Plantation Spacing Affects Early Growth

of Planted Virginia Pine

T. E. RUSSELL

SUMMARY

Spacings ranging from 4 x 4 to 8 x 8 ft did not affect

15year height growth of Virginia pines planted on a

cutover Cumberland Plateau site. Wider spacings

produced trees of larger diameters than did closer

spacings; closer spacings had more basal area and

volume. Although height to the base of the live crown

increased as spacing narrowed, self-pruning was

poor at all spacings.

Additional keywords: finus virginiana Mill., artificial regeneration of pines.

STUDY OBJECTIVES

The role of spacing in the early growth of planted

pines has been researched in numerous studies

throughout the South, but few spacing studies have

included Virginia pine. Specific information on the

response of this species to planting density is lacking

for the Cumberland Plateau, where Virginia pine is an

important commercial species.

In 1961, this study was started near Sewanee,

Tennessee, to test the effects of spacings of 4 x 4,6 x

6, and 8 x 8 ft on performance of unthinned Virginia

pine over a30-year rotation. Expecting that the 4 x 4 ft

spacing would produce mainly trees of small diameter but anticipating that future markets might accept small trees, I included this unusually close

spacing to get information on the yields obtainable at

high planting densities. Also, self-pruning is notoriously poor in Virginia pine, so another goal was to see

if self-pruning could be improved by planting at a high

density. This note presents results halfway through

the planned rotation.

STUDY AREA

The study was carried out on the Cumberland

Plateau at an elevation of 1,940 ft. Plots are near the

crest of a broad ridge, on gentle slopes with a west to

southwest aspect. Soils are well-drained fine sandy

loams of the Ramsey, Hartsells, and Lonewood

series. Depth to bedrock varies from less than 20

inches to almost 4 ft. This area is typical of the

thousands of acres of drier-than-average Plateau

sites where Virginia pine is more productive than

native hardwoods.

Before conversion to pine, the stand had about 50

ft* of basal area per acre mainly in either culls or

low-grade chestnut oaks, scarlet oaks, and white

oaks of sawtimber size. Besides reproduction of

these species, the sparse understory contained

blackgum, hickories, sourwood, hairy locust, and

sumac. The area also had a fairly heavy but spotty

ground cover of huckleberries.

STUDY METHODS

Virginia pine was bar planted in February. Seedlings were 1-O stock grown by the Hiwassee Land

Company at its Rose Island nursery. Seed had been

collected in McMinn County, Tennessee, about 100

miles northeast of Sewanee, and from trees of above

average form and growth rate. Within 1 month after

planting, existing hardwoods were deadened by applying an oil-herbicide solution as a basal spray to

stems under 4 inches d.b.h. or in frills to trees larger

than 4 inches d.b.h. All sprouts or invading hardwood

seedlings were cut each spring for 5 years after

planting. A few scattered, large hardwoods that

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.

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recovered from the initial treatment were eliminated

by tree injection.

8 x 8 ft spacing - significantly less than the 18.2 ft for

pines planted at 4 x 4 ft.

Spacings of 4 x 4,6 x 6, and 8 x 8 ft were tested on

0.25acre plots and replicated four times in randomized blocks. Measurements were taken on a

central plot that was about 0.1 -acre but varied slightly

in size depending on spacing. Survival, diameter,

and basal area data include all trees on the measurement plots. Total heights and stem characteristics

are based on a sample. I selected this sample so that

the numbers of trees measured in every l-inch

diameter class were proportional to the numbers of

stems in the diameter class on an individual plot.

Results were interpreted by analysis of variance;

differences stated as significant were tested at the

0.05 level.

Average d.b.h. increased uniformly from the

closest to the widest spacing, but basal area was

significantly higher only on plots planted at 4 x 4 ft

(table 1). Total volumes corresponded closely with

basal areas, increasing as plantation density increased. Volume per square foot of basal area averaged about 14 ft3 at all spacings.

Diameter distributions

Survival

RESULTS

The distribution of diameters in this 15-year-old

plantation further emphasizes the effect of planting

density on the development of young Virginia pines

(table 2). The 6 x 6 ft spacing yielded more trees per

acre in the 5-inch and 1argerd.b.h. classes than either

closer or wider spacings. However, there were over

three times as many 7- and 8-inch stems at 8 x 8 than

at 6 x 6 ft.

Survival 5 years after planting was 94 percent or

better for all spacings. At 10 years survival averaged

84 percent for the 4 x 4 and 6 x 6 ft spacings and 93

percent for the 8 x 8 f-t spacing, a significant difference. Mortality continued to be a factor in these

stands. After 15 years, survival was 54 percent for 4 x

4, 74 percent for 6 x 6, and 86 percent for 8 x 8 ft

spacings (table 1).

Table P.-Distribution of diameters as related to initial plantation

spacing

Spacing d.b.h. class (inches)

VW

1 2 3 4 5 6 7 8 All

________________________----Trees per acre -------_--______________

Table 1 .-He& of spacing on survival, diameter, basal areas,

and volumes after 15 years

4x4 3 185 465 438 278 92 18 2 1481

6x6 - 40 180 220 290 155 25 2 892

8x8 9 31 127 175 156 76 14 588

spacing

(feet) Survival d.b.h. Basal area Volumes1

Ftz Ft3

Percent Inches per acre per acre

4x4 54 a2 4.0 a 129 a 1830 a

6x6 74 b 4.7 b 108 b 1520 b

8x8 86 c 5.4 c 95 b 1300 b

‘Cubic feet volumes per acre for entire stem, less bark.

2Means in each line followed by different letters are significantly

different at the 0.05 level of probability.

On plots planted at 4 x 4 ft only 26 percent of

surviving pines are 5 inches d.b.h. or larger and thus

merchantable for pulpwood under current local standards. In stands planted at 6 x 6 and 8 x 8 ft merchantable stems averaged 53 percent and 72 percent of the stands, respectively. The proportion of

planted trees that both survived and reached merchantable size in 15 years ranged from 14 percent for

the 4 x 4 to 62 percent for the 8 x 8 ft spacing.

CONCLUSIONS

Growth

Total heights averaged 32.7 ft and varied less than

1 ft among spacings. Despite considerable differences in soils among the 12 plots, mean heights from

the poorest plot to the best plot varied by only 4.2 ft.

Effects of site on height growth of Virginia pine may

not be fully expressed by 15 years.

Planting at high densities failed to improve selfpruning. Dead branches persisted to within 1 ft of the

ground for all spacings. Height to the base of the live

crown, however, averaged only 15.2 ft for pines in the

The 6 x 6 and 8 x 8 ft spacings produced about the

same number of merchantable trees, but the wider

spacing had more 7- and 8-inch trees and thus would

be preferred under present marketing conditions.

High basal area and a corresponding high biomass

can be produced by young stands planted at 4 x 4 ft.

But planting this many trees per acre is expensive

and excessive early mortality of Virginia pine in such

dense stands is likely. Extremely close spacings will

be attractive only where stems smaller than 5 inches

d.b.h. can be utilized and then only if rotations of not

much longer than 10 years are planned.

T. E. Russell is Principal Silviculturist at the Sewanee Silviculture Laboratory, maintained at Sewanee, Tennessee, by the Southern

Forest Experiment Station, Forest Service-USDA, in cooperation with the University of the South.

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