United States 

Agriculture 

Forest Service 

Southern Forest 

Experiment Station 

New Orleans, 

Louisiana 

Research Paper 

SO-283 

June 1994 

Seasonal and Cumulative Loblolly Pine 

Development Under Two Stand Density 

and Fertility Levels Through Four 

Growing Seasons 

James D. Haywood 
A loblolly pine (Pinus taedcr L.) plantation was subjected to two cultural 

treatments to examine seasonal and cumulative pine development in the 9th 

through 12th growing seasons: (1) pine stocking was either reduced by thuuung 

to 303 trees per acre at a 12- by 12-ft spacing or the plots were left uncut with an 

original density of 1,210 trees per acre at a 6- by 6-ft spacing, and (2) either no 

fertilizer was applied or rliammoniurn phosphate was broadcast at 134 Ib of 

phosphorus and 120 lb of nitrogen per acre. Competing vegetakion was controlled 

on all plots. Thmmg resulted in less spring helght growth in the 9th and 10th 

growing seasons than not cutting, but thinning in& diameter growth each 

year. Beghnhg in the 10th growing season, fertilization in& height, diameter, and basal area per acre growth, with the effect of fertilization on diameter 

growth being most pronounced on the thinned plots (a thinning by fertilization 

interaction). Therefore, fertilization of thinned plots was more beneficial than 

thinning alone, and thinning alone resulted in less heat and basal area per acre 

growth than the other treatment combinations for the 4-year period. 
Seasonal and Cumulative Loblolly Pine Development Under Ih Stand Density and Fertility Levels 

Through Four Growing Se85olls 

James D. Haywood 

INTRODUCTION 

The likelihood that fertilization will in- volume 

increment in pole- to sawlog-sized loblolly pine (Pinus 

taeda L.) stands is greatly dependent on the initial 

stand basal area per acre (Moehring 1966, Wells and 

others 1976, Widsor and Reines 1973). Therefore, the 

fertilization of stands that had been thinned is often 

much more beneficial for increasing diameter and 

height increment than either fertilization or thinning 

alone (Jones and Broerman 1977). The cumulative 

effect is to increase net volume (and value) per tree left 

in thinned stands as fertilization acts to speed up site 

reoccupancy GhUard 1981,I3aUard and others 1981). 

Both thimmg and fertilization Muence stand development, but it is not clear when the effect of cultural 

treatments occurs during the growing season. In this 

study, loblolly pine height and diameter measurements 

were made periodically over 4 years to determine: (I) 

when growth responses to thinning and fertilization 

occur and (2) what the cumdative growth responses to 

these two cultural p&i~ were. 

STUDY AREA 

The 2.8-acre site, located in Rapides Pariah, Louisiana, is a gently sloping Beauregard silt loam (Plinthtiquic Paleudub, fine-silty, tdiamq thermic) soil. Soil 

drainqp is adequate, and slope ia sufficient that water 

does not pond. The site was planted with loblolly pine 

seedlings at a 6- by 6-ft spacing in May 1981. The 

planting stock was container seedlings that had been 

grown in styrofoam blocks for 14 weeks. Mom than 97 

percent of the planted trees survived through 1987, 

when this study was initiakd. The 3 percent that did 

not survive did not create any openings in the stand 

canogy. Loblolly pine was the dominant vegetation as 

measured by basal area per acre, frequency of occur 

rence, and occupancy of the canopy. Diameters at 

breast height (d.b.h.'s) of all pine trees were measured 

in September 1987. These data indicated that pines 

of similar size were evenly distributed across the 

site. 

METHODS 

Experimental Mgn and 'hatment 

In April 1988, the understory hardwood trees, 

shrubs, brush (including Rubus spp. and Smilax spp.), 

and herbaceous plants were cut with a tractor drawn, 

rotary mower. Twelve research plots were established 

with each plot containing 13 rows of 13 trees each (0.14 

acre). 

Ik.eatments were randomly assigned to the l2 plots in 

a 2 by 2 factorial arrangement with 3 replications as 

follows: 

1. Thinning. Plot stodsing was either reduced to 303 

trees per acre in November 1988, at the end of the 

eighth growing season, or the plots were left uncut 

with an onginal density of 1,210 trees per acre. 

2. Fertilization. Either no fertilizer was applied or 

diammonium phosphate was broadcast at 667 lb 

per acre (134 lblacre of phosphorus and 120 lb/acre 

of nitrogen) in April 1989 at the begimmg of the 

ninth growing season. This choice and rate of fertilizer was based on prior knowledge of loblolly 

pine response to fertilization on a Beauregard silt 

loam soil (Tiarks 1982). 

On the thinned plots, the trees were removed to leave 

a 12- by 12-ft spacing by cutting every other row of 

trees and every other tree in the uncut m. This left 

12 pines on the interior measurement area of each cut 

plot. The plots were not selectively thinned to avoid 

biasing the comparison of the thinned and uncut plots. 

The purpose of thinning was not to impmve the population of trees, but rather to compare growth between 

like populations of trees growing under different management practices On the uncut plots, 12 trees were 

systematically selected for oallecting height data, rather 

than measuring the height of every tree. The same 

selection scheme was used to choose these l2 trees as 

was used to choose the residual trees on the thinned 

plots. The l2 selected trees on each plot were banded 

with red paint at about 5.5 ft to ensure relocation. All 

trees on the interior measurement areas were marked 

with a blue painted line at d.b.h. for consistent resampling. 

James D. Haywwd is a sikicuiturist at the Alaandria Forestry Cenh 

Experiment Station, Pin&, LA 71360. 

; U.S. Department of Agridture, Fmt Service, Southern Forest 
Competition from other plant species was not a factor in this research. Therefore, ail remaining Large 

woody vegetation and vines were cut, and the herbaceous and small woody competitors were sprayed with 

glyphosate in April 1989. The plots were rotary mowed 

3 weeks later and retreated with glyphosate later in the 

growing season to maintain weed control. In 1990, the 

plots were again sprayed with herbicide and mowed. 

In 1991 and 1992, the vines were cut and the plots 

sprayed with glyphosate and a mixture of 2,4-D, 

dicarnba, and dichloroprop and rotary mowed 3 weeks 

after spraying. 

Measurements and Eqmrhental Mgn 

The interior measurement area was that portion of 

each plot ongudy occupied by the central seven rows 

of seven trees each (0.04 am?). On March 27,1989, pine 

tree diameters (of all trees on the interior measurement area) were measured to the nearest 0.1 inch with 

a diameter tape, and total heighta (of the l2 seleded 

trees only) were measured with a clinometer to the 

nearest 0.5 ft. This measurement provided a baseline 

covariate for future analygeg. The plots were again 

measured on July 5 and October 2, 1989; March 19, 

June 13, October 29, and December 14,1990; March 8, 

June 24, September 24, and December 4, 1991; and 

March 23, June 17, September 17, and December 3, 

1992. 

Data were analyzed by analgses of covariance with 

the cavariate being the original heqht, diameter, or 

basal area per acre data (a = 0.06). These analyses 

determined that seasonal differences among treatments in 1989 and 1990 were important, but seasonal 

effeds did not occur in 1991 and 1992. Therefore, the 

reported dependent variables were the periodic growth 

differences in the spring, aumxner, and fall of 1989 and 

1990, as well as the cumulative (yearend) growth differences throughout the 4-year period. 

The spring-growth periods were from March 27 

through July 5, 1989 (100 days), and fmm March 19 

through June 13, 1990 (86 days). The summergrowth 

periods were from July 5 thmugh October 2,1989 (89 

days), and from June 13 thm@ October 29,1990 (138 

days). The fall-growth periods were from October 2, 

1989 thmugh March 19, 1990 (168 days), and from 

October 29 through December 14,1990 (46 days). 

RESULTS AND DISCUSSION 

Thinning to 303 pine trees per acre at age 8 resulted 

in less total height growth through age l2 compared to 

no thinning (fig. 1). The dampening effect of thinning 

In height g.n~ rth was most pronounced in the spring of 

the 9th and 10th growing seasons (table 1). Thinning 

did not affect height growth in the 11th and 12th 

growing season^ (fig. 1). Ginn and others (1989) alao 

reported an early suppression in loblolly pine height 

growth from reduction in stand stocblng. 

Fertilization inrreased total height growth for the 

&year period, but the effect of fertilization on height 

growth was not evident until the 10th growing season, 

when height growth was increased on the uncut plots 

in spring 1990 (see the thinnung by fertilization interaction effect in table 1). Height growth on both the 

thinned-fertilized and uncut-fertilized plots inin summer 1990 (fig. 1, table 1). Thus, the effect of 

fertilization on heqht growth was delayed, whereas the 

effect of thinning on height growth was immediate. 

The cumulative influence of thinning and fertilization on pine height growth was additive for the 4-year 

period (fig. 2). Periodic height growth averaged ll.6, 

14.4, 9.5, and 12.7 ft from the 9th thmugh 12th growing seasons on the uncut-unfertilized, uncut-fertilized, 

thinned-unfertilized, and thinned-fertilized treatments, reqedvely. 

Thinning significantly increased diameter growth of 

the residual trees for the &year period (fig. 1). The 

seasonal effect of thinning on diameter growth was 

immediate, and this positive growth response was significant every season from spring 1989 through summer 1990 (table 1). 

Fertdhtion significantly in& seasonal diame 

ter growth in Bummer 1989 and 1990 (fig. 1, table 1). 

Other studies have shown that initial stand basal area 

greatly influences pine tree responses to fertilization 

(Moehring 1966, Wells and others 1976, Wmdsor and 

Reines 1973), and fertilization of thinned stands is 

often more beneficial than either fertilization or stand 

density reduction alone (Jones and Broerman 1977). 

This was demonstrated by a swicant thinning by 

fertilizer interaction effect on diame&r growth at the 

end of 1990,1991, and 1992 (table I), with fertilFzation 

having little cumulative benefit on pine diameter 

growth on the uncut plots (fw l,2). Periodic diameter 

growth for the 4-year period averaged 0.7,0.8,18, and 

2.6 inches on the uncut-unfertilized, uncut-fertilized, 

thinned-unfertilized, and thinned-fertilized treatments, respectively. 

Thinning resulted in less cumulative basal area 

growth per acre than no hmhg at a probability > 

F-value = 0.1372 (table 11, and the uncut and thinned 

treatments averaged a 44.8- and 38.8-ft2 gain in basal 

area per acre for the Pyear period, respectively (fig. 1). 

Fertilization increased cumulative basal area growth, 

espeaally on the thinned plots (Q. 2), but there was no 

smc8nt thinning by fertilization interaction effect 

in the cumulative basal area per acre analysis (probability > F-value = 0.4135; table 1). The 4-year gain 

in basal area was 41, 49, 32, and 46 ft2 per acre 

on the uncut-unfertilized, uncut-fertilized, thinnedunfertilized, and thinned-fertilized treatments, respectively. 
7 

8. I 

- - UNCUT, UNFERTILIZED 

--- UNCUT, FERTILIZED 

- .-- THINNED, FERTILIZED 

-.----- 

- 

Figclr% L-Chnr&k MY hcigk -, d bawl ar#r per oen in the 9th throrrgh 12th 

wing serruwu Ibr thinning and fkdhth hmhnenta 
Thble 1. -A.obabrlity of a greater F-value for the main effect treatments and mntemctmn term when compnng seasod and curmrlcmvc Mht, 

dumeter, and basal area per acre growth of Iabldly pcne In the 9th thrwgh 12th grwgng seasons (1989 thnwgh 1992T 

Growing Eeamns 

Variable 9th loth 11th 12th 

q- Spring Summer Fall Yearend Spring Summer Fall Yearend Yearend Yearend 

Height growth 

Thinning 0.0042 0.6832 . . . . + 0.0024 0.0013 0.2905 0.4172 0.0004 0.0002 0.0038 

Fertilizer 0.6114 0.5813 . . . . 0.4796 0.1421 0.0055 0.8574 0.0431 0.0007 0.0007 

Thin x fert.2 0.8882 0.1506 . . . . 0.2391 0.0343 0.9839 0.9265 0.3925 9.8758 0.7084 

Diameter growth 

Thinning 0.0075 0.0001 0.0202 0.0004 0.0012 0.0001 0.0708 0.0001 0.0001 0.0001 

Fertilizer 0.3643 0.0046 0.0627 0.1476 0.1653 0.0002 0.3964 0.0066 0.0051 0.0026 

Thin x fert." 0.7190 0.0507 0.9345 0.1762 0.0382 0.0692 0.0785 0.0307 0.0312 0.0309 

Baealdacregmwth 

Thinning 0.0376 0.0908 0.8027 0.0143 0.3736 0.8376 0.5710 0.0383 0.0682 0.1372 / Fertilizer 0.0985 0.0080 0.0008 0.5008 0.9515 0.0003 0.7297 0.0078 0.0067 0.0092 

Thin x fert.: 0.2558 0.8308 0.0660 0.2981 0.1554 0.3328 0.1691 0.2080 0.1746 0.4135 

'Probabilities are from anal* of covmhm with the initial height, diameter, md basal area per acre data, taken in March 1989, as the 

covariete. The eccepted level of &p%cance was a = 0.05. 

+ Irmam&a data; no anal* was made. 

* The thinning by fern interaction. 

UN- FERTILIZED UNFERTILIZED FERTILIZED FERTILIZED 

UNCUT TREATMENTS THINNING TREATMENTS 

F'igure 2.-E%odic increment fur Wly pine height, diameter, and and ~IW 

per acre in the 9th thmugh 12th gnwing seasons as a resjumse to 

thinning and fertilizuiion treatmenfa 
To conclude, managers -.'ing to accelerate diameter growth in dense young stands of loblolly pine should 

do more than just apply fertilizer. Rather, overstocked 

stands will most likely have to be commercially or precommercially thinned before fertilization will benefit 

diameter and basal area increment. Thinning alone 

increases diameter growth, but thinning will have a 

negative effect on loblolly pine height increment for the 

first 2 years after cutting. This effect may still be 

evident in later years because height growth returns to 

its prethinning pattern rat her than accelerating its 

growth pattern. Thinning alone resulted in less basal 

area growth per acre than the other three treatment 

combinations for the 4-year period. 

Ballad, R. 1981. Nitrogen fertilization of established 

loblolly pine stands: a flexible silvicultural technique. In: Barnett, James P., ed. Proceedings of the 

1st biennial southern silvicultural research conference; 1980 November 6-7; Atlanta, GA. Gen. 

Tech. Rep. 50-34. New Orleane, LLA: U.S. Department of Agrhlture, Farest Service, Southern FOP 

est Ekperiment Station: 223-229. 

Ballad, R.; Duzan, H.W.; Kane, M.B. 1981. Thinning 

and fertilization of loblolly pine plantations. In: 

Barnett, James P, ed. Proceedings of the Ist biennial southern eilvi* research conference; 1980 

November 6-7, Atlanta, GA Gen. Tedh. Rep. 50-34. 

tion: 100-104. 

Ginn, S.E.; ,cller, J.R.; Cazell, B.H.; Kreh, R.F. 1989. 

Physiological responses to thinning in eight-year old 

loblolly pine on the Viiginia Piedmont. In: Miller, 

James H., comp., Proceedings of the 5th biennial 

southern silvicultural research conference; 1988 

November 1-3; Memphis, TN. Gen. Tech. Rep. 

SO-74. New Orleans, LA: U.S. Department of Agnculture, Forest Service, Southern Forest Experiment Station: 67-73. 

Jones, S.B.; Broerman, F.S. 1977. Thinning and fertilization of sixteen year old loblolly pine. Woodlands 

Res. Notes 34. Savannah, GA: Union Camp Corporation, Woodlands Research Department. 2 p. 

Moehring, D.M. 1966. Diameter growth and foliar 

nitrogen in fertilized loblolly pines. Res. Note SO-43. 

New Orleans, LA: U.S. Department of Agriculture, 

Forest Service, Southern Forest Experiment Station. 3 p. 

Tiarks, Allan E. 1982. Phosphorus sorption curves for 

evaluating phosphorus requirements of loblolly pine 

(Pinus taedcr). Communications in Soil Science and 

Plant Analysis. 13(8): 619-631. 

Wells, Card G.; Crutchfield, D.M.; Trew, I.F. 1976. Rveyear volume increment from nitrogen fertilization in 

thinned plantations of pole-size loblolly pine. Forest 

Science. 22(1): 06-90. 

Wmdsor, Carltan L, Jr.; Reba, M. 1973. Diameter 

growth in lobldy pine af€er fertilization. Journal of 

Forestry. 71(10): 659-661. 
Haywood, James D. 1994. Seasonal and cumWve loblolly pine Mop 

ment under two stand density and fdty llevela through four gmwing seasons. Rea Pap. SO-283. New Orleans, LA. U.S. Department of 

Agriculture. Forest Service, Southern Forest Experiment Station. 5 p. 

A loblolly pine stand was subjected to two cultural treatments to 

determine treatment effects in the 9th through 12th growing seasons. 

T in lesa spring height growth in the 9th and 10th 

growing seasons than no thinning, but thinning resulted in more 

diameter growth each year. Fertilization increased height and diameter growth beginning in the 10th growing season, with the effect of 

fertilization on diameter growth being most pronounced on the 

thinned plota 

Keyummh Intermediate harvesting, nitrogen and phosphorus fertilization, Pinus kredcr L, thuining. 
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