transfer of calcium from the forest floor to the
mineral soil. Calcium is immobilized in the
forest floor and is made available to plants
slowly through mineralization reactions.
Burning rapidly releases calcium from the forest
floor, allowing it to leach into the mineral
soil and become more available for plant
nutrition.

McKee (1982) studied effects of prescribed
burning on other nutrients such as magnesium and
potassium. In all cases, prescribed burning had
no adverse effects on nutrient contents of soils
in the Santee fire plots. With some treatments,
particularly annual burning, soil fertility was
increased. The litter layer was partially
removed by all burning treatments, but never
entirely. Even though an unknown quantity of
nutrients was lost to the atmosphere during
burning, the major effects of fire were
apparently a stimulation of nitrogen fixation
and a redistribution of nutrients from the
understory and forest floor to mineral soil.

Tree Growth

Since many variables control tree growth,
results of different studies on the effects of
prescribed burning on growth are often con-
flicting. In general, fire is not recommended
where pines are less than 3.5 m tall. Shorter
trees are susceptible to needle scorch and stem
damage, which can retard growth or kill the
tree. As pines become taller, their buds and
needles are protected from the heat of the fire
and their bark is generally thick enough to
insulate the stem. If prescribed fires control
competing understory plants or improve soil
fertility, growth rates of overstory pines may
be increased.

The Santee fire plots were designed to study

effects on understory vegetation with little
consideration to tree growth. Detailed records

16


Mortality (percent)

Mortality (percent)

10

40

80
70

60 fF

~ Sweetgum
soseene Blackgum

—— Oaks

— Waxmyrtle

40

1
ty
50 i ?
/
i

30

20

lo

° 5 10 15, 20 25
Years

A. Annual Summer Burn

‘Sweetgum
ow Blackgum
—— Oaks

70 —--— Waxmyrtle

Years

B. Biennial Summer Burn

Figure 5.--Cumulative mortality of
hardwood roots over 26 years of prescribed
burning.


hotspots, particularly during summer burns,
killed a few of these large hardwoods. Number
of stems 5 to 10 cm d.b.h. was dramatically
reduced by all burning treatments. Stems of
this size were susceptible to top-kill, and
burning was frequent enough to prevent sprout
growth into this size class. Because of
sprouting from surviving rootstocks, number of
hardwood stems less than 2.5 cm d.b.h. was
increased by all burning treatments except
annual summer burning. Annual summer burning
eventually killed roots of all understory
hardwoods, leaving only grasses and forbs on the
forest floor. The roots of oaks had lower
mortality rates than those of other understory
species--a competitive advantage under a regime
of frequent burning.

Removal of understory vegetation by
prescribed fires, particularly annual burning,
is of practical significance. These fires
create stands that have an open "parklike"
appearance. Without the dense brush, which is
typical of unburned stands of the Southeast,
forests are more accessible to people, wildlife,
and equipment. Costs of cultural treatments to
the stand, such as fertilization and thinning,
are reduced, large animals are more free to move
within the stand, and woody stems are replaced
by more palatable forbs and succulent sprouts.
Since pine seedlings have reduced competition
for growing space, the chances for pine regen-
eration after harvest are improved. The
greatest benefit of controlling understory
vegetation is probably protection from wildfire
by reducing fuel concentrations. If a wildfire
should occur, its intensity would be much lower
in an area that was frequently burned than in an
area with a heavy fuel load. As a result, there
is less damage to forest resources and fire
suppression is easier.

Even though the Santee fire plots have been
burned many times, no adverse changes to the
chemical or physical properties of these sand
and silt loam Coastal Plain soils have been

20


ABSTRACT

Prescribed fire provides many benefits in southern
pine stands. A study begun in 1946 provides a unique
opportunity to observe long-term changes in understory
vegetation, soil properties, and overstory tree growth
caused by repeated burning.

Keywords: Backing fire, headfire, understory
hardwoods, nitrogen, phosphorus, calcium, basal area.

Introduction |

Fire has been a major ecological force in
the evolution of southern forests. As a result,
plant communities in the South not only tolerate
fire, but actually require it to exist (Cooper
1961). Evidence of early fires can be found as
buried layers of charcoal in peat beds (Cooper
1961), in scars from lightning strikes on
petrified trees (Komarek 1974), and in the
writings of early travelers (Bartram 1791).
Indians and early European settlers often used
fire to drive game and improve habitat for both
wild and domestic animals. These fires also
helped control insects and dense underbrush.

Today, prescribed fire--fire set under
planned conditions to accomplish specific
management objectives--is an accepted tool for
the management of southern pine forests. Like
the Indians and early settlers, foresters use |
fire to improve habitat for wild and domestic |
animals and to control the density of understory
vegetation. Prescribed burning provides several |
benefits to forest management: it consumes |
living and dead fuels (fig. 1), reducing the
incidence and damage of wildfires; it can
improve growth rates of overstory pines by
killing vegetation that would otherwise compete
for water and nutrients; it prepares sites for
seeding or planting; and it controls certain
diseases of pines. During the past decade, the
area prescribed burned each year in the South
has increased from 0.8 million ha to over 2 |
million ha (Wade 1985).


of the number and size of trees were not kept
throughout the 41-year history of the study.
Because of the unique long-term nature of the
study, efforts were begun in 1984 to examine
tree growth rates in relation to burning treat-
ments. If repeated prescribed burning affected
growth rates, changes should be visible in tree
growth rings. Increment cores (cylindrical
sections drilled from tree stems) were extracted
at breast height from all trees in all plots.
Estimates of stem diameters in past years were
determined by subtracting the width of each
annual growth ring (measured from increment
cores) from the present diameter of the tree.
Estimates of diameters were used to calculate
stand basal area (a measure of stand density
defined as the sum of the cross-sectional area
of all trees at 1.37 m above ground).

Basal area per hectare for each burning treat-
ment throughout the study is shown in figure 12.
As tree stems grow, stand basal area increases
until one or more trees die. Since records of
tree mortality were not kept, figure 12 represents

Basal Area (m*/ha)

10 +
° 10 20 30 40

Years Since Study Establishment

Figure 12.--Cumulative basal area of trees
surviving from 1946 through 1984 by
burning treatment.



McKee, William H., Jr. 1982. Changes in soil fertility
following prescribed burning on Coastal Plain pine
sites. Res. Pap. SE-234. Asheville, NC: U.S.
Department of Agriculture, Forest Service,
Southeastern Forest Experiment Station. 23 pp.

Pyne, Stephen J. 1982. Fire in America. Princeton, NJ:
Princeton University Press. 654 pp.

Ralston, Charles W.; Hatchell, Glyndon E. 1971.
Effects of prescribed burning on physical properties
of soils. pp. 68-83. In: Prescribed burning
symposium proceedings. Asheville, NC: U.S.
Department of Agriculture, Forest Service,
Southeastern Forest Experiment Station.

Wade, Dale D., comp. 1985. Prescribed fire and smoke
management in the South: conference proceedings;
1984 September 12-14; Atlanta, GA. Asheville, NC:
U.S. Department of Agriculture, Forest Service,
Southeastern Forest Experiment Station. 194 pp.

Wells, Carol G. 1971. Effects of prescribed burning on
soil chemical properties and nutrient availability.
pp. 86-97. In: Prescribed burning symposium
proceedings. Asheville, NC: U.S. Department of
Agriculture, Forest Service, Southeastern Forest
Experiment Station.

23


407

35

30

25

—— Periodic Winter
Periodic Summer
Control

Height (m)
8

—— Annual Winter
—.—.— Annual Summer

oO 10 20 30 40 50 60 70 80
Years Since Stand Establishment

Figure 13.--Mean height of sampled trees
by burning treatment from 1905 through
1984.

phosphorus and calcium availability, no fer-
tilization studies in the Coastal Plain have
shown positive responses to these elements in
trees of this age. In addition, soil moisture
is rarely limiting to pine growth on these
poorly drained Coastal Plain sites, even when
competing vegetation is not controlled.

Conclusions

The Santee fire plots provide an unusual
opportunity to observe changes to a southern
pine forest ecosystem caused by repeated pre-
scribed burning over a span of over four
decades. These study plots show that prescribed
burning can effectively control understory
vegetation. The degree of control is dependent
upon the season and frequency of burning and the
size and species of vegetation. Understory
hardwoods over 10 to 15 cm d.b.h. were not
severely damaged by low-intensity burns and
therefore cannot be controlled by low-intensity
burning, even on an annual basis. Occasional

19



soil was not reduced by periodic burning and was
increased slightly by annual burning in winter
or summer. Wells (1971) showed nitrogen losses
of 112 kg per ha through volatilization during
prescribed fires. However, nitrogen was quickly
replaced in the soil through nitrogen fixation.
Annual burning allows establishment of
herbaceous leguminous plants, which have nodules
on their roots containing nitrogen-fixing
species of Rhizobium bacteria. Fixed nitrogen

Phosphorus (Kg /ha)

14

20

C21] Forest Floor

Mineral Soil

'6 0-10 cm

Control Periodic Periodic Annual Annual
Winter Summer Winter Summer

Burning Treatment

Figure 10.--Total phosphorus in the forest
floor and available phosphorus in the top
10 cm of mineral soil after 30 years of
prescribed burning.


aboveground portions of these trees are
generally too small to survive most fires, but
their root systems survive and produce sprouts
after each fire. Burns have been frequent
enough to prevent the growth of sprouts into a
larger size class. Only a few individuals
between 5 and 15 cm are present on periodically
burned plots. Trees of this size class are
susceptible to top-kill from occasional flareups
or hotspots in the fire. Since hotspots occur
more often during the summer, fewer trees of
this intermediate size class have survived in
plots burned in the summer than in those burned
in the winter.

Study plots burned annually in winter (fig.
2D) or biennially in summer (fig. 2E) have large
numbers of hardwood and shrub stems less than
1m tall. During each fire, these stems are
top-killed. However, both of these treatments
allow the vegetation at least one full growing
season to recover from fire. Many root systems
survived these treatments and resprouted.
Biennial summer burns generally led to greater
coverage by grasses than annual winter burns.

Annual summer burning has nearly eliminated
understory woody vegetation (fig. 2F). Burning
has been frequent enough and of sufficient
intensity to kill root systems of all hardwood
and shrub species, and the understory is domi-
nated almost entirely by grasses and forbs.
Seedlings of hardwood and shrub species appear
occasionally, but they do not survive the next
fire.

The Southeastern Forest Experiment Station
has monitored changes in understory vegetation
caused by burning since the study was estab-
lished. Previous descriptions of various
vegetative characteristics have been given by
Chaiken (1949), Cushwa and others (1966), Lewis
and Harshbarger (1976), and Lotti and others
(1976). The most recent survey of understory
characteristics was completed by Langdon (1981)
after 30 years of prescribed burning. The
understory has changed little since the 30th

6




Description of the Study |

Study plots are on the Santee Experimental |
Forest in Berkeley County, SC, and on the |
Westvaco Woodlands in neighboring Georgetown |
County. Both areas are on a Pleistocene terrace
on the lower Coastal Plain at 7.5 to 9.0 m above
sea level. Soils include a variety of series
but are generally described as poorly drained
Ultisols of medium to heavy texture. Soils are |
considered productive with a site index of 27 to

30 m for loblolly pine at age 50. In 1946,
forests of both study sites consisted of
unmanaged, but well-stocked, even-aged stands of
loblolly pine. The Santee stand was 42 years
old when the study was initiated, while the
Westvaco stand was 36 years old. Both stands
had resulted from natural regeneration after
logging.

Six treatment plots, 0.1 ha in size, were
established in each of five replications. Three
replications are on the Santee Experimental
Forest and two are on the Westvaco woodlands.
Treatments include: (1) periodic winter
burning, (2) periodic summer burning, (3)
biennial summer burning, (4) annual winter
burning, (5) annual summer burning, and (6) an |
unburned control.

All winter burning was done on December 1 or
as soon afterward as weather permitted. Summer
burning was done on or soon after June 1.

Annual burning has continued since December 1946 |
for a total of 41 consecutive years. Periodic |
burns are conducted when 25 percent of the

understory hardwood stems reach 2.5 cm in

diameter at breast height (d.b.h.). This

prescription has resulted in variable burning

intervals ranging from 3 to 7 years. At

present, seven periodic burns have been con-

ducted. Biennial summer burning was added to

the study in 1951 and it has been done 19 times

to date.

Burning techniques were selected to ensure
complete coverage of the plot by fires of the
lowest practical intensity. Selection was made


Figure 1.--Low-intensity prescribed fires
provide multiple benefits for southern
pine forests.

Even though prescribed burning is accepted
today, its widespread use is relatively new.
Fire protection policies of the U.S. Department
of Agriculture, Forest Service, State forestry
agencies, and forest industry prevented the use
of prescribed fire in the early decades of the
20th century. Even light burning was prohibited
on the newly established national forests of the
South. Prescribed burning for fuel reduction
gained acceptance in the 1940's and 1950's, but
only after a series of wildfires showed the
disastrous consequences of fire exclusion (Pyne
1982). As fire use in southern forests
increased, so did the need for a better under-
standing of its long-term effects on forest
ecosystems.

An ongoing experiment by the Southeastern
Forest Experiment Station is providing the most
comprehensive available information about
changes to southern pine ecosystems caused by
repeated burning over a long period. The
experiment, known as the Santee Fire Plot Study,
was established in 1946. This Paper summarizes
the observed effects on understory vegetation,
soil properties, and overstory tree growth.

2



becomes incorporated into the top layer of soil,
thus improving soil fertility. Jorgensen and
Wells (1971) noted that annual winter and summer
burning also appeared to increase nitrogen
fixation by nonsymbiotic bacteria. Numbers of
waxmyrtle, which has a symbiotic relationship
with a nitrogen-fixing actinomycete (Frankia),
were increased by periodic burning in summer or
winter (fig. 6), but nitrogen content of the
mineral soil was unchanged.

All burning treatments reduced total
phosphorus content of the forest floor (fig. 10)
but increased available phosphorus content in
the top 10 cm of mineral soil. This finding is
significant for phosphorus-deficient Coastal
Plain soils. Increases in available soil
phosphorus created by frequent burning may
increase vigor and growth of crop trees.

T1Forest Floor

250 5 EI Mineral Soi!
0-10cm

200

100

Calcium (kg/ha)

Control Periodic Periodic Annual Annual
Winter Summer Winter ‘Summer

Burning Treatment
Figure 11.--Exchangeable calcium in the

forest floor and mineral soil after 30
years of prescribed burning.

Burning did not change the calcium content
in the combined forest floor and top 10 cm of
mineral soil (fig. 11). However, there was a

15



C. Periodic Summer Burn D. Annual Winter Burn

OE us he

E. Biennial Summer Burn F. Annual Summer Burn

Figure 2.--Understory vegetation on the
Santee fire plots after 36 to 41 years of
prescribed burning by various combinations
of season and frequency.



observed. Soil productivity may have been
improved by increases in available phosphorus,
exchangeable calcium, and organic matter in the
mineral soil. Increased phosphorus availability
is particularly important because most Coastal
Plain soils are deficient in phosphorus. Total
nitrogen in the soil was not reduced by
burning. It increased slightly after annual
winter and summer burning due to increased
abundance of nitrogen-fixing legumes and forbs.
All burning treatments reduced the thickness of
the forést floor but rarely exposed mineral
soil.

Limited records of the number and size of
overstory pines on each plot over the duration
of the study made an analysis of the effects of
prescribed burning on tree growth difficult.
Increment core and stem analysis of trees living
in 1984 showed no significant changes in diam-
eter or height growth that could be attributed
to prescribed burning. This result was somewhat
unexpected because reduced competition from
understory vegetation and increased soil fer-
tility should enhance growth. However, these
changes occurred gradually over time. Since the
overstory pines were approximately 40 years old
when the study began, they may have been too
old to benefit by the time these site changes
reached significant levels. Although pine
growth was not increased by burning, the fact
that growth rates were not decreased is quite
important. Several studies have shown retarded
growth rates in young stands when fires were of
sufficient intensity to scorch needles or damage
stems. The chance of this occurring on the
Santee fire plots was high because of the large
number of fires conducted, particularly during
the early years of the study when understory
vegetation provided abundant fuels. When fires
are conducted with proper care, damage to the
stand can be avoided. Careful burning allows
the forest manager to achieve many benefits at
minimal cost.

21



United States
Department of
Agriculture

Forest Service

Southeastern Forest
Experiment Station

General Technical
Report SE-45

Long-Term Studies

of Prescribed Burning
in Loblolly Pine Forests
of the Southeastern
Coastal Plain

Thomas A. Waldrop

David H. Van Lear

F. Thomas Lloyd
William R. Harms



1000

900

[2] 5-10. cm abn

I-15 cm d.bh,

800 F

Toor EZ 15-20 cm abn.
HB 20 cmap. and over

600

500 F

400

300

Stems (number / ha)

200 F

100 F

Control Periodic Periodic Annual Biennial Annual
Winter ‘Summer Winter ‘Summer ‘Summer

Burning Treatment

Figure 4.--Diameter distribution of all
understory hardwoods over 5 cm d.b.h. by
burning treatment after 30 years of
prescribed burning.

The number of stems in all diameter classes
over 5 cm d.b.h. was reduced by all burning
treatments (fig. 4). Control plots had over 900
stems per ha between 5 and 10 cm d.b.h.,
compared with 140 or less in all burned plots
after 30 years of treatment. The reduction in
numbers is less obvious in larger diameter
classes. Control plots had 220 stems per ha 10
to 15 cm d.b.h., compared with 145 or less in
burned plots. Trees in this size class were
tall enough and had sufficient bark thickness to
survive most low intensity burns. However,
localized hotspots of sufficient intensity to
kill these larger trees occur occasionally. For
hardwoods over 15 cm d.b.h., there are no
obvious differences in stem numbers between
control plots and plots subjected to winter
burning. Winter prescribed burns rarely
produced lethal temperatures for the cambium or
buds of these large trees. A few trees in these
larger size classes have been killed during
summer burns when hotspots are more likely to
occur.

8



year of the study, so Langdon's results are
summarized here.

The total number of hardwood stems less than
2.5 cm d.b.h. has been significantly increased
by most burning treatments (fig. 3). In gen-
eral, the greater the frequency of burning the
greater the number of small hardwood stems.
When fires top-kill small trees, surviving root
systems often produce multiple sprouts, causing
a net increase in the total number of stems per
hectare. Numbers of sweetgum, one of the most
prolific sprout-producing species in the South-
east, changed most dramatically. Total number
of stems of all species in annual winter burn
plots is nearly five times greater than in
unburned plots. The exception to this trend is
annual summer burning. Top-kill early in the
growing season halts carbohydrate production
when carbohydrate reserves normally in the root
system are at their lowest levels. When summer
burns are repeated annually, carbohydrate
reserves are eventually depleted and root
systems die. The only small hardwoods present
after annual summer burns are those germinated
from seed between fires.

50
[ESD Misc. Hardwoods
40 Oaks
~ WB Bockgum
o
= sok EE) sweetgum
fo}
fe}
2
= at
a
=
2
O 10F
° —
Control Periodic.=—=Periodic_~=— Annual Biennial Annual
Winter Summer Winter ‘Summer Summer

Burning Treatment

Figure 3.--Number of understory hardwoods less
than 2.5 cm d.b.h. after 30 years of prescribed
burning by treatment and species group.


The Forest Service, U.S. Department of
Agriculture, is dedicated to the principle of
multiple use management of the Nation’s forest resources
for sustained yields of wood, water, forage, wildlife, and
recreation. Through forestry research, cooperation with the
States and private forest owners, and management of the
National Forests and National Grasslands, it strives—as
directed by Congress—to provide increasingly greater
service to a growing Nation.

USDA policy prohibits discrimination because of race,
color, national origin, sex, age, religion, or handicapping
condition. Any person who believes he or she has been
discriminated against in any USDA-related activity should
immediately contact the Secretary of Agriculture,
Washington, DC 20250.




at the time of burning based on prevalent fuel
and weather conditions. In general, backing
fires (slow moving, cool fires that back into
the wind) were used on periodically burned plots
having thick underbrush or when hot and dry
weather increased the risk of high-intensity
fires. Headfires (fast-moving fires burning in
the same direction as the wind) or strip head-
fires (several headfires parallel to each other)
were used on annually burned plots with little
underbrush and when fuels were too moist to
support a backing fire.

Understory Vegetation

Since fire has been a component of southern
forests for millennia, most native plants have
adapted to its presence and are not eradicated
by prescribed fires. However, density of each
species can be affected. Because different
plant species have different adaptive strategies
to fire, the various combinations of season and
frequency of burning on the Santee fire plots
have produced obvious differences in structure
and species composition of understory vegetation
(fig. 2).

Unburned control plots (fig. 2A) have been
undisturbed for approximately 80 years. Under-
story vegetation consists almost entirely of
large tree and shrub species adapted to living
in the shade of overstory pines. Practically
every size class of hardwoods from 2.5 to 50 cm
d.b.h. is represented in control plots.

Periodic winter burns (fig. 2B) and periodic
summer burns (fig. 2C) have created two distinct
size classes of understory vegetation. Hard-
woods over 15 cm d.b.h. are as common on peri-
odically burned plots as they are on unburned
controls. At the beginning of the study, these
trees were old enough to be protected by thick
bark and tall enough that their buds were above
the intense heat of the first fire. Understory
hardwoods over 15 cm d.b.h. have survived on all
treatment plots. The other common size class is
composed of stems less than 5 cm d.b.h. The

4


the basal area of only those trees that survived
until 1984. Differences in the height of these
curves represent differences in numbers and sizes
of trees in treatment plots today. Differences in
tree sizes and numbers are due to chance plot
selection rather than treatment effects. If
burning treatments alter tree growth rates, the
effect would be shown as differences in the slopes
of these curves rather than as differences in the
relative heights.

All curves in figure 12 are generally paral-
lel, indicating that burning has not affected
diameter growth rates. When growth rates were
subjected to analysis of variance, the statisti-
cal test indicated that the differences between
treatments were not significant. Therefore, none
of the burning treatments increased or decreased
rates of diameter growth on overstory pines of
the Santee fire plots.

Height growth was studied with a standard
stem-analysis procedure on felled sample trees.
This procedure provides estimates of height
growth during each year of a tree's life. Mean
tree height for each treatment throughout the |
lives of these stands is shown in figure 13. i
Curves are very close together, indicating that
trees in various treatment plots have had
similar height growth patterns. During the past
30 years, trees in annual winter and summer burn
plots appear to have slightly reduced rates of
growth. These differences were not significant,
however, when compared by analysis of variance.

The lack of statistically significant
differences in diameter and height growth was
unexpected. We expected that control of com-
peting vegetation and increased soil fertility
resulting from prescribed burning would improve
growth rates. However, overstory pines averaged
40 years old at the beginning of the study and
were probably too old to respond by the time
these site changes reached significant levels.
Even though McKee (1982) showed increases in

18




Contents

Introduction. .....

Description of the Study .

Understory Vegetation .
Soil Properties ...
Tree Growth ......
Conclusions .....

Literature Cited... .

e
o
FwR

12
16
19
22


Stems (1,000/ha)

Crown Coverage (percent)

150

125

EES misc

HB sumac
Pepperbush
Waxmyrtie
3 cauperry
(2) Bueverry

° 1
Control Periodic Periodic Annual Biennial Annual
Winter Summer Winter ‘Summer Summer

Burning Treatment

Figure 6.--Number of shrubs by species and
treatment after 30 years of prescribed

burning.

90

Bot

70F

60

50

40

Hardwoods
[| Vines:
Shrubs
iss83) Forbs:
ED crosses

yy

30

20F

lof

Periodic
‘Summer

Periodic
Winter

‘Annual
Winter

Control

Burning Treatment

‘Annual
‘Summer

Biennial
Summer

Figure 7.--Percent crown coverage of all

understory plants less than 1.

5 m tall

after 30 years of prescribed burning.

11



Organic Matter (kg/ha)

Nitrogen (Kg/ha)

CJForest Floor

80, EE) Mineral Soil
00 0-10cm

70,000 F

60,000

50,000

40,000 F

30,000 F

20,000

10,000

Periodic Periodic Annual Annual
Winter ‘Summer Winter ‘Summer

Control
Burning Treatment
Figure 8.--Organic matter in the forest

floor and mineral soil after 30 years of
prescribed burning.

1800 [Forest Floor
E=3Mineral Soil

1600 F 0-10cm
1400
1200
1000 F
800 +
600 +
400 F
200 F

°

Control Periodic Periodic Annual Annual
Winter Summer Winter ‘Summer

Burning Treatment

Figure 9.--Total nitrogen in the forest
floor and mineral soil after 30 years of
prescribed burning.

13



Long-Term Studies of Prescribed Burning

in Loblolly Pine Forests of the
Southeastern Coastal Plain

Thomas A. Waldrop, Research Forester
Southeastern Forest Experiment Station
Clemson, South Carolina

David H. Van Lear, Professor
Department of Forestry
Clemson University
Clemson, South Carolina

F. Thomas Lloyd, Research Forester
Southeastern Forest Experiment Station
Charleston, South Carolina

William R. Harms, Project Leader
Southeastern Forest Experiment Station
Charleston, South Carolina

September 1987

Southeastern Forest Experiment Station
P.O. Box 2680
Asheville, North Carolina 28802


Literature Cited

Bartram, William. 1791. Travelsthrough North and South
Carolina, Georgia, East and West Florida. New York:
Dover Publications, Inc. 414 pp.

Chaiken, L.E. 1949. The behavior and control of under-
story hardwoods in loblolly pine stands. Tech. Note
72. Asheville, NC: U.S. Department of Agriculture,
Forest Service, Southeastern Forest Experiment
Station. 27 pp.

Cooper, Charles F. 1961. The ecology of fire.
Scientific American 204(4):150-160.

Cushwa, Charles T.; Brender, Ernst V.; Cooper,
Robert W. 1966. The response of herbaceous
vegetation to prescribed burning. Res. Note SE-53.
Asheville, NC: U.S. Department of Agriculture,
Forest Service, Southeastern Forest Experiment
Station. 2 pp.

Jorgensen, J.R.; Wells, C.G. 1971. Apparent nitrogen
fixation in soil influenced by prescribed burning.
Soil Science Society of America Proceedings
35(5) :806-810.

Kormarek, E.V., Sr. 1974. Effects of fire on temperate
forests and related ecosystems: Southeastern United
States. pp. 251-277. In: Kozlowski, T.T.; Ahlgren,
C.E., eds. Fire and ecosystems. New York: Academic
Press.

Langdon, 0. Gordon. 1981. Some effects of prescribed
fire on understory vegetation in loblolly pine
stands. pp. 143-153. In: Wood, Gene W., ed.
Prescribed fire and wildlife in southern forests:
Proceedings of a symposium. Georgetown, SC: The
Belle W. Baruch Institute of Clemson University.

Lewis, Clifford E.; Harshbarger, Thomas J. 1976. Shrub
and herbaceous vegetation after 20 years of
prescribed burning in the South Carolina Coastal
Plain. Journal of Range Management 29(1):13-18.

Lotti, Thomas; Klawitter, Ralph A.; LeGrande, W.P.
1960. Prescribed burning for understory control in
loblolly pine stands of the Coastal Plain. Stn. Pap.
116. Asheville, NC: U.S. Department of Agriculture,
Forest Service, Southeastern Forest Experiment
Station. 19 pp.

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Waldrop, Thomas A.; Van Lear, David H.; Lloyd, F. Thomas;
Harms, William R. 1987. Long-term studies of prescribed
burning in loblolly pine forests of the Southeastern
Coastal Plain. Gen. Tech. Rep. SE-45. Asheville, NC: U.S.
Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station. 23 pp.

Prescribed fire provides many benefits in southern pine
stands. A study begun in 1946 provides a unique opportunity
to observe long-term changes in understory vegetation, soil
properties, and overstory tree growth caused by repeated
burning.

KEYWORDS: Backing fire, headfire, understory hardwoods,
nitrogen, phosphorus, calcium, basal area.

Waldrop, Thomas A.; Van Lear, David H.; Lloyd, F. Thomas;
Harms, William R. 1987. Long-term studies of prescribed
burning in loblolly pine forests of the Southeastern
Coastal Plain. Gen. Tech. Rep. SE-45. Asheville, NC: U.S.
Department of Agriculture, Forest Service, Southeastern
Forest Experiment Station. 23 pp.

Prescribed fire provides many benefits in southern pine
stands. A study begun in 1946 provides a unique opportunity
to observe long-term changes in understory vegetation, soil
properties, and overstory tree growth caused by repeated
burning.

KEYWORDS: Backing fire, headfire, understory hardwoods,
nitrogen, phosphorus, calcium, basal area.

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Biennial summer burning was added to the
study to provide a comparison with annual summer
burning in a study of the survival of the root
systems of four hardwood species. Individual
trees were observed repeatedly to determine the
number of annual or biennial summer burns
required to kill their root systems. With
annual summer burning (fig. 5A), mortality was
fairly rapid for sweetgum and waxmyrtle, nearly
100 percent within 8 years. Oaks and blackgum
were more difficult to kill with annual summer
fires. Biennial summer burning (fig. 5B) was
less effective in killing root systems of all
species tested. After 26 years (13 burns),
mortality among the oak species remained less
than 50 percent. With biennial burning, root
systems have an entire growing season to
recover. Apparently, that time is sufficient
for carbohydrate reserves to accumulate enough
to allow some resistance to fire.

Shrubs have also been affected by season and
frequency of burning (fig. 6). Shrub density
was increased by both periodic burning treat-
ments due to increased sprouting of waxmyrtle
and pepperbush. Shrubs are less resistant to
frequent burning than understory hardwoods.

Only a few stems of blueberry and sumac remain
in plots burned annually in summer.

Total crown coverage for all types of
understory plants is shown for each treatment in
figure 7. Control plots are covered mostly by
shrubs with some grasses, vines, and hardwoods.
Total coverage is increased by periodic burns
due to increased sprouting of hardwoods after
winter and summer burns and increased abundance
of vines after winter burns. Total coverage
after annual winter burns is similar to that in
control plots, but species composition has
changed. Burning has greatly reduced the shrub
component, which has been replaced by grasses
and forbs. After biennial summer burns,
coverage by shrubs, vines, and hardwoods is
similar to that after annual winter burns.
However, grasses and forbs are more common,

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providing an increase in total coverage. In
annual summer burn plots, almost all of the
shrubs, vines, and hardwoods that were dominant
in 1946 have been replaced by grasses and
forbs.

Soil Properties

Fear of soil damage resulting from con-
sumption of the forest litter layer has long
been a concern of foresters. However, evidence
indicates that low-intensity prescribed burns
do not adversely affect soils. Ralston and
Hatchell (1971) concluded that large changes in
soil physical properties can only be expected
from wildfires of high intensity. Low-intensity
prescribed burns leave a protective mat of
unburned litter on the forest floor. This mat
reduces raindrop impact and minimizes soil
erosion and plugging of soil macropores.

McKee (1982) studied effects of repeated
prescribed burning on several soil properties in
the Santee fire plots. The various burning
treatments caused significant changes to the
amount of organic matter in the forest floor and
top 10 cm of mineral floor (fig. 8). All burning
treatments reduced the depth of the litter
layer, thus significantly reducing the amount of
organic matter on the forest floor. In the top
10 cm of mineral soil, a different pattern was
observed. Periodic winter or summer burns had
little effect on soil organic matter content.
Although not statistically different, average
soil organic matter levels were higher on plots
burned annually in winter and summer than those
on control plots. Probable causes are a greater
abundance of fibrous-rooted grasses and forbs on
frequently burned plots (fig. 7), plus
accumulation of charred material in the soil
profile.

Total nitrogen content of the forest floor
was significantly reduced by all burning
treatments due to reduced accumulation of litter
(fig. 9). However, nitrogen content of mineral

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