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SO-266

Density and Age Affect Performance of

Containerized Loblolly Pine Seedlings

James P. Barnett

SUMMARY

Loblolly pine seedlings were grown in 1 x 5 inch

biodegradable plastic tubes for 10, 12, and 14

weeks at densities of 42, 84, 126, and 168 per

square foot. Seedling density and age significantly

affected seedling development at time of outplanting, and density became more important as

greenhouse growing times increased. All

morphological characteristics measured when

seedlings were planted-height, diameters, root

and shoot dry weights, and proportion of seedlings

with secondary needles-were correlated

significantly with field survival, height, and

growth. Stem dry weights were most closely

related to field performance. Best seedling

development and performance were obtained at

the lowest seedling density.

Additional keywords: Pinus taeda, seedling

development, seedling survival, seedling

physiology, seedling morphology.

INTRODUCTION

Low seedbed densities in bare-root nurseries

improve early height growth of southern pines

after outplanting (Shipman 1966, Switzer and

Nelson 1963). Few studies have tested density

where other factors such as container volume

remain constant (Hocking and Mitchell 1975).

The work of Tanaka and Timmis (1974) with

Douglas-fir and Harris et al. (1972) with several

hardwoods shows that density in containers can

influence seedling morphology. Generally, low

densities produce shorter, thicker-stemmed plants

with greater shoot and root dry weights and more

cold-hardiness. Thisstudydetermined how loblolly

pine in containers responded to various spacings

and how seedling age influenced development at

these spacings.

MATERIALS AND METHODS

Stratified loblolly pine seeds from a central

Louisiana source were sown into biodegradable

polycaprolactone tubes (Clendinning et al. 1974)

containing a commercial potting medium of peat

and vermiculite. The hexagonal tubes were about 1

inch in diameter by about 5 inches long. Densities

tested were 168,126,84, and 42 tubes per square

foot. Tubes rested against one another at 168/ft2.

At lower densities, vermiculite was used to fill

spaces and maintain proper distances among

tubes. Seeds were sown every 2 weeks so that

seedling ages of 10, 12. and 14 weeks were

available for field planting. Treatments were

replicated five times in a completely randomized

design. ,.AY

Southern Forest Experiment Station/T-10210 U.S. Postal Services Bldg., 701 Loyola Avenue, New Orleans. La. 70113

Forest Service, US. Department of Agriculture.

Serving Alabama, Arkansas, Louisiana, Mississippi, Eastern Oklahoma, Tennessee. Eastern Texas.
From about 3 weeks after sowing, seedlings

were watered to saturation weekly with a water

soluble nutrient. solution (NPK 20-l 9-l 8). The

greenhouse was under natural photoperiod, and

temperatures were 24O C t 4O during the growing

period.

Seedlings heights, diameters at ground line,

shoot and root dry weights, and proportion of

seedlings with secondary needles were measured

on five seedlings from each replication when

seedlings were planted. Planting was done on a

moderately drained silt-loam soil that had been

disked earlier. Seedlings were planted June 28,

1976, after a 1.8 inch rain, ,and 6.6 inches of rain

fell during the next 2 months, 2.2 inches less than

normal. Field survival was determined 2 months

after planting. Survival and heights were

measured in the fall dormant season and again 1

and 2 years later. Correlation coefficients were

computed so morphological characteristics could

be related to field performance. Level of probability

was 0.05.

RESULTS AND DISCUSSION

Initial Seedling Development

Generally, measured characteristics increased

with increasing age and decreasing density (table

1). But how much seedling density affected these

characteristics varied with age. Differences due to

seedling density were much greater at 12 and 14

weeks of age than at 10 weeks.

Field Survival

” Two months after outplanting, survival averaged

94 percent for all treatments. Even with this high

survival,. seedling density in the greenhouse

significantly affected field performance. Seedlings

of all ages grown at 42/ft* survived better than

those grown at 126 or 168/ft* (table 2). Survival

trends were similar in February 1977, 1978, and

1979. In February 1979, seedlings grown at 42/ft*

averaged 96 per,cent survival, but those grown at

168/ft* had only 85 percent survival.

Although seedling age did not affect field

survival initially or after one complete growing

season in the field, significant differences did

occur in February 1978 and 1979. Seedlings

planted at 10 weeks had 86 percent survival, but

12-week seedlings had 92 percent and 14-week

seedlings had 93 percent by February 1979.

Apparently the smaller seedlings were not able to

compete as well as larger seedlings with surrounding vegetation.

Heights

Seedling heights were closely related to condition of seedlings when they were planted.

Seedlings grown for 12 and 14 weeks at low

densities were taller in the field than were

seedlings grown 10 weeks at the low densities

(table 3).

in February 1979, about 2% years after outplanting, seedlings planted after 14 weeks at 42/ft*

were over 1 ft taller than those grown 14 weeks at

168/ft*. But density of seedlings planted at 10

weeks of age had little effect on heights. Only0.15-

ft difference in height was evident among 1 O-week

seedlings after 2% years.

Growth

Amount of growth during the 1977 and 1978

growing seasons shows that density and age

treatments continue to affect field performance

after planting (table 4). During the 1978 season,

larger seedlings from the 42/ft* density and the

12- and 14-week growing periods maintained

growth of l/2 foot more than other age-density

treatments.

Correlations With Field Performance

Correlation coefficients (table 5) show that all

initial seedling characteristics measured were

significantly related to field survival, heights, and

growth. Coefficients between seedling

characteristics and survival increased as field

exposure lengthened; for example, stem weight at

2 months after’outplanting had a coefficient of

0.67, but this had increased to 0.84 when survival

was measured 2% years later. This increase in

correlation reflects losses of small, weakseedlings

that survived early but then could not compete

successfully. Stem weight was the characteristic

most closely related to survival. Height and

diameter were significantly related to survival but

had the lowest correlations of characteristics

James P. Barnett is Principal Silviculturist, Southern Forest Experiment Station, Forest Service-USDA, Pineville, Louisiana

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Table 1 .-Averege cherecteristics of loblolly pine seedlings grown under greenhouse conditions et

varying ages and densities

- -

Seedling Characteristics

Seedling Seedling Height Stem Root Stem Secondary

age density diameter weight weight needles

Weeks Mo./ft.2 _ _ _ _ _ -Mil/imeter- - - - - _ Percent

1 0 168 72 .9 16 68 10

126 58 .8 14 62 5

8 4 91 1.4 37 142 6 5

42 82 1.2 27 127 3 0

1 2 168 7 1 1.0 2 6 9 9 3 5

126 108 1.4 46 200 7 5

84 9 6 1.2 4 2 194 80

42 118 1.5 4 9 301 100

1 4 168 121 1.2 2 3 162 7 5

126 102 1.3 4 2 204 9 5

8 4 121 1.3 5 7 253 9 5

4 2 129 1.6 7 8 333 100

Table 2.-Average field survival of loblolly pine seedlings grown under greenhouse conditions at

varying ages and densities

Seedling Seedling

age densitv 2 mo.

Field survival

Feb.1977 Feb.1978 Feb. 1979

Weeks No. /ft2 -------------------Percent-------------------

1 0 168 90 8 9 8 8 8 6

126 9 0 8 9 8 5 8 3

8 4 9 0 8 9 8 2 8 1

4 2 9 9 9 8 9 6 9 4

1 2 168 9 3 9 1 8 8 8 6

126 9 5 9 5 9 4 9 2

8 4 9 7 9 7 9 6 9 5

4 2 9 8 9 8 9 8 9 7

1 4 168 8 8 8 7 8 6 8 4

126 9 6 9 6 9 3 9 3

8 4 9 8 9 8 9 8 9 8

4 2 9 8 9 8 9 7 9 8

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measured. This lower correlation was probably

caused by densities at which seedlings grew.

Degree of association of seedling propertieswith

heights decreased as time passed in the field (table

5). This decrease is logical because environment

influences heights more the longer plants are in

the field. Largest correlation coefficients occurred

between stem weight and field height.

At the end of 1978, correlations continued to be

strong between stem weight at outplanting and

amount of growth, with a coefficient of 0.87.

Coefficients of all other characteristics with stem

weight were lower but still statistically significant.

RECOMMENDATIONS

As longer seedling culture periods are used,

density becomes more important. Loblolly pine

seedlings need to grow 12 to 14 weeks to be large

enough to perform well in the field. With those

cultural periods, which density is most economical

is unclear. Such an analysis must wait for

additional growth data. But densities should

probably not exceed 1 OO/ft2. If cost of greenhouse

space is ignored, 42/ft* seems best.

LITERATURE CITED

Clendinning, Robert A., Steven Cohen, and James

E. Potts.

1974. Biodegradable containers: degradation rates and fabrication techniques. In

Proc.: Symp. North Am. Containerized For.

Tree Seedling. Great Plains Agric. Count.

Publ. 68:244-254.

Harris, R. W., A. T. Leiser, P. L. Neel, D. Long, N. W.

Stice, and R. G. Maire.

1972. Spacing of container-grown trees in the

nursery. J. Am. Sot. Hort. Sci. 97:503-506.

Hocking, D., and D. L. Mitchell.

1975. The influences of rooting volumeseedling espacement and substratum density

on greenhouse growth of lodgepole pine,

white spruce, and Douglas-fir grown in

extruded peat cylinders. Can. J. For. Res.

5 :440-45 1

Shipman, R. D.

1966. Low seedbed densities can improve

early height growth of planted slash and

loblolly pine seedlings. Tree Plant. Notes

76124-29.

Switzer, G. L., and L. E. Nelson.

1963. Effects of nursery fertility and density on

seedling characteristics, yield, and field performance of loblolly pine (Pinus taeda L.). Soil

Sci. Sot. Am Proc. 27:461- 464.

Tanaka, Yasuomi, and Roger Timmis.

1974. Effects of container density on growth

and cold hardiness of Douglas-fir seedlings. ln

Proc.: Symp. North Am. Containerized For.

Tree Seedling. Great Plains Agric. Count.

Publ. 68:181-l 86.

Table 3.-Average height ofloblollypine seedlingsgrown under

greenhouse conditions at varying ages and densities

Seedling Seedling Height

age density Feb. 1977 Feb. 1978 Feb. 1979

Weeks lQO./fP _ _ _ _ _ _ _ _ _ _ _ _ _ _-Feet _ _ _ _ _ _ _ _ _ _ _ _ _ _ _

1 0 168 0.33 1.41 2.59

126 .34 1.35 2.48

8 4 .34 1.35 2.36

4 2 .39 1.52 2.74

1 2 168 .36 1.53 2.84

126 .40 1.51 2.88

8 4 .47 1.76 3.20

4 2 .50 2.02 3.81

1 4 168 .42 1.50 2.76

126 .45 1.52 2.82

84 .52 1.84 3.47

42 .59 2.14 3.81

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Table 4.-Growth of loblolly pine seedlings outplanted after

development under greenhouse conditions at

varying ages and densities

Seedling Seedling

age density

Growth

1977 1978

Weeks No. /ftz ..________ Feet ___....---

10 168 1.07 1.19

126 1 .oo 1.13

8 4 1 .Ol 1 .Ol

4 2 1.12 1.22

1 2 168 1.17 1.32

126 1.10 1.37

8 4 1.29 1.44

4 2 1.52 1 .78

1 4 168 1.08 1.26

126 1.07 1.30

8 4 1.32 1.63

4 2 1.56 1.67

Table 5.-Correlation coefficients relating seedling characteristics at time of planting to field

performance’

Survival (%) Height (ft) Growth (ft)

Seedling 2 mo. Feb. Feb. Feb. Feb. Feb. Feb.

characteristics 1977 1978 1979 1977 1978 1979 1977 1978

Height (mm) .42 .48 .70 .60 .83 .77 .72 .64 .71

Diameter (mm) .55 .59 .53 .59 .71 .73 .64 .62 .59

Root wt. (mg.) .68 .72 .68 .76 .89 .85 .81 .78 .76

Stem wt. (mg) .67 .72 .73 .84 .94 .91 .89 .85 .87

Sec. needles (%) .51 .58 .57 .64 .82 .75 .71 .62 .72

1 A correlation coefficient of 0.553 is necessary for statistical significance at the 0.05 level.

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