United States

Department of

Agriculture

Forest Service

Southern Research

Station

Research Paper

SO-296

Understory Vegetation 3

Years after Implementing

Uneven-Aged Silviculture in

a Shortleaf Pine-Oak Stand

Michael G. Shelton and Paul A. Murphy
SUMMARY

The effects of retaining overstory hardwoods on understory

vegetation were determined after implementing uneven-aged silviculture using single-tree selection in a shortleaf pine-oak stand

(Pinus e&in&a Mill. and Quercus spp.) in the Ouachita

Mountains. Treatments were the following hardwood basal areas

(square feet per acre) and spatial arrangements: 0, 15grouped,

15-scattered, 30-scattered, and an untreated control. Pine basal

area was reduced by harvesting to 60 ft”/acre in all treatments

except the control, and the desired hardwood basal area and

arrangement were achieved by injecting unwanted hardwoods

with herbicide. Monitoring was conducted at 10 permanent locations within each 0.5-acre plot of the randomized, complete block

design with four replications. Pine regeneration during the first

growing season following harvest was virtually nil because there

was little advance regeneration and the preceding seed crop was

poor. A good seed crop occurred during 1989 (180,000 sound pine

seeds per acre), resulting in a mean of 2,730 seedlings per acre the

following growing season with no significant differences among

treatments. Mortality over the next 2 years reduced this base to

1,925 seedlings per acre for the O-hardwood treatment and 0

seedlings per acre for the control. Oak regeneration averaged 2,370

rootstocks per acre after the third growing season and had a mean

milacre stocking of 63 percent; no significant differences occurred

among treatments. Pine regeneration was judged to be adequate

for the O-hardwood treatment and within openings for the 15

grouped treatment but was inadequate elsewhere. Results indicate the importance of overstory-understory relationships in

uneven-aged silviculture.

September 1997

Southern Research Station

P.O. Box 2680

Asheville, NC 28802
Understory Vegetation 3 Years after Implementing Uneven-Aged

Silviculture in a Shortleaf Pine-Oak Stand

Michael G. Shelton and Paul A. Murphy

INTRODUCTION

Knowledge about implementing uneven-aged silviculture in shortleaf pine (Pinus echinatu Mill.) stands

is very limited (Murphy and others 1991). Techniques

and guidelines developed for loblolly (Z? tuedu LJ-shortleaf pine stands at the Crossett Experimental Forest

in the Coastal Plain of Arkansas (Reynolds 1959,

1969; Reynolds and others 1984) may be adaptable,

but most of the Crossett experience applies to managing existing uneven-aged pine stands or rehabilitating

understocked pine stands. Stands in the Ouachita

Mountains are mostly mature pine-oak (Quercus spp.)

stands that have developed an even-aged character,

and a hardwood component is desired to enhance the

stand’s nontimber resources. Such stands pose a

unique set of problems: (1) some hardwoods must be

removed to create a favorable environment for the

establishment and development of pine regeneration,

(2) a reverse-J diameter distribution must be developed, which will likely take several decades, and (3)

the response of suppressed pines of the original stand

to release is questionable (Shelton and Murphy 1991,

1993).

This ongoing research was initiated in 1988 by

personnel with the USDA Forest Service’s Ouachita

National Forest and Southern Research Station. The

study focuses on some of the problems of applying

uneven-aged silviculture in mature pine-oak stands

on poor sites; such stands are common on public

lands, and knowledge is needed concerning alternative silvicultural systems. Study objectives are to test

the traditional application of uneven-aged pine silviculture using single-tree selection and to determine

the limits for hardwood retention within this system.

Response of understory vegetation is reported here

for the first 3 years after implementation of the study

METHODS

Study Area

The study was installed in the Winona Ranger

District of the Ouachita National Forest in Perry

County, AR. Plots were oriented along an east-west

ridge, which is typical of the physiography of the

Ouachita Mountains. Elevations ranged from 640 to

790 ft above sea level. Blocks were located with the

following slope positions: the lower, middle, and upper

north slopes and the upper south slope. Slopes of individual plots ranged from 8 to 21 percent, and aspects

ranged from north to northwest on the north-slope

positions and from southeast to southwest on the

south-slope position.

Soils of the study area are mapped as the

Carnasaw and Pirum series, both Typic Hapludults.

These are well drained, 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.

Site index for shortleaf pine averaged 57 ft at 50

years and ranged from 53 to 64 ft, which is typical of

upland sites in the Ouachita Mountains (Graney

1992). The lower north slope was slightly higher in

site index than the other three slope positions (61 versus 56 ft). Site index averaged 53 ft at 50 years for

white oak (Quercus ulbu L.) and 54 ft for black oak (Q.

uelutinu Lam.).

Vegetation in the study area was typical of much of

the forested landscape in the Ouachita Mountains,

where upland forests are dominated by shortleaf pine

and mixed oaks (Guldin and others 1994). Overstory

basal area (trees 2 3.6 inches in d.b.h.1 in this mature,

second-growth, shortleaf pine-oak stand averaged 90

ft’lacre for shortleaf pine and 32 ft’lacre for hardwoods before treatment implementation. Oaks

accounted for 84 percent of the total hardwood basal

area. White oak was the most prevalent hardwood,

with lesser amounts of post oak (Q. stellutu

Wangenh.), black oak, blackjack oak (Q. murilundicu

Muenchh.), and southern red oak (Q. fulcutu Michx.).

The remaining 16 percent of the hardwood basal area

was composed of ash (Frczxinus spp.), hickory (Curyu

spp.), red maple (Acer rubrum L.), serviceberry

(Amelunchier urboreu [Michx. f.1 Fern.), blackgum

(Nyssu sylvuticu Marsh.), and dogwood (Cornus florida L.). The understory was mainly composed of

regeneration of the more shade-tolerant species and a

Michael G. Shelton and Paul A. Murphy are research foresters at the Forestry Sciences Laboratory, U.S. Department of Agriculture, Forest

Service, Southern Research Station, Monticello, AR 71656; in cooperation with the School of Forest Resources and the Arkansas Agricultural

Experiment Station, University of Arkansas at Monticello, Monticello, AR 71656.
variety of common shrubs, such as huckleberries

(Vaccinium spp.) and hawthorns (Crutuegus spp.).

Overstory pines and oaks in the initial stand

ranged in age from 30 to over 110 years (Shelton and

Murphy 1991). However, most of the pines were 50 to

80 years old, and the oaks were 40 to 70 years old. The

scarcity of younger trees in the overstory indicated

that regeneration and subsequent development in

both the pines and oaks had been limited for 30 to 40

years of stand development before implementation of

the study

Study Design and Treatments

Sixteen square 0.5-acre plots were installed and surrounded by a 58.2-ft isolation strip that received the

same treatment. Basal area of overstory pines (trees 2

3.6 inches in d.b.h.) was reduced to 60 ft’lacre in all

plots. Hardwood treatments were the following basal

areas (square feet per acre) and spatial arrangements

for overstory trees: 0, 15-grouped, 15-scattered, and

30-scattered. In the scattered arrangements, hardwoods were uniformly distributed across each plot,

whereas hardwoods in the grouped arrangement were

located outside the openings in the pine canopy (fig. 1).

For the grouped arrangement, no attempt was made to

create openings in the pine canopy other than those

occurring as a matter of course in the application of

single-tree selection. Openings in the pine canopy

ranged from 0.1 to 0.25 acre and often extended from

the 0.5-acre plots into the isolation strip. Thus, the

grouped spatial arrangement was similar to the Ohardwood treatment within openings and to the 30-

scattered treatment outside openings. Treatments

were assigned in a randomized, complete block design

with four replications of each treatment.

The pine component was regulated using the basal

area-maximum diameter-quotient (BDq) method of

single-tree selection (Farrar 1984). Targets were 60

ft’lacre for basal area, 18 inches for maximum d.b.h.,

and a quotient of 1.2 for l-inch diameter classes.

Targets for maximum diameter and quotient were followed as closely as feasible because the stand lacked a

balanced reverse-J diameter distribution characteristic of uneven-aged structure (fig. 2). Hardwood retention favored the higher quality red and white oaks;

these were typically the larger hardwoods in the study

area.

Plots were harvested from December 1988 through

early March 1989 using mules to skid logs to landings. Because no local markets existed for hardwoods, all hardwoods 2 1 inch in d.b.h. that were not

specifically designated for retention were injected

with triclopyr amine during April 1989. Herbicide

treatments were applied by contract crews following

label directions; research crews did some followup

injection work.

In 1991, permanent 0.5-acre plots were established

in untreated areas adjacent to each block to serve as

untreated controls.

Measurements

During March 1989, all retained pines and hardwoods (2 3.6 inches in d.b.h.) in the 0.5-acre plots were

measured for d.b.h., and the location of each stem was

mapped by determining azimuth and distance from

plot center. About one-third of the trees were measured for height, crown dimensions, and age. Ten permanent points were systematically located within each

0.5-acre plot for monitoring the development of understory vegetation. The monitoring points were located

such that none was closer than 30 ft from the 0.5-acre

plot boundary and 88 ft from the isolation boundary

Seedbed conditions after harvest were evaluated at

12 locations spaced along a 22-ft line transect that

was centered at each of the 10 permanent monitoring

points. The direction of the transect was randomly

selected for each permanent point. Seedbed condition

at each location was classified as undisturbed litter,

disturbed litter, exposed mineral soil, logging debris,

or some natural feature, such as a rock or natural

coarse woody debris (diameter 2 4 inches).

Pine seedlings were inventoried in milacre plots

(3.72 ft in radius) centered around the permanent

monitoring points by the following size classes: < 0.5,

0.6 to 2.5, 2.6 to 4.5 and 2 4.6 ft in height and I 0.5

inch in d.b.h. Pine saplings (stems with a d.b.h. of 0.6

to 3.5 inches) were inventoried in O.Ol-acre plots

(11.78 ft in radius) centered around each permanent

monitoring point. Inventories were conducted in June

1989, June 1990, December 1990, and October 1991.

The 1989 and 1990 inventories were restricted to pine

regeneration. However, all woody vegetation was

inventoried in 1991 by species or species group using

the previously described size classes. Muhiple-stemmed rootstocks were tallied as one individual, evaluating the tallest stem for size. In the December 1990

and October 1991 inventories, the two tallest pine

seedlings (if any) on each milacre plot were selected as

the dominant pine seedlings and were measured for

groundline diameter, height, and crown width.

Preharvest conditions were estimated during the

1989 inventory by measuring woody vegetation on 30

temporary milacre plots located in untreated areas

adjacent to each block. Permanent control plots were

evaluated in the 1991 inventory and thereafter.

Percentage of coverage for understory vegetation

was estimated on milacre plots by the following

groups: grasses, herbs, vines, shrubs, hardwoods,

pines, and total coverage. Evaluations were conducted in June, because coverage was observed to maximize before the summer droughts that typically occur

on these sites. All evaluations were conducted by the

2
same person. Coverage was evaluated during 1989,

1990, and 1992, or the first, second, and fourth growing seasons, respectively, after harvest.

In 1989 and 1990, pine seed production was monitored from October through February of the next year

in four 0.9-ft’ seed traps (Cain and Shelton 1993) on

each O.&acre plot. The seed traps were located about

30 ft from the center of the plot in a square pattern

and about 100 ft from the outer boundary of the plot.

Collections were made during the middle and end of

the October to February period. Seed production was

not monitored in the E-grouped treatment or the

control at that time. Viability was determined by

O-HARDWOODS

15SCAlTERED

splitting seeds and inspecting the contents (Bonner

1974). Seeds with full, firm, undamaged, healthy tissue were judged to be potentially viable and were tallied as sound seeds.

Percentage of coverage for the canopy was determined in June 1992 using a spherical densiometer at

4.5 ft above each permanent monitoring point.

Photosynthetically active radiation (PAR) was determined at 4.5 ft above each permanent monitoring

point during clear sky conditions on August 2, 1991,

using an 80-sensor Sunfleck Ceptometer (Decagon

Devices, Inc., Pullman, WA). Ten readings were taken

across each milacre plot. Measurements were taken

15GROUPED

_ 30-SCAlTERED

PINE @ HARDWOOD

20 Fr

Figure 1. - Spatial distribution of pine and hardwood tree crowns observed for the block on the upper north-slope position.

Crown width is drawn to scale and was calculated from d.b.h. using prediction equations developed from the

data.

3
SHORTLEAF PINE 15-SCAlTERED HARDWOODS

- 4 6 8 10 12 14 16 18 20 - 4 6 8 10 12 14 16 18 20 22

D.B.H. ( INCHES )

Figure 2. -D.b.h.4ass distribution for shortleafpine before and after harvest and hardwood control; the target

distribution is for a basal area of 60 ft’lacre, a maximum d.b.h. of 18 inches, and a quotient of 1.2 for l-inch

d.b.h. classes. An example of the d.b.h.4ass distribution for hardwoods is shown for the 15-scattered treatment.

between 1030 and 1330 solar time. Measurements

also were made in full sunlight, which permitted the

calculation of relative light intensity (PAR at 4.5 ft

expressed as a percentage of PAR in full sunlight).

Data Analysis

Mean values for understory vegetation were calculated for the 10 regeneration subplots in each O.&acre

plot. Milacre plots were considered to be stocked by

pine and deciduous woody species if at least one individual of seedling size was present to represent the

species or species group. To facilitate data presentation, deciduous species were grouped as follows: oaks,

other overstory trees, midcanopy trees, and shrubs.

The other overstory trees included blackgum, hickory,

ash, and sweetgum (Liquidambar styracifha L.), and

the midcanopy trees included red maple, serviseberry,

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

virginiana L.), and black cherry (Prunus serotina

Ehrh.). The shrubs were huckleberries, hawthorns,

plums (Prunus spp.), and several other common

species. Mean seedling height of deciduous groups

was calculated from the number of rootstocks in each

height class and the class midpoint.

Analysis of variance for a randomized, complete

block design was used to compare expressions of

understory vegetation and stand conditions among

treatments. Differences among treatment means

4

were isolated by using the Ryan-Einot-Gabriel-Welsch

Multiple Range Test (P = 0.05). This procedure,

which is one of the most powerful step-down, multiple-range tests available, controls the experimentwise error rate (SAS Institute 1989).

RESULTS AND DISCUSSION

The Post-Harvest Environment

Canopy coverage and light intensity were both

strongly related to prevailing stand conditions (fig.

3). The untreated control had 93 percent canopy coverage indicating the closed nature of the canopy. This

resulted in a PAR that was only 13 percent of full

sunlight at 4.5 ft above ground. By contrast, the Ohardwood treatment had the lowest canopy coverage

(55 percent) and the greatest PAR (59 percent of full

sunlight). Retention of successive increments of

hardwoods increased canopy coverage and correspondingly reduced PAR. This relationship reflected

the combined effects of the increase in total basal

area and the fact that hardwoods tend to produce

more shade per unit of basal area than pines. This

result occurs because hardwoods have broader leaves,

larger crowns, and shorter heights than pines

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

Values for the 15-grouped treatment are a weighted
mean of two conditions-an open environment within canopy gaps where hardwoods were removed, and

a closed environment outside the openings where

hardwoods were retained.

Harvesting resulted in fairly low levels of soil disturbance (table 1). These results reflect the use of

mules for skidding and the relatively low volume harvested (a mean of 3,800 fbm Schribner per acre) when

compared to harvests implementing even-aged reproduction cutting methods such as clearcut, seed tree,

and shelterwood. No significant differences were

observed among treatments, and averages were 76,

10, 8, and 4 percent for undisturbed litter, disturbed

litter, logging debris, and mineral soil, respectively.

Soil disturbance from logging generally creates favorable seedbed conditions for pine regeneration by

exposing mineral soil and disturbing litter (Shelton

and Wittwer 1992). However, adequate pine regeneration can become established in a seedbed of undisturbed litter if ample seed production occurs (Cain

1991, Grano 1949).

Production of Shortleaf Pine Seeds

Seed production was not monitored during 1988,

the year of harvest. However, production was apparently poor because virtually no new seedlings were

observed during the following growing season. Seed

production during 1989 averaged 180,000 sound seeds

per acre, and no significant differences occurred

among the treatments (table 2). This seed crop is considered a good one for shortleaf pine stands in the

Ouachita Mountains (Shelton and Wittwer 1996).

Another seed crop failure occurred in 1990 when seed

production averaged only 3,100 sound seeds per acre.

This episodic pattern of seed production is fairly typical for shortleaf pine stands (Wittwer and Shelton

1992).

CANOPY COVERAGE

loo - MSE=35.8 8

”

HDkDS GRdUSPED

15 30- CONTROL

SCAllERED

HARDWOOD

The percentage of total seeds that are sound is

an expression of seed quality During each year of

evaluation, the O-hardwood treatment had the highest percentage of sound seeds, and the 30-scattered

treatment had the lowest, but differences were not

significant (table 2). Yocom (1971) observed that

releasing shortleaf pine trees significantly increased

the percentage of sound seeds. The percentage of

sound seeds varied substantially between the years,

averaging 42 percent in 1989 and 2 percent in 1990.

Shelton and Wittwer (1996) reported that the percentage of sound seeds increased significantly with

the size of the shortleaf pine seed crop, approaching

75 percent in bumper years.

The lack of significant differences among the

treatments for seed production may indicate that

more time is needed before the pines respond to

release. Others have observed that hardwood control

and release by thinning enhance pine seed production. Yocom (19711, for example, reported that the

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 ft”/acre)

resulted in the greatest seed production. However,

the influence of stand conditions on the seed production of shortleaf pine is far less than the inherent

variation due to environmental factors and cone and

seed consumers.

Density of Shortleaf Pine Seedlings

An average of only 177 pine seedlings per acre

occurred during the 1989 growing season, which followed harvesting (table 3). This result reflected the

suspected poor seed crop during the preceding year

and the absence of advance regeneration in the initial

stand. However, the good seed crop in 1989 resulted

PAR AT 4.5 FT

MSE = 62.9

P>F = 0.0001

o- 16- 16- 30- CONTROL

HDWDS GROUPED SCAllERED

TREATMENT

Figure 3. - Canopy coverage of the overstory and photosynthetically active radiation (PAR at 4.5 ft expressed as a

percentage of PAR in full sunlight) occurring after treatment implementation. Bars with different letters are significantly different fP=O.O5).

5
Table 1. -Seedbed conditions after the initial harvest implementing uneven-aged silviculture in a shortleafpine-hardwood stand

Hardwood treatment* Mean

Seedbed 15 ft’lacre 15 ft’/acre 30 ft?acre square

condition 0 ft’lacre grouped scattered scattered error t P>F

Undisturbed litter

Disturbed litter

Mineral soil

Logging debris

Natural feature

______________________________--- percent of area _________________----------------

73 80 71 81

10 8 13 8

4 2 6 2

9 8 8 6

4 3 1 2

5.60El 0.22

2.01El 0.32

6.6730 0.14

2.2731 0.84

9.06EO 0.67

*Columns may not sum to 100 percent because of rounding.

tin this and the other tables, values for mean square error are in exponential format; for example, 1.23E4=1.23X10’=12,300.

Table 2. -Annual production and percentage of sound shortleaf pine seed after the initial harvest implementing uneven-aged silviculture

in a shortleaf pine-hardwood stand

Hardwood treatment* Mean

Seed 15 ft*/acre 30 ft’lacre square

crop 0 ft’lacre scattered scattered error P>F

_________________ Thousands of sound seeds per acre __________________

1989 197.0 144.0 200.0

1990 3.1 3.1 3.1

___________---------- Sound seeds (percent of total) ---------------------

1989 44.5 42.7 38.4

1990 3.1 2.3 1.4

*The 15 ft*/acre-grouped treatment and control were not monitored during this period.

6.7839 0.58

3.4837 1.00

1.81E2 0.81

2.15El 0.91

Table 3. -Density of shortleafpine seedlings after the initial harvest implementing uneven-aged silviculture in a shortleafpine-hardwood stand

Seedling density (number per acre) by hardwood treatment* Mean Heig:

clas s

-- Feet --

5 0.5

0.6 to 2.5

Total seedlings

I 0.5

0.6 to 2.5

Total seedlings

5 0.5

0.6 to 2.5

15 ft*/acre 15 ft*/acre 30 ft’lacre

0 ft’lacre grouped scattered scattered ControG

___________________________ 1989: Middle of first growing season ----------------------------

150 50 25 100 217

275 0 0 25 42

425 50 25 125 259

____________------------- 1990: Middle of second growing season ---------------------------

3,800 1,650 1,825 3,500 .

75 50 0 25

3,875 1,700 1,825 3,525 .

___________________________ 1990: End of second growing season ----------------------------

2,225 625 575 800 . .

100 25 0 50

square

error

3.8634

5.4634

8.7534

3.8736

4.1733

3.8936

9.4835

3.9633

P>F

0.66

0.44

0.34

0.34

0.44

0.33

0.12

0.21

Total seedlings 2,325 650 575 850 . . . 9.9335 0.11

s 0.5

0.6 to 2.5

___________________---------- 1991: End of thira’ growing lemon _____ _______ _ ____ __ __________

325ab 100ab 75ab 450a Ob 3.8634 0.03

1.600a 400b 50b 25b Ob 3.8735 0.02

Total seedlings 1,925a 500ab 125b 475ab Ob 5.3135 0.02

*Row means followed by different letters are significantly different.

ptaller seedlings or saplings were observed.

Temporary control plots were evaluated during the first growing season; no evaluations were made during the second growing season;

permanent plots were evaluated in the third growing season.

6
in an average of 2,730 pine seedlings during the middle of the 1990 growing season, with no significant

differences among treatments. Seedling density was

reduced by subsequent mortality to an average of

1,100 seedlings at the end of the 1990 growing season;

treatment differences were not significant. The mortality rate during the 1990 growing season was about

40 percent in the O-hardwood treatment and 80 percent in the 30-scattered treatment. This first-year

mortality was exacerbated by a drought that developed because of low summer precipitation. The precipitation during June, July, and August at the nearby Perry, AR, weather station totaled 5.6 inches,

which was 5.1 inches below normal. Soil samples collected during this period from the surface 2 inches

had only 6.8, 7.4, and 7.7 percent moisture for the Ohardwood, E-scattered, and 30-scattered treatments,

respectively (mean square error=0.522; P>F=0.18).

About 0.6 percent of the sound seeds produced in

1989 resulted in established seedlings at the end of

the 1990 growing season. This value is similar to the

seedling-to-seed ratios reported elsewhere for natural

shortleaf pine regeneration. Yocom and Lawson

(19771, for example, reported a seedling-to-seed ratio

of 0.4 percent for undisturbed areas within a seedtree stand in the Ouachita Mountains and 1 percent

for disturbed areas. Haney (1962) observed a

seedling-to-seed ratio of 0.3 percent for undisturbed

areas and 2.0 percent for scarified areas in a sawtimber stand. In poorly stocked shortleaf pine stands,

untreated areas had a seedling-to-seed ratio of 0.4

percent, and burned areas had a ratio of 1.3 percent

(Maple 1965).

Significant differences among the treatment means

for seedling density did not become apparent until the

end of the 1991 growing season, when most seedlings

were 2 years old (table 3). More and taller seedlings

were observed in the O-hardwood treatment, and values progressively declined as additional hardwoods

were retained. Over 80 percent of the seedlings in the

O-hardwood treatment was in the 0.6 to 2.5-ft height

class, whereas only 5 percent of the seedlings in the

30-scattered treatment was in this height class. The

decrease in seedling density through time reflected

mortality. Seedling mortality over the 1990-91 growing seasons was 50 percent for the O-hardwood treatment compared to 86 percent for the 30-scattered

treatment. Mortality principally resulted from competition with overstory trees and understory vegetation.

There was little competition among pine seedlings

at this stage of development because of the small

size and scattered distribution of the seedlings.

Competition from the understory vegetation was

apparently secondary to that of the overstory trees

because the best seedling survival occurred in the Ohardwood treatment where understory vegetation

was most prolific.

A few pine seedlings were able to survive in the 15-

and 30-scattered treatments, but no seedlings were

observed in the control plots. Other researchers have

observed that pine seedlings can become established

under a dense canopy and persist for several years

before dying (Becton 1936, Wahlenberg 1960). This

observation suggests that newly established pine

seedlings are moderately shade tolerant but become

shade intolerant with age. Bormann (1956) reported,

for example, that the photosynthetic efficiency of

loblolly pine seedlings at low light intensities declined

substantially as secondary growth characteristics

developed.

Stocking of Shortleaf Pine Seedlings

Milacre stocking of pine seedlings displayed a similar pattern to that of density, except that significant

differences among treatments occurred earlier than

those for density (table 4). Stocking was 15 percent or

less for all treatments in 1989, the first growing season after harvest. After the good seed crop of 1989,

stocking increased to about 60 to 90 percent during

the middle of the 1990 growing season, but differences

among treatments were not significant. Stocking then

declined to 30 to 65 percent at the end of the 1990

growing season, and the O-hardwood treatment had

significantly higher stocking than the 15grouped and

15-scattered treatments. In 1991, stocking for

seedlings < 0.5 ft tall was greatest for the 30-scattered

treatment, while stocking for seedlings 0.6 to 2.5 ft tall

was greatest for the O-hardwood treatment.

Percentage stocking is often a better measure of

regeneration success than density because stocking

expresses the spatial distribution of seedlings, whereas density does not. Stocking is less sensitive to the

clumped-spatial pattern that often occurs with natural regeneration (Daniels 1978). For example, one of

the milacre plots inventoried in 1990 had 23 pine

seedlings, which contributed the equivalent of 2,300

seedlings per acre to the mean for the 10 milacre plots

but only 10 percent for stocking.

The generally accepted minimum stocking limits

for pine regeneration in uneven-aged pine stands is 50

percent stocking and 200 submerchantable stems per

acre (Cain and others 1987). Only the O-hardwood

treatment was above both of these thresholds in 1991.

The 15grouped treatment would be considered adequately stocked within the openings created by hardwood removal.

Density and Stocking of Deciduous Rootstocks

The number and stocking of hardwood rootstocks

in the seedling size class were generally not significantly affected by treatments (table 51. The possible

exception to this is percentage stocking for the other

7
Table 4. - Stacking of shortleafpine seedlings after the initial harvest implementing uneven-aged silviculture in a shortleafpine-hardwoad stand

Milacre stocking (percent) by hardwood treatment* Mean

Heig?t

15 ft’/acre 1.5 ft’/acre 30 ft’lacre square

class 0 ft’/acre grouped scattered scattered ControG error P>F

-- Feet -- ____________________------- 1989: Middle of first growing season ----------------------------

I 0.5 10.0 5.0 2.5 5.0 7.5

0.6 to 2.5 7.5 0.0 0.0 2.5 4.2

Total stocking 15.0 5.0 2.5 7.5 9.2

____________________----- 1990: Middle of second growing season ---------------------------

< 0.5 72.5 67.5 62.5 92.5 . . .

0.6 to 2.5 7.5 5.0 0.0 2.5 . . .

Total stocking 75. 0 67.5 62.5 92. 5

5 0.5

0.6 to 2.5

________________________--- 1990: End of second growingseason _______________ _____________.

65.0a 32.513 30.0b 4O.Oab . .

10.0 2.5 0.0 2.5 .

Total stocking 65.0a 35.0b 30.0b 40.0ab

5 0.5

0.6 to 2.5

Total stocking

____________________-------- 1991:End of third growingseason ____ ___ ________________-------

17.5ab 7.5ab 7.5ab 30.0a O.Ob

52.5a 25.Oab 5.0b 2.5b O.Ob

52.5a 25.Oab 12.5b 30.0ab O.Ob

7.7831 0.79

3.9731 0.44

7.60El 0.37

2.5332 0.11

4.17El 0.44

2.4032 0.10

1.90E2 0.02

2.50El 0.09

2.1732 0.04

1.3832 0.03

2.5832 0.003

3.1432 0.01

-

*Row means followed by different letters are significantly different.

?No taller seedlings or saplings were observed. Total stocking was based on the presence of seedlings in either size class and therefore is

not additive.

STemporary control plots were evaluated during the first growing season; no evaluations were made during the second growing season;

permanent plots were evaluated in the third growing season.

Table 5. -Density and stocking of deciduous rootstocks in the seedling-size class in 1991, the third growing season after the initial harvest

implementing uneven-aged silviculture in a shortleaf pine-hardwood stand

Hardwood treatment* Mean

15 ft’/acre 15 ft’lacre 30 ft’/acre square

Species group 0 ft’/acre grouped scattered scattered Control error P>F

__________________________________ Density(number per acre) ___________________________________

Oaks 1,850 2,325 3,500 1,450 2,725 2.0536 0.35

Other overstory trees 2,950 2,400 1,875 1,675 350 1.9636 0.17

Midcanopy trees 900 2,550 1,100 1,950 675 3.7136 0.63

Shrubs 4,350 6,825 8,450 9,210 12,450 3.7337 0.46

Total rootstocks 10,050 14,100 14,925 14,285 16,200 2.9537 0.59

Oaks

Other overstory trees

Midcanopy trees

Shrubs

_________________________________ Milmre stocking (percent) ____________________________________

57.5 57.5 77.5 52.5 70.0

52.5a 57.5a 37.5ab 45.0a 15.0b

30.0 40.0 32.5 37.5 27.5

35.0 67.5 65.0 57.5 60.0

2.9332 0.27

1.7432 0.006

3.7832 0.88

3.4432 0.17

Total stockine+ 90.0 92.5 100.0 90.0 95.0 5.00El 0.29

*Row means followed by different letters are significantly different. No rootstocks were observed in the sapling-size class.

+Total stocking was based on the presence of rootstocks in any deciduous species group and therefore is not additive.

8
overstory tree group, which includes species that are

intermediate in shade tolerance, such as blackgum,

ash, and hickory. Stocking in this group averaged 48

percent for treatments that were harvested and treated with herbicides, compared to 15 percent for the

untreated control. This difference might reflect

sprouting of top-killed stems or development from

seeds. There was a respectable component of oak

regeneration in all treatments, averaging 2,370 rootstocks per acre and 63 percent stocking. Shrubs were

the most common deciduous group present, averaging

over 8,000 rootstocks per acre and 57 percent stocking. Huckleberries were the most common shrub.

Deciduous rootstocks in the seedling size class after

harvest reflect several sources: (1) development from

seeds, (2) advanced regeneration that was below the

minimum size limit for herbicide treatment, and (3)

sprouting of stems that were top killed during the logging operation and herbicide application.

A total of 28 woody species or species groups was

recorded for the seedling size class across the study

area; included were one pine, seven oaks, four other

overstory trees, seven midcanopy trees, and nine

shrubs. The number of species or species groups present in the plots did not vary significantly across

treatments, but the means followed a distinctive

order: 11.2 for O-hardwoods, 11.0 for E-grouped, 10.2

for l&scattered, 10.0 for 30-scattered, and 8.8 for the

control (mean square error=0.517; P>F=0.30).

Curiously, Cain and Shelton (1994) also recorded 28

woody species or species groups in the understory of a

mature pine-hardwood 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. This comparison

demonstrates the richness of understory woody

species on these poor Ouachita Mountain sites and

the resiliency of the understory to stand disturbances.

Size of the Dominant Seedlings

After the 1990 growing season, groundline diameter of dominant pine seedlings in the O-hardwood

treatment averaged 37-percent larger than that of

seedlings in the 30-scattered treatment (table 6).

However, differences among treatments for crown

width and height were not significant. In fact, the

mean total heights were surprisingly uniform across

all treatments at this time, ranging from only 0.18 to

0.24 ft. Large increases in all seedling dimensions

occurred during the 1991 growing season, the

seedlings’ second year. Seedlings in the O-hardwood

and 15grouped treatments doubled or tripled in each

dimension, whereas seedlings in the 30-scattered

treatment changed substantially only in groundline

diameter. The larger crown widths of seedlings in the

O-hardwood and 15grouped treatments (about 0.5 ft)

indicate that these seedlings had developed secondary

needles, whereas the smaller crown widths of

seedlings in the 30-scattered treatment (0.12 ft) indicate the presence of only juvenile needles.

Mean height of deciduous rootstocks was significantly different among treatments for the oaks and

midcanopy trees (table 7). Means were generally

greatest for the O-hardwood, 15grouped, and control

treatments. These results probably reflect greater

growth rates resulting from the lower overstory competition in the O-hardwood and 15grouped treatments and the fact that seedling-sized stems were not

top killed by stand disturbances in the control plots.

Mean height of the deciduous species in 1991 was

considerably greater than that of the dominant pines

(an overall mean of 0.6 ft for the dominant pines versus a mean of 1.3 ft for all deciduous groups). These

results reflect a difference in the reproductive strategy

of the two groups-pine regeneration principally

develops from seeds, and deciduous groups principally

Table 6. -Mean size of the two dominant shortleafpine seedlings (if any) within each milacre plot during the second and third growing

seasons after the initial harvest implementing uneven-aged silviculture in a shortleaf pine-hardwood stand

Hardwood treatment* Mean

15 ft’lacre 15 ft’/acre 30 ft’lacre square

Property+ 0 ft*/acre grouped scattered scattered Control$ error P>F

Groundline diameter

Crown width

Height

___________-----____-_---------- 1990: Second growing season ____________________ _____________

0.054a 0.049a 0.041ab 0.034b

0.15 0.14 0.14 0.11

0.22 0.24 0.18 0.20 .

4.473-5 0.01

2.273-3 0.67

2.233-3 0.32

_________--------___-_----------- 1991: Third growing season __________________________________

Groundline diameter 0.13 0.14 0.10 0.06 1.743-3 0.10

Crown width 0.48a 0.47a 0.26ab 0.12b . 1.263-2 0.003

Height 0.74 0.82 0.58 0.30 . l.O6E-1 0.19

*Row means followed by different letters are significantly different.

+Groundline diameter is in inches; crown width and height are in feet.

kontrol plots were not evaluated during 1990; no shortleaf pine seedlings were observed in milacre plots during the 1991 inventory.

9
*Row means followed by different letters are significantly different

?Weighted by the number of rootstocks present for each group.

develop from advance regeneration and sprouts.

Experience elsewhere has shown that the height

growth of pine regeneration will usually exceed that of

deciduous species on upland sites when the pines are

free to grow and are in the grand period of growth

(Wahlenberg 1960). Thus, this relative ranking of pine

and hardwood height is expected to be short-lived for

the O-hardwood treatment and within openings for the

l&grouped treatment.

Understory Coverage

Vines, grasses, and herbs responded rapidly to the

reduction in overstory competition and to the disturbance brought about by harvesting and herbicide

application; and the responses were strongly related

to the treatments (table 8). Vines were the only group

in which significant differences occurred among the

treatments in 1989, the first growing season after

harvest. Significant differences among the treatment

means for grasses and herbs became apparent in 1990

and were still apparent in 1992; coverage was greatest for the O-hardwood and 15grouped treatments

and progressively declined as additional hardwoods

were retained. By contrast, coverage of shrubs did not

significantly vary among the treatments nor did substantial changes occur through time. Hardwood coverage increased substantially through time, especially

for the O-hardwood and l&grouped treatments, but

differences among treatments were not significant.

Coverage of pines began to appear in 1992; the greatest values occurred for the O-hardwood treatments

and declined as additional hardwoods were retained.

Treatment means were significantly different for

total coverage in 1990 and 1992. Total coverage for

the O-hardwood treatment was more than twice that

for the 30-scattered treatment and the control. 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 1981, Schuster 1967).

10

Table 7. -Mean total height of deciduous rootstocks in the seedling-size class in 1991, the third growing season after the initial harvest

implementing uneven-aged silviculture in a shortleaf pine-hardwood stand

Hardwood treatment* Mean

15 ft*/acre 15 ft’/acre 30 ft’/acre square

Species group 0 ft’/acre grouped scattered scattered Control error PrF

_______________________________________ Total height (feet) _________________________________________

oaks 1.5ab 1.6a l.lbc 0.9c 1.6a 5.403-2 0.001

Other overstory trees 1.6 1.9 1.4 1.4 1.1 7.05E-1 0.70

Midcanopy trees 1.2ab 2.0a 0.8b 0.8b l.Ob 2.17E-1 0.02

Shrubs 1.3 1.2 0.9 1.0 1.2 4.053-2 0.22

Mean height+ 1.6 1.5 1.1 1.0 1.3 6.023-2 0.04

,.

CONCLUSIONS AND MANAGEMENT

IMPLICATIONS

The amount and spatial distribution of natural

pine regeneration depends on seed supply, seedbed

conditions, and environmental conditions. Of these

causal factors, the treatments evaluated in this study

principally affected the environmental conditions

that govern the survival and growth of seedlings. The

linkage between study treatments and environmental

conditions was most easily demonstrated for levels of

PAR in the understory but undoubtedly involved

other factors that were not measured, such as soil

moisture, temperature and, perhaps, nutrients.

Because of shortleaf pine’s shade intolerance, seedling

development will be suppressed to some extent by any

reproductive cutting method retaining an overstory.

Thus, successful application of uneven-aged silviculture must compromise between retaining an adequate

overstory stocking for acceptable merchantable

growth and reducing overstory stocking sufficiently

to provide the environmental conditions needed for

regeneration. The growth rates of pines in both the

overstory and understory will be below the short-term

potential, but this compromise provides a system that

should be sustainable through time.

Recurring pine regeneration is crucial for the longterm sustainability of uneven-aged stands featuring

shortleaf pine as the dominant species. Retaining

hardwoods within the single-tree selection system will

most severely affect environmental conditions in the

understory. Hardwoods apparently suppress the

development of pine seedlings to a greater degree than

do an equivalent basal area of pines, which reflects

differences in crown and foliar features. Thus, acceptable limits for hardwoods within an uneven-aged pine

stand are apparently low, even if the pine basal area is

reduced accordingly. Early results of this study show

that retaining as little as 15 ft’/acre of hardwood basal

area in a scattered distribution with a pine basal

area of 60 ft’/acre (the 15-scattered treatment) will
prevent the establishment and development of sufficient pine regeneration to sustain long-term production of pine timber. However, reducing the pine basal

area to 45 ft”/acre might allow the retention of 5 to 10

ft’lacre of scattered hardwoods (Baker and others

1996).

Early results suggest that a hardwood basal area of 15

ft’lacre can be retained outside the openings in the pine

canopy (the 15grouped treatment) while still obtaining

adequate pine regeneration within openings. However,

the success of this treatment will not be certain until

long-term developmental rates of regeneration are fully

evaluated. In addition, the feasibility of implementing

the 15grouped treatment needs to be adequately tested

at an operational level. This treatment was difficult to

implement even on these small research plots because of

problems in determining where opening boundaries

occurred within the pine canopy Obviously, creating

openings to promote stand regeneration would have

been easier using group selection, where both pines and

hardwoods are removed within well-defined openings

(Murphy and others 1993).

Because of the high rates of seedling mortality

observed during the first growing season, this study

shows that the prompt removal of competing hardwoods is critical to establishing pine seedlings, especially if soil moisture is limited. Thus, hardwood basal

areas of 15 ft”/acre or greater should be substantially

reduced no later than the beginning of the growing

season following an acceptable pine seed crop.

However, retaining hardwoods until an acceptable

pine seed crop occurs would be beneficial to seedling

establishment, because hardwoods suppress the development of competing understory vegetation.

Results show that adequate pine regeneration will

occur in shortleaf pine stands in the Ouachita

Table 8. - Coverage of understory vegetation after the initial harvest implementing uneven-aged silviculture in a shortleafpine-hardwood stand

Coverage (percent) by hardwood treatment*

15 ft’/acre 15 ft’iacre 30 ft’iacre

Mean

square

Growing seasonT 0 ft’/acre grouped scattered scattered Control$ error P>F

______________________________________________ Grasses _________________________________________________

2.3 1.5 0.8 1.0 2.2

17.9a 7.lb 6.2b 2.9b

33.2a 12.6b 12.9b 4.9bc 1.8~

1989

1990

1992

1.23EO 0.24

1.68El 0.003

1.87El 0.0001

_______________________________________________ Herbs __________________________________________________

0.7 0.4 0.2 0.3 0.6

7.2a 8.4a 1.5b l.lb

3.2ab 3.6a 1.6ab 1.9ab 0.9b

1989

1990

1992

l.OlE-1 0.24

9.2230 0.01

1.30EO 0.03

_______________________________________________ Vines __________________________________________________

5.5a 5.2ab 5.lab 2.0b 7.2a

9.6a 11.9a 10.6a 3.9b . . .

17.0ab 23.3a 14.3ab 6.6b 9.6ab

1989 2.7630 0.01

1.14El 0.04

5.30El 0.05

1989

______________________________________________ Shrubs _________________________________________________

3.9 8.3 6.0 8.4 9.1

3.6 4.6 3.9 3.1 .

5.2 5.8 5.6 6.8 10.8

1.69El 0.39

1.69El 0.96

2.4731 0.53

___________________________________________ Hardwoods _______________________________________________

2.4 5.1 3.7 5.2 5.6

4.5 7.5 5.2 4.2

17.0 19.4 11.2 9.8 14.5

1989

1990

1992

4.4230 0.23

2.07El 0.74

6.40El 0.45

_______________________________________________ pines __________________________________________________

0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0

1.5a 0.5b 0.2b 0.2b 0.0

_________________________________________ Total coverage %___________________________________________

14.8 20.5 15.8 16.9 23.9

40.8 36.6ab 26.3bc 15.6~

69.8a 59.6a 41.8b 27.6b 33:3b

2.333-l 0.01

3.3331 0.21

4.7731 0.03

6.60El 0.0001

*Row means followed by different letters are significantly different.

+These are the first (1989), second (1990), and fourth (1992) growing seasons after harvest.

*Temporary control plots were evaluated in 1989; no evaluations were made in 1990; permanent plots were evaluated in 1992.

§Total coverage is often less than the sum of individual species groups because of multiple occupancy.

11
Mountains when: (1) the traditional guidelines for

uneven-aged pine silviculture are imposed (that is,

the O-hardwood treatment), (2) the seed supply and

environmental conditions are acceptable, and (3) the

competing understory vegetation is low. More time,

however, is needed to fully assess developmental

rates of regeneration and to evaluate the growth of

overstory trees. Although traditional guidelines for

uneven-aged pine stands exclude a hardwood component at a local scale, hardwoods can still be retained

at the stand level in natural occurrences along

drainages or in clumps or clusters (called an areawise distribution of hardwoods). Permissible levels

of hardwood retention within this spatial pattern

are probably not limited by biology, as long as the

pine-dominated matrix is sufficiently large to provide

relative freedom from the edge effects of retained

hardwoods. Rather, landowner objectives and operational concerns will probably dictate realistic limits.

The area-wise distribution of pines and hardwoods in

uneven-aged stands under single-tree selection

seems to have a number of advantages: (1) a favorable environment is provided for the shade-intolerant pine regeneration, (2) a significant hardwood

component can be retained, (3) species-site relationships are optimized, (4) sensitive areas are protected, (5) hardwoods are protected during silvicultural operations, (6) stand regulation and marking

are simplified, and (7) a varied wildlife habitat is

provided.

LITERATURE CITED

Baker, James B.; Cain, Michael D.; Guldin, James M.;

Murphy, Paul A.; Shelton, Michael G. 1996.

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Asheville, NC: U.S. Department of Agriculture,

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Becton, WR. 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.

Bonner, FT. 1974. Seed testing. In: Schopmeyer, C.S.,

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tueda seedlings during ontogeny Ecology. 37(l):

70-75.

Cain, Michael D. 1991. Importance of seedyear,

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Arkansas. Res. Pap. SO-268. New Orleans, LA: U.S.

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1987. Precommercial thinning of pine regeneration

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Cain, Michael D.; Shelton, Michael G. 1993.

Modification of GSA metal wastebaskets for use as

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stands. Forest Science. 24: 260-266.

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

production is related to hardwood crown cover.

Journal of Forestry. 58(7): 564-566.

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stands. In: Karr, Bob L.; Baker, James B.; Monaghan,

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loblolly pine ecosystem (West Region); 1984 March

20-22; Jackson, MS. Mississippi State, MS:

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129-154.

Graney, David L. 1992. Site index relationships for

shortleaf pine. In: Brissette, John C.; Barnett,

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Rock, AR. Gen. Tech. Rep. SO-90. New Orleans,

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Station: 29-49.

12
Haney, Glenn E 1962. Seedbed scarification aids

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60: 400-402.

Joyce, L.A.; Baker, R.L. 1987. Forest overstoryunderstory relationships in Alabama forests. Forest

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Maple, William R. 1965. Shortleaf pine stands five

years after seedfall on prepared sites. Res. Note

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the Ouachita Mountains. Southern Journal of

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Murphy, Paul A; Shelton, Michael G.; Graney, David

L. 1993. Group selection-problems and possibilities for the more shade-intolerant species. In:

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Phillip E.; Rink, George, eds. Proceedings of the

9th central hardwood conference; 1993 March

8-10; West Lafayette, IN. Gen. Tech. Rep. NC-161.

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Southwestern Naturalist. 12(4): 339-364.

Shelton, Michael G.; Murphy, Paul A. 1991. Age and

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October 30-November 1; Memphis, TN. Gen. Tech.

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regeneration and understory vegetation 1 year

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Bently. 1993. Overstory-understory relationships

in natural loblolly pine-hardwood stands: implications for wildlife habitat. In: Brissette, John C., ed.

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natural shortleaf pine stands. In: Brissette, John

C.; Barnett, James I?, camps. Proceedings of the

shortleaf pine regeneration workshop; 1991

October 29-31; Little Rock, AR. Gen. Tech. Rep.

SO-90. New Orleans, LA: U.S. Department of

Agriculture, Forest Service, Southern Forest

Experiment Station: 113-123.

Yocom, Herbert A. 1971. Releasing shortleaf pine

improves seed production. Res. Note SO-125. New

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

Forest Service, Southern Forest Experiment

Station. 2 p.

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10-11.

13

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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 herbicides

selectively and carefully Follow recommended practices for the disposal of surplus pesticides

and their containers.

Shelton, Michael G.; Murphy, Paul A. 1997. Understory vegetation 3

years after implementing uneven-aged silviculture in a shortleaf

pine-oak stand. Res. Pap. SO-296. Asheville, NC: U.S. Department of

Agriculture, Forest Service, Southern Research Station. 13 p.

The effects of overstory hardwood basal area and spatial arrangement on the establishment of shortleaf pine regeneration are

described in this publication. Results indicate the importance of

overstory-understory relationships in uneven-aged silviculture.

Keywords: Natural regeneration, pine-hardwood stands, Pinus echinatu Mill., site preparation, uneven-aged silviculture.
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