Impact of competing vegetation on yield of the southern pines [Sept. 1985]

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59 GEORGIA FOREST
RESEARCH PAPER

Sept. 1985

V.

yV

Impact Of Competing Vegetation
On Yield Of The Southern Pines

By Glenn R. Glover and Dale F. Dickens p
ecejv d

MAY 3 1988

RESEARCH

DIVISION

C
uGA LiSmls

GEORGIA FORESTRY COMMISSION J

About The Authors

Glenn R. Glover is Assistant Professor of Forest Biometrics in the Alabama Agricultural Experiment Station and School of Forestry, and Associate Director of the A. U. Silvicultural Herbicide Cooperative, Auburn University, Alabama. He has a B. S. in Forest Management, and an M. S. in Quantative Methods from Auburn University; and a Ph. D. in Forest Biometrics from VPI&SU. Glover's research is presently focused on evaluating the effect of competing vegetation on southern pine growth and yield.

Dale F. Dickens is Research Forester, Georgia Kraft Corporation, Coosa, Georgia, with primary responsibilities in fertilization and herbicide research. He received a B. S. in Forest Management and is completing an M. S. in Forest Biometrics at
Auburn University. Dickens was a Grad-
uate Research Assistant at the time this research was accomplished.

ACKNOWLEDGMENTS
The authors would like to thank the Georgia Forestry Commission and Dow Chemical Company for major funding support for this project, and Velsicol Chemical Company and
E. I. duPont deNemours for additional funding support. The following forest industries and organizations provided time and help in locating and allowing access to comparisons and often provided aid in measurement: American Can Company (James Martin, Ron Neal); Auburn University; Chesapeake Corporation (Jim Willis, Steve Simmons); Continental Forest Industries (Ken Xydias); Georgia Kraft Corporation (John Gill, Henry
Griswold); Georgia Pacific (Steve Kennerly); Tennessee River Pulp and Paper (Maurice
Hamm, Rick Applegate); USDA-Forest Service (Dr. William Boyer, Dr. Charles McGee,
Dr. Eugene Shoulders); and Westvaco Corporation (John Gnegy). Other companies and
organizations who located installations which were not measured are also appreciated for
their time and interest.
2/Georgia Forestry Commission

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INTRODUCTION
One of the major problems in growing southern pines is competition from hardwood and herbaceous vegetation for
moisture, nutrients and light. Uncontrolled vegetation can reduce survival as well as growth of the desired pines. Use of chemical herbicides to control unwanted
vegetation has been common in forestry
for three decades, but the long term effect on growth has seldom been documented. This fact became obvious during the 2,4,5-T controversy of the
late 1970's (USD A 2,4,5-T Assessment
Team, 1979). Within most organizations, a forester's opinion is no longer sufficient to justify the expense of chemical vegetation control. Economic criteria, such as rate of return on investment,
must now be considered. To evaluate
these criteria, yield information reflecting the effect of vegetation control is needed.
As with most endeavors in forestry, the installation and remeasurement of studies comparing vegetation control to no control is a very long term venture. Recognition of the need for yield information relating to vegetation control has recently prompted establishment of studies, however results are several years away. In an attempt to provide interim information on pine yield response to
vegetation control, the project reported
on herein was initiated. The major objective of the project was to locate and measure southern pine stands where there was an existing direct comparison of
chemical vegetation control to other control methods, or to no control.

Impact Of Competing Vegetation
On Yield Of The Southern Pines
By Glenn R. Glover and Dale F. Dickens
Georgia Forestry Commission/3

1

PROCEDURES
Southern forest industries and organizations and chemical companies were asked to identify areas where replicated studies, paired plots, or operational comparisons of chemical vegetation control versus other methods or no control had been installed. For a comparison to be considered, an untreated or mechanically treated area had to be present within the same stand as the treated area. Stands which were treated entirely with chemicals, having no control area for comparison, were not measured. Vegetation control at any age was permissible, but at

least three years had to have passed since treatment to allow for pine response. Pine stands ranging from three years to 36
A years old were located. description of
each measured stand is given in Table 1. If measurement plots had been pre-
viously established, they were located and remeasured. If measurement plots had not been established, a 0.1-acre circular pine measurement plot was established in the center of small treatment plots, or a series of 0.1-acre plots were systematically established throughout large treated areas. Diameter breast height (dbh) to the nearest 0.1 inch, crown class, damage and species were observed for each pine stem
within a measurement plot. A representa-

tive subsample of at least 10 pines per plot was measured for total height, to the
nearest foot. Merchantable height, in number of 16.3-foot logs, to the nearest one-half log, was observed for each sawtimber pine. In stands less than 10 years old, each pine stem was also classified by the Virginia Division of Forestry Free-To-
Grow Classification (Zutter, et al. 1985).
A 0.02- to 0.1-acre hardwood measure-
ment plot, depending on hardwood stem density, was established concentrically within each pine measurement plot. When there were fewer than about 1000 hardwood stems per acre, the entire pine measurement plot area was used for hardwood measurement. As hardwood stem

Table 1. Location and establishment information for measured comparison

Study
Dubberly
Escambia
Fayette
Floyd County
Grass Creek
Hobbs-Western Marston
Mock
Palatka
Pickens Piedmont
Pineville
Rochelle Ross
Savannah Town
Sewanee Shannon
Summerville-1
Summerville-2 Summerville-3
Summerville-6
Summerville-8
Summerville-9
Summerville-10 Summerville-1 Upson County Waddels

Location

Establishment information

Long Co., GA
Escambia Co., AL
Fayette Co., AL
Floyd Co., GA
King and Queen
Co., VA
Hardin Co., TN
Charles City
Co., VA
Jasper Co., SC
Putnam Co., FL
Pickens Co. AL
King and Queen Co.,VA
Rapides Parrish,
LA Hardin Co. TN
Hardin Co., TIM
Effingham Co., GA Franklin Co., TN Floyd Co., GA
Dorchester Co., SC
Dorchester Co., SC Dorchester Co., SC
Dorchester Co., SC
Dorchester Co., SC
Dorchester Co., SC
Dorchester Co., SC Dorchester Co., SC
Upson Co., GA
New Kent Co., VA

Harvested spring, 1970; entire site roller chopped and burned, summer, 1970; site prep study overlaid; machine planted with loblolly pine January, 1973 Seed tree regeneration of longleaf pine; seed trees removed, regeneration averaged approximately 10 years old at time of treatment in 1957 Conversion study; harvested 1958; mechanical and chemical treatments applied in fall, 1958 and spring, 1959; hand planted in 1959 with loblolly pine Harvested in 1970; two pass roller chopped in 1971; direct seeded in January, 1972, with
loblolly pine
Loblolly pine plantation, planted 1974
Sheared in 1966; ineffective burn; direct seeded January, 1967, with loblolly pine Loblolly pine plantation, planted 1973
Harvested 1965; planted stand destroyed by wildfire, 1969; harrowed and bedded in fall, 1969; machine planted February, 1970, with slash pine. Slash pine plantations (3), two planted in 1965, one planted in 1967; all sites were chopped and bedded Burned October, 1962; injected, August, 1963; hand planted January, 1963, with loblolly
pine
Loblolly pine plantation, planted 1974
Loblolly pine underplanted in a hardwood overstory in 1948
Disked 1976; machine planted in 1976 with loblolly pine Part bedded in 1978, part not bedded; planted in February, 1979, with loblolly pine
Harvested in 1972; KG and bedded, fall, 1972; planted early, 1973, with loblolly pine
Sheared and chopped, 1976; planted March, 1977, with loblolly pine at an 8'x10' spacing Site preparation study (rootraking, Velpar, check); planted March, 1978, with loblolly pine
100% KG bladed and windrowed in 1958; burned February, 1959; planted in 1959 with
loblolly pine
50% KG bladed in June, 1959; burned October, 1959; planted in 1959 with loblolly pine Drained cypress/hardwood swamp; 100% KG bladed in 1957; planted in 1958 with loblolly
pine
Drained cypress/hardwood swamp; no mechanical preparation; burned January, 1954; planted in 1954 with loblolly pine 60-70% brush drummed in July, 1956; burned November, 1957; planted in 1957 with
loblolly pine
Drained cypress/hardwood swamp; 60-70% brush drummed and burned in December, 1956; planted 1957; sprayed with 2,4,5-T in 1958 100% dozer bladed and burned in January, 1961; planted in 1961 with loblolly pine 50% brush drummed and burned in February 1956; planted in 1956 with loblolly pine
Site prepared with rolling brush cutter; direct seeded following 1961 growing season with loblolly pine Loblolly pine plantation, planted 1977

(Note: all establishment dates are given at the beginning of the growing season-i.e. a stand shown as being planted in 1970 was planted during the 1969-70 planting season.)
4/Georgia Forestry Commission

Table 2. Description of physiography/soils and treatments by study

Study name
(age at treatment, measurement)

Physiography/
soils

1
Treatment information

Dubberly
(0,11)

Escambia (10,37)
Fayette (0,24)
Floyd (61/2 ,11)

Grass Creek
(5,9)

Hobbs-Western

(6

/1 2

,18)

Marston
(5,10)
Mock
(0,14)

North End
(5,10) Palatka
(12,19-WD) (12,19-PMD) (10,17-VPPD) Pickens
(5,20)
Piedmont
(4,9)

Coastal plain, Leefield-Pelham
complex soil
Coastal plain
Upper coastal
plain
Ridge and valley Montevallo soil series, rocky, shallow silt-loam 5-20% slope Upper coastal plain, sandy loam sandy clay loam

Split-split plot design, with 3 blocks: (a) site prep whole plots: (1) chop and burn; (2) chop, burn and bed; and (3) chop, burn, triple flat harrowed with bedding (note: chop and burn in summer, 1970; harrowing and bedding in July, 1972) (b) Herbicide subplots: (1 ) weed control (2 lb a.i./ac 2,4,5-T + 5 lb a.i./ac. dalapon + 4 lb a.i./ac. simizine)--for hardwoods and herbaceous weeds; (2) no weed control; (c) Fertilizer sub-subplots: (1) fertilized (40 Ib/ac P + 100 Ib/ac N); (2) no fertilizer
Two release treatments applied by helicopter in May, 1957: (1) 1 lb. a.i./ac 2,4,5-T ester in 4% gallons of water (basically ineffective, used as a "check"); (2) 3 lb a.i./ac 2,4,5-T ester in 4% gallons of water
Seven site preparation treatments: (1) bulldozed and piled; (2) check-- no treatment; (3) hardwoods girdled-- no herbicide; (4) tube injection of herbicide; (5) ax frill plus herbicide; (6) Brady chain frill plus herbicide; (7) mist blown herbicide (note: all herbicide treatments consisted of a mixture of half 2,4-D and half 2,4,5-T at a concentration of 4 lb a.e./gallon)
1 X 20 ch strips treated with helicopter on July 14, 1978, 0.5 ch buffers. Herbicides included: (1) triclopyr amine 1 lb. a.i./ac; (2) triclopyr amine, 0.5 lb a.i./ac plus 1 pint/100 gallons X77 surfactant; (3) triclopyr ester, 1 lb a.i./ac; (4) triclopyr ester, 0.5 lb a.i./ac plus 1 pint X77
surfactant; (5) glyphosate, 1 lb a.i./ac; (6) glyphosate, 2 lb a.i./ac; (7) 2,4,5-T ester, 2 lb a.i./ac; (check plots were obtained from buffer areas) 0.25 ac plots treated April, 1979 with (1) 1.0 lb a.i./ac: and (2) 1.25 lb a.i./ac hexazinone (as Velpar 2cc Gridball); (3) untreated check

soil
Interior low plateau
Coastal plain
Coastal plain Leon-Blanton soil
Coastal plain
Lower coastal
plain
Coastal plain
Coastal plain

10X40 ch block operationally treated with 5/8 gal 2,4,5-T (1.25 lb a.i.) +1 gallon diesel +6 3/8

gallons water per acre in June, 1972. Untreated block in same stand adjacent to treated area

used as a check

39 acres operationally sprayed in June, 1973 by helicopter with 2 lb 2,4,5-T a.i. in 1/2 gallon

diesel + 4 gallons water per acre; remainder of plantation untreated

Split plot design with 4 blocks: (a) fertilizer whole plots: (1 ) 40 Ib/ac P + 100 Ib/ac N; (2) no

fertilizer; (b) herbicide subplots: (1) simizine, April, 1970; (2) paraquat, May, 1970; (3) no weed control

26 acres operationally sprayed in June, 1973, by helicopter with 2 lb 2,4,5-T a.i. in y2 gallon

diesel + 4 gallons water per acre; remainder of plantation untreated

Three sets of paired plots (approx. 0.12/ac each)-- all vegetation other than planted pines con-

trolled; other plot untreated. One set of plots classified as well drained, another as somewhat

poorly and moderately well drained, and the other very poorly and poorly drained. Plots were
originally part of Univ. of Ga. PMRC Competing Vegetation Study

Middle 40-acre portion of a 100-acre tract operationally treated with 2 lb a.i./ac 2,4,5-T in

May, 1968; remaining 60 acres untreated, used as a check

48

acres operationally

sprayed

in

June,

1973,

using

a

helicopter with

2

lb

a.i./ac

2,4,5-T

in

/1 2

gallon diesel+4 gallons water per acre; remainder of plantation untreated, used as a check

(Table 2 Continued on Page 6)

density increased above 1000 stems per acre, measurement of the entire pine measurement plot area would have taken an inordinate amount of time, so the hardwood measurement plot area was reduced to 0.05 or 0.02 acre, maintaining a minimum sample of 30 hardwood stems. All sample hardwood stems 0.5 inch dbh and larger were tallied by one-inch diameter class, 10-foot height class and species.
For each comparison, information regarding date and type of stand establishment, treatments and rates applied, date treated, forest type, site index, average slope, soil type, drainage and stand history (including injury, fire history, pre-
vious stand, etc.) was noted, when available. In addition, percent slope and aspect were observed at each pine measure-
ment plot location. A summary of

physiography/soils and treatments is given in Table 2.
RESULTS AND DISCUSSION
Table 3 is a summary of pine and hardwood measurements by treatment. All but five of these studies were hardwood control comparisons. The other five (Dubberly, Mock, Palatka, Ross and Savannah Town) were primarily herba-
ceous or understory vegetation control studies and will be discussed separately. Examination of this table reveals a great
deal of variation in pine and hardwood response to herbicide treatment. In some cases, such as Grass Creek, hardwoods were increasingly controlled (fewer, smaller hardwood stems on herbicide treated plots) and a corresponding greater

pine yield was realized with increasing rates of herbicide. But in other cases, such as Pickens and Summerville-3, herbicide treatment did not seem to have an effect. All but one of the comparisons showing no response or negative response of pine yield to herbicide application were operational comparisons using 2, 4,5-T, where initial conditions, herbicide rates and application techniques were often not closely controlled. Results from 2,4,5-T are known to be highly variable, depending on species composition, weather conditions, etc., and misapplication could result in pine damage or mortality.
Considering the inherent variability in operational comparisons, and the fact that several of the research comparisons were installed as tests of rates, timing, soil interactions, etc., the entire story is
Georgia Forestry Commission/5

1
M Q?Jt *:&** "'.''
2. Description of physiography/soils and treatments (continued).

Study na
(age at trc-atment,
urement
Pineville 0,1,2),36)
Rochelle
(2,7)
Ross
(0,4)
Savannah Town
(0,11)
Sewanee
(0,6)
Shannon
(0,5)
Summerville-1 (3,25)
Summerville-2 (3,25)
Summerville-3 (4,26)
Summerville-6 (8,30)
Summerville-8 (5,27)
Summerville-9 (5,27)
Summerville-10 (1,23)
Summerville-1 (6,28)
Upson
(0,6)
Waddels
(3,6)

Physiography/
soils
Coastal plain, silt and very fine
sandy loam
Interior low plateau

1
Treatment information

Ten treatments, two replications were installed--only one replication remained intact. Plots

were 0.25 acre. Treatments: (1 ) plant in openings, no release; the following 9 treatments were planted at regular intervals, selective release included control of hardwood stems greater than 3 inches dbh; complete release included control of hardwood stems greater than 0.5 inches
dbh: (2) AMS selective release immediately after planting with (Ammate); (plot destroyed, no

data available) (3) selective release immediately after planting by girdling; (4) selective release,

AMS 1 year after planting, with

(Ammate); (5) selective release, 1 year after planting, by

AMS girdling; (6) selective release, 2 years after planting, with

(Ammate); (7) selective release,

AMS 2 years after planting, by girdling; (8) complete release, immediately after planting with

(Ammate); (9) complete release, immediately after planting, by girdling; (10) no release

(1) 1 lb a.i./ac hexazinone (Velpar 2 cc Gridball); (2) untreated check; 75' X 75' treatment

plots

Interior low

Factorial with split-plot design: (a) site preparation whole plots: (1) bedded; (2) not bedded;

plateau, Shutuba- (b) fertilizer subplots: (1) fertilized with DAP; (2) not fertilized; (c) herbicide sub-plots:

Pickwick complex (1) hexazinone (Velpar liquid) at 1 lb a.i./ac; (2) no herbicide. (NCSFFC Regionwide Study

silt-loam to fine No. 7)

sandy loam soil

Coastal plain, Stilson series
soil

Split plot design, with 4 blocks: (a) fertilizer whole plots (1) 200 Ib/ac CSP; (2) 476 Ib/ac ammonium sulfate; (b) herbicide subplots: (1) no weed control; (2) first season weed control with 2 lb a.i./ac 2,4,5-T + 2.5 lb a.i./ac dalapon + 4 lb a.i./ac simazine; (3) annual weed

control using same treatment as in (2)

Ridge and valley, Completely randomized design, 1-acre plots: (1) all stems 4.5 ft. or taller injected with

Hartsells sandy

picloram + 2,4-D (Tordon 101 R); (2) untreated

loam soil

Piedmont

Site preparation comparison: (1) rootraking; (2) hexazinone 2 lb a.i./ac (Velpar 2cc Gridball);

(3) untreated

Lower coastal

3.8 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

3 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

4 acres operationally released with 2,4,5-T, 2 lb a.e/ac, June 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

4 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

4 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

5 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

4 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain

untreated, used as a check

Lower coastal

5 acres operationally released with 2,4,5-T, 2 lb a.e./ac, June, 1962; remainder of plantation

plain
Piedmont
Loamy fine sand

untreated, used as a check

Operational release comparison: (1) 1.5 lb a.i./ac 2,4,5-T in Vz gallon diesel + 3% gallons water

per

acre;

(2)

2

lb

a.i./ac

2,4,5-T

in

1
/2

gallon

diesel

+

31 /a

gallons

water;

(3)

check

Three replications of five treatments (replications were on ridge, northwest slope, and

with sandy clay subsoil 9-24"

southeast slope), 0.20 acre treatment plots: (1) 1.25 lb a.i./ac hexazinone (Velpar 2cc Gridball); (2) 1.5 lb a.i./ac hexazinone (Velpar 2cc Gridball); (3) 1.25 lb a.i./ac hexazinone (Velpar

below surface

granules); (4) 1.5 lb a.i./ac hexazinone (Velpar granules); (5) check

i
a.i. = active ingredient
a.e. = acid equ ivalent

Table 3. Summary of pine and hardwood information by study and treatment.

Study

(treatment,

2

measurement age) Treatment

Number
of trees per acre pine hard.

Basal

area

per acre

(sqft)

pine

hard.

O.B. volume per acre (cu ft)
pine

Dubberly
(0,11)

CB,WC, F CB,WC, NF CB, NWC, F CB, NWC, NF CBB,WC, F CBB,WC, NF

6/Georgia Forestry Commission

552 312

79.3

474 102

47.2

542 900

62.5

624 189

66.6

629 232 116.3

561

29

96.4

3.4 1279.5 0.6 779.8 7.2 1041.1 1.0 1219.8 2.2 2234.8 0.2 1791.4

Mean dbh
(in)
Pi ne hard.

5.0

1.1

4.1

1.0

4.3

1.2

4.1

1.0

5.7

1.2

5.5

1.0

Mean
total height
(ft)
pine hard.

Percent
hardwood
basal area (%)

31

15

25

10

28

11

28

11

39 13

38

12

4.1 1.3 10.3 1.5 1.9 0.2

Table 3. Summary of pine and hardwood information (continued).

Study

(treatment,

2

measurement age) Treatment

Number
of trees per acre pine hard.

Basal

area

per acre

(sqft)

pine

hard.

0. B.
volume
per acre (cuft)
pine

CBB, NWC, F

620 254

77.7

CBB, NWC, NF

774

29

83.1

CBHB, WC, F

639

29 115.6

CBHB, WC,NF

620

44 104.3

CBHB, NWC, F

620

58

98.3

CBHB, NWC, NF 658

29

83.3

CB, mean

548 376

63.9

CBB, mean

646 136

93.4

CBHB, mean

634

40 100.4

WC, mean

579 125

93.2

NWC, mean

640 243

78.6

F, Mean

600 298

91.6

NF, mean

618

70

80.2

2.4 1442.1 0.2 1462.6 0.2 2186.0 0.3 1841.4 0.5 1659.8 0.0 1493.2 3.0 1080.0 1.2 1732.7 0.5 1795.1 1.2 1685.5 1.9 1386.4 2.6 1640.6 0.4 1431.4

Escambia (10,37)

1 lb 2,4,5-T 3 lb 2,4,5-T

358 454 653 471

61.2 74.4

24.6 2587.8 9.0 4933.4

Fayette (0,24)

Bulldoze
Hand girdled
Injection+herb.
Ax frill+herb.
Chain frill+herb. Herbicide, mean Check

474 837 212 980 371 914 433 878 449 934 418 909 204 1045

167.2 70.5
126.1 153.3 149.2 142.9
16.9

16.3 59.4 19.9 14.8 18.5 17.7 108.7

4393.1 1763.9 3356.8 4002.9 3912.8 3757.5
359.0

Floyd County

(6

1
/2,11)

Grass Creek
(5,9)

1 lb triclopyr
amine 0.5 lb triclopyr amine + 77
1 lb triclopyr ester 0.5 lb triclopyr
ester + X77
1 lb glyphosate 2 lb glyphosate 2 lb 2,4,5-T
Herbicide, mean Check

1360
907
480 1160
947 907 547 901 588

1093
1107
1293 1067
1680 1427 1467 1305 1348

1.25 1b Velpar, 2cc 1 lb Velpar, 2cc Check

760 1333 783 1500 760 2183

46.4
36.5
12.1 35.7
29.9 35.5 31.1 32.5 22.8
52.7 49.6 43.6

10.6
8.9
11.2 12.1
25.8 19.8 21.1 15.6 16.0
10.6 18.7 25.5

867.5
616.7
183.0 573.9
569.6 609.4 461.7 554.5 317.2
596.1 505.0 474.3

Hobbs-Western (6%. 18)

1.25 lb 2,4,5-T
Check

432 1636 227 1926

51.5 34.1

39.2 1147.4 50.6 647.9

Marston
(5,10)

2 lb 2.4,5-T
Check

458 1136 774 1810

22.8 22.1

13.4 23.8

252.3 313.3

Pickens (5,20)

2 lb 2,4,5-T Check

336 838 331 1032

108.6 112.3

18.3 2984.0 36.0 3150.1

Piedmont
(4,9)
Mock
(0,14)

2 lb 2,4,5-T Check

810 264 768 1470

F,WC (simazine)

454 194

F,WC(paraquat)

427 375

F.NWC

508 230

NF,WC(simazine) 536 145

NF,WC( paraquat) 445 351

NF,NWC

490 254

F, mean

463 266

NF, mean

487 250

WC(simazine),mean 490 170

WC( paraquat), mean 436 363

WC,mean

463 266

NWC, mean

499 242

44.2 38.9
89.2 70.8 81.8 96.9 75.0 82.1 80.6 84.7 93.1 72.9 83.0 82.0

1.7 10.9

513.3 479.2

2.2 1821.6 2.2 1551.1 3.6 1643.1 1.0 1944.4 6.9 1492.3 2.0 1544.9 2.7 1671.9 3.3 1660.5 1.6 1883.0 4.6 1521.7 3.1 1702.4 2.8 1594.0

Mean dbh
(in)
pine hard.

4.5

1.1

4.3

1.0

5.6

1.0

5.5

1.0

5.2

1.0

4.6 0.0

4.4

1.1

5.0

1.1

5.2

1.0

5.2

1.0

4.5

1.0

5.0

1.1

4.7

1.0

5.1

2.7

4.0

1.8

7.9

1.6

7.5

2.9

7.6

1.7

7.9

1.6

7.6

1.7

7.7

1.7

3.6

3.6

2.2

1.2

2.5

1.2

2.2

1.2

2.1

1.3

2.2

1.5

2.5

1.4

2.8

1.4

2.4

1.3

2.2

1.3

3.4

1.1

3.2

1.2

3.1

1.3

4.8

1.8

5.4

1.9

2.8

1.3

2.1

1.4

7.2

1.6

7.7

2.2

2.9

1.1

2.8

1.1

5.9

1.4

5.4

1.0

5.2

1.3

5.6

1.0

5.3

1.5

5.3

1.1

5.5

1.2

5.4

1.2

5.8

1.2

5.4

1.3

5.6

1.2

5.3

1.2

Mean
total height
(ft)
pine hard.

33

16

28

7

37

6

37

22

34

21

32

28

12

34

12

35

16

34

13

30

13

34

14

31

12

Percent
hardwood
basal area (%)
3.0 0.2 0.2 0.3 0.5 0.0 4.3 1.3 0.2 1.3 2.6 3.3 0.6

48 20

45

13

28.7 10.8

57

16

52 28

56 16

56

18

56

17

56

17

31

28

8.9 45.7 13.6
8.8 11.0 11.1 86.5

17

13

18.7

17

12

19.7

12

11

15

12

48.1 25.3

16

12

17

12

18

13

16

12

15

12

21

10

20

14

21

15

46.3 35.8 40.4 33.4 49.0
16.8 27.4 36.9

31

18

35

18

43.2 59.6

15

13

14

13

37.1 52.0

52

17

56 20

14.4 24.3

16

10

17

12

3.7 22.0

41

13

2.4

40

9

3.0

38

10

4.2

39

9

1.0

38

14

8.4

37

10

2.3

40

11

3.2

38

11

3.9

40

11

1.7

39

12

5.7

40

11

3.7

38

10

3.3

Georgia Forestry Commission/7

Table 3. Summary of pine and hardwood information (continued).

Study

(treatm

2

measurement age) Treatment

Number
of trees per acre
pine hard.

Basal area per acre (sqft) pine hard

North End
(5,10)

2 lb 2,4,5-T Check

1122 1138 942 2270

50.5 42.9

7.7 16.5

Palatka (12,19) (12,19)
(10,17)

WC-WD NWC-WD WC-PMD NWC-PMD WC-VPPD NWC-VPPD
WC,mean NWC,mean

639

141.2

0.0

639 222 142.6 5.6

489

126.9 0.0

489

22 118.1

0.5

704

154.5

0.0

680 195 167.3 6.1

611

140.9 0.0

603 146 142.7 4.1

Pineville {(0,1 ,2) ,36)

Open planting
no release
Girdle,selective
immediately
AMS, selective
1 year later Girdle, selective 1 year later
AMS, selective
2 years later
Girdle, selective
2 years later
AMS, complete
immediately
No release Girdle, mean AMS, mean No release, mean
Selective,
immediately, mean
Selective, 1 year later
Selective,
2 years later, mean Complete, immediately, mean

280
230 210
205 330 240
230
180 226 257 230 230
208
285
230

195
125
120
140 840 370
140
260 175 367 228 125
130
605
102

122.7 125.8
137.1
126.5 93.5
155.9 116.5 "108.5
30.0 115.7 115.6 125.8 131.8
124.7 114.2

29.6 3.7 0.7 3.6
13.6 12.5
4.4
14.7 5.5 6.2
22.2 3.7
2.2
13.1
3.3

Rochelle
(2,7)

1 lb Velpar Check

460 580 510 1485

26.0 19.3

4.0 17.2

Ross
(0,4)

B,F,WC B,F,NWC B,NF,WC B,NF,NWC NB,F,WC NB,F,NWC NB,NF,WC
NB,NF,NWC
B,mean NB,mean F,mean NF,mean WC,mean
NWC.mean

580 70 600 60 565 103 590 47 412 212 585 158 478 258 607 225 584 70 520 213 544 125 560 158 509 161 596 122

14.7

0.4

6.1

0.3

14.8 0.6

6.2

0.3

10.4

1.2

5.8

0.9

9.4

1.5

4.8

1.3

10.5

0.4

7.6

1.2

9.3

0.7

8.8

0.9

12.3

0.9

5.7

0.7

0. B. volume per acre (cuft)
pine
663.9 642.9

Mean dbh
(in)

pine hard.

2.5

1.1

2.7

1.1

3393.8 3325.5 3020.6 2940.9 3714.0 4210.2 3376.1 3492.2

6.2 0.0

6.3

1.9

6.7

0.0

6.6 0.5

6.2

0.0

6.6 2.0

6.4 0.0

6.5

1.5

4065.0

8.3 3.6

4608.7

9.8 2.0

4662.9

10.8

1.0

4594.8

10.1

2.1

3083.8

6.6

1.6

6102.0

10.2

2.1

4074.4

9.5 0.8

3733.0 4821.4 3940.4 3899.0 4608.7

9.7

1.8

9.8

1.8

9.0

1.1

9.0

2.7

9.8 2.0

4628.9

10.4

1.6

4592.9

8.4

1.9

4027.2

9.3 0.8

Mean
total height
(ft)
pine hard.

16

11

17

10

51

49

10

50

52

12

50

54

12

50

52

11

63 23

79

14

74

9

73 16

50 14

79

17

73

5

63 16

76

13

66 20

63 20

79

14

74

12

64

16

73

6

283.0 258.2
134.5 54.7
139.5 54.7 90.4 50.1 78.2 42.6 95.9 65.3 82.4 78.8
110.9 50.5

3.1

1.1

2.5

1.3

2.1

1.0

1.3

1.0

2.1

1.0

1.3

1.0

2.1

1.0

1.3

1.0

1.8

1.0

1.1

1.0

1.7

1.0

1.6

1.0

1.7

1.0

1.6

1.0

2.0

1.0

1.3

1.0

17

11

16

16

12

8

9

9

12

9

9

8

12

9

9

8

11

9

9

9

10

8

10

9

10

8

10

9

12

9

9

8

Percent
hardwood
basal area (%)
13.2 27.8
0.0 3.8 0.0 0.4 0.0 3.5 0.0 2.6
19.4
2.8
0.5
2.8
12.7
7.4
1.8
11.9 3.7 5.6
15.7 2.8
1.7
10.1
2.7
13.3 47.1
2.8 5.1 4.0 4.0 10.3 14.1 13.7 21.0 4.0 14.8 8.1 10.7 7.7
,,.,

Savannah Town F,WC(1styear)

574 508

96.0

2.8

1724.9

5.4

1.0

37

12

2.8

(0,11)

F,WC(annual)

639

58 108.4 0.3

1996.2

5.5

1.0

38

10

0.3

F,NWC

537 450

80.8

2.8

1377.0

5.1

1.0

34

11

3.3

NF,WC(1styear)

566 310

99.3

1.7

1926.0

5.5

1.0

36

14

1.7

NF,WC(annual)

566

87

91.7

0.5

1550.1

5.2

1.0

34

9

0.2

NF.NWC

523 242

80.1

1.3

1384.8

5.2

1.0

34

10

1.6

WC(1st year), mean 570 409

97.7

2.3

1825.5

5.5

1.0

36

13

2.3

8/Georgia Forestry Commission

^^^MsetanBHHH
Table 3. Summary of pine and hardwood information (continued).

Study

(treatment,

2

measurement age) Treatment

Number
of trees per acre
pine hard.

Basal area per acre (sq ft) pine hard.

WC(annual),mean

602

72 100.1

0.4

WC,mean

586 241

98.9

1.3

NWC.mean

530 346

80.5

2.1

F,mean

584 339

95.1

2.0

IMF, mean

552 213

90.4

1.2

Sewanee
(0,6)

Tordon injected Check

523 1113 529 1693

20.8 11.6

7.4 15.4

Shannon
(0,5)

2 lb Velpar Rootrake Untreated

375 950 580 295 680 770

6.3 18.8

4.2

1.6

0.4 83.1

Summerville -1 (3,25)

2 lb 2,4,5-T Check

294 215 156.4 8.3

318 516 171.1

9.4

Summerville -2
(3,25)

2 lb 2,4,5-T Check

294 265 282 552

144.0 158.2

7.8 14.7

Summerville -3
(4,26)

2 lb 2,4,5-T
Check

196 666 144 764

138.1 123.7

31.9 44.9

Summerville -6 (8,30)

2 lb 2,4,5-T Check

192 452 208 656

159.1 37.5 160.0 34.5

Summerville-8 (5,27)

2 lb 2,4,5-T Check

232 200 164 524

167.8 2.8 144.4 46.4

Summerville -9 (5,27)

2 lb 2,4,5-T Check

146 220 124 618

108.3 12.5 93.7 42.9

Summerville -10
(1,23)
Summerville 11
(6,28)

2 lb 2,4,5-T Check 2 lb 2,4,5-T Check

342

80 168.9 7.3

220 180 137.1 17.7

142 156 135.4 17.1

230

88 170.2

8.2

Upson
(6,22)

2 lb 2,4,5-T Check

736 1711 409 1771

78.5 29.6 86.1 39.8

Waddels
(3,6)

1.25 lb 2cc Velpar 1.5 lb 2cc Velpar 1.25 lb Velpar granule 1.5 lb Velpar granule Check
2cc Velpar, mean Velpar granule, mean

613 657 587
623
430 635 605

466 427 2450
970
2750 446 1710

40.2 33.0 39.1

4.3 3.3 23.8

38.8 8.0

22.5 36.6 39.0

23.2 3.8
15.9

O. B. volume per acre (cu ft)
pine
1773.2 1799.3 1380.9 1699.4 1620.3

Mean dbh
(in)

pine hard.

5.4

1.0

5.4

1.0

5.2

1.0

5.3

1.0

5.3

1.0

228.6 175.2

2.6

1.1

1.8

1.2

99.3 44.9
6.8

1.7

1.4

1.1

1.0

0.4

3.2

5234.5 5969.9

9.8

2.4

9.9

1.6

4540.0 5418.2

9.3

1.8

10.0

1.8

4651.4 4626.1

11.1

2.8

12.1

2.8

5864.9 5803.9

12.2

3.5

12.1

2.6

6422.6 5496.2

11.2

1.1

12.5

3.7

3799.2 3359.2

11.4

2.8

11.9

3.3

5415.8 4204.2 4966.3 6465.5

9.3

3.8

10.4 4.4

13.1

4.2

11.4 4.0

1856.7 1877.5

4.1

1.5

6.1

1.7

396.0 312.7 392.0

3.3

1.1

2.9

1.1

3.3

1.1

393.8

3.2

1.2

225.3 354.4 392.9

3.0

1.1

3.1

1.1

3.2

1.2

Mean
total height
(ft)
pine hard.

36

10

36

11

34

10

36

11

35

11

15

11

13

13

12

15

9

11

4 23

66

14

75

15

66

14

72

15

72 28 78 28

78 26 79 25

82

9

82 35

73 25 74 33

69 30 65 34 79 34 82 32

30

16

42 20

15

9

13

9

16

10

15

10

15

11

14

9

16

10

Percent
hardwood
basal area (%)
0.3 1.3 2.5 2.1 1.2
26.2 57.3
58.3 27.6 99.5
5.1 5.2
5.1 8.5
18.8 26.6
19.1 27.8
1.6 24.3
10.3 31.4
4.1 11.4 11.2
4.6
27.4 31.6
9.7 9.1 37.8
17.1
50.8 9.4
27.5

WC=Weed Control
F=Fertilizer
CB=Chop, burn B=Bedded

WD=Well drained
NWC=No weed control
NF=Not fertilized CBB=Chop, burn, bed

NB=Not bedded
PMD=Poorly-moderately drained
CBHB=Chop, burn, harrow, bed VPPD=Very poorly-poorly drained
Georgia Forestry Commission/9

not revealed if one looks solely at treat-
ment means. A more important relation-
ship is pine yield versus the amount of hardwood present in the stand, regardless of herbicide treatment. One relationship which can be examined is pine yield
(square feet of basal area or cubic foot
yield) versus hardwood basal area. Figure I shows this relationship for the Floyd County comparison. Note the high variability and lack of a definitive trend. Figure 2 shows a transformed relationship where hardwood basal area has been ex-
pressed as a percentage of the total basal area (pine plus hardwood). Variation is greatly reduced and a trend is obvious.
Relative hardwood basal area appears to be a better indicator of hardwood effects and probably aids in standardizing other site and stand effects.
Burkhart and Sprinz (1984) developed a yield model which incorporated this effect of hardwood basal area. Using measurements from the Fayette study at age II and age 24, they noted that percent hardwood basal area on a plot by plot basis remained constant over time. That
is, if a plot had 30% hardwood basal area at age 11, it would still have 30% hardwood basal area at age 24. Although pines
tend to grow faster than hardwoods, apparently pine mortality and hardwood ingrowth combine to maintain the constant proportion of hardwood basal area. This means that once hardwoods become established in a pine stand, pines do not "out-grow" and dominate the hardwoods, and that hardwoods remain as competition which adversely affects pine yield.
This concept of constant proportion of hardwood basal area supports the idea
that measurement of the amount of hardwood basal area in a stand several years after treatment (as was done in this ef-
fort) should be an adequate indicator of initial hardwood density and/or treatment effectiveness. This assumes, of course, that hardwood stocking was equivalent across plots at time of treat-
ment -- not always a good assumption,
particularly in operational comparisons. The apparent lack of effectiveness of
chemical treatment in some operational comparisons may be due to the violation of this assumption, as illustrated in Figure 3 for Summerville-3. The two plots with highest pine volume yield and among the lowest percent hardwood basal areas are untreated--that is, these plots apparently
did not have a high proportion of hard-
wood basal at time of treatment. Like-
wise, the plot with the next to highest proportion of hardwood and next to lowest pine yield is a treated plot, indicating the treatment was ineffective. This points out that a comparison of treatment means alone is not sufficient. It also indicates the importance of proper plot layout during herbicide study establishment and the need to determine initial pine and hardwood stocking.
Figure 4 (Summerville-6) also illustrates a strong negative effect of percent
10/Georgia Forestry Commission

70


60

50
(0
UJ 40
D<C
8ASAL
o
FINE
20
10



























0-

1

i

i

10

15

20

25

30

HARDWOOD BASAL AREA (sq.ft.)

Figure 1. Per acre basal area comparison of pine and hard-
wood at Floyd County (age 11).

r-- 35

70

60

50

40
<
UJ
<cr -<i 30 Vm<) UzJ
Q. 20

10

04-

10

20

30

40

50

60

70

80

HARDWOOD BASAL AREA(%)

Figure 2.

Pine basal area per acre to percent hardwood basal area comparison at Floyd County (age 1 1).

1

6000
5500
5000
10
d 4500
S 4000

2,4,5 -T s Check

3000 25002000 1500

10

20

30

40

50

60

HARDWOOD BASAL AREA(%)

Figure 3. Pine Cubic foot volume per acre to percent hardwood basal area comparison at Summerville-3
(age 26).

5000-


4500-

4000-


cd
o

3500-

3 O 3000-
111
5 3
-I
5 2500-
UJ

2000-







15001000500-
0-











20

40

60

80

% HARDWOOD BASAL AREA ( )


--t
100

Figure 5. Pine cubic foot volume per acre to percent hardwood basal area comparison at Fayette (age 24).

8000
7500
7000
6500
CD
b 6000 r
D
5500 5
5000
4500
4000
3500
3000

2.4,5-T Check

10

20

30

HARDWOOD BASAL AREA (%)

_, *_
40

Figure 4. Pine cubic foot volume per acre to percent hardwood basal area comparison at Summerville-6
(age 30).

X

60

X



X



50
*
+
C 40

X

a

s *.

DC
< 30 -

<

<

-

CD

20

X
a
A
a

* Piedmont 2,4,5-T

Piedmont Check

10

x Northend 2,4,5-T

Northend Check

a Marston, 2,4.5-T
A Marston, Check

A

A A

&

a

10

20

30

40

50

60

HARDWOOD BASAL AREA (%)

Figure 6.

Pine basal per acre to percent hardwood basal
area comparison at Piedmont, Northend and Marston (age 10) 3 .

Values for Piedmont adjusted from age 9 to 10 using mean
annual increment.

Georgia Forestry Commission/7

.

hardwood basal area on pine yield but a
lack of treatment effect. Values in Table 3 indicate that no differences exist be-
tween treated and check mean volume,
basal area, etc. Additional figures (Figures 5-7) exhib-
it similar trends as noted in Figures 2-4. The Fayette Site Preparation Study, Figure 5, is one of the best documented older replicated herbicide studies in the
South. Hardwood basal area ranges from near to 100%, allowing examination of the pine yield across a wide range of hardwood levels. The trend in Figure 5 is very well defined. Note that pine yield at 30% hardwood basal area is approximately
one-half that at 4% hardwood basal area.
This reduction in pine yield is apparent in almost all of the measured comparisons, if hardwood is present in a pine stand, yield will be affected, and evidently affected dramatically at relatively low levels of hardwood stocking.
Figure 6 shows three operational comparisons in separate stands which were treated the same day in Virginia. Piedmont was selected as a pine stand which would normally not be considered to need release (note the relatively low percent hardwood basal area levels). North End was a stand which was marginally in need of release, and Marston was judged to definitely be in need of release. Piedmont was one year younger than the other two stands and for this figure only
its basal area yields have been increased by one year's growth (based on age 9 mean annual increment). Note the consistent trend in pine basal area yield relative to percent hardwood basal area for the three stands combined.
Figure 7 shows two research comparisons at different ages, Sewanee at age 6 and Grass Creek at age 9. In each case the trend of pine yield in basal area and percent hardwood basal area is well defined. This figure also illustrates how a trend will probably look over time in the same
stand.
There were five herbaceous or understory vegetation control research studies (no operational comparisons). All but one were installed as fertilization/weed control comparisons, with two also including different site preparation treatments. Table 4 is a summary from Table 3 showing weed control effects on pine survival, basal area, volume, dbh and total height. All studies except Palatka show an increase in pine size and yield with weed control. Palatka was three sets of paired plots treated for understory shrub and herbaceous weed control at age 10 (one plot) or 12 (two plots).
The three studies in the Georgia coastal plain, Dubberly, Mock and Savannah
Town, show an average 25% increase in
volume yield, or about 0.36 cord per acre per year. Chemicals used in these studies were not as effective in controlling herbaceous weeds as chemicals presently being tested and used. Indications from more recent studies with better weed control
12/Georgia Forestry Commission

Before herbicide application, each stand should be evaluated as to the need for vegetation control and the availability of suitable and effective herbicide treatments.
60-

50-

- 40-I
CO
<
Ul
C<C 30 < C<O
CO
zUJ 20
a.

* Grass Creek, 1.25 lb VELPAR

a a

10-

x Grass Creek, 1.00 lb VELPAR Grass Creek, Check

A Sewanee, TORDON

id Sewanee, Check

04

10

20

30

40

50

60

70

HARDWOOD BASAL AREA(%)

Figure 7.

Pine basal area per acre to percent hardwood basal area comparison at Grass Creek (age 9) and Sewanee (age 6)

are that even greater gains can be made from control of herbaceous weeds. One of the newer chemicals, hexazinone, was
used at Ross and although the study is still young, basal area and volume show
more than a 100% increase at age 4, with a 0.7-inch increase in mean dbh and 3-foot increase in mean height. Other reported studies show similar results (Zutter, 1984; Knowe, et al., 1985).
CONCLUSIONS
The high variability and inconsistent treatment effects found in the operation-
al comparisons, particularly those treated with 2,4, 5-T, were unexpected. More consistent treatment effects and yield trends were noted in better controlled research studies. Looking beyond treatment means and examining the relationship
between pine yield and amount of hardwood in the stand resulted in stable relationships across most comparisons,
operational or research.
It is obvious from this data that increasing occurrence of hardwoods in pine stands is well correlated with decreasing pine yield. The logical assumption is that it is competition from the hardwood component which is the cause of this yield reduction. Although this set of data is not suitable for growth and yield model development, it is empirical evidence that
current ideas regarding the effects of
hardwoods on pine growth are valid. The fact that herbicide application did
not always increase pine yield is not indicative of the effect of vegetation control (i.e. herbicide application does not necessarily imply vegetation control). Before herbicide application, each stand should be evaluated as to the need for vegetation control and the availability of suitable and effective herbicide treat-
ments. As data become available from
studies specifically designed to evaluate the effect of competing vegetation on pine growth and yield, better models describing these effects will be developed. Until that time, this set of data should provide guidelines for determining the need and gains from control of competing vegetation.

Table 4. Summary of pine information for h erbaceous vegetation control ccimparisons

Study (treatment, measurement age)

Treatment

Dubberly
(0,11)

WC NWC

Number
of trees per acre
579 640

Basal area per acre (sqft)

O.B. volume per acre
(cu ft)

93.2 78.6

1685.5 1386.4

Mean dbh
(in)
5.2 4.5

Mean
total height (ft)
34 30

Mock
(0,14)

WC(Simazine) 490

93.1

1883.0

5.8

40

NWC

499

82.0

1594.0

5.3

38

Palatka (12,19; 10,17)

WC NWC

611

140.9

3376.1

6.4

50

603

142.7

3492.2

6.5

52

Ross
(0,4)

WC NWC

509

12.3

110.9

2.0

12

596

5.7

50.5

1.3

9

Savannah Town

WC (1st year) 570

97.7

1825.5

5.4

36

(0,11)

WC (annual) 602

100.1

1773.2

5.4

36

NWC

530

80.5

1380.9

5.2

34

WC=Weed NWC=No Weed Control

II" '
(

"'


\ l\

Although pines tend to grow faster than hardwoods, apparantly pine mortality and hardwood ingrowth combine
to maintain the constant proportion
of hardwood basal area.

Georgia Forestry Commission/13

LITERATURE CITED Burkhart, H. E. and P. T. Sprinz. 1984. A model for assessing hardwood competition effects on yields of loblolly
pine plantations. FWS-3-84, School of Forestry and Wildlife Resources, VPI&SU, Blacksburg, Va. 55pp. Knowe, S. A., L. R. Nelson, D. H. Gjerstad, B. R. Zutter, G. R. Glover, P. J. Minogue, and J. H. Dukes, Jr. 1985.
Four-year growth and development of planted loblolly pine on sites with competition control. SJAF, 9:1 1-15.
USDA 2,4, 5-T Assessment Team. 1979. The biologic and economic assessment of 2,4, 5-T. Areport of the 2,4, 5-T assessment team to the rebuttable presumption against registration of 2,4, 5-T. USDA Technical Bulletin Num-
ber 1671, February, 1979. 445pp Zutter, B. R. 1984. 1979 Herbaceous weed control loblolly pine growth response study, fifth-year results. Auburn
University Silvicultural Herbicide Cooperative Research Note 84-8. Auburn University, Ala. 4 pp. Zutter, B. R., G. R. Glover and D. F. Dickens. 1985. Competing vegetation assessment systems in young southern
pine plantations. In Proceedings of Third Biennial Southern Silvicultural Research Conference, Atlanta, Ga., November 7-8, 1984, pp279-286.
14/Georgia Forestry Commission

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