4D United States

Department of

Agriculture

6” -1

m

- Southern

Forest Service

Foreat

Rmearch N6te

so-345

Experiment Station Mav 1988

Competition Impacts on Growth of Naturally Regenerated

Loblolly Pine Seedlings

Michael D. Cain

SUMMARY

Intensive competition control was used for 3 years

in a naturally regenerated, even-aged stand of loblolly and shortleaf pines (Pinus taeda L. and P.

echinata Mill.) in southern Arkansas. Treatments

included: no competition control, woody competition -... .-. .,

control, herbaceous comp$ition $ontrol, and totai -... _. ---

control of nonplnevegetation. Controiof herb&e&us

vegetation resulted in statistically significant pine

growth gains in height, groundline diameter, and

volume per tree. Control of only woody competition

did not improve pine growth compared to untreated

checks.

Addltlonal keyword@: Herbaceous competition

control, herbicides, Pinus teeda L., P. echinata Mill.,

woody competition control.

INTRODUCTION

When properly planned, natural pine regeneration’

is a viable management alternative to artificial regen-’

eration for restocking pine sites and can be particularly attractive to private, nonindustrial forest landowners because the cost of stand establishment is

lower (Williston and Balmer 1974). On cutover areas,,

natural regeneration of loblolly and shortleaf pines

(Pinus raeda L. and P. echinata Mill.) is considered

successful if density averages at least 1,500 seedlings

per acre at the end of the first year of establishment,

or 700 per acre at the beginning of the third year

(Grano 1987), and milacre stocking is at least 80

percent (Trousdell1983). Even so, there is increasing

evidence from research in loblolly plantations to

suggest that competing vegetatio-n c-an cause sub:

stantial loss in pine growth during the first 5 years

following establishment (Haywood and Tiarks 1981,

Nelson and others 1981, Knowe and others 1985,

Tiarks and Haywood 1988, Zutter and others 1988,

Miller and others 1987). This study was conducted to

investigate the interrelationships among woody and

herbaceous competition components and to assess

the impact of these competition components on

establishment, survival, and growth of naturally

regenerated loblolly and shortleaf pines.

METHODS

Study Area

The study is located on two 5-acre clearcuts within

the Crossett Experimental Forest in southern Arkansas. Prior to clearcutting, these areas contained

uneven-aged stands of loblolly and shortleaf pines

that ranged up to 28 inches in d.b.h. with about 100

pines per acre and about 9,000 fbm (Doyle scale) saw

log volume per acre. Hardwoods that were 1 inch and

larger in groundline diameter (g.1.d.) were stem

injected in the summer of 1980 with herbicide. Prescribed burning with backfires was done in the

winters of 1979 and 1980.

A seed tree regeneration cut in the spring of 1981

left five seed pines per acre. In August 1983, the

3-year-old rough-was mowed with a Hydra-axe to a

‘height of about 2.5 feet, above established pine

seedlings, to insure a uniform treatment area. Seed

trees were removed immediately after mowing.

Soils are Bude (Glossaquic Fragiudalf) and

Providence (Typic Fragiudalf) silt loams. These soils

are usually wet in winter and dry in summer and have

a site index of 85 to 90 feet for loblolly pine at age 50.

Southern Forest Expwiment StatloM402lO U.S. Postal SewIce Bldg., 701 Loyol8 Avenue, NW Orlaans, La. 70113

Meet 8ewice, U.S. Department of A9rlculturo.

Sawlng Alabama, Arkansas, Loulrlar, Mlssisslppl, E. Oklahoma, lbn~wo, E. Texas, Puerto Rico, U.S. Vlr9ln Islands

1
Study Estrbllshment and Treatments

Sixteen treatment plots measuring 104 by 104 feet

(0.25 acre) were established in the fall of 1983 using a

randomized, complete block design with four replications of four treatments. Interior measurement plots

were 66 by 66 feet (0.1 acre),and each plot contained

10 systematically established, permanent milacres

for data collection.

Four competition control treatments were initiated

during the 1984growing season and were maintained

as follows:

Check-Untreated mixture of woody and herbaceous vegetation that invaded the study areas

following removal of the midstory and overstory

pines and hardwoods. The 3-year-old rough was

mowed in August 1963 with no additional treatment.

Woody control--All standing and sprouting hardwoods, shrubs, and woody vines were controlled

annually by singlestem treatments with herbicides.

Herbaceous control-Forbs, grasses, weeds, and

vines were controlled annually using preemergent and postemergent herbicides.

Total control-A combination of herbicides was

used annually to control all nonpjne vegetation: _ .

Measurements and Data Analysis

Competition levels of woody and herbaceous

species have been assessed annually in late summer

to document the degree of treatment success. Woody

rootstocks were counted by species and by l-foot

height classes on each milacre. Percent ground cover

of herbaceous vegetation (grasses, forbs, vines, and

semiwoody plants) was determined by ocular estimation to the nearest 10 percent within each milacre.

Herbaceous generathat covered more than 15 percent

of a milacre were recorded.

Prior to treatment and annually at the end of each

treatment period, pine seedlings were counted on

each of the 10 milacres per plot for calculation of

density and percent stocking. In addition, 50 pine

seedlings-principally loblolly-on each plot were

randomly selected, tagged for identification, and

measured at the end of each gi’owing season for total

height (to the nearest 0.1 foot) and g.1.d. (to the

nearest 0.04 inch).

Analysis of variance was used to evaluate treatment differences in competition and pine survival,

stocking, and density. Analysis of covariance was

used to evaluate pine growth in g.l.d., height, and

volume for tagged seedlings usin~-initiai-&T;?&

height, and volume respectively as the covariates.

Mean volumes of survjving measurement seedlings

werecalculated from:C(total height)(g.l.d.)? Duncan’s

Multiple Range Test-was used to partition mean

differences between treatments. Percent data were

analyzed following arcsine,/proportion transformation. These analyses were carried out at the0.05 level

of significance.

RESULTS AND DISCUSSION

Competing Vagetatlon

After 3years of herbicide applications, density and

size of woody competition and percent cov8r by

herbaceous vegetation were significantly reduced in

accordance with treatment definitions when compared to untreated checks (table 1). Although reduced, competing species were not eliminated.

The most prevalent woody competitors across all

plots after 3 years of treatment were Callicarpe

americana L., Rhus copallina L., and Vacciriium spp.

Although thesesmall shrubs comprised 69 percent of

all species inventoried, they should become less of a

problem in terms of site occupancy once the pines

have achieved crown closure. Major recurring tree

species were Acer rubrum L., Diospyros vlrginiana L.,

Quercus falcata Michx., and Sassafras albidum

(Nutt.) Nees, but these four species accounted for

less than 15 percent of the total hardwood density.

The remaining 16 percent of all woody stems was

divided among 17 other species at the end of 3 years

of treatment.

The most prominent herbaceous vegetation types

after 3 years were grasses and vines, regardless of the

degree of competition control. Milacre stockings of

the five predominant herbaceous genera in the fall of

the third year of treatment were: Lonicera japonicaMichael D. Cain is research forester, Forestry Sciences Laboratory, Southern Forest Experiment Station, Forest Service-USDA, Monticello,

AR, in cooperation with the Department of Forest Resources and the Arkansas Agricultural Experiment Station, University of Arkansas at

Monticello. Cooperation was also provided by the Georgia-Pacific Corp.; SASF Wyandotte Corp.: Dow Chemical Co.: E.I. duPont

deNemours 8 Co.; and Monsanto Agricultural Products Co.

The use of trade, firm, or corporation names in this publication is for the information and convenience of the reader. Such use does not

constitiute an official endorsement or approval by the U.S. Department of Agriculture of any product orsewiceto theexclusion of others that

may be suitable.

2
Table 1 --Mean density and height of woody species and percent ground cover by

herbaceous s$scies after 3 years of intensive competition control in a

stand of natural lob/o//y-shortleaf pine regeneration

Woody competkon Herbaceous vegetation

Treatments Density Total height ground cover

._-_ _ .

Stems/acre Ft Percent

Check 10,800at 3.4a 98.a

Woody control 2,375 bc 2.0 b 99a

Herbaceous control 4,900 b 3.9a 10 b

Total control 75 c 0.8 c 14 b

Error mean square 590 0.4 1 5

-tWithit+column means followed by the same letter are not significantly

different at the 0.05 level.

Thunb., 79 percent: Rubus spp., 78 percent: Uniola

spp., 84 percent; Andropogon spp., 43 percent: and

Smilax spp., 30 percent. Another 13 herbaceous

genera of grasses, vines, forbs, and semiwoody

plants were recorded, but they were of less importance overall when compared to the five genera listed_

above. Although most grasses disappear as fully

‘stocked pine stands matuie, shade-tolerant vines

such as L. iaponica can be a persistent problem in

pine management (Cain 1985).

Pine Seedling Responro to Treatment

When the study was being installed, pretreatment

pineaeedling density averaged only 1,338 stems per

acre with 47 percent milacrestocking. A bumper pine

seed crop the winter after the study installation

produced an average of 13,000 pine seedlings per

acre and 96 percent milacre stocking by the end of

the first year of competition control. Pine seedling

density generally declined across ail treatments

through the third year but still averaged over 9,000

stems per acre (table 2) and exceeded the minimum

recommended density of 700 stems per acre (Grano

1967) thought to be needed in the third year for

successful natural regeneration of loblolly and shortleaf pines on clearcut sitee.

Table P-Pine reedllng density m d milacro stocking after 3 year8

of intonsfve competition contra/

Treatment8 Denrity Miiacrr Mocking

Stqmrlacre

Check 9,3iOabt

P?rcent

100

Woody control 5,600 b 66

Hrrbaceour control 14,000~ loo’

Total control 8,100 b 9 6

Error mean square 932 . . .

tWlthin-column mean8 followed by the earn0 letter are not

significantly different at the 0.06 level.

-

Milacre stocking of pine seedlings (table 2) after 3

years of treatment was more than adequate for

natural regeneration based on published recommendations (Trousdelll963). By the end of the third year

of competition control, the majority of natural pine

seedlings ranged in height from 1 to 3 feet for both

density and milacrastocking variables, regardless of

treatment.

Height and diameter gains of measurement pines

increased each year across all treatments as the

seedlings grew above competing species. Nevertheless, pine growth gains were most apparent where

herbaceous species were controlled (fig. 1). Statistically significant increases in height and g.1.d.

growth during both the second and lird years on

blots where hbrbeceous competition was tionfrolled

resulted in significant volume gains for measurement

pines on both tot& control plots and herbaceous

control plots as compared to pine volume growth on

check or woody control plots (table 3). Where only

woody species were controlled, there was no significant improvement in pine growth through the third

year when compared with pine growth on untreated

check plots. Even though herbaceous competition

had a negative impact on seedling growth, there was

no reduction in survival of measurement pines during

the first 3 years of the study (table 3).

One long-term investigation, on sites similar to

ones in the present study, showed that small clearcuts of about 5 acres will naturally regenerate with

pines that seed-in from bordering loblolly and shortleaf seed trees and will develop into well-stocked

stands even with low-intensity site preparation and

without followup control of competition (Baker and

Murphy 1982). In that investigation, however, the

imported vine, L. japonica, was not yet a problem to

successful pine regeneration in the South. In a more

recent study, Cain (1985) found that a dense ground

cover of L. japonice and associated herbaceous

vegetation not only reduced growth of naturally

regenerated loblolly and shortleaf pine seedlings but

- - ---

3

:
.

TREATMENi’

CHECK

WOODY

CONTROL

HER%ACEOU9

CONTROL

TOTAL

CONTROL

(Note that initial seedling size

was unequal among treatments

at the time of study installation.)

7 6 5 4 3 2

TOTAL HEIQHT (feet)

1 0 . 0.4 0.8 1.2 1.6 2.0

G.L.D. fiiches)

2.4

Figure l.-Height and groundline diameter (g.1.d.) growth trends for surviving measurement pines by treatment during 3 years of

competition control.

also inhibited pine establishment from natural seedfall. Therefore the typeof herbaceous vegetation that

is present on an area may determine the degree of.

control needed for pine establishment and growth.

MANAGEMENT IMPLICATIONS

In managing for natural lobfolly and shortleaf pine

regeneration, there are at least two circumstances

where intensive competltion control would be justified from an operational standpoint. Both circumstances are correlated with poor to average pine seed

crops.

The first would be where density and stocking of

pine seedlings are less than optimum for successful

regeneration, and a dense cover of woody and

herbaceous vegetation on the site precludes further

pine establishment even when a pine seed source is

available. In this situation, some form of site disturbance such as temporary control of competition

would increase the likelihood that supplemental pine

regeneration would occur. For example, at the time

that the present study was installed, 3 years after a

seed-tree regeneration cut, loblolly and shortleaf

pine seedling density (1,338 trees per acre) and

milacre stocking (47 percent) were marginal when

compared to the recommended levels of 700 trees per

acre and 80-percent milacre-stocking. A bumper pine

seed crop during the winter of study establishment, in

combination with site disturbance (mowing), resulted in high pine seedling density and stocking on all

plots, including checks, 1 year later.

The second would be where the pine seed source

has been removed from an area, but density and

stocking of established pine seedlings are at or

somewhat below the recommended levels for successful natuial regeneration~lnthissituation, pine release

could b8 beneficial fOf th8 landOWn8r. lnt8nSiV8

control of herbaceous vegetation in the present

study, for example, resulted in real growth gains for

pin8 Seedlings Compared to untreated checks or

compared t0 pines on plots where Only woody vegetation was controlled. Therefore such treatments

could at least maximize growth of established pin8

seedlings in understocked stands on sites Where

4
Table 3--Surv:val and mean volume growth of 200 measurement pines per

treatment.

-

Third-year Mean volume per tree

Treatments survival Initial 2nd-yr growth 3rd-yr growth

-

Percent ___-----__-________-_ lnChJ _-_-----________________

Check 95at 4 a 23a 104a

Woody control 93a 6 a 16a 97a

Herbaceous control 9aa 5 a 63 b 348 b

Total control 93a 3 a 63 b 383 b

Error mean square 4 2 6 366 7,532 ---

+Withm-column means followed by the same letter are not significantly

different at the 0.05 level.

there is no opportunity for additional n&J-al pine

seeding, thereby avoiding the costs and lost time

associated with starting over using artificial

regeneration.

LITERATURE CITED

Baker, James B.; Murphy, Paul A. 1982. Growth and

yield following four reproduction cutting methods

in loblolly-shortleaf pine stands-a case study.

Southern Journal of Applied Forestry. 6: 66-74.

Cain, Michael D. 1985. Japanese honeysuckle and

associated ground cover inhibit establishment and

growth of pine seedlings in all-aged stands. In:

Proceedings, 3rd biennial southern silvicultural

research conference; 1984 November 7-8; Atlanta,

GA. Gen. Tech. Rep. SO-54. New Orleans, LA: U.S.

Department of Agriculture, Forest Service, Southern Forest Experiment Station: 300-304.

Grano, Charles X. 1967. Growing loblolly and shortleaf pine in the Midsouth. Farmers’ Bull. 2102.

Washington, DC: U.S. Department of Agriculture:

27~.

Haywood, J. D.; Tiarks, A. E. 1981. Weed control and

fertilization affect young pine growth. in: Proceedings, 34th annual meeting of Southern Weed

Science Society; 1981 $anuary 20-22; Dallas, TX.

Champaign, IL: Southern Weed Science Society:

145-151.

Knowe, Steven A.; Nelson, Larry R.; Gjerstad, Dean

H.; Zutter, Bruce R.; Glover, Glenn R.; Minogue,

Patrick J.; Dukes, James H., Jr. 1985. Four-year

growth and development of planted loblolly pine

on sites with competition control. Southern Journal

of Applied Forestry. 9: 11-15.

Miller, James H.; Zutter, Bruce; Zedaker, Shepard M.;

Cain, Michael; Edwards, M. Boyd; Xydias, G. Kenneth; Applegate, A. R.; Atkins, R. Lee; Campbell,

Sam; Daley, Edward; Hollis, Charles; Knowe, Steven

A.; Paschke, J. 1987. A region-wide study of loblolly pine seedling growth relative to four com’petition levels after two growing seasons. In: Proceedings, 4th biennial southern silvicultural

research confere’nce; 1986 November 4-6; Atlanta,

GA. Gen. Tech. Rep. SE-42. Asheville, NC: U.S.

Department of Agriculture, Forest Service, Southeastern Forest Experiment Station: 581-591.

Nelson, Larry R.; Pedersen, Richard C.; Autry, Lanny

L.; Dudley. Stuart: Walstad, John D. 1981. Impacts

of herbaceous weeds in young loblolly pine plantations. Southern Journal of Applied Forestry.

5: 153-l 58.

Tiarks, Allen E.; Haywood, James D. 1986. Pinus

taeda L. response to fertilization, herbaceous plant

control, and woody plant control. Forest Ecology

and Management. 14: 103-l 12.

Trousdell, Kenneth B. 1963. Lbblolly pine regeneration from seed-what do site preparation and

cultural measures buy? Journal of Forestry. 61:

441-444.

Williston, Hamlin L.; Balmer, William E. 1974. Managing for natural regeneration. Forest Manage. Bull.

Atlanta, GA: U.S. Department of Agriculture, Forest

Service, Southeast Area State and Private Forestry.

6 P.

Zutter, B. R.; Glover, G. R.; Gjerstad, D. H. 1986.

Effects of herbaceous weed control using herbicides on a young loblolly pine plantation. Forest

Science. 32(4): 882-899.

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