SUMMARY

Natural regeneration is a practical and inexpensive option for

many existing southern pine forests, provided there is an adequate

seed source and other stand conditions are controlled. However,

seed production in natural stands of southern pines varies due to

a wide range of environmental and biotic influences. It is important, then, to understand the biological processes that affect seed

production in natural stands. The physiology of cone and seed

production is reviewed here, and this information is applied to

natural stand situations. With this knowledge, foresters will be

better able to manipulate stands to improve and predict seed production and, therefore, make natural regeneration more reliable.
Producing Seed Crops to Naturally Regenerate Southern Pines

James P. Barnett and Ronald 0. Haugen

INTRODUCTION

In recent years, emphasis has changed from

clearcutting and artificial regeneration of southern

pines to seed-tree, shelterwood, and selection harvesting methods, which rely on natural regeneration. This

has raised several issues related to the potential success of these natural systems. One of the most critical

is the adequacy of cone and seed production. During

the last 30 to 40 years, Wakeley (1954) and numerous

subsequent researchers focused on the cone and seed

problems of regeneration by planting and seeding;

little effort went into understanding these problems

as related to natural regeneration.

Early research indicated great variability in the frequency of good seed crops of the major southern pines

(USDA 1948)-loblolly (Pious taeda L.), slash (P.

elliottii Engelm.), shortleaf (P. echinata Mill.), and

longleaf (I? palustrisMill.). The number of years a

stand could bear adequate seed crops was documented

to a limited degree in early publications (USDA 1948).

But with current emphasis on extending rotation

length on national forest land, there are still uncertainties about the effect of tree age on cone and seed

productivity.

These and other questions related to the biology of

cone and seed production in natural stands dictate that

current knowledge about the processes of cone and

seed production be applied to natural regeneration

methods.

PERIODICITY OF SEED CROPS

Wakeley (1954) assembled data on seed production

from a major survey of cone crops of the southern pines

from Maryland to Texas from 1931 to 1941. He reported occasional years of heavy seed production by

all species throughout most of the southern pine region. There also are years of widespread failure. Such

general bumper crops and failures occur in no predictable pattern. Typically, however, cone production

varies by species and locality, with good crops occurring every 3 to 10 years.

Loblolly pine is a moderate seed producer. It seeds

abundantly near the Atlantic and gulf coasts but much

less regularly in inland areas (McQuilkin 1940,

Wakeley 1947). Seed crops of a 70-year-old stand in

the North Carolina Piedmont ranged from 18,000 to

nearly 300,000 seeds per acre during a 13-year period

(Pomeroy and Korstian 1949).

Slash pine is a good seed producer, with heavy crops

occurring about once every 3 years. However, because

of its narrower geographic range, it may be more susceptible to complete crop failures (Wakeley 1954).

Seed production of longleaf pine is extremely variable from year to year and place to place. Some opengrown trees will bear cones every year, but good

general crops are sporadic. During a 21-year period

in south Mississippi, there were two heavy seed crops,

seven medium, five light, and seven failures (Maki

1952). Boyer (1987) observed that the frequency of

acceptable cone crops ranged from 3 years out of 4 to

0 over a period of 19 years. The frequency of good crops

appeared to be lower nearer the gulf coast than farther inland. Many poor cone crops are due to causes

other than lack of strobi1i.l In another south Mississippi study, abundant strobili appeared every year for

6 years, but only one good cone crop resulted (Allen

and Coyne 1956).

Shortleaf pine is a less prolific seeder nearly everywhere; it is particularly poor along the western and

northern edges of its ranges in the Ouachita and Ozark

1 Female flower or strobilus refers to the reproductive bud from

the time it becomes visible until pollination. Conelet refers to this

structure from pollination until it starts enlarging in the second

year; thereafter, the term cone is used.

James P Barnett is chief silviculturist, Alexandria Forestry Center, U.S. Department of Agriculture, Forest Service, Southern Forest

Experiment Station, Pineville, LA 71360; Ronald 0. Haugen is silviculturist, U.S. Department of Agriculture, Forest Service, National

Forests in Texas, Lufliin, TX 75901.

1
GRO

BEG

Figure 1. - The pine reproductive cycle (adapted from Stanley 1958).

Mountains ofArkansas and Oklahoma (Liming 1945).

In most of its range, shortleaf may have adequate crops

at intervals of 3 to 6 years (Grano 1965).

This variability in cone and seed crops seems unpredictable. However, by understanding the processes

that affect strobili formation and the causes of losses

during maturation, it should be possible to anticipate

good years and to manipulate stands in order to produce more consistent seed crops.

PROCESSES THAT AFFECT STROBILI

FORMATION

The first step in sexual reproduction in conifers is

the initiation of flower buds or strobili. In southern

pines, nearly 3 years occur between the time of stro2

bili initiation and seed maturity (fig. 1). Strobili initiation begins in late July and August (Eggler 1961,

Mergen and Koerting 1957), but female flowers do not

become visible until midwinter. Initiation may occur

any time during a 2-month period. Little is known

about the chemical and physiological mechanisms of

reproduction in trees. However, at least five factors

contribute to flower induction: (1) induction hormones,

(2) nutrient relationships, (3) soil moisture, (4) light

conditions, and (5) temperature. These are briefly discussed in relation to southern pine seed production.

Flower-Inducing Hormones

As early as 1880, Sachs postulated that some special agent effective in flower production was induced

under proper environmental conditions. Fraser (1958)
stated that the physiological conditions of a plant during growth or flowering are probably controlled by

small amounts of specific growth substances such as

a florigen. One hint that a florigen might exist is the

fact that in photoperiod-sensitive plants, something

must transmit a flowering stimulus from the leaves

to the stem tips, where initiation of primordia occurs

(Kozlowski and others 1991). Growth regulators have

been applied to try to increase cone production. Gibberellic acid, which has received research attention

for the past 15 years, has occasionally stimulated cone

production in conifers (Ross and Greenwood 1979). But

these treatments have been used only in seed-production or orchard situations. Mechanical treatments such

as girdling or strangulation have been used singly and

in conjunction with gibberellic acid and have been

more effective than chemicals alone in promoting flowering (Wheeler and Bramlett 1991). Mechanical treatments impede translocation of carbohydrates and

hormones in the phloem. When downward movement

of organic solutes is blocked, they tend to diffuse into

the xylem and are translocated upward in the transpiration stream (Kozlowski 1971). Longman and

Wareing (1958) demonstrated that bending branches

from a vertical to a horizontal or downward position

increased flowering of Japanese larch (Larix leptolepis

Murray). This response to change in branch position

is likely due to a change in organic solute diffusion.

Neither application of growth regulators nor indirect

methods such as mechanical injury are consistently

effective for all southern pine species. Mechanical

treatments may, in fact, be harmful over a period of

years (Barnett 1993) and have little application to

natural stands.

Nutrient Relationships

Minerals are involved in all major phases of reproductive growth, including initiation of primordia. Mineral requirements of reproductive growth are high, and

a balanced supply ensures normal development of reproductive tissues, primarily by maintaining a large,

physiologically active leaf surface, which in turn produces the metabolites and growth regulators required

for development of strobili, cones, and seeds (Kozlowski 1971).

Hoekstra and Mergen (1957) applied 20 or 40 lb/

acre of 7-7-7 or 3-18-6 nitrogen, phosphorus, potassium (NPK) fertilizers to al-year-old slash pines in

the spring. These treatments increased flower production an average of 59 percent over the controls. The

7-7-7 fertilizer was more than twice as effective as the

3-18-6 fertilizer, suggesting the importance of the nitrogen application rate. The effect of fertilization on

flowering persisted for 2 years. This and other studies (Shoulders 1968) indicate that to stimulate flowering in southern pines, fertilizers should be applied

in the early spring before strobili are formed. Fertilizers appear to mainly effect a single seed crop. Thus,

continuous high production of seeds usually requires

repeated fertilizer applications.

Shoulders (1967) treated longleafpines with 15-25-10

NPK fertilizer annually for several years and found

that flower production was stimulated in a complex

manner, with rainfall and individual tree variables

modifying the nutrient effect (fig. 2). In three stands

in northeastern North Carolina, the loblolly pine seed

crop was positively correlated with the May-to-July

rainfall of 2 years earlier and negatively correlated

with the size of the seed crop 2 years earlier (Wenger

1957).

Soil Moisture

Induction of flowering in southern pines is increased

by high soil moisture during spring growth and lower

moisture just before differentiation of strobili. For example, increases in February and March rainfall increased the response of slash pine flowering to

fertilization, and high rainfall in April, or May through

July, decreased it (Shoulders 1968). The results were

somewhat different for longleaf pine. High rainfall in

April, May, June, and July of the year before flowering greatly increased female flowering (Shoulders

1967), whereas wet weather through the entire growing season favored production of male flowers. As a

result, large crops of female and male flowers did not

necessarily coincide (Boyer 1981). Flowering varied

by inherent flowering capacity, rate of fertilizer application, and rainfall during April and May.

Light

Although flower bud formation of many kinds of

plants is affected by photoperiod, light intensity effects flowering of tree species more. Shirley (1936)

reported that high light intensity favors fruit and seed

production more than vegetative growth in several tree

species. The higher flowering capacity is presumably

due to the large amount of available carbohydrates

resulting from high photosynthetic activity (Kramer

and Kozlowski 1960). Fowells and Schubert (1956) reported that nearly all observed cones produced by ponderosa (I? ponderosa Laws) and sugar (E! lambertiana

Doug-l.) pines were borne on dominant trees, whereas

only 1 to 1.5 percent were on codominant trees.

Within a tree crown, the vigor of branches also influences flowering and cone development. The more

vigorous branches in the upper and middle two-thirds

of the crowns of red pine (l? resinosa Ait.) produced

more and larger cones than did the less vigorous

branches of the lower one-third where the light level

3
UNFERTILIZED

LOW PRODUCER MEDIUM PRODUCER

FEB. & MAR. FEB. & MAR.

RAIN (INCHES) RAIN (INCHES)

FERTILIZED

MEDIUM PRODUCER

FEB. & MAR.

RAIN (INCHES)

lb ii

FEB. & MAR.

RAIN (INCHES)

LEGEND

6 INCHES OF I9 INCHES OF

MAY, JUNE, & MAY, JUNE, &

JULY RAIN JULY RAIN

Figure 2. - Effect of fertilizers and rainfall on estimated flower production of slash pine. Data are for low, medium, and high producing

trees with different rates of fertilization and rainfall in the spring and summerpreceding flower-bud formation. Average flower

yields were assumed to he 30 per tree for low, 95 for medium, and 150 for high producers. Production 2 years earlier was set at

35, 105, and 1,7,51, respectively (adapted from Shoulders 1973).
is much lower (Dickmann and Kozlowski 1971). Quality and quantity of seeds were also related to cone size.

Cone volume increased with number of full seeds per

cone, total dry weight of seeds per cone, and number

of scales per cone (Dickmann and Kozlowski 1971).

Increased cone and seed production following thinning

of loblolly pine stands (Wenger 1954) further corroborates the importance of tree vigor to flowering and

fruiting. Crown release is often followed by an increase

in male flowers as well as female flowers, which increases pollen production and viable seeds per cone.

Temperature

Summer temperature has been found to affect seed

and cone production of some species (Bramlett 1965,

Fraser 1958, Lester 1967), but not specifically southern pines. Temperature has primarily affected flower

development. Boyer (1978) used accumulation of degree-day heat sums to predict timing of southern pine

pollen shed. Using a base of 50 “F and a starting date

of January 1, accumulation of degree-days monitors

the progress of flower development. However, this type

of information is most useful for seed-orchard managers and others interested in pollen collection; it is not

particularly useful for those managing natural stands.

STAND CONDITIONS AFFECTING SEED

PRODUCTION

Once the processes of flower initiation and development are understood, it is easier to manipulate environmental conditions to favor cone and seed production.

Stand density, nutrition, genetics, tree age and size,

and topography are discussed in relation to processes

that influence seed production.

Stand Density

Crown release or thinning is the most common and

successful method known to stimulate flowering in

forest trees. Thinning increases three of the variables

essential to seed production: light, nutrients, and

moisture. Although the higher light intensity probably exerts the greatest influence, the total response

to release is undoubtedly due to a combination of these

factors (Bilan 1960). Early observations of loblolly pine

indicated that residual trees on cut-over areas produced more cones than did trees in uncut stands

(Chapman 1923). Silvicultural practices were found

to influence seed production-both shelterwood (Hebb

1955, Pomeroy and Korstian 1949) and alternate-strip

.

0 IO 2 0 3 0 4 0 5 0 6 0 7 0 60 9 0 100

BASAL AREA (FT2/ACRE)

Figure 3. - Four-year yield of viable seeds per square foot ofloblolly-shortleafpinf seed-tree basal

area in relation to stand basal area (adapted from Grano 19701.

5
cutting (Trousdell 1950) increased the seed production of residual trees. Wenger (1954) determined that

loblolly pine cone production on released trees was 7

to 10 times that of unreleased trees. Similar responses

have been reported for longleaf pine (Allen 1953,

Croker 1952), slash pine (Cooper and Perry 1956, Halls

and Hawley 1954), and shortleaf pine (Phares and

Rogers 1962).

Residual stand densities greatly influence quantities of seed produced. In a study of seed yield and quality in loblolly-shortleaf pine selection stands, Grano

(1970) reported that production per square foot of

basal area decreased curvilinearly with increasing

basal area (fig. 3). Total and viable seed production

increased with increasing basal areas up to 70 ft2/acre

and then declined. These results appear consistent

with other southern pines. Boyer and White (1989)

recommend that the preparatory cut of longleaf pine

for shelterwood regeneration reduce basal area to a

maximum of 70 ft2/acre. Then, the longleaf pine

shelterwood seed cut itself should reduce basal area

to about 30 ft2/acre. Particularly for longleaf pine, seedling establishment is improved with further reduction

in stand densities.

nutrition

The use of fertilizers in southern pine forests continues to increase, so it is not unreasonable to expect

its use in stands at various times during their rotation. The compatibility of fertilization to increase cone

and seed production and fertilization to promote

growth has been questioned. Kramer and Kozlowski

(1960) state that when trees are not nutrient deficient,

adding large amounts of nitrogenous fertilizers

may decrease seed production by increasing vegetative growth. However, most studies of fertilization of

the southern pines show that moderate nitrogen applications in typical southern forest soils, usually low

in nitrogen, do increase seed production. Fertilizing

with large amounts of potassium (252 lb/acre) and

phosphorus (180 lb/acre) with a moderate rate of nitrogen (120 lb/acre) doubled seed production in a

37-year-old natural shortleaf pine stand (Brinkman

1962).

Fertilizers are normally applied earlier in stand

development than is needed for seed production; however, there is merit to an application late in the rotation that can stimulate development of newly

established stands. Fertilizing while there is a crown

canopy will reduce development of understory grasses

and herbaceous plants that compete for nutrients and

improve seedling response. Particularly

where seed production is inadequate, fertilization

could be considered both for seed production and seedling growth.

Tree Age and Size

Many stands may now be grown on rotations of 100

years or more because of environmental concerns and

issues related to threatened and endangered species.

Can these older trees produce adequate quantities of

seeds to support natural regeneration?

A few studies have evaluated the effect of stand age

on seed production. Barnett and McLemore (1961)

found no differences in seed production or quality from

longleaf pine stands ranging from 21 to 85 years.

Wenger (1957) reported the results of a ‘I-year study

of loblolly pine seed crops that involved one stand 95

years old and two others 145 years old. Advancing age

apparently had no detrimental effect on seed production. All three stands produced from 50,000 to 800,000

seeds per acre annually. Lawson (1986) indicates that

leaving very old (100 years or older), slow-growing

shortleaf pines should be avoided. But if trees are vigorous, there is probably no age limitation.

Croker and Boyer (1975) state that longleaf pine

cone production by individual tree is affected by site

quality, stand density, tree size, and genetic predisposition. The best producers are dominant trees 15 inches

or more in diameter, with large crowns and a history

of past cone production, as evidenced by old cones

under trees. A longleaf pine tree 15 inches in d.b.h.

will produce, on the average, more than twice as many

cones as a 12-inch tree, and a 19-inch tree, more than

twice as many cones as the 15-inch tree (Boyer and

White 1989). But, for a given basal area, per-acre cone

production is not greatly changed by increasing tree

size above 15 inches in d.b.h., as the increase in cone

production per tree is largely offset by the reduction

in number of trees per acre.

Wakeley (1954) stated that southern pine cones

should not be rejected because of tree age. Pines of 7

to 15 years produce seeds of good quality, and excellent seeds have been collected from 280-year-old shortleaf pines and 350-year-old longleaf pines. Once trees

have reached seed-bearing age, seed production rarely

declines with advancing age, provided that the trees

remain healthy and vigorous (Smith 1962).

Genetic is~osition

Fruitfulness is hereditary to some degree, and cone

crops of individual trees are closely related to past

production (Pomeroy 1949, Wenger 1954). Croker

(1964) found that over a 5-year period, longleaf pine

cone production was influenced more by inherent fruitfulness of individual trees than by fertilization and

irrigation. It is important, then, when sufficient trees

are available, to select residuals based on past cone

production as we11 as other criteria. This can be done

by observing the numbers of cones both on trees and

on the ground under individual trees.

6
TwmapJw

Topography usually does not affect seed production

on most sites across the South. However, in mountainous areas, such as the Ouachita and Ozark Highlands, slope and aspect can strongly influence seed

production. Air temperature at the base of slopes may

be 5 to 12 “F cooler than a few hundred feet up the

slope (Hungerford and Babbitt 1987). Aspect also

greatly influences temperature, light, and soil moisture conditions. South- and west-facing slopes are

warmer and drier than the north- and east-facing

slopes due to greater exposure to sunlight. These environmental differences affect species distribution and

also cone and seed production. The specific responses

to topography will vary by location, species, and climate, but slope and aspect are important considerations in managing natural stands. For example, the

female strobili on pines on the lower portions of northfacing slopes may frequently be subjected to freeze

injury.

POTENTIAL LOSSES DURING THE

MATURATION PROCESS

Early initiation of large quantities of female strobili does not necessarily guarantee production of good

seed crops. Of nearly 28,000 strobili tagged on selected

clones of the 4 major pine species over 4 years, only

41 percent developed into cones (McLemore 1977).

Others have noted that when abundant strobili were

produced on longleaf pines each year over a B-year

period, only one good cone crop resulted (Allen and

Coyne 1956). Several factors are responsible for these

losses.

Insect and Animal Damage

Most losses during maturation are caused by insects.

McLemore (1977) attributed 98 percent of the strobili

and conelet losses of the four major species in a Louisiana seed orchard to insects. Losses over the 4-year

period of the study were higher in shortleaf and

longleaf pines than loblolly and slash pines. In a study

of shortleaf pine, Bramlett (1972) reported that overall survival from flowering to the mature cone stage

varied annually from 3 to 65 percent and averaged 29

percent over a 6-year period. Major losses were attributed to insects. DeBarr and Ebel(1974) and Ebel

and Yates (1974) also reported high losses of southern

pine conelets due to insects. Most losses are caused

by Dioryctria spp., but several other insects are involved at various stages of development. Losses, as a

percentage of the total crop, are particularly heavy

during poor seed years. Also, insect populations and

damage tend to build if there are several consecutive

years of medium to good cone production.

Losses due to animals such as squirrels are a problem in localized areas. Bramlett (1972) reported that

squirrels reduced maturing cones by 42 percent between July and September during 1 year of a 6-year

study. Again, the problem seems to be most serious

when crops are poor.

Weather-Related Injury

The primary weather-related losses are spring frosts

during flowering, extended droughts, and isolated occurrences such as hail. Temperatures of 25 to 28 “F

severely damaged developing female flowers of shortleaf pine, whereas undeveloped flowers protected by

bud scales escaped with little damage (Campbell 1955).

A late-season freeze killed 30 percent of female flowers on a sample of 23 shortleaf pines in the Virginia

Piedmont (Bramlett and Hutchinson 1964). In both of

the above instances, juvenile foliage on several hardwoods was also damaged. Apparently, frost injury to

hardwood leaves may forecast poor pine seed crops.

Frost damage occurs most frequently on the north

slopes of the mountainous portions of a species’ range

where temperature fluctuations are great.

Losses due to hail, drought, and wind storms occur

infrequently. In localized areas, these factors can significantly reduce cone production. McLemore (1977) reported that an April hail storm broke branches bearing

20 percent of the female flowers in 1 year of 4 studied.

FORECASTING SEED CROPS

The most common way to predict seed crops in advance of cone maturity is by evaluating flowers or

immature cones. Although procedures for predicting

seed crops 20 months in advance of maturity, based

on estimates of female flowers, have been developed

for southern pine seed orchards (Fatzinger and others 1988), binocular ground counts of flowers are unsatisfactory estimators of seed production in forest

stands (Shoulders 1968). Croker’s (1971) research on

estimating flower crops of longleaf pines indicated that

flowers are highly visible for only about 2 weeks between early flower development and growth of the

needles. During this short period, a factor of 1.5 can

be used to estimate total numbers of flowers; outside

of this period, flowers could not be reliably predicted.

Under stand conditions, these estimates do not adequately predict cone and seed production nearly 2

years later.

Wenger (1953) estimated the number of maturing

loblolly pine cones in late summer with reasonable

7
accuracy by counting visible cones through binoculars

from a single vantage point and doubling the number.

Binocular counts made in midsummer on only 4 to 5

percent of loblolly pines in a seed orchard provided

good crop estimates (Wasser and Dierauf 1979). Webb

and Hunt (1965) used a similar approach to estimate

cone crops in a slash pine seed production area with

success. Seidel(1970) successfully used a two-person

counting system in a 40-year-old shortleaf pine seedproduction area. The numbers of sound seeds per cone

may vary between years (McLemore 1975), and it is

advisable to estimate this number as well as the number of cones (Bramlett and Hutchinson 1964). Techniques to predict numbers of seeds per cone and cones

per bushel are well documented (McLemore 1962,

1972).

Trousdell(1950) described a method of forecasting

annual variations in loblolly pine seed crops in natural stands. The procedure consists of counting the previous-, current-, and next-year’s cones on sample

branches obtained from felled trees. This technique

assumes that the relative seed yield from the old cones

is known and the increase or decrease in the number

of cones measures the expected change in seed crops.

Read (1953) applied the method to shortleaf pine and

found regeneration success was closely related to the

seed crops forecasted by this technique.

Technology now exists to improve the quality of these

predictions. Solar-powered, automated weather stations are frequently used to monitor the weather conditions at research sites. Brissette and others (1992)

report on the types of environmental data collected

over a several-year period at a remote site in the

Ouachita Mountains of Arkansas. Installing such

equipment in natural stands where regeneration is

expected could provide data to verify rainfall, temperature, and light relationships that have affected seed

production in earlier studies. Increasing knowledge

of these relationships should provide silviculturists

and land managers the means to forecast seed crops

in time to prepare the site and complete other tasks

in anticipation of good seed crops.

CONCLUSION

Seed crops in natural southern pine stands vary

greatly according to environmental and biotic influences. This variability lowers the reliability of natural regeneration in these stands. Applying knowledge

of physiology of flower initiation and cone and seed

production should help foresters better manage stands

to increase seed production. A better understanding

of the biology of production should also improve their

ability to forecast seed crops.

Allen, R.M. 1953. Release and fertilization stimulate

longleaf pine cone crop. Journal of Forestry. 51: 827.

Allen, R.M.; Coyne, J.F. 1956. Insect problems in forest-tree genetics. Journal of Forestry. 54: 193.

Barnett, J.P.; McLemore, B.F. 1961. Tree age unimportant in longleaf seed viability. SO For. Notes 135.

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

Forest Service, Southern Forest Experiment Station.

[Not paged].

Barnett, J.P. 1993. Merits of using mechanical treatments to stimulate cone production of slash and

longleaf pines. In: Proceedings of the 22nd southern forest tree improvement conference; 1993 June

14-17; Atlanta, GA. Atlanta, GA: Southern Forest

Tree Improvement Committee: 59-64.

Bilan, M.V. 1960. Stimulation of cone and seed production in pole-size loblolly pine. Forest Science.

6: 207-220.

Boyer, W.D. 1978. Heat accumulation: an easy way to

anticipate the flowering of southern pines. Journal

of Forestry. 76: 20-23.

Boyer, W.D. 1981. Pollen production and dispersal as

affected by seasonal temperature and rainfall patterns. In: Franklin, E.C., ed. Pollen management

handbook. Washington, DC: U.S. Department ofAgriculture. 587: 2-9.

Boyer, W.D. 1987. Annual and geographic variations

in cone production by longleaf pine. In: Proceedings

of the 4th biennial southern silvicultural research

conference; 1986 November 4-6; Atlanta, GA. Gen.

Tech. Rep. SE-42. Asheville, NC: U.S. Department

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Experiment Station: 73-76.

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of longleaf pine. In: Proceedings of the symposium

on the management of longleaf pine; 1989 April

4-6; Long Beach, MS. Gen. Tech. Rep. SO-75. New

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

94-113.

Bramlett, D.L. 1965. Shortleaf pine seed production

in the Piedmont. Res. Note SE-38. Asheville, NC:

U.S. Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station. 4 p.

Bramlett, D.L. 1972. Cone crop development records

for six years in shortleaf pine. Forest Science.

18: 31-33.

Bramlett, D.L.; Hutchinson, J.G. 1964. Estimating

sound seed per cone in shortleaf pine. Res. Note SE18. Asheville, NC: U.S. Department of Agriculture,

Forest Service, Southeastern Forest Experiment

Station. 2 p.

Brinkman, K.A. 1962. Fertilizers increase seed production of shortleaf pine in Missouri. Tree Planters’

Notes. 53: 18-19.

8
Brissette, J.C.; Andries, C.D.; Stangle, C.M. 1992.

Monitoring the weather at a planting site on the

Winona Ranger District, Ouachita National Forest.

In: 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: 205-210.

Campbell, T.E. 1955. Freeze damages shortleaf pine

flowers. Journal of Forestry. 53: 452.

Chapman, H.H. 1923. The recovery and growth of

loblolly pine after suppression. Journal of Forestry.

21: 729-735.

Cooper, R.W.; Perry, J.H. 1956. Slash pine seeding

habits. Southern Lumberman. 193: 198-199.

Croker, T.C., Jr. 1952. Early release stimulates cone

production. SO. For. Notes 79. New Orleans, LA:

U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station. [Not paged].

Croker, T.C., Jr. 1964. Fruitfulness of longleaf trees

more important than culture in cone yield. Journal

of Forestry. 62: 822-823.

Croker, T.C., Jr. 1971. Binocular counts of longleaf pine

strobili. Res. Pap. SO-127. New Orleans, LA: U.S.

Department of Agriculture, Forest Service, Southern Forest Experiment Station. 2 p.

Croker, T.C., Jr.; Boyer, W.D. 1975. Regenerating

longleaf pine naturally. Res. Pap. SO-105. New Orleans, LA: U.S. Department of Agriculture, Forest

Service, Southern Forest Experiment Station. 21 p.

DeBarr, G.L.; Ebel, B.H. 1974. Conelet abortion and

seed damage of shortleaf and loblolly pines by a

seedbug, Leptoglossus corculus. Forest Science.

20: 165-170.

Dickman, D.I.; Kozlowski, T.T. 1971. Cone size and

seed yield in red pine. American Midland Naturalist. 85: 431-436.

Ebel, B.H.; Yates, H.O., III. 1974. Insect-caused damage and mortality to conelets, cones, and seed of

shortleaf pine. Journal of Economic Entomology.

67: 222-226.

Eggler, W.A. 1961. Stem elongation and time of cone initiation in southern pines. Forest Science. 7: 149-159.

Fatzinger, C.W.; Muse, H.D.; Miller, T.; Bhattacharyya,

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10

Barnett, James P.; Haugen, Ronald 0. 1995. Producing seed crops to

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The biological processes that affect seed production in natural

southern pine are documented, and information that will allow

foresters to manipulate stands in a manner to improve and predict

seed production is provided. As a result, natural regeneration should

become a more reliable technique.

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