United States

Department of

Agriculture

Forest Service

Southern Forest

Experiment Station

New Orleans,

Louisiana

Research Paper

SO-268

Importance of Seedyear,

Seedbed, and Overstory for

Establishment of Natural

Loblolly and Shortleaf Pine

Regeneration in Southern

Arkansas

Michael D. Caín
S-Y

A study was installed in two uneven-aged, pine-hardwood stands in southern

Arkansas to determine the effects of different seedyears and seedbed conditions on first-year density and quadrat stocking of natural loblolly and

shortleaf pine (Pi~us taeda L. and P. echinata Mill.) regeneration. When the

study was installed, merchantable basal area averaged about 120 square feet

per acre, with 50 percent of that in pines and 50 percent in hardwoods. Pine

seedling counts relative to seedcatch in 5 succeeding years were compared on

untreated check plots and on plots where hardwoods were controlled by stem

injection of herbicides. Injected plots contained both undisturbed seedbeds

(pine-hardwood litter) and disturbed seedbeds (mineral soil exposed).

During the 5-year study, seedcrops ranged from a complete failure to over 1

million potentially viable seeds per acre. Pine seedling densities were well correlated with the seedcrops. Pine seedling density and quadrat stocking were

significantly less and generally unacceptable on uninjected plots compared to

density and stocking on injected plots. Plots with exposed mineral soil had a

smaller seeds-per-seedling ratio than inject-only plots, but gains in pine seedling density as a result of raking were not as great as those achieved by injection alone.

December 1991
Importance of Seedyear, Seedbed, and Overstory for

Establishment of Natural Loblolly and Shortleaf Pine

Regeneration in Southern Arkansas

Michael D. Cain

INTRODUCTION

Although planting pine seedlings for regeneration

purposes is an accepted practice throughout the

South, most of the loblolly and shortleaf pines (Pinus

taeda L. and P. echinata Mill.) that are being harvested today carne from natural regeneration. For

continued success with natural stand management,

four requirements must be met when regenerating

stands of loblolly and shortleaf pine: (1) a suitable

seedbed, (2) an adequate supply of seeds, (3) sufficient

soil moisture for seed germination and seedling establishment, and (4) freedom from excessive competition

after establishment.

A number of research studies have been conducted

in the vicinity of Arkansas (Gemmer 1941, Grano

1949, Grano 1971, Liming 1945, Phares and Liming

1961) and elsewhere in the Southeastern United

States (Pomeroy 1949, Pomeroy and Trousdell 1948,

Trousdell 1950, 1954, 1963, Trousdell and Langdon

1967) to determine the relationship of these four requirements to the establishment of natural loblolly

and shortleaf pine regeneration. However, many of

the earlier investigations incorporated intensive site

disturbance in combination with logging activity,

were conducted in a single seedyear, or used direct

seeding in place of natural seedfall. In view of these

irregularities, up-to-date information is needed to

supplement or confirm results obtained from historical investigations.

The purpose of this study was to determine the density and quadrat stocking of natural loblolly and

shortleaf pine seedlings relative to the abundance of

seed produced from uneven-aged pine stands, with

and without hardwood control. The study included

both disturbed and undisturbed seedbeds, which were

prepared over a period of 5 years to account for the

variability of natural seedcrops. Logging was excluded from the study because favorable seedbed conditions created by cultural treatments can be masked

by seedbeds created by logging disturbance (Trousdell

1963). For this investigation, the pine-hardwood

stands were specified by relative basal area, with

basal area for merchantable-size pines ranging from

50 to 80 percent of total basal area (Cain 1989).

METHODS

Study Areas

The study was conducted in two test areas on the

Crossett Experimental Forest in southern Arkansas.

Soil in the study areas is Bude (Glossaquic

Fragiudalf) and Providence (Typic Fragiudalf) silt

loam, and site index is 85 to 90 feet at 50 years for

loblolly pine (USDA 1979). Annual precipitation

averages 55 inches; extremes are wet winters and dry

autumns.

Test Area A.-At the time of study installation, this

uneven-aged stand consisted of mature loblolly and

shortleaf pines that averaged 19 inches in diameter at

breast height (d.b.h.); the 10 largest pines averaged 76

years old. Merchantable pine basal area averaged 69

square feet per acre, and understory and midstory

hardwood basal area averaged 60 square feet per acre.

The understory was relatively open, with no pine

regeneration and very little herbaceous vegetation because of shading from the midstory and overstory. The

last improvement cut was in 1963.

Test Area B.-Compared to test area A, this uneven-aged stand contained more pines in the smaller

size classes, averaging ll inches in d.b.h., but average

age of the 10 largest pines was 63 years. For pines less

than 4 inches in d.b.h., density averaged about 14

trees per acre. Basal area averaged 63 square feet per

acre for the pine component and 55 square feet per

acre for understory and midstory hardwoods. Herbaceous vegetation was sparse. No harvesting had

taken place since 1967.

Michael D. Cain is a research forester at the Forestry Sciences Laboratory, U.S. Department of Agriculture, Forest Service, Southern

Forest Experiment Station, Monticello, AR 71655, in cooperation with the Department of Forest Resources and Arkansas Agricultura1

Experiment Station, University of Arkansas at Monticello.

1
The only known disturbance on the two test areas

before study installation was prescribed burning in

February 1980. The fires were co01 and did not consume the litter down to mineral soil.

Treatments

The effects of annual seedfall, hardwood midstory

and overstory, and seedbed preparation on the establishment of loblolly and shortleaf pine regeneration

were studied. Seedcrops were monitored during each

of five consecutive seedyears, beginning with the

winter of 1985-86.

The absence of pine regeneration in these stands

might have been the result of overstory and midstory

hardwoods shading the forest floor. To investigate

this possibility, hardwoods greater than 1 inch in

groundline diameter were stem injected on designated

plots in the summer before each scheduled seedyear.

The herbicides Tordon@ 101R (undiluted) and Roundup@ (50-percent solution in water) were used for

deadening the hardwoods. Tordon was the principal

herbicide, but Roundup was used to control sweetgum

(Liquidambar styraciflua L.) and ash (Fraxinus L.

spp.), which are resistant to Tordon.

Undisturbed and disturbed seedbeds were tested in

the following manner. On one-half of each injected

plot, the pine-hardwood litter was left undisturbed

(inject-only treatment). On the other half, mineral soil

was exposed by use of a tractor-mounted raking

device and by hand-raking (inject/rake treatment).

The litter removal techniques were meant to simulate

mineral soil exposure that could be achieved operationally by prescribed burning or logging disturbance,

but soil displacement was minimal. Raking was always completed just before October 1 of scheduled

seedyears. There was no mineral soil exposure nor

hardwood injection on check plots.

Experimental Design

Each test area contained 4.4 acres, with 18 plots

measuring 66 by 66 feet (O.l-acre plots). Year of seeding and undisturbed checks were randomly assigned

to the 18 plots within each test area. During any one

seedyear, seedbed treatments were replicated on

three O.l-acre plots per test area. The same three

check plots per test area were used during each of the

five seedyear assessments.

Using a split-plot design, disturbed and undisturbed seedbeds were assigned at random to 0.05acre

subplots within each O.l-acre gross plot. To achieve

that design, plots were split in a north-South direction. On the interior 0.025 acre of each 0.05-acre subplot, a series of eight systematically established circular quadrats of 0.3 milacre each were used to inventory seedling catch. After the fifth year, two circular

quadrats of 0.00125 acre were systematically established on each interior 0.025 acre for assessing height

class distribution of pine regeneration and percent

ground cover.

Measurements

Once plots were established, overstory pines were

inventoried by 1-inch d.b.h. classes on al1 O.l-acre

plots. Basal area was computed on a plot-by-plot

basis.

A %oth-milacre seed collection trap was placed at

the center of each 0.05-acre subplot, 2 feet above

ground. Seedtraps were installed after raking and

before October 1 of each seedyear on those plots that

had been injected the preceding summer, and on the

three check plots in each test area. Seed counts were

made weekly from October through February. Pine

seeds collected in traps were cut open, and those containing fully developed gametophyte tissue were

judged as potentially viable (Bonner 1974). That

process was repeated for each seedyear, with 24

seedtraps monitored per year.

At the end of a single growing season following the

designated seedyear, pine seedling counts were taken

within the eight circular quadrats per interior 0.025

acre, and percent quadrat stocking of seedlings was

based on these counts. The six check plots were

similarly inventoried but on an annual basis. Only

first-year pine seedlings were counted after each

seedyear.

When pine seedling counts were made for a particular seedyear on the 0.05-acre subplots, overstory

pine d.b.h. measurements were taken on those same

subplots for computation of basal area. These data

were to be used as independent variables in

covariance analysis, but basal area proved to be nonsignifícant and was subsequently abandoned as a

covariate.

Depth of litter was measured at the time of seedling

inventories on each sample quadrat in undisturbed

subplots where hardwoods had been injected the previous year, as well as on untreated check plots. Litter

depths were taken to the nearest 0.1 inch.

After the fifth-year inventory, pine seedling counts

were taken by 1-foot height classes on al1 plots that

had been monitored during the 5-year study. At the

same time, ocular assessments of percent vegetative

ground cover (hardwood, pine overstory, pine seedlings, and herbaceous vegetation) were estimated to

the nearest 10 perzent.
Data Analysis RESULTS AND DISCUSSION

Analyses of variance were used after the fifth year

to evaluate pine seedling density and percent quadrat

stocking relative to seedyear and seedbed treatments.

Data from check plots were compared to that from the

inject-only and inject/rake plots (check VS. inject/rake

comparison), and data from inject-only plots were

compared to injectirake plots according to a split-plot

design (inject VS. rake comparison).

Pine Seed Production

In al1 analyses, data from each of the two test areas

were analyzed separately only when test areas were

significantly different. Duncan’s New Multiple Range

Test was used to isolate differences between seedyear

means. Percent quadrat stocking and percent ground

cover were analyzed following arcsine dproportion

transformation. Linear regressions were generated to

illustrate the relationship of pine seedling density to

the number of potentially viable seeds. Al1 analyses

were carried out at the 0.05 leve1 of significance.

During the 5-year study, annual production of

potentially viable seeds across seedbed treatments

ranged from about 3,000 per acre (poor seedcrop) to

over 1 million per acre (bumper seedcrop) (table 1).

There was a statistically significant interaction between seedyears and seedbed treatments for the

check versus inject/rake comparison only. That interaction is attributed mainly to the change in magnitude of seeds collected on check plots, which

averaged higher in 1990 relative to numbers on injectirake plots (table 1).

The mean number of viable seeds collected on injected plots averaged 26 percent more than the mean

number of seeds per acre collected on check plots

(table 1). Those differences may, however, be more apparent than real. Seed-producing pines were the

Table l.-Pine seed production and first-year seedling density on three seedbed treatments during

fiue seedyears

Measurement

variable

and seedyear

Seedbed Seedbed

Seedyear Seedyear

Check Injectirake mean* Inject Rake mean*

Seed production ___.___________________ potentially uiable see& /acre (thousands) -------- --- ---------- ---

1986 1.7 3.3 2.5a 3.3 3.3 3.3a

1987 993.3 1390.0 1191.7c 1343.3 1436.7 139o.oc

1988 50.0 58.3 54.2a 50.0 66.7 58.3a

1989 321.7 296.7 309.213 336.7 256.7 296.713

1990 43.3 23.3 33.3a 16.7 30.0 23.3a

Seedbed mean 282.0 354.3 350.0 358.7

Mean square error 1.4910ElO 1.4684310

P>F’ (Seedbed) (0.03) (0.78)

P>Ft (Seedyear) (0.00) (0.00)

P>Ft (Seedbed by seedyear) (0.00) (0.55)

Seedling density ______________________________ _________ stems/acre _______________ _ ____ _____________..___________

1986 174 174 174a 7 0 278 174a

1987 14931 277049 14599013 191250 362847 27704913

1988 729 3993 2361a 1042 6944 3993a

1989 1597 13577 7587a 6320 20834 13577a

1990 798 1181 990a 1111 1250 1181a

Seedbed mean 3646 59195 39959 78431

Mean square error 9.1121308 1.8905309

P>Ft (Seedbed) (0.00) (0.00)

P>Ft (Seedyear) (0.00) (0.00)

P>Ft (Seedbed by seedyear) (0.00) (0.00)

*Within each measurement variable, columnar means followed by the same letter are not significantly different at the 0.05 level.

+The probability of obtaining a larger F-ratio under the null hypothesis.
dominant trees on these plots and overtopped

midstory hardwoods by 50 feet or more. Hardwood

trees on check plots retained their leaves well into the

peak period of pine seedfall, and those leaves ser-ved

as barriers to keep pine seeds from falling directly

into the seedtraps. In contrast, on injected plots,

hardwood leaves had either withered or dropped off

before pine seedfall began each year and did not

hinder seed collection.

The bumper seedyear in 1987 produced over a million potentially viable seeds per acre and was significantly better than any other seedyear (table 1).

The better-than-average seedyear of 1989 produced

significantly more seeds than the average seedyear of

1988 or the below-average seedyears of 1986 and

1990. Those differences held true for al1 plot locations.

The proportion of overstory shortleaf pines to al1 pines

in these mixed stands averaged 30 percent or less;

consequently, shortleaf pines made only a small contribution to overa11 seed production.

Pine seedfall tended to reach maximum intensity in

November (fig. 1). The exceptions to that rule were

the two extreme seed production years. During the

bumper seedyear of 1987, seedfall remained high

through January. Similarly, during the poor seedyear

of 1986, no seeds were found in traps until December.

For the seedyears 1988,1989, and 1990, more than 90

percent of potentially viable seeds had fallen by the

end of December. During the bumper seedyear of

1987, however, 90 percent seedfall was not achieved

100.000

until early February. These data suggest that the

benefits of natural pine seedfall would be maximized

in most years if seedbed preparation was completed

before early autumn.

Pine Seedling Density

Pine seedcrops were an accurate indicator of firstyear seedling density. The bumper seedyear of 1987

produced the most pine seedlings, and the poor

seedyear of 1986 produced the fewest (table 1). Because of extreme variation within seedyears, the

bumper seedcrop was the only one to produce statistically significant differences in mean density between

seedyears. These analyses also were done using seeds

per acre as a covariate, but the covariate was subsequently deleted because there was no improvement

in the results.

There were statistically significant interactions between seedbed treatments and seedyears for the

check versus injecffrake comparison and the inject

versus rake comparison. These interactions are attributed to a change in the magnitude of response

(table 1). The mean density on injected plots exceeded

the density on check plots every year except 1986.

Seedling density was also similar on inject-only and

on rake plots in 1990 but was distinctly different in al1

other years.

Seedbed treatments resulted in a 1,500 percent increase in the number of fírst-year seedlings compared

(Bumper) 1987 (Average) 1988 (Above 1989 average) (Bedzrage)V( 1 ‘90) WY’:,

-.-.-.+-.-.-.- . . . . . 0 _..... 1 3 ---*--- _.._.. - * __ _

/ , , , , / , 1 , , , , , , , / , , , , ,

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 7 18 19 20 21

October

2 2

November December .JaMlly Februaty

TIME @VEEKS)

Figure 1. - Trends in weekly pine seed production by seedyear.

4
to check plots (table 1). Exposure of mineral soil in

combination with hardwood injection produced 96

percent more seedlings than injection alone.

It is often speculated that more intensive site

preparation is needed in below-average seedyears in

order to produce an adequate stand of natural pine

seedlings. Nevertheless, results of this study indicate

that hardwood injection alone was suffcient to

produce an adequate density of pine seedlings in al1

but the poorest seedyear (1986). In regulated unevenaged loblolly-shortleaf pine stands, a rule of thumb is

that density of natural pine regeneration should be

200 stems per acre, with at least 50-percent milacre

stocking. In 1986, even raking in combination with

hardwood injection resulted in a seedling catch (278

trees per acre) that would be borderline, at best, for

uneven-aged management (Cain and others 1987) and

totally inadequate for even-aged management (Grano

1967). Consequently, the added expense of more intensive site preparation would not be justified when

relying on natural pine regeneration in a poor

seedyear. On the other hand, a ground cover of herbaceous vegetation at the time of scheduled pine

regeneration would almost certainly require more intensive site preparation than hardwood injection

alone, even during good seedyears (Cain 1991).

The linear relationships of the common logarithm of

first-year pine density to the common logarithm of the

number of potentially viable seeds exhibited high coefficients of determination (r-2) (hg. 2). The best correlations were achieved where the hardwood component

had been deadened. On check plots, an average of 114

potentially viable seeds were required to produce a

single seedling. That compares to 22 seeds per seedling on inject-only plots and 12 seeds per seedling on

inject/rake plots.

There was a significant interaction between

seedyear and seedbed treatments for the inject versus

Check Inject-only Inject/Rake

mu ---- *---. 0

+“‘ ..?

/

logYo= 0.1046 + 0.6107 logXc Root MSE=0.44 r2=0.69 n=22

S,.’

, ::

,‘.’

logYI =-0.0769 + 0.7713 IogX, Root MSE=0.47 r2=0.95 n=24

, ,:

,‘:. IogYR =-0.1913 + 0.6515 IogX, Root MSE=0.46 r2=0.94 n=25

1 2 3 4 5 6 7

POTENTIALLY VIABLE SEEDS (LOG NUMBEWACRE)

Figure 2. - Relationship of the common logarithm of first-year pine seedling

density to the common logarithm of the number of potentially viable

seeds.
rake comparison of seeds per seedling. More seeds

were required to produce a seedling on inject-only

plots compared to rake plots in 1986, -87, -88, and -89;

however, the opposite was true in 1990. For main effects, 1989 was the only seedyear of the five to require

signifícantly more seeds per seedling. One explanation is that, in 1989, over 26 inches of precipitation

were recorded on the Experimental Forest from May

through August, compared to an average of about 16

inches for the same 4 months in the other 4 years. Excess moisture may have increased the activity of

damping-off fungi that, in turn, killed more seedlings

in 1989 and resulted in a higher seeds-per-seedling

ratio by the end of that growing season.

Quadrat Stocking of Pine Seedlings

Quadrat stocking was one variable for which there

were statistically significant differences between test

areas; consequently, data were analyzed separately

by test area (table 2). Poorer stocking of pine seedlings

(stems less than 1 inch in d.b.h.1 in test area B compared to test area A was attributed to more prolifíc

herbaceous competition and a greater density of merchantable-size pines (hg. 3).

For the check versus injectjrake comparison of

quadrat stocking, there was a significant interaction

between seedyears and seedbeds in test area B, but

not in test area A (table 2). On test area B, there was

a change in the direction of response; that is, check

plots had higher quadrat stocking than inject/rake

plots following the 1986 seedcrop but less stocking in

subsequent years. That anomaly was not apparent in

test area A, where quadrat stocking was consistently

higher on injectirake plots compared to check plots in

al1 5 years (table 2). For main effects, inject/rake plots

averaged 24-percent better quadrat stocking than

check plots in both test areas.

Test area B also had significant seedyear by

seedbed interactions for the inject versus rake comTable 2.- Quadrat stocking offirst-yearpine seedlings on three seedbed treatments during five

seedyears

Test area

Seedbed

Seedyear

Seedbed

Seedyear

and seedyear Check Injectirake mean* Inject Rake mean*

Test urea A ~~~~~~~~~~~~~~~~ _ ~~~~~~~~~~~~~~~~~~----_ ----percenb -----.________--------------.-------------------

1986 2 8 5a 0 17 8a

1987 77 100 88d 100 100 1ooc

1988 2 3 6 3 43bc 4 2 8 3 62b

1989 3 7 79 58~ 71 8 7 79bc

1990 2 5 33 29b 37 2 9 33a

Seedbed mean 3 3 57 5 0 63

Mean error square 186.12 128.84

P>F$ (Seedbed) (0.00) (0.01)

P>FS (Seedyear) (0.00) (0.00)

P>FS (Seedbed by seedyear) (0.27) (0.10)

Test urea B _________________------- _ ~_________~~~~~~~~~percentf _____________---.______________________ _ ..______

1986 8 2 5ab 4 0 2 a

1987 6 4 100 82d 100 100 100d

1988 6 17 12b 0 3 4 17b

1989 8 8 0 44c 63 9 6 8Oc

1990 0 4 2 a 0 8 4 a

Seed mean 17 4 1 33 48

Mean error square 69.05 118.18

P>F$ (Seedbed) (0.00) (0.01)

P>FS (Seedyear) (0.00) (0.00)

P>F$ (Seedbed by seedyear) (0.00) (0.03)

*Within test areas, columnar means followed by the same letter are not significantly different

at the 0.05 level.

+Based on the presente of at least one pine seedling per quadrat.

%‘he probability of obtaining a larger F-ratio under the null hypothesis.
1 3 5 7 9 ll 13 15 17 19 21 23 25 27 29 31

DIAMETER BREAS1 HEIGHT (INCHES)

Figure 3. -ZnitiaZ pine diameter distribution by test area compared to the desirable distribution for a regulated

uneven-aged stand of loblolly-shortleaf pines.

parison, but no significant interaction occurred in test

area A (table 2). Significant interaction was attributed to a lack of stocking on the inject-only plots in

1988 and 1990.

Raking to expose mineral soil produced significantly better quadrat stocking of first-year pine seedlings

than hardwood injection alone in both test areas

(table 2). Even so, raking was not effective in producing adequate stocking of first-year pine seedlings

during the poor (1986) or the below-average (1990)

seedyears. Those two seedyears produced signifícantly less and totally inadequate quadrat stocking,

regardless of test area. Understocking also occurred

on Test Area B following the average seedcrop of 1988.

Pine Seedling Size and Overstory Basal Area

Density of pines was plotted relative to their height

across al1 five seedyears to illustrate the distribution

of seedlings by size class on inject-only and inject/rake

plots (fig. 4). Exposure of mineral soil made no substantial contribution to the subsequent growth of pine

seedlings. Another point of interest is that naturally

regenerated pine seedlings can be expected to grow no

taller than 8 feet duríng a 5year period if basal area

10' '

l I I I 1 I I I

4 1 2 3 4 5 6 7 8

HEIGHT CLASS (FEEl-)

Figure 4. - Height class distribution of pine seedlings by seedbed

treatment after 5 years.

of merchantable-size pines averages about 64 square

feet per acre on silt loam soils, even when overtopping

hardwoods are intensively controlled.

Overstory pine basal area ranged from 60 square

feet per acre on inject/rake plots to 67 square feet per

acre on inject-only plots, with no statistically significant differences between seedbed treatments for

the check versus inject/rake comparison or the inject

versus rake comparison. Such basal area levels are

well within those recommended-55 to 75 square feet

per acre-for the establishment of loblolly and

shortleaf pine regeneration from natural seedfall in

uneven-aged stands (Reynolds and others 1984).

Most overstory pines on Test Area A were larger

than 15 inches in d.b.h., whereas the majority of pines

on test area B ranged from 3 to 16 inches in d.b.h. (hg.

3). Height to live crown averaged 68 feet (high shade)

for overstory sample pines on test area A, compared

with 40 feet (low shade) for sample pines on test area

B. Even though overa11 basal area was similar, a

greater density of midstory and overstory pines as

well as low shade is less desirable for pine seedling

growth than high shade from fewer overstory pines.

These factors may have contributed to significantly

lower quadrat stocking of pine seedlings on test area

B compared to test area A (table 2).

7
After 5 years, hardwood trees that were 1 inch in

d.b.h. and larger averaged 65 square feet per acre on

check plots in test area A and 72 square feet per acre

on check plots in test area B. At that time, hardwoods

made up 49 percent and 51 percent of total basal area

on check plots in test area A and B, respectively.

When the study was installed, oaks (Quercus spp.

L.) comprised 69 percent of the 60 square feet of

hardwood basal area per acre across al1 plots on Test

Area A and 50 percent of the 55 square feet per acre

on Test Area B. The largest oaks were Q. alba L., Q.

falcata Michx., Q. nigra L., and Q. stellata Wangenh.

Predominant midstory and understory hardwoods included Acer rubrum L., Cornus florida L., Liquidambar styraciflua L., Nyssa syluatica Marsh., and Ulmus

alata Michx. Sweetgums and blackgums accounted

for 15 percent of total hardwood basal area on both

test areas A and B. At the time of study establishment, the crowns of these hardwoods formed a

closed canopy that resulted in complete shading of the

forest floor. Hardwoods exhibited the classic reversedJ diameter distribution common in uneven-aged

stand structure, and hardwood d.b.h.‘s ranged from 1

to 20 inches.

Natural pine regeneration is most likely to occur if

hardwood basal area is substantially less than 20 percent of total basal area in regulated uneven-aged

loblolly-shortleaf stands (Cain 1989). Although unproven, preliminary results of light attenuation measurements in uneven-aged pine-hardwood stands suggest that when pine and hardwood basal area are

equal, the pines shade the forest floor only half as

much as the hardwoods.1 Given these facts, natural

pine regeneration might be expected to fail when a

well-distributed mixture of pine and hardwood basal

area exceeds 60 and 8 square feet per acre, respectivelY*

Litter Depth and Vegetative Ground Cover

The forest floor litter on check and inject-only plots

consisted of hardwood leaves, pine needles, and other

detritus that had fallen from trees. Mean litter depth

after the first year of treatment averaged 1.3 inches; it

was the same after the last year of treatment. Obviously, annual input of litter was in equilibrium with

decomposition. Grano (1949) studied the effects of litter on the establishment of loblolly and shortleaf pine

from natural seedfall in the Crossett Experimental

Forest. He found that the depth of pine-hardwood lit-

‘Shelton, M.G. 1991. Unpublished data. Field notes on file

with USDA Forest Service, Southern Forest Experiment Station,

Monticello, AR 71655.

8

ter averaged 1.3 inches on milacres that contained

over 7,000 first-year pine seedlings per acre. He concluded that a good seedling stand was not dependent

on disturbance of that litter on these sites. Results of

the present investigation tend to confirm that conclusion.

In addition to basal area from overstory pines and

hardwoods, another measure of competition effects on

pine seedling establishment is percent ground cover

by various vegetative components. After 5 years,

hardwoods on check plots produced 90 percent cover,

and that degree of cover contributes to an understanding of why there was a lack of pine seedlings on

those plots. Because of multistoried layers, overstory

pines provided 24-percent cover on check plots, and

herbaceous vegetation added another 18 percent. Herbaceous vegetation included forbs, grasses, semiwoody plants, and vines.

In contrast to check plots, the principal cover component on the inject-only and inject/rake plots was

herbaceous vegetation, which averaged more than 50

percent when al1 years were combined. Within 3 years

after injection, reinvading hardwoods produced about

5 percent ground cover, while herbaceous vegetation

contributed over 75 percent ground cover (fig. 5). By

the fourth year however, these hardwoods began to

100

Q o

30

i”

p

im

g J 40

8

tP

2 0

1 0

0

-

Hardwood Herbaceous Overstory Pine

t

ground cover ground cover ground cover

\ I---

--es- . . . . <.

Undisturbed 1 2 3 4 5

TIME AFTER HARDWOOD CONTROL (YEARS)

Figure 5. - Five-year trends in vegetative ground cover following

hardwood control by inject-only and inject lrake

treatments.
exert more shading on the forest floor, which resulted

in a decrease of the herbaceous cover. In the fifth year,

cover from reinvading hardwoods generally exceeded

that of the pine overstory.

After 5 years, ground cover from pine seedlings

averaged more than 40 percent on plots that were injected in 1986, the poorest seedyear. These seedlings

obviously carne from the bumper seedcrop of 1987.

Therefore, an opportunity exists to naturally seed

areas with pine even though a seedcrop failure may

occur during the year of seedbed treatment-unless,

of course, seedtrees are eliminated from the site.

During this 5-year study, there were never two successive seedcrop failures.

MANAGEMENT IMPLICATIONS AND

CONCLUSIONS

Of al1 the variables examined in this 5-year study,

the one that stands out as the main inhibitor of

natural pine regeneration was shading by midstory

and overstory hardwoods that averaged from 55 to 60

square feet of basal area per acre when the study

began. That was true despite the fact that two out of

five seedyears produced better-than-average

seedcrops.

The poor seedyear of 1986 produced an average of

2,500 potentially viable seeds per acre, a number totally inadequate to establish an operational stand of

pine seedlings. Seedcrops in al1 other seedyears

averaged 30,000 or more potentially viable seeds per

acre and resulted in satisfactory density of pine seedlings on plots where hardwoods were controlled.

However, percent stocking of pine seedlings was not

always adequate, even during average seedyears.

When seedyears were average or better, hardwood

injection alone was sufficient to produce an adequate

density of pine seedlings. Simply eliminating the

hardwood midstory and overstory resulted in a

fivefold reduction in the seeds-per-seedling ratio that

was required on untreated check plots. The seeds-perseedling ratio on inject-only plots was cut in half by

exposing mineral soil (raking), but that enhancement

procedure was apparently less effective than hardwood injection alone. Only in the poor seedyear of

1986 did injection alone result in inadequate density

of pine seedlings for uneven-aged management when

compared to injection plus mineral soil exposure.

Even so, raking to expose mineral soil did not produce

adequate quadrat stocking of pine seedlings following

the 1986 seedcrop. Therefore, the use of intensive site

preparation treatments cannot be recommended for

seedbed amelioration during a poor seedyear. If overtopping hardwoods are controlled just before

scheduled cycle cuts in uneven-aged stands of loblolly

and shortleaf pines, then logging activity during those

cycle cuts should expose enough mineral soil to

facilitate natural pine regeneration on silt loam soil

during most seedyears.

It must be emphasized that herbaceous vegetation

on the forest floor was sparse when the inject-only and

injectirake treatments were applied each year. Consequently, intensive competition control of herbaceous

ground cover was not needed in this study. When the

forest floor is covered by an abundance of forbs, grasses, vines, and semiwoody plants, then intensive control measures will be required to ensure an adequate

stand of pine seedlings even during good seedyears

(Cain 1991). Seedbed treatments to enhance natural

pine regeneration should be completed by early

autumn.

LITERATURE CITED

Bonner, F.T. 1974. Seed testing. In: Seeds of woody

plants in the United States. Agrie. Handb. 450.

Washington, DC: U.S. Department of Agriculture:

136-152.

Cain, Michael D. 1991. Hardwoods on pine sites: competition or antagonistic symbiosis. Forest Ecology

and Management. 44: 147-160.

Cain, Michael D. 1989. Relative basal area as it applies to pine-hardwood mixtures in the Upper

Coastal Plain. In: Proceedings of pine-hardwood

mixtures: a symposium on management and ecology of the type; 1989 April18-19; Atlanta, GA. Gen.

Tech. Rep. SE-58. Asheville, NC: U.S. Department

of Agriculture, Forest Service, Southeastern Forest

Experiment Station: 189-196.

Cain, Michael D.; Baker, James B.; Murphy, Paul A.

1987. Precommercial thinning of pine regeneration

in uneven-aged stands. In: Proceedings of the 4th

biennial southern silvicultura1 research conference;

1986 November 4-6; Atlanta, GA. Gen. Tech. Rep.

SE-42. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station: 419-424.

Gemmer, Eugene W. 1941. Loblolly pine establishment as affected by grazing, overstory, and seedbed

preparation. Journal of Forestry. 39: 473-477.

Grano, Charles X. 1949.1s litter a barrier to the initial

establishment of shortleaf and loblolly pine

reproduction? Journal of Forestry. 47: 544-548.

Grano, Charles X. 1967. Growing loblolly and shortleaf pine in the Midsouth. Farmers’ Bull. 2102.

Washington, DC: U.S. Department of Agriculture.

27 p.

Grano, Charles X. 1971. Conditioning loessial soils for

natural loblolly and shortleaf pine seeding. Res.

Note SO-1 16. New Orleans, LA: U.S. Department of

9
Agriculture, Forest Service, Southern Forest Experiment Station. 4 p.

Liming, Franklin G. 1945. Natural regeneration of

shortleaf pine in the Missouri Ozarks. Journal of

Forestry. 43: 339-345.

Phares, Robert E.; Liming, Franklin G. 1961.

Shortleaf pine direct-seeding success affected by

month of seeding, release method, and weather.

Journal of Forestry. 59: 804-807.

Pomeroy, K.B.; Trousdell, K.B. 1948. The importance

of seed-bed preparation in loblolly pine management. Southern Lumberman. 177: 143-144.

Pomeroy, Kenneth B. 1949. The germination and initial establishment of loblolly pine under various

surface soil conditions. Journal of Forestry. 47:

541-543.

Reynolds, R.R. 1959. Eighteen years of selection timber management on the Crossett Experimental

Forest. Tech. Bull. 1206. Washington, DC: U.S.

Department of Agriculture, Forest Service. 68 p.

Reynolds, R.R.; Baker, James B.; Ku, Timothy T.

1984. Four decades of selection management on the

Crossett Farm Forestry Forties. Bull. 872. Fayetteville, AR: University of Arkansas, Division of

Agriculture, Agricultura1 Experiment Station. 43 p.

Trousdell, Kenneth B. 1950. Seed and seedbed requirements to regenerate loblolly pine. Sta. Pap.

No. 8. Asheville, NC: U.S. Department of Agriculture, Forest Service, Southeastern Forest Experiment Station. 13 p.

Trousdell, Kenneth B. 1954. Favorable seedbed conditions for loblolly pine disappear 3 years after logging. Journal of Forestry. 52: 174-176.

Trousdell, Kenneth B. 1963. Loblolly pine regeneration from seed-what do site preparation and cultural measures buy? Journal of Forestry. 61: 441-

444.

Trousdell, Kenneth B.; Langdon, 0. Gordon. 1967.

Disking and prescribed burning for loblolly pine

regeneration. Journal of Forestry. 65: 548-551.

U.S. Department of Agriculture. 1979. Soil survey of

Ashley County, Arkansas. Washington, DC: USDA

Soil Conservation Service and USDA Forest Service, in cooperation with Arkansas Agricultura1 Experiment Station. 92 p. and maps.

10
Cain, Michael D. 1991. Importance of seedyear, seedbed, and overstory for establishment of natural loblolly and shortleaf pine

regeneration in southern Arkansas. Res. Pap. SO-268. New Orleans, LA: U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station. 10 p.

First-year density and quadrat stocking of naturally established

loblolly and shortleaf pine regeneration were monitored for five

consecutive seedyears on disturbed and undisturbed seedbeds.

Compared to untreated checks, additional gains in pine seedling

density as a result of exposing mineral soil were not as great as

initial gains achieved by control of overtopping hardwoods.

Keywords: Basal area, forest floor, hardwood control, herbaceous

vegetation, litter depth, Pinus echinata Mill., P. taeda L., seeds per

seedling, uneven-aged management.

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