United States

Department of

Agriculture

Forest Service

Development of Understory Vegetation

in Pine and Pine-Hardwood Shelterwood

Stands in the Ouachita Mountainsthe First 3 Years

Southern

Research Station

Research Paper

SRS8

Michael G. Shelton
The Author:

Michael G. Shelton, Research Forester, Southern Research

Station, U.S. Department of Agriculture, Monticello, AR 71656-35 16.

The use of trade or firm names in this publication is for reader information and does not imply

endorsement by the U.S. Department of Agriculture of any product or service.

This publication reports research involving pesticides. It does not contain recommendations for

their use, nor does it imply that the uses discussed here have been registered. All uses of pesticides

must be registered by appropriate State and/or Federal agencies before they can be recommended.

CAUTION: Pesticides can be injurious to humans, domestic animals, desirable plants, and fish or

other wildlife-if they are not handled or applied properly. Use all pesticides selectively and

carefully. Follow recommended practices for the disposal of surplus pesticides and pesticide

containers.

September 1997

Southern Research Station

P.O. Box 2680

Asheville, NC 28802
Development of Understory Vegetation in Pine

and Pine-Hardwood Shelterwood Stands in the

Ouachita Mountains-the First 3 Years

Michael G. Shelton

Abstract

The shelterwood reproduction cutting method using two overstory

compositions (a pine basal area of 30 ft* per acre with and without 15 ft’

per acre of hardwoods) and two methods of submerchantable hardwood

control (chain-saw felling with and without stump-applied herbicide) was

tested in a 2x2 factorial, split-plot design with four randomized complete

blocks. Production of sound pine seeds after treatment was marginal to

good, averaging 39,000,28,000, and 155,000 per acre in 1990, 1991, and

1992, respectively. AAer the third growing season, pine seedlings

averaged 1,550 stems per acre and 54 percent milacre stocking; no

significant differences occurred between either overstory or hardwood

control treatments. Hardwood reproduction after treatment generally

reflected the amount and composition that was present in the original

stand, with oaks averaging 8 IO rootstocks per acre and 48 percent milacre

stocking. The size of pine reproduction in the pine overstory treatment

was twice as large as that in the pine-hardwood overstory treatment, and

fewer of the stems in the pine overstory treatment were overtopped by

understory vegetation. Total coverage of understory vegetation after 3

years was greater in the pine overstory treatment (68 percent) than in the

pine-hardwood overstory treatment (46 percent) and was slightly greater

for manual than chemical hardwood control (60 versus 55 percent).

Results indicate that 15 fi2 per acre of scattered hardwoods can be retained

through at least 3 years after harvest, but additional monitoring will be

needed to determine the long-term success of reproduction. Early results

suggest that the herbicide treatment was not justified in the stand and site

conditions tested in this study; contributing factors were the abundant pine

seed production and low levels of competing vegetation.

Keywords: Even-aged silviculture, natural regeneration, pine-hardwood

stands, Pinus echinata Mill., shelterwood reproduction cutting method,

site preparation.

Introduction

The shelterwood reproduction cutting method is a versatile

way of naturally regenerating even-aged or two-aged stands

that is increasingly being used on national forest lands. The

shelterwood method gradually removes mature trees in a

series of partial cuts and retains more trees than other evenaged reproduction cutting methods. The higher density of

retained trees may satisfy some silvicultural and landowner

objectives by making the stand more visually pleasing

during regeneration and increasing timber yields through the

enhanced growth of these high-quality trees. Shelter-wood

stands also tend to have high rates of seed production,

which may improve chances for successful natural

regeneration in areas where low or erratic seed production is

a limiting factor. For example, Brender and McNab (1972)

reported that shelterwood stands in the lower Piedmont

produced enough seeds for successful regeneration 50

percent of the time compared to 2 1 percent for seed-tree

stands. The shelterwood method may be favorable in

regenerating shortleaf pine (Pinus echinafu Mill.) stands in

the Ouachita Mountains, where seed production is variable

(Shelton and Wittwer 1996) and may reduce the intensity of

site preparation needed.

On many public and nonindustrial private lands, hardwood

retention is desired to enhance nontimber resources, and a

pine-hardwood mixture is the target composition in the

regenerated stand. The objectives of this study are to test the

traditional application of the shelterwood reproduction

cutting method in shortleaf pine-oak (Quercus spp.) stands,

to evaluate the effects of hardwoods retention within this

system, and to determine type of submerchantable

hardwood control needed. The development of understory

vegetation is reported for the first 3 years after harvesting

and hardwood control.

Methods

Study Area

The study area was located on the Winona Ranger District

of the Ouachita National Forest in Perry County, AR.

Orientation was along an east-west ridge typical of the

physiography of the Ouachita Mountains. Elevations ranged

from 640 to 8 10 feet (fi) above sea level. Blocks were

located along the lower, middle, and upper north slope and

the upper south slope. Slopes of individual subplots ranged

from 5 to 26 percent, and the aspect was south on the

south-slope position and ranged from north to east on the

north-slope positions.

Soils of the study area are mapped as the Camasaw and

Pirum series, both Typic Hapludults. These are welldrained, moderately deep soils that developed in colluvium

and residuum weathered from sandstone and shale. Natural

fertility and organic matter are low, and the soils are

strongly acidic.
I

Site index for shortleaf pine averaged 60 ft at 50 years,

ranging from 56 to 65 fi; this is typical of upland sites in the

Ouachita Mountains (Graney 1992). The lower north slope

had a slightly higher site index than the other slope positions

(62 versus 59 ft). White oak (Q alba L.) site index averaged

54 ft at 50 years. The dominant pines were slightly older

than the dominant white oaks (66 versus 6 1 years).

The vegetation in the study area was typical of the forested

landscape in the Ouachita Mountains, where mature,

second-growth shortleaf pine and mixed oaks dominate

upland forests (Guldin and others 1994). Preharvest

overstory basal area in trees at least 3.6 inches (in) diameter

at breast height (d.b.h.) averaged 74 ft* per acre for shortleaf

pine and 4 1 ft’ per acre for hardwoods. Oaks accounted for

92 percent of the hardwood basal area. White oak was the

most prevalent hardwood followed by post oak (Q stellata

Wangenh.), black oak (Q. velutina Lam.), blackjack oak (Q.

marilandica Muenchh.), and southern red oak (Q. falcata

Michx.). The remaining 8 percent of the hardwood basal

area was ash (Fruxinus spp.), hickory (Cave spp.), red

maple (Acer rubrum L.), serviceberry [Amelanchier arborea

(Michx. f.) Fem.], blackgum (Nyssa sylvatica Marsh.), and

dogwood (Cornusflorida L.). The understory consisted of

tree reproduction, mainly the more shade-tolerant species,

and a variety of common shrubs, such as huckleberries

(Vuccinium spp.), snowbell (Sty-ax grandifolius Ait.), and

hawthorns (Cratuegus spp.).

Study Design and Treatments

The study was a 2x2 factorial, split-plot design with four

randomized complete blocks. Two overstory compositions

(pine-only versus pine-hardwood) were established in eight

3.5-acre whole plots, each split into two 1.75-acre subplots

for testing two hardwood control methods (manual versus

chemical control of submerchantable hardwoods). Each

subplot consisted of a 0.7-acre measurement area (103 by

295 ft) and an isolation strip of about 1.05 acre. The

isolation strip for a subplot was 66 ft wide when adjacent to

the untreated stand, 50 ft wide when adjacent to the

neighboring whole plot that made up the block, and 20 fi

wide along the internal boundary separating the two

subplots within a whole plot. Within each 0.7-acre

measurement area, 18 permanent points were systematically

located to monitor understory vegetation. These points were

at least 80 ft from the external boundary of the whole plot

and 50 ft from the internal boundary separating the two

subplots.

Overstory treatments-Target retention for all overstories

was 30 fi2 per acre of pine basal area. The pine overstory

treatment had no hardwoods; retention in the pine-hardwood

overstory was 15 fi* per acre of hardwoods and 30 ft2 per

acre of pines. Pine seed trees were selected for a past history

of high cone production, a d.b.h. of 12 to 16 in, good vigor

and stem quality, and a uniform spatial distribution.

Selection criteria were sometimes relaxed to achieve the

target basal area. Large, well-formed, vigorous red and

white oaks were preferred for the hardwood component, but

less desirable species or low-quality stems were sometimes

kept to meet the target basal area.

Whole plots were temporarily subdivided into seven 0.5-

acre areas to facilitate marking the target basal areas for

overstory trees and to insure a fairly uniform distribution.

All merchantable pines, except seed trees, were harvested

using rubber-tired skidders and tree-length skidding from

November 1989 to early January 1990. A commercial

firewood vendor harvested merchantable hardwoods r6 in

d.b.h. beginning in early April 1990 but was stopped shortly

afterward by wet weather. Harvesting resumed in July and

was completed in October. Firewood was hauled to a central

location in the front bucket of a farm tractor.

Figure 1 shows the diameter-class distribution before and

after harvest and hardwood control. The harvest narrowed

the normal distribution of the pine component. The stand

was essentially harvested from below with additional

removal of a few low-quality trees and poor seed producers

from the larger diameter classes. The hardwood component

initially had a typical reverse-J distribution, but the harvest

and submerchantable control treatment created a normal

distribution by retaining the larger white and red oaks.

The pine harvest removed an average basal area of 46 ft’ per

acre. Harvested pine volume averaged 3,800 board feet

Scribner per ace for sawtimber and 427 ft3 per acre for

pulpwood. Residual pine volume averaged 3,600 board feet

Scribner per acre and did not vary significantly with

treatments. Pine basal area averaged 28 ft’ per acre after

harvest and ranged from 25 to 3 1 ft’ per acre for individual

subplots. The average pine seed tree was 13.6 in d.b.h. and

64 ft tall. On pine-hardwood plots, residual hardwoods

averaged 16 ft* per acre for basal area and 4 15 ft3 per acre

for volume. Retained hardwoods averaged 8.4 in d.b.h. and

52 fi tall and were virtually all oaks (82 percent white oaks

and 16 percent red oaks by volume).

2
SHORTLEAF PINE HARDWOODS

161 70 1

................................... :::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::::~ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ............ . . . . . . . . . . . . . . . . . . . . . . . . . ................................. ................................,

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ....... . .... . . . . . . . . . . . . . . . . . . . . . ...............................p

.............................. _ ...............................,

.............................. ............................ ..............................,

” 4 6 6 10 12 14 16 18 20 22. ” 4 6 8 10 12 14 16 18

D.B.H. ( INCHES)

Figure l-Diameter at breast height (d.b.h.)-class distribution for shortleaf pine and hardwoods before and after implementing the

shelterwood reproductive cutting method.

BEFORE TREATMENT

60 AFTER TREATMENT --_____

Table l-Number of submerchantable hardwoods (1 to 5 inches d.b.h.) controlled using manual and chemical methods

in shelterwood stands with pine and pine-hardwood overstory compositions

Species group

Pine overstory

Manual Chemical

Pine-hardwood

overstory

Manual Chemical

Overstory Hardwood conhol

treatment treatment

MSE P MSE P

____________Stemsperacre____________

oaks 65 45 90 65

Other trees canopy 50 58 60 45

Midcanopy trees 12 8 12 10

Shrubs 2 2 5 2

Total 129 113 167 122

MSE = mean square error; P = probability level.

1,760 0.36 992 0.20

16,400 .95 1,260 .84

223 .88 65 .39

229 .64 562 .75

5,940 .58 1,510 .16

Submerchantable-hardwood control-Submerchantable

woody stems in the l- to j-in d.b.h. classes were counted

on 10 temporary 0.0 l-acre plots (11.78 fi in radius)

systematically located in each subplot just before applying

hardwood control treatments. Hardwood control treatments

began in mid-August 1990, toward the end of the hardwood

harvest, and were completed in early September 1990.

Treatments were either manual (chain-saw felling) or

chemical (chain-saw felling follgwed immediately by

application of undiluted Garlon 3A to the stump). Average

stump height in the manual control treatment (0.73 ft) did

not significantly differ from that in the chemical treatment

(0.76 ft). Submerchantable stems treated during hardwood

control averaged 133 stems per acre (table 1). Most were

oaks or other canopy trees. No significant differences

occurred with either the overstory treatments or the

3
hardwood control treatments. Submerchantable pines, which

were chain-saw felled but not treated with herbicide,

averaged six stems per acre. No sprouting was observed,

although young shortleaf pines often sprout after being topkilled.

Measurements

A preharvest inventory was conducted for reproduction in

September 1989. All woody plants in the seedling-size class

(~0.5 in d.b.h.) were counted on 10 temporary milacre plots

(3.72 ft in radius) in each subplot by species or species

group and the following size classes: ~0.5 ft, 0.6 to 2.5 ft,

2.6 to 4.5 ft, and 4.6 ft and taller but 50.5 in d.b.h. Multiplestemmed rootstocks were tallied as one individual,

evaluating size for the tallest stem. Woody saplings (stems

with a d.b.h. of 0.6 to 3.5 in) were counted by species or

species group and l-in d.b.h. classes on O.Ol-acre plots

centered around each temporary point.

In March 1990, all retained pines and hardwoods (~3.6 in

d.b.h.) on the 0.7-acre subplots were measured for d.b.h.,

and stem location was mapped by determining azimuth and

distance from plot center. All pines and about one-third of

the hardwoods were measured for height and crown

dimensions. In each subplot, age was determined for about

four pines and four white oaks that were dominants or

codominants.

Seedbed conditions after harvesting and hardwood control

were evaluated at 12 locations spaced along a 22-ft line

transect centered around each permanent point. Transect

direction was randomly selected for each permanent point.

Seedbed conditions were classified as undisturbed litter,

disturbed litter, exposed mineral soil, slash from both

logging and hardwood control, or some natural feature such

as a rock or natural coarse woody debris (diameter 24 in).

Postharvest inventories in early September 1991 and late

August 1993 followed the same procedures as the

preharvest inventory, except reproduction plots were

centered around the 18 permanent points. In the 199 1

inventory, the two tallest pine seedlings present on each

milacre plot (if any) were measured for ground-line

diameter, height, and crown width. In the 1993 inventory,

the two tallest pines and the two tallest two hardwoods on

the O.Ol-acre plot were measured for ground-line diameter,

height, and crown width. Measured hardwoods were

classified as being from: (1) advance reproduction that was

too small to be controlled, (2) sprouting of submerchantable

trees that were cut during hardwood control, (3) sprouting

of harvested merchantable trees, and (4) sprouting of trees

damaged during logging. Classification of trees near the

merchantability limit was based on the presence or absence

of the cut stem; those cut and left were classified as

submerchantable, while harvested stems were classified as

merchantable. The herbicide treatment of all cut

submerchantable stems was uncertain because some trees

may have been cut by loggers for access. During each

reproduction inventory, the same person estimated coverage

of understory vegetation (grasses, herbs, vines, shrubs,

hardwoods, pines, and total vegetation) on all milacre plots.

From October 1990 to February 1993, pine seed production

in each 0.7-acre subplot was monitored in three 0.9-f? seed

traps (Cain and Shelton 1993). Seed traps were located

along the subplot’s center line at least 120 fi from the

boundary with the untreated stand and 100 fi from the

boundary with the adjacent whole plot. Collections were

made during the middle and the end of each October-toFebruary period. Viability was determined by splitting seeds

and inspecting the contents (Bonner 1974). Seeds with full,

firm, undamaged, and healthy tissue were judged to be

potentially viable and were tallied as sound seeds.

Photosynthetically active radiation (PAR) was determined at

4.5 ft aboveground on 10 temporary milacre plots located

along the subplot’s center line during clear sky conditions

between 1030 and 1330 solar time on August 1, 1991, using

an 80-sensor Sunfleck Ceptometer (Decagon Devices, Inc.,

Pullman, WA). Ten readings were taken across each milacre

plot. Several measurements were also made in full sunlight

for calculating relative light intensity (PAR at 4.5 fi

expressed as a percentage of PAR in full sunlight). Canopy

coverage was determined using a spherical densitometer at

4.5 ft above each of the 18 permanent points during the

1993 inventory.

Data Analysis

Milacre plots were considered stocked by pine or deciduous

woody species if at least one seedling was present for the

species or species group; similarly, O.Ol-acre plots were

considered stocked if at least one sapling was present.

Means were calculated for understory variables for each

0.7-acre subplot. To facilitate data presentation, deciduous

species were grouped as oaks, other canopy trees,

midcanopy trees, or shrubs. Other canopy trees included

blackgum, hickory, ash, and sweetgum (Liquidambar

styraczjha L.); midcanopy trees included maple,

serviceberry, dogwood, elms (Ulmus spp.), persimmon

(Diospyros virginiana L.), and black cherry (Prunus

4
serotina Ehrh.). Shrubs included huckleberries, hawthorns, the chemical treatment produced less slash (32 percent) than

plums (Prunus spp.), snowbell, and several other common the manual treatment (40 percent). The chemical hardwood

species. Data were analyzed by analysis of variance for a control was applied several weeks after the manual

2x2 factorial, split-plot randomized complete block design treatments, possibly resulting in additional leaf fall during

using the SAS procedure GLM (SAS Institute 1989). Since this period and, thus, less slash when trees were felled. Slash

there were only two levels for each factor, means were not from harvesting and hardwood control averaged 36 percent

separated but were presented with the associated mean coverage, which was much higher than the 7 percent slash

square error (MSE) and probability level (P). Significance observed in a nearby uneven-aged harvest that removed a

was accepted at P50.05. Shortleaf pine site index was similar pine volume but no hardwoods (Shelton and

calculated from Graney and Burkhart (1973); white oak site Murphy, in press). Large amounts of slash apparently

index was calculated from Farrar (1985). resulted from the robust crowns of felled hardwoods.

Results And Discussion

The Postharvest Environment

The most common seedbed conditions after harvesting and

hardwood control were undisturbed litter and slash,

averaging 44 and 36 percent coverage, respectively (table

2). The harvesting intensity was lower for pine-hardwood

treatment because some hardwoods were retained. This

resulted in a higher percentage of undisturbed litter for the

pine-hardwood overstory treatment (5 1 percent) compared

to the pine treatment (38 percent). Exposed mineral soil was

2.8 percent coverage for the manual hardwood control

treatment compared to 5.2 percent for chemical control. One

reason for this small but significant difference may be that

Canopy coverage and light intensity were both strongly

related to overstory treatments (fig. 2). Canopy coverage in

the pine overstory was about 30 percent; retaining 15 fi2 per

acre of hardwoods essentially doubled coverage to 60

percent. The higher canopy coverage associated with

hardwood retention resulted in less PAR reaching the

understory; PAR averaged about 80 percent of full sunlight

for the pine overstory treatment compared to 50 percent for

the pine-hardwood overstory treatment. The coverage and

PAR of the overstory treatments reflected differences in

total basal area (that is, 30 versus 45 ft’ per acre) and

differences in the crown features of pines and hardwoods.

Hardwoods tend to produce more shade and canopy

coverage than an equivalent basal area of pines, because

they have large crowns, short heights, and broad leaves

(Shelton and Murphy 1993, Tappe and others 1993).

Table 2-Seedbed conditions after harvesting and applying manual and chemical methods of submerchantable

hardwood control in shelterwood stands with pine and pine-hardwood over-story compositions

Seedbed

condition

Pine overstory

Manual Chemical

Pine-hardwood

overstory

Manual Chemical

Overstory

treatment

MSE P

Hardwood control

treatment

MSE P

Undisturbed litter

Disturbed litter

Mineral soil

Slashb

Natural feature

_____-_____ Percent of area - - - - - - - - - - -

36.1 39.4 52.3 48.8 10 0.004 21.2 0.96

15.4 18.2 6.8 15.5 19 .08 33.7 .lO

3.7 4.6 1.9 5.7 4 .71 .4 .0003”

42.9 35.6 36.9 28.1 46 .14 54.0 .07

1.8 2.2 2.1 1.8 2 .93 3.4 .95

MSE = mean square error; P = probability level.

LI The interaction of the overstory and hardwood control treatments was significant (P = 0.004).

b Includes slash from both logging and hardwood control.
I

HARDWOOD CONTROL:

q MANUAL q CHEMICAL

CANOPY COVERAGE PAR

80 MSE = 22.2, P = 0.001

HARDWOOD CONTROL :

=

60

MSE 17.7, /J = 0.46

I3

2 40

z!

20

PINE PINEHARDWOOD

OVERSTORY

RSTORY: MSE = 42.6, P = 0.004

HARDWOOD CONTROL : MSE = 59.1,

80

60

0

PINE

TREATMENT

PINEHARDWOOD

Figure 2-Canopy coverage of the overstory and photosynthetically active radiation (PAR expressed as a percentage of that in full sunlight)

occurring in shelterwood stands with pine and pine-hardwood overstory compositions and manual and chemical methods of submerchantable

hardwood control. (h4SE = mean square error; P = probability level).

ID BEFORE HARVEST

1 2 3 4 5

D.B.H. CLASS ( INCHES)

Figure 3-Diameter at breast height (d.b.h.)-class distribution of submerchantable hardwoods before and after the harvest

implementing the shelterwood reproduction method.

6
Table 3-Annual production of sound shortleaf pine seeds in shelterwood stands with pine and pine-hardwood

overstory compositions and manual and chemical methods of submerchantable hardwood control

Pine overstory

Pine-hardwood Overstory Hardwood control

overstory treatment treatment

Seed year Manual Chemical Manual Chemical MSE P MSE P

1990

1991

1992

Total

-

- - - _ _ _ _ _ Thousands per acre - - - - - - - - -

66.8 50.1 20.9 16.7 2,710 0.23 249 0.23

33.4 25.0 16.7 37.6 528 .87 366 .54

141.9 171.1 133.5 175.2 3,870 .95 4,450 .33

242.1 246.2 171.1 229.5 4,940 .30 4,870 .40

1990

1991

1992

Mean”

_ _ _ _ _ _ _ _ Percent of total seeds - - - - - - - - -

12.5 15.1 11.6 5.6 124 .42 3 0 .56

18.3 16.5 31.8 29.6 1,140 .49 574 .87

48.1 56.7 55.2 66.9 266 .37 124 .12

30.2 33.1 31.1 36.7 212 .78 40 .23

MSE = mean square error; P = probability level

’ Weighted mean based on 3-year totals.

The potential for hardwood sprouting was large, even for

the plots where submerchantable hardwoods were

chemically treated. Before harvest, submerchantable-size

classes contained 240 stems per acre, but damage during

harvesting reduced density to 133 stems per acre (fig. 3).

Losses were especially high in the smaller d.b.h. classes,

where trees were broken off or uprooted during the

harvesting of merchantable trees. In addition, some

submerchantable trees were cut by loggers for access. The

density of merchantable hardwoods averaged 92 stems per

acre before harvesting. All were harvested in the pine

overstory treatment, compared to an average of 52 stems per

acre harvested in the pine-hardwood treatment.

Shortleaf Pine Seed Production

Some sound seeds were produced for each of the 3 years

after harvest and hardwood control, averaging 39,000,

28,000, and 155,000 per acre in 1990, 1991, and 1992,

respectively (table 3). No significant differences occurred

among treatments. Mean annual seed production in this

stand (74,000 sound seeds per acre) was about 25 percent

lower than the long-term mean for shortleaf pine stands in

the Ouachita Mountains (Shelton and Wittwer 1996).

However, yearly shortleaf pine seed crops vary greatly, and

a longer observation period is needed to validate

comparisons. The higher 1992 seed production seems to

support the common belief that at least 2 years are required

for the pine reproductive cycle to respond to release.

However, a nearby uneven-aged stand, harvested several

years before this one, also had a good seed crop in 1992.

The absence of significant differences among the treatments

for seed production may indicate that more time is needed

for trees to respond to release. In addition, pine seed trees

were released to some extent by harvesting and hardwood

control in both overstory treatments. Others have observed

that hardwood control and release by thinning enhances

pine seed production. Yocom (197 l), for example, reported

that cone production of shortleaf pine trees doubled when

all competing trees within 30 ft were removed. In a shortleaf

pine thinning study, Phares and Rogers (1962) found that

the lowest basal area (50 fi2 per acre) had the greatest seed

production. However, the influence of stand conditions on

shortleaf pine seed production is far less than the inherent

variation due to environmental factors and seed and cone

consumers.
Table 4-Density and stocking of sbortleaf pine seedlings in shelterwood stands with pine and pine-hardwood overstory

compositions and manual and chemical methods of submerchantable hardwood control

Growing

seaso#

Pine overstory

Manual Chemical

Pine-hardwood Overstory Hardwood control

overstory treatment treatment

Manual Chemical MSE P MSE P

Preharvest

First

Third

Preharvest

First

Third

_______-- Density (stems per acre) - - - - - - - - - -

50 125 125 75 10,600 0.82 8,120 0.79

486 764 667 430 127,000 .70 81,500 .89

1,010 1,940 1,740 1,510 257,000 .61 699,000 .43

______-- Milacre stocking (percenti - - - - - - - -

2 10 12 5 42 .50 62 1.00

28 40 38 29 457 .94 184 .76

40 58 57 62 328 .33 149 .10

MSE = mean square error; P = probability level.

0 Inventories conducted in 1989 for preharvest, 1991 for the first growing season, and 1993 for the third growing

The percentage of the total seeds that were sound averaged

11 percent in 1990,24 percent in 1991, and 57 percent in

1992, with no significant differences among treatments. The

greatest percentage of sound seeds was observed for the

most abundant seed crop. Shelton and Wittwer (1996) also

observed that the percentage of sound seeds increased with

the size of the shortleaf pine seed crop, approaching 75

percent in bumper years.

Shortleaf Pine Seedlings

Density averaged only 94 seedlings per acre before

harvesting and hardwood control, reflecting the closed

canopy condition and high level of overstory competition

(table 4). After harvesting and hardwood control, seedling

density increased to 590 seedlings per acre after the first

growing season and 1,550 seedlings per acre after the third,

indicating that some seedlings became established from

each succeeding seed crop. Seedlings became established

despite fairly large amounts of slash and undisturbed litter.

Thus, a few favorable microsites can provide acceptable

regeneration when seed production is abundant. No

significant differences occurred between overstory or

hardwood control treatments. However, hardwoods have

been shown to substantially reduce the establishment of

shortleaf pine reproduction when levels were greater than

those tested in this study (Becton 1936, Shelton and

Murphy, in press). Milacre stocking of pine seedlings

displayed a pattern similar to density (table 4). Stocking

averaged 7 percent before treatment, but gradually increased

to 45 percent after the first growing season and 54 percent

after the third.

Over the 3-year period, about 0.7 percent of the sound seeds

yielded established seedlings, which agrees well with other

studies of natural shortleaf pine regeneration: 0.3 percent in

undisturbed areas and 2.0 percent in scarified areas in a

sawtimber stand (Haney 1962), 0.4 percent in untreated

areas and 1.3 percent in burned areas in a poorly stocked

stand (Maple 1965), 0.4 percent in undisturbed areas and

1 .O percent for disturbed areas in a seed-tree stand (Yocom

and Lawson 1977), and 0.6 percent after the initial harvest

in a nearby shortleaf pine-hardwood stand (Shelton and

Murphy, in press).

The generally accepted minimum stocking limit for pine

reproduction in natural, even-aged pine stands is 700 stems

per acre and 40 percent milacre stocking (Campbell and

Mann 1973, Grano 1967). All overstory and hardwood

control treatments either met or exceeded this limit after the

third growing season.

8
Table 5-Density of deciduous rootstocks in the seedling-size class (~0.5 inches d.b.h.) in shelterwood stands with

pine and pine-hardwood overstory compositions and manual and chemical methods of submerchantable hardwood

control

Species group

and

growing season

Pine overstory

Manual Chemical

Pine-hardwood

overstory

Manual Chemical

Overstory

treatment

MSE P

Hardwood control

treatment

MSE P

Oaks

Preharvest

First

Third

Other canopy trees

Preharvest

First

Third

Midcanopy trees

Preharvest

First

Third

Shrubs

Preharvest

First

Third

Total

Preharvest

First

Third

--------Rootstocksperacre--------

1,020 1,350 875 775 1.5lE5 0.16

972 694 667 1,000 2.57E5 1 .oo

680 694 820 1,060 7.78E4 .17

325 600 200 375 1.64E5 .45

694 1,190 805 944 2.67E5 .80

1,030 1,010 778 1,060 1.45E5 .62

575 600 2,050 650 4.36E6 .52

417 806 1,530 472 7.3lE5 .43

500 1,030 916 694 1.97E5 .86

7,620 4,580 7,220 9,220 5.8OE6 .18

3,750 3,610 6,190 6,530 1.52E7 .26

4,970 5,190 6,170 7,580 1.54E7 .43

9,540 7,130 10,345 11,020 1.58E7 .32

5,833 6,300 9,192 8,946 1.07E7 .16

7,180 7,924 8,684 10,394 1.25E7 .35

4.89E5 0.76

2.36E5 .91

1.22E5 .50

1.26E5 .25

2.92E5 .28

3.4lE5 .67

2.15E6 .38

8.42E5 .49

2.95E5 .59

2.36E7 .84

9.46E6 .95

2.04E7 .73

1.99E7 .71

1.38E7 .95

2.36E7 .69

MSE = mean square error; P = probability level; MSE is presented in exponential format, for example, 1.23E4=1.23X10’=12,300.

Deciduous Rootstocks in the Seedling-Size Class

Treatments had no significant effect on the density of

deciduous rootstocks in the seedling-size class (table 5). The

sources of deciduous rootstocks after harvest and hardwood

control were development from seeds, advance reproduction

that was below the minimum size for hardwood control, and

sprouting of stems that were cut or damaged during

harvesting. After the third growing season, there were about

equal numbers of oaks, other canopy trees, and midcanopy

trees, which averaged 8 10,970, and 780 rootstocks per acre,

respectively. Shrubs were the most common group,

accounting for about two-thirds of the total.

Oak density averaged 1,005 rootstocks per acre before

harvest. Their density decreased slightly after harvest and

hardwood control to 830 rootstocks per acre after the first

growing season and 8 10 rootstocks per acre after the third.

Milacre stocking of oak rootstocks averaged 49 percent

before harvest, 47 percent after the first growing season, and

48 percent after the third. There was an acceptable

component of the preferred oak species in the regenerated

9
stand, with white oak accounting for 38 percent of the oak

density after the third growing season, followed by the

desirable red oaks [black, northern red (Q. rubru L.), and

southern red oaks] at 33 percent.

Density of other canopy trees, which initially averaged 375

rootstocks per acre, increased substantially after harvest and

hardwood control to 9 10 rootstocks per acre after the first

growing season and 970 rootstocks per acre after the third

growing season. Milacre stocking for this group averaged

18 percent before harvest and increased to 4 1 and 43

percent after the first and third growing seasons,

respectively.

Midcanopy trees, which averaged 970 rootstocks per acre

before harvest, decreased slightly to 8 10 rootstocks per acre

after the first growing season and 780 rootstocks per acre

after the third growing season. Milacre stocking for this

group averaged 28 percent before harvest, 29 percent after

the first growing season, and 34 percent after the third.

After the third growing season, the number of woody

species or species groups per subplot averaged 12.6 for the

pine overstory treatment and 11 .O for pine-hardwood

overstory treatment (MSE=4.48, P=O.O2). Hardwood

control treatments did not differ significantly, averaging

11.9 species for the manual control treatment and 11.8

species for the chemical treatment (MSE=0.562, FO.91).

After the third growing season, the seedling-size class

contained 24 woody species or species groups including 1

pine, 7 oaks, 4 other canopy trees, 6 midcanopy trees, and 6

shrubs. Cain and Shelton (1994) recorded 28 woody species

or species groups in the understory of a mature, pinehardwood stand on a good coastal plain site (site index of

about 90 ft at 50 years) that had not been disturbed for over

50 years. The similarity of the diversity in these widely

differing stands demonstrates the resiliency of the

understory to disturbance and the richness of understory

woody species on these poor Ouachita Mountain sites.

Reproduction in Sapling-Size Classes

Density of shortleaf pine saplings averaged only seven

stems per acre before harvesting, indicating that the high

stocking of overstory trees suppressed development of pine

reproduction (table 6). After the third growing season, a few

pine saplings appeared in the pine overstory treatment, but

variation was so great that the treatment difference was not

significant. These saplings probably developed from

advance reproduction.

Deciduous saplings averaged 184 stems per acre before

harvest, and the distribution was 36 percent oaks, 38 percent

other canopy trees, 17 percent midcanopy trees, and 9

percent shrubs (table 6). The hardwood control treatment

was thorough, resulting in almost no saplings after the first

growing season. By the end of the third growing season,

however, sapling density had increased to near preharvest

levels. The density of deciduous saplings in the pine

overstory treatment (270 stems per acre) was significantly

greater than that in the pine-hardwood overstory treatment

(110 stems per acre), reflecting the increased competition

from retained overstory hardwoods. Effects of hardwood

control treatments were also significant after the third

growing season, when sapling density was about 40 percent

greater for the manual hardwood control than the chemical

hardwood control. The herbicide application suppressed the

sprouting of treated stumps.

Reproduction Size

The pine overstory treatment resulted in larger shortleaf

pine reproduction than that of the pine-hardwood treatment

by an average of 2.1 times for ground line diameter, 1.6

times for crown width, and 1.3 times for height (table 7).

After the third growing season, pine reproduction in the

pine overstory treatment was more than twice as large as

that in the pine-hardwood overstory treatment for all

dimensions. Hardwood control treatments did not

significantly affect the size of pine reproduction after the

first growing season. After the third growing season,

chemical hardwood control resulted in significantly larger

pine reproduction than manual control for the pinehardwood overstory treatment but significantly smaller

reproduction for the pine overstory treatment. A possible

explanation for this difference may involve a subtle shift

from woody to herbaceous vegetation in the pine overstory

treatment. Herbaceous vegetation, which can severely

suppress the early development of pine reproduction (Cain

1988), might have been quicker to respond to the reduced

sprouting of hardwoods caused by the herbicide application

than pine reproduction. By contrast, pine reproduction in the

pine-hardwood overstory treatment may have been under

more woody competition because of: (1) the relatively small

size of reproduction, (2) the greater shading by the

overstory, and (3) the suppression of herbaceous vegetation

by the overstory.

Because of their larger size, the dominant pine reproduction

was overtopped by understory vegetation only 2 1 percent of

the time in the pine overstory treatment compared to 36

percent in the pine-hardwood treatment (table 8). The

10
Table 6-Density of pines and deciduous saplings (20.6 to 3.5 inches d.b.h.) in shelterwood stands with pine and pinehardwood overstory compositions and manual and chemical methods of submerchantable hardwood control

Species group

and

growing season

Pine-hardwood

Pine overstory overstory

Manual Chemical Manual Chemical

_ _ _ _ - _ - - --Stemsperacre-----------

Overstory Hardwood

treatment control treatment

MSE P MSE P

Pines

Preharvest

First

Third

Oaks

Preharvest

First

Third

Other canopy trees

Preharvest

First

Third

Midcanopy trees

Preharvest

First

Third

Shrubs

Preharvest

First

Third

Deciduous total

Preharvest

First

Third

0 15 0 12

0 0 0 0

12 3 0 0

68 88 45 55 1,440

0 0 0 0 __

188 139 44 51 3,840

50 80 52 70

0 0 0 0

60 47 28 24

25 10 18 68 7,120 .60 2,880 .54

2 0 2 0 6 1 .oo 4 .21

44 42 61 12 517 .62 1,050 .16

22 18 10 15 1,080 .68

0 0 0 0 __ __

2 2 2 2 0 1 .oo

165 210 125 220 12,200 .80 5,120

2 0 2 0 6 1.00 4

294 230 135 89 4,700 .02 1,040

373

0 _-

57

1,720 .87 990 .18

__ -_ __ __

1,650 .26 2,210 .73

0.91

__

.14

248 0.13

__ __

62 .26

.24 567

__ __

.03 1,650

50

__

12

.25

__

.17

1.00

__

1 .oo

.10

.21

.Ol

MSE = mean square error; P = probability level.

(1 No saplings were recorded, and thus, analysis of variance was not conducted

11
Table ‘I--Mean size of the dominant shortleaf pine reproduction in shelterwood stands with pine and pine-hardwood

overstory compositions and manual and chemical methods of submerchantable hardwood control

Property”

Pine overstory

Manual Chemical

Pine-hardwood

overstory

Manual Chemical

Overstory

treatment

MSE P

Hardwood control

treatment

MSE P

__________ - First growing season - - - - - - - - - - -

G.1.d. (in) 0.30 0.29 0.13 0.15 0.0012 0.003 0.0005 0.43

Crown width (ft) .69 .65 .40 .45 .0113 .02 .0048 .86

Height (f?) .81 .67 .38 .78 .1670 .49 .2230 .60

___________ Third growing season - - - - - - - - - - -

G.1.d. (in) .91 .79 .29 .35 .0187 .004 .OOll .07b

Crown width (ft) 2.00 1.77 .83 .90 .0646 .004 .0029 .03b

Height (ft) 4.65 4.07 1.85 2.02 .3760 .004 .0191 .03b

MSE = mean square error; P = probability level; g.1.d. = groundline diameter.

L1 The largest two seedlings or saplings (if present) were measured in milacre plots after the firstgrowing season and O.Ol-acre plots after the third

P

owing season.

The interaction of the overstory and hardwood control treatments was significant at P<O.O5.

Table 8-Overtopping of the dominant pine reproduction by understory vegetation after the third growing season in

shelterwood stands with pine and pine-hardwood overstory compositions and manual and chemical methods of

submerchantable hardwood control

Species group

Pine overstory

Manual Chemical

Pine-hardwood Overstory

overstory treatment

Manual Chemical MSE P

Hardwood control

treatment

MSE P

Grasses

Herbs

Vines

Shrubs

Hardwoods

Pinesb

Total

- - - - - Percent of stemsa overtopped - - - - -

0 1.5 0 0.8 2.2 0.65 1.4 0.10

0 0 1.1 .8 3.5 .39 0.1 .36

.7 1.5 2.5 1.8 1.0 .I3 4.9 .99

2.9 4.5 14.0 9.2 10.3 .02 65.2 .72

15.4 13.4 23.6 18.9 26.7 .08 85.3 .49

0 .7 0 1.0 2.0 .86 1.5 .21

19.0 21.6 41.2 32.5 76.5 .04 156.0 .60

MSE = mean square error; P = probability level.

’ The largest two seedlings or saplings (if present) in O.Ol-acre plots.

b From pine reproduction outside the reproduction plot or, if inside the plot, from the largest pine overtopping the next-to-largest.

12
Table 9-Mean size of the dominant hardwood reproduction after the third growing season in shelterwood stands with

pine and pine-hardwood overstory compositions and manual and chemical methods of submerchantable hardwood

control

Propertya

Pine overstory

Manual Chemical

Pine-hardwood Overstory

overstory treatment

Manual Chemical MSE P

Hardwood

control treatment

MSE P

G.1.d. (in)

D.b.h. (in)

Crown width (ft)

Height (fi)

G.1.d. (in)

D.b.h. (in)

Crown width (ft)

Height (ft)

G.1.d. (in)

D.b.h. (in)

Crown width (ft)

Height (ft)

________________ O&s________________

1.47 1.51 1.04 1.04

.74 .66 .44 .40

4.21 4.40 3.67 3.48

8.71 8.08 7.05 6.34

___________ Othercanopytrees-----------

1.20 1.34 .94 1.06

.48 .60 .35 .39

3.54 4.38 3.64 4.07

7.54 8.47 6.95 6.87

__________ - - Midcanopy trees - - - - - - - - - - - -

1.25 1.08 1.11 .85

.69 .67 .63 .32

4.36 3.92 4.06 3.32

9.66 9.61 9.92 6.92

0.009 0.002 0.005 0.73

.006 .006 .026 .50

.211 .05 .071 .86

1.550 .07 .221 .03

.105 .19 .090 .43

.027 .13 .061 .52

.807 .83 .863 .22

.881 .lO 3.840 .68

.098 .22 .032 .20

.030 .08 .023 .18

1.080 .28 .139 .19

4.880 .27 2.580 .25

MSE = mean square error; P = probability level; g.1.d. = groundline diameter.

’ Based on the largest two deciduous rootstocks occurring in O.Ol-acre plots.

difference between the hardwood control treatments was not

significant. Overtopping of the dominant pine reproduction

by overstory trees was also strongly related to overstory

treatment, averaging 20 percent for the pine overstory

treatment and 37 percent for the pine-hardwood overstory

treatment (MSE=77.6, P=O.O02).

Oak reproduction showed a response to overstory treatments

similar to shortleaf pine, although the magnitude was not as

great (table 9). Differences were significant for ground line

diameter, d.b.h., and crown width but not for height. Oak

reproduction from the chemical hardwood control treatment

(7.2 ft) was slightly shorter than that from the manual

treatment (7.9 I?). This was the only significant difference

observed for the hardwood control treatments. For the other

canopy trees and midcanopy trees, reproduction also tended

to be slightly larger under the pine overstory treatment, but

these differences and differences between the hardwood

control treatments were not significant.

Hardwood reproduction was considerably larger than

shortleaf pine reproduction after the third growing season

(fig. 4). This reflected a difference in the principal

reproductive strategy of the two groups-seeds for pines

versus advance reproduction and sprouts for hardwoods.

Experience elsewhere has shown that the height growth of

free-to-grow pine reproduction will eventually exceed that

of hardwoods on most upland sites (Wahlenberg 1960).

Although less is known about the long-term growth rates of

reproduction beneath a partial canopy, this study suggests

that pine growth will be suppressed to a greater degree than

hardwood growth. For example, the suppression of height

growth by retained overstory hardwoods was 56 percent for

13
10

t

•$j PINE-HARDWOOD

PINES OAKS OTHER

CANOPY

TREES

MIDCANOPY

TREES

Figure k--Mean total height of dominant reproduction after the third growing season in sheltenvood stands with pine and pinehardwood overstory compositions

pine reproduction but only 20 percent for oaks, 14 percent

for other canopy trees, and 12 percent for midcanopy trees.

Sources of the dominant hardwood reproduction were from

advance reproduction or the sprouts from cut

submerchantable trees, cut merchantable trees, or trees

damaged during logging. Of these sources, the herbicide

application was limited to stumps of submerchantable stems

cut during the chemical hardwood control treatment. The

source of the dominant deciduous reproduction was

influenced by the hardwood control treatment (fig. 5). More

of the dominant hardwood stems came from cut

submerchantable stems in the manual hardwood control

treatment (26 percent) than in the chemical treatment ( 13

percent). Advance reproduction was the dominant hardwood

reproduction 6 1 percent of the time for the chemical

hardwood control treatment and 47 percent for the manual

treatment. This difference probably reflected the reduced

sprouting of the herbicide-treated stumps, which favored

advance reproduction as the dominant reproduction. The

high susceptibility of oaks to Garlon 3A was indicated by

their low representation as dominant reproduction in the

chemical hardwood control treatment.

Understory Coverage

First growing season-Grasses, herbs, and hardwoods

responded rapidly to the stand disturbance and the reduction

in overstory competition (table 10). Herbs showed the

greatest response, increasing about 20 times over preharvest levels in the pine overstory treatment and 5 times in

the pine-hardwood overstory treatment. The most common

herb was fueweed (Erechtites hieracijblia Raf.), which

often flourishes after disturbance. By contrast, coverage of

vines and shrubs was generally greatest before treatment,

and the first-year growth for these groups apparently did

14
7 0

6 0

CHE.

‘, I--l ’ MAN.

SPECIES GROUPS:

0 MIDCANOPY TREES

q OTHER CANOPY TREES

H OAKS

-AMAN. CHE

ADVANCE CUT TREES CUT TREES LOGGING

REPRO- 1 - 5 INCHES 2 6 INCHES DAMAGE

DUCTION I D.B.H. D.B.H. I

SPROUTS

Figure 5-Origin of the dominant hardwood reproduction in shelterwood stands three growing seasons after controlling submerchantable

hardwoods by manual (MAN.) and chemical (CHE.) methods. Herbicide was applied only to trees I to 5 inches diameter at breast height (d.b.h.)

in the chemical control treatment.

not compensate for the losses incurred during disturbance.

All vegetative groups except the pines were present in the

stand before harvest and were able to respond rapidly to

dominate the understory after the first growing season. The

coverage of pines was nil at this time. Total vegetative

coverage essentially doubled in the pine overstory treatment

compared to an increase of only 17 percent in the pinehardwood overstory treatment. A similar response of the

understory community has been described for a wide variety

of reproduction cutting methods and overstory conditions

(Blair and Brunett 1976, Ehrenreich and Crosby 1960,

Joyce and Baker 1987, Nixon and others 198 1, Schuster

1967).

Third growing season-Most groups increased in coverage

between the first and third growing seasons (table 10). The

exception was herbs, which declined almost as dramatically

as they bloomed immediately after stand disturbance. The

hvo overstory treatments were significantly different for all

groups except pines, and total vegetative coverage averaged

68 percent in the pine overstory treatment compared to 46

percent in the pine-hardwood overstory treatment.

Differences in coverage between hardwood control methods

were small and only significant for herbs and total

vegetation. Herbs had slightly greater coverage in the

chemical hardwood control treatment. This may be the

result of reduced coverage of hardwoods and shrubs, which

were the only groups treated with herbicide. However, it

may also be an anomaly because the coverage of shrubs and

hardwoods was only slightly lower for chemical hardwood

control, and these treatment differences were not significant.

Total vegetative coverage for the chemical hardwood

control averaged 55 percent compared to 60 percent for the

manual treatment.

15
Table lO-Coverage of understory vegetation in shelterwood stands with pine and pine-hardwood over-story

compositions and manual and chemical methods of submerchantable hardwood control

Species group

and

Pine overstory

Pine-hardwood Overstory Hardwood control

overstory treatment treatment

growing season Manual Chemical Manual Chemical MSE P MSE P

Grasses

Preharvest

First

Third

Herbs

Preharvest

First

Third

Vines

Preharvest

First

Third

Shrubs

Preharvest

First

Third

Hardwoods

Preharvest

First

Third

Pines

Preharvest

First

Third

Total vegetatior?

Preharvest

First

Third

4.6 1.6 3.0 2.8 2.4 0.77 3.9 0.15

11.2 11.9 9.0 4.6 13.3 .08 12.1 .32

25.5 24.4 11.4 10.1 71.7 .04 35.3 .70

1.0 0 .4 .5 .3 .82 .4 .23

10.1 9.7 2.2 2.3 6.5 .Ol 11.0 .90

1.3 3.1 .4 1.5 .l .Ol .4 .004

5.1 4.4 8.5 6.9 15.2 .23 7.6 .42

7.4 4.0 4.9 4.1 2.2 .21 7.2 .17

14.7 9.5 8.9 6.6 4.0 .02 13.7 .09

9.2 7.8 11.9 11.6 53.5 .44 34.4 .78

4.2 3.4 8.8 7.0 5.4 .04 7.0 .36

8.6 6.5 15.7 10.5 12.8 .05 19.8 .15

4.1 4.8 2.8 4.2 8.4 .56 7.4 .46

10.7 10.7 8.4 7.0 6.9 .11 11.2 .70

27.2 26.5 16.4 17.3 23.2 .03 34.5 .97

0 0 0 0

0 0 0 0

1.9 2.7 .2 .3

(I __

__

3.9

__

__

.lO

__

__

.9

__

__

.21

21.4 17.3 25.1 24.3 52.8 .24 21.5 .33

42.9 39.0 33.1 24.6 16.7 .Ol 35.5 .08

70.3 66.4 49.1 42.7 9.3 .OOl 16.7 .05

MSE = mean square error; P = probability level

a No coverage was recorded, and thus, analysis of variance was not conducted.

b Total vegetation coverage is often less than the sum of the species groups because of multiple occupancy.

16
Conclusions and Management Implications

These early results show that the shelterwood method can

effectively regenerate mixed pine-hardwood stands in the

Ouachita Mountains when combined with low-cost, lowimpact site preparation that controls the submerchantable

trees left after harvesting. Despite substantial undisturbed

litter and slash after harvesting and hardwood control, the

stand had enough favorable microsites to establish

acceptable shortleaf pine and hardwood reproduction. Pine

reproduction principally came from seeds dispersed after

treatment, but hardwoods developed from advance

reproduction and sprouting. This difference in reproduction

strategy gives hardwoods an initial growth advantage.

However, pines usually grow rapidly after establishment,

providing acceptable reproduction when the density and

stocking levels are similar to those reported here.

Overstory hardwood retention within a shelter-wood pine

stand will have the most significant impact on

environmental conditions in the understory. Overstory

hardwoods appear to suppress development of pine

reproduction to a greater degree than an equivalent pine

basal area, reflecting differences in the crown features

between the two species groups. The limit for retaining

hardwoods within a shelterwood pine stand appears to be

fairly low. These early results suggest that 15 ft’ per acre of

hardwood basal area in a scattered distribution can be

retained for at least the first few years after the reproduction

cut. This seems logical based on the generality that

hardwoods produce about twice the overstory competition

as the same pine basal area. An overstory basal area of 30 ft*

per acre of pines and 15 ft* per acre of hardwoods is

equivalent to a pine overstory 60 ft2 per acre, which is

generally considered to provide an acceptable environment

for the development of pine reproduction in uneven-aged

stands (Baker and others 1996). However, the long-term

success of either overstory treatment is doubtful unless

overstory trees are removed entirely or periodically reduced

to acceptable stocking levels. Although subsequent

harvesting will damage existing reproduction, Grano (1961)

found that the loss in pine milacre stocking was only 10

percent for a basal area removal of 3 1 ft2 per acre and 16

percent for 42 ft* per acre.

The upper limit for acceptable overstory stocking has not

been well established in even-aged reproduction cutting

methods, probably because traditional guidelines call for

overstory removal as soon as reproduction reaches

acceptable levels. Undoubtedly, the pine-hardwood

overstory treatment of this study will reach the upper limit

for acceptable stocking much sooner than the pine overstory

treatment. For example, annual basal area growth in this

study was about 0.75 ft2 per acre for pines and 0.75 ft2 per

acre for hardwoods. Thus, the pine overstory treatment

should take well over 20 years to reach a basal area of 75 ft*

per acre, which is considered the upper stocking level for

adequate development of pine regeneration in uneven-aged

pine stands (Baker and others 1996). Because of its higher

initial stocking, the pine-hardwood overstory treatment

should reach this upper limit in 7 years when projected basal

areas are 35 ft* per acre for pines and 20 ft* per acre for

hardwoods (equivalent to a pine basal area of 35 + 2 X 20 =

75 ft2 per acre). Of course, this prediction needs

confirmation by the continued monitoring of overstory and

understory dynamics in this study, but the general contrast

between overstory treatments is clear-in the pine-hardwood

overstory treatment, stocking must be reduced within 5 to

10 years after harvest to sustain the development of

regeneration.

Because merchantable hardwoods were removed in this

study during harvesting, subsequent hardwood control

treatments were low in intensity and cost. The chemical

control treatment was restricted to the stumps of individual

stems in the l- to 5-in d.b.h. classes and, therefore, applied

to only a fraction of the total hardwoods in the stand. The

herbicide application effectively controlled the sprouting of

some-but not all-species. Early results suggest that the

chemical control treatment was not justified in the

conditions tested here because it failed to substantially

improve the amount, size, or overtopped status of shortleaf

pine reproduction. Other conditions had more influence on

the acceptable establishment of shortleaf pine reproduction,

including the abundant pine seed production and the low

initial levels of competing vegetation.

Literature Cited

Baker, James B.; Cain, Michael D.; Guldin, James M. [and others].

1996. Uneven-aged silviculture for the loblolly shortleaf pine forest

types. Gen. Tech. Rep. SO-1 18. Asheville, NC: U.S. Department of

Agriculture, Forest Service, Southern Research Station. 65 p.

Becton, W.R. 1936. Effects of varying densities of hardwood cover on

growth and survival of shortleaf pine reproduction. Journal of Forestry.

34(2): 160-164.

Blair, Robert M.; Brunett, Louis E. 1976. Phytosociological changes

after harvest in a southern pine ecosystem. Ecology. 57(l): 18-32.

Banner, F.T. 1974. Seed testing. In: Schopmeyer, C.S., tech. coord. Seeds

of woody plants in the United States. Agric. Handb. 450. Washington,

DC: U.S. Department OfAgriculture: 136-152.

17
Brender, E.V.; McNab, W.H. 1972. Loblolly pine seed production in

the lower Piedmont under various harvesting methods. Journal of

Forestry. 70(6): 345-349.

Cain, Michael D. 1988. Competition impacts on growth of naturally

regenerated loblolly pine seedlings. Res. Note SO-345. New Orleans,

LA: U.S. Department of Agriculture, Forest Service, Southern Forest

Experiment Station. 5 p.

Cain, Michael D.; Shelton, Michael G. 1993. Modification of GSA

metal wastebaskets for use as seed and litter traps. Engineering Field

Notes. 26(3): 65-69.

Cain, Michael D.; Shelton, Michael G. 1994. Indigenous vegetation in a

southern Arkansas pine-hardwood forest after a half century without

catastrophic disturbance. Natural Areas Journal. 14(3): 165-174.

Campbell, T.E.; Mann, W.F., Jr. 1973. Regenerating loblolly pine by

direct seeding, natural seeding, and planting. Res. Pap. SO-84. New

Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern

Forest Experiment Station. 9 p.

Ehrenreich, John H.; Crosby, John S. 1960. Herbage production is

related to hardwood crown cover. Journal of Forestry. 58(7): 564-566.

Farrar, Robert M., Jr. 1985. Schnur’s site-index curves formulated for

computer applications. Southern Journal of Applied Forestry. 9(l): 3-5.

Graney, David L. 1992. Site index relationships for shortleaf pine. In:

Brissette, John C.; Bamett, James P., camps. Proceedings of the

shortleaf pine regeneration workshop; 1991 October 29-3 1; Little Rock,

AR. Gen. Tech. Rep. SO-90. New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest Experiment Station: 142-

157.

Graney, David L.; Burkhart, Harold E. 1973. Polymorphic site index

curves for shortleaf pine in the Ouachita Mountains. Res. Pap. SO-85.

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In: Brissette, John C., ed. Proceedings of the seventh biennial southern

silvicultural research conference; 1992 November 17-19; Mobile, AL.

Gen. Tech. Rep. SO-93. New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest Experiment Station:

333-341.

Shelton, Michael G.; Murphy, Paul A. [In press]. Understory vegetation

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Forest Service, Southern Research Station.

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Overstory-understory relationships in natural loblolly pine-hardwood

stands: implications for wildlife habitat. In: Brissette, John C., ed.

Proceedings of the seventh biennial southern silvicultural research

conference; 1992 November 17-19; Mobile, AL. Gen. Tech. Rep. SO93. New Orleans, LA: US. Department OfAgriculture, Forest Service,

Southern Forest Experiment Station: 613-619.

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Forestry. l(2): 1 O-l 1.

18
Shelton, Michael G. 1997. Development of understory vegetation in pine and pinehardwood shelterwood stands in the Ouachita mountains-the first 3 years. Res.

Pap. SRS-8. Asheville, NC: U.S. Department of Agriculture, Forest Service,

Southern Research Station. 18 p.

This publication describes the development of pine and hardwood reproduction after

shelterwood cutting in pine-hardwood stands. Results demonstrate the importance of

overstory-understory relationships in reproduction cutting methods that retain

overstory trees. However, the method of submerchantable hardwood control (manual

versus chemical) may be unimportant if the pine seed production is good and the

level of competing vegetation is low.

Keywords: Even-aged silviculture, natural regeneration, pine-hardwood stands,

Pinus echinata Mill., shelterwood reproduction cutting method, site preparation.

1 I
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