.

Treatment Age

Site Initial

index diameter

Thinned

Nonthinned

Thinned

Nonthinned

(yea@

5 0

5 0

5 2

5 2

(feet) (inches)

RED OAKS

6 2 8.18

6 2 8.48

WHITE OAK

5 9 8.26

5 9 7.89

Basal

area

(W/acre)

6 8

120

6 6

123

Fertilizer treatments

Fertilizers used were ammonium nitrate (34-O-O)

and diammonium phosphate (18-46-O). Fertilizer

treatments were: (i) no fertilizer (control), (ii) 200 Ibs

N + 45 Ibs P per acre (200 lb treatment), (iii) 400 Ibs N

+ 45 Ibs P per acre (400 lb treatment). Fertilizers

were surface broadcast on a 0.01 acre circular plot

surrounding each tree. Fertilizer was applied in late

April 1975 about 1 week after trees leafed out.

RESULTS AND DISCUSSION

Response to Thinning

After two growing seasons neither the red oaks nor

white oak had responded to thinning (table 2).

Diameter growth of thinned and nonthinned white

oak control trees averaged about 0.12 inch per year

for the 1975-76 growing seasons. Nonthinned red

oak controls averaged 0.13 inch per year while thinned trees averaged about 0.12 inch. But, as indicated

in figure 2, the nonthinned trees had indicated a

slightly higher growth rate before thinning.

Response to Fertilization

Fertilization significantly increased growth of both

red and white oaks (table 2). Mean annual diameter

growth for red oak was 0.18 and 0.23 inch for the

thinned 200- and 400-lb treatments, 52 and 97 percent increases over growth of controls. Response of

red oak nonthinned trees was not as dramatic but

averaged 40 and 58 percent greater than the controls

for the 200- and 400-lb treatments.

Our results for fertilized and thinned red oaks compare favorably with the initial response of red oaks to

fertilization in New York (Mitchell and Chandler 1939,

Karnig 1972), but are greater than responses of black

oak in the Missouri Ozarks (Watt 1974) and red oaks

in West Virginia (Auchmoody and Smith 1977) and

the Tennessee Valley (Farmer and others 1970).

Response for fertilized but nonthinned red oak trees

was fairly close to that found by Farmer and others

(1970) for red oaks in the Tennessee Valley.

The significant growth response of red oaks to

increasing levels of nitrogen was essentially linear

over the range of 0 to 400 Ibs per acre. Watt (1974),

working with thinned black oak in the Missouri

Ozarks, also reported a linear diameter growth response t6 increasing levels of N fertilization up to 900

Ibs per acre.

Diameter growth of thinned white oaks was not

significantly different for the 200- and 400-lb treatments but was 95 and 86 percent greater than growth

of nonfertilized trees. Response for thinned white

oaks was greater than responses to fertilization reported elsewhere (Mitchell and Chandler 1939,

Farmer and others 1970, Ward and Bowersox 1970).

Mean annual diameter growth for nonthinned white

oaks was 48 percent greater than controls for the

200-lb treatment and 74 percent greater for the

Table P.-Mean annual diameter growth response to fertilization

for thinned and nonthinned red and white oaks.

Fertilizer

treatment

Thinned Nonthinned

Growth Response’ Growth Response’

Control

200 lb

400 lb

Control

200 lb.

400 lb.

(inches)

.116

,180

.233

.117

.228

.218

6) (inches)

RED OAKS

- .129

5 2 .180

9 7 ,204

WHITE OAK

- .119

9 5 .176

8 6 .207

w

-

4 0

5 8

-

4 8

7 4

‘Percent increase over control.

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400-lb treatment. Response of nonthinned white oak

was similar to that of white oak in the Tennessee

Valley (Farmer and others 1970).

Unlike red oaks, white oak did not respond significantly to increasing levels of N. Ward and Bowersox

(1970) reported no significant increases in white oak

diameter growth between N applications of 60 and

180 Ibs per acre but did observe an increase in 5-year

gross volume growth between lower and higher N

levels when N was combined with lime.

In the Boston Mountains of Arkansas, differences

between red oaks and white oak in response to fertilization are probably due to inherent differences in site

requirements. A recent site quality investigation for

upland oaks in the Boston Mountains (Graney 1977)

found that red oaks were highly sensitive to changes

in site and soil characteristics. White oak, however,

had similar site indices over a wide range of site and

soil conditions. Although response for both red and

white oaks to fertilization indicates that N (and possibly P) limits growth in this area, requirements for

white oak are apparently satisfied with lower levels of

fertilization than are those of red oaks.

Before thinning and fertilization, patterns of both

red and white oak diameter growth (after the wet

growing seasons of 1967 and 1968) reflected increasing crown and root competition in the overstocked stands (figs. 2 and 3). With few exceptions,

crowns of sample trees were small and by remeasurement in 1976 had not begun to expand

much. Red oak diameter growth declined from a

maximum of about 0.22 inch in 1968 to about 0.12

inch in 1974 (fig. 2). White oak diameter growth declined from a high of about 0.18 inch in 1968 to about

0.11 inch before thinning and fertilization (fig. 3). The

slight increase in control diameter growth for red oaks

and white oak in the 1975-76 growing seasons probably reflected the wet 1975 growing season.

Among fertilized red and white oaks, thinned trees

had slightly higher diameter growth rates than nonthinned trees, but differences were not significant.

Our results are only for 2 years, and effects of thinFigure 2.-Mean annual diameter growth 1961-74 and response

to fertilization for thinned and nonthinned red oaks.

ning on fertilized trees may become more apparent in

later remeasurements.

Two-year results of this study indicate that growth

of pole-sized red and white oaks in overstocked

stands can be significantly increased by fertilization.

Studies in other areas have indicated the maximum

response of upland oaks to fertilization occurs within

the first 3 years and then declines over a period of

years. We will continue to monitor diameter growth in

this study for a minimum of 5 years or until no further

response is observed.

LITERATURE CITED

Auchmoody, L. Ft., and H. Clay Smith.

1977. Response of yellow-poplar and red oak to

fertilization in West Virginia. Soil Sci. Sot. Am. J.

41: 803-807.

Farmer, R. E., Jr., G. W. Bengtson, and J. W. Curlin.

1970. Response of pine and mixed hardwood

stands in the Tennessee Valley to nitrogen and

phosphorus fertilization. For. Sci. 16: 130-136.

Graney, D. L.

1977. Site index predictions for red oaks and white

oak in the Boston Mountains of Arkansas. U.S.

Dep. Agric. For. Serv. Res. Pap. SO-139, 9 p.

South. For. Exp. Stn., New Orleans, La.

Karnig, Jack J.

1972. Nitrogen fertilizer increasesdiametergrowth

of northern red oak. J. For. 70: 629.

Mitchell, Harold L., and Robert F. Chandler, Jr.

1939. The nitrogen nutrition and growth of certain

deciduous trees of northeastern United Staes.

Black Rock For. Bull. 11, 94 p.

Ward, W. W., and T. W. Bowersox.

1970. Upland oak response to fertilization with nitrogen, phosphorus, and calcium. For. Sci. 16:

113-120.

Watt, Richard F.

1974. Response to fertilization of oaks in the Missouri Ozarks. Agron. Abst., Amer. Sot. Agron.,p.

179.

61-65 66 67 68 69 70 71 72 73 74 75-76

YEAR

Figure 3.-Mean annual diameter growth 1961-74 and response

to fertilization for thinned and nonthinned white oak.

e U.S. GOVERNMENT PRINTING OFFICE: 1978-672-040