Growlngu ea8on Burns for

Control of Hardwoods in

Longleat Ine Stands

Wllllam D, Boyer
SUMMARY

Experimental spring and summer burning for control of hardwoods was conducted in longleaf pine (Pinus palustris Mill.) stands in southwestern Alabama.

When two summer burns were conducted 2 years apart in stands of mainly mature

longleaf pine, most hardwood mortality occurred after the second fire-mainly

among stems that had suffered complete top-kill after the first fire. Only hardwoods

in the l-inch d.b.h. class suffered over 50-percent mortality, and mortality among

stems in the 4-inch and larger d.b.h. classes was negligible. Fire damage to some

upland hardwood species increased with increasing density of overstory pine,

probably because needle-litter fuels burn hotter than hardwood leaf-litter fuels. A

single hot summer fire was more destructive to longleaf pines than to hardwoods;

pine mortality in the l- through 4-inch d.b.h. classes was as great after the first fire

as hardwood mortality in the same diameter classes after both fires. Significant

mortality also occurred among pines in the 16-inch and larger d.b.h. classes after

the first fire. Summer burning for hardwood control in existing longleaf pine stands

is inadvisable because of the danger of unacceptably high pine mortality. Hardwood

damage caused by single spring fires in longleaf pine seedling stands seemed less

affected by timing of the burn than by burning conditions affecting fire intensity.

July 1990
Growing-Season Burns for Control of Hardwoods

. in Loagleaf Pine Stands

. William D. Boyer

INTRODUCTION

Hardwood control is often necessary for the regeneration and optimum development of southern pines, especially longleaf pine, which is particularly sensitive to

competition. Fire is the least expensive cultural treatment available to control small hardwoods in pine stands

and to reduce or eliminate hardwood encroachment into

the midstory. The use of fire is preferred over more costly

mechanical or chemical treatments if it can reliably

achieve hardwood control objectives without excessive

damage to the pines.

Prescribed burns conducted during the growing

season are more effective than those conducted in the

dormant season in controlling small hardwoods in

southeastern pine stands (Brender and Cooper 1968,

Chaiken 1952, Ferguson 1961, Grano 1970, Grelen 1975,

Hodgkins 1958, Langdon 1971, Lotti and others 1960,

Trousdell 1970, Waldrop and others 1987). Although

periodic winter fires in the upper Coastal Plain of

Alabama resulted in the top-kill (death of all

aboveground portions of the plant) of hardwoods up to

3 inches in d.b.h. and were as effective as periodic summer fires in complete kill of understory hardwoods, they

were less effective than summer fires in reducing the size

and vigor of sprouts (Chen and others 1975). Grano

(1970) found that winter fires can cause top-kill in

hardwoods with basal diameters as great as 3.5 inches,

but he also found that these hardwoods would later

sprout prolifically. Waldrop and others (1987) reported

that annual winter fires did not reduce the number of

sprouts per tree and actually resulted in many more stems

per acre than winter fires at longer intervals.

On an Atlantic Coastal Plain site, prescribed summer

fires caused top-kill in most hardwoods up to 4 inches in

d.b.h. and many as large as 6 inches in d.b.h. (Riebold

1955). Complete top-kill by summer fires was found to

average about 50 percent for trees in the 2-inch d.b.h.

class, more for smaller trees, and progressively less for

larger size classes on both upper Coastal Plain (Ferguson

1961) and Piedmont pine sites (Brender and Cooper

1968). While single fires may result in hardwood top-kill,

they destroy very few rootstocks (Langdon 1971). Successive annual summer fires have been found to be highly

effective in killing hardwood rootstocks, thus reducing

William D. Boyer is principal silviculturist, George W. Andrews Forestry Sciences Laboratory, maintained at Auburn, Alabama by the Southern

Forest Experiment Station, Forest Service-USDA, in cooperation with Auburn University.

the total number of woody stems (Chaiken 1952, Grano

1970, Trousdelll970, Waldrop and others 1987).

Four successive annual summer fires in the lower

Coastal Plain flatwoods eliminated about 50 percent of

small hardwood stems and reduced the size and vigor of

the rest (Chaiken 1952). Summer fires at less frequent

intervals, even biennial summer fires, are less effective in

causing complete-kill, as hardwoods always have at least

one growing season in which to recover from burning.

Summer fires, however, are more damaging to small

longleaf pines (Pinudpalustis Mill.) than fires in the

winter or spring (Grelen 1975).

Fires early in the growing season, soon after leaves

are fully expanded, should be the most effective for

weakening and eventually killing deciduous hardwoods,

as root reserves have reached their lowest point at this

time (Woods 1955). However, relatively little information is available on spring burning for control of

hardwoods. In one study, the number of surviving

hardwood stems up to and including the 3-inch d.b.h.

class were reduced with each successive spring burn

(Harrington and Stephenson 1955). In another, the number and size of hardwood sprouts were less with a spring

burn than with a winter or late-summer burn (Ferguson

1961). Furthermore, spring burns are beneficial in that

they are more effective than winter burns (or no burns)

in promoting height-growth initiation by grass-stage

longleaf pine seedlings (Grelen 1983, Maple 1977).

In this paper the results of two studies aimed at in-’

creasing our knowledge of the effects of spring and summer burning on longleaf pines and on common hardwood

competitors are reported. Both studies were installed in

the Escambia Experimental Forest’ in southwestern

Alabama.

PROCEDURE

Summer Burns

In the first study, the effects of summer burns conducted in 1976 and 1978 were observed. The 2%acre

study area consisted primarily of mature longleaf pines

‘Maintained by the Southern Forest Experiment Station, Forest

Service-USDA, in cooperation with the T R. Miller Mill Company.

1
with a hardwood midstory that had survived periodic

prescribed winter fires. Basal area of pines was 49 ft2 per

acre, 45 percent of which was in trees 15.6 to 26.5 inches

in d.b.h. and 32 percent of which was in trees 7.6 through

15.5 inches in d.b.h. Basal area of hardwoods averaged 15

ft2 per acre, 70 percent of which was in trees 3.6 inches

in d.b.h. and larger. The study area had last been burned

in February 1974.

The first summer burn was conducted on July 23,

1976. Flank fires were used. This fire was very intense,

burning through brushy streamside borders to running

water. During the burn, air temperatures reached 99 “F

and relative humidity was as low as 34 percent. The last

rain before the fire, according to a recording rain gauge

less than a mile from the study site, was 0.8 inch on July

14.

The second burn, on August 15, 1978, was of much

lower intensity and was rained out an hour after ignition,

when only about half of the study area had burned. At the

start of the fire, air temperature was 94 “F and relative

humidity was 52 percent. By the end of burning, air

temperature had fallen to 80 “F, and relative humidity

had risen to 98 percent. The last rain before the fire was

0.1 inch on August 13. The balance of the study area was

burned on August 21, 1978. Air temperatures ranged

from 93 to 97 “F and relative humidities from 53 to 57

percent. The previous rain had been 0.1 inch on August

1.9. Headfires were used, and estimated fireline intensity,

derived from flame lengths (Nelson 1980), averaged

about 100 BTU/ft/sec.

Fifty sampling points were established in the summerburned study area during the December 1976 through

January 1977 period. A BAF (basal area factor) 10 wedge

prism was used to estimate basal area in pines and

hardwoods at each sample point. All pines and

hardwoods intercepted by the prism were selected,

marked, and examined. To increase the sample size, all

other pines and hardwoods in the l-inch d.b.h. class and

larger (>0.5-inch d.b.h.) within 17 feet of each sample

point were selected, marked, and examined in October

1977. Sample trees killed by the fire were not excluded.

There were 557 pine and 277 hardwood sample trees, of

which 187 hardwoods were on the upland and 90 in

streambottoms. The species distribution of sample trees

is given in table 1.

At the time of the first examination, the following

information was recorded for each sample tree:

1. Species.

2. D.b.h.

3. Whether living or killed by fire.

4. Proportion of live crown killed by fire, estimated to

nearest 10 percent.

5. Presence or absence of sprouting. When sprouting

was present, then it was recorded as originating from: (a)

roots or root collar, or (b) aboveground stems or

branches.

Table l.---Species distribution of sample trees in the study area

Soecies Number

Pine l

Longleaf (Pinuspalustris Mill)

Slash (Z? elliottii Engelm. var. elliottii)

Loblolly.(P. taeda L.)

Upland hardwoods

511

4 5

Dogwood (Comusflorida L.)

Bluejack oak (Quercus incana Bart.)

Post oak (Q. stellata Wangenh.)

Water/willow oaks (Q. nigra L., Q. phellos L.)

Turkey oak (Q. laevis Walt.)

Blackjack oak (Q. marilandica Muenchh.)

Southern red oak (Q. falcata Michx.)

Blackgum (Nyssa sylvatica Marsh.)

Persimmon (Diospyros virginiana L.)

Streambottom hardwoods

Titi (Cyrilla racemiflora L., Cliftonia monophylla

8 9

2 3

2 1

1 3

1 0

4

4

1 9

4

(Lam.) Britton ex Sarg.) 5 2

Red maple (Acer rubrum L.) 1 7

Gallberry (ZZex coriacea (Pursh) Chapm.) 1 1

Sweetleaf (Symplocos tinctoria (L.) LHer.) 4

Sweetbay (Magnolia virginiana L.) 3

Black cherry (Prunus serotina Ehrh.) 3

The sample trees selected by the prism-intercept

method were examined in April and again in October

1977. All sample trees were examined in October 1978,

following the second fire, and again in May 1979.

Recorded at each examination were:

1. Proportion of preburn live crown still alive, estimated to nearest 10 percent.

2. Presence or absence of sprouting, as described previously.

Spring Burns

The second study tested the effects of spring burns on

oaks and dogwoods at three distinct stages of phenological development. Burning took place in 1980 and 1981.

Four experimental blocks were established in clearcut

regeneration areas where longleaf pine seedling stands

were overtopped by hardwood brush. All four blocks had

been burned periodically. Blocks 1 and 2 had last been

burned in the winter of 1978, and blocks 3 and 4 had last

been burned in the spring of 1979. Blocks 1 and 2 were

to be burned in 1980, and blocks 3 and 4 were to be

burned in 1981.

Each block contained nine plots. Each gross plot was

1.5 by 2 chains in size and consisted of a l-chain by

1.5-chain net plot surrounded by a 0.25-chain isolation

border. Each of three burning treatments was randomly

assigned to three of the nine plots in each block. Three

shoots on each of five dogwoods in each block were

marked for observation. Treatments were spring burns

that were conducted as soon as possible after sample

dogwoods reached one of the following phenological

stages:
1. Bud break beginning; vegetative buds cracked but

leaves not yet visible.

2. Bud break complete; leaflets visible on all sample

shoots.

3. Full leaf; all sample shoots in full leaf (leaves no

longer expanding).

Wherever possible, 10 dogwoods and 20 oaks within

each of the 36 plots were selected and marked for observation. Not all plots contained the necessary number of

trees, and the sample consisted of 296 dogwoods and 767

oaks. Species, diameter at 6 inches above groundline, and

total height were recorded for each sample tree.

Forty-three percent of the oaks were bluejack, 19

percent water or willow oak, 14 percent southern red oak,

14 percent post oak, 9 percent turkey oak, and 1 percent

blackjack oak. ?f-ee diameters 6 inches above groundline

ranged from 0.6 to 3.1 inches. Forty-six percent of the

sample trees were in the l-inch diameter class (0.6 to 1.5

inches), 49 percent were in the 2-inch class, and the

remaining 5 percent were in the 3-inch class.

At the end of the first and second growing seasons

after burning, the fate of each sample tree was recorded

by a number:

1 =Dead, with no sprouts.

2=Suffering from complete top-kill. All aboveground

parts dead. Sprouts only from roots or root collar.

3=Suffering from top-kill, but with sprouts along

mainstem or branches.

4=Partial crown survival, with or without sprouts.

5 =No apparent effect.

A numerical value for overall impact of fire in each

plot was obtained by averaging the above values for all

sample trees in a plot.

The following information was also obtained for each

sample tree:

1. Percent age of live crown reduction (excluding

sprouts), based on preburn crown, estimated to the

nearest 10 percent.

2. Number and average length of sprouts originating

from roots or root collar.

Before each burn, surface organic litter was sampled

to determine fuel load. Five 0.96 ft2 sample plots were

randomly located in each 0.15-acre net plot. The organic

layers in these sample plots were collected, ovendried at

80 “F, and weighed. All living green plant material in each

sample plot was also collected, dried, and weighed. After

each burn, the residual organic litter in five randomly

distributed 0.96 ft2 sample plots in each net plot was

collected, ovendried, and weighed. Fuel consumption

was estimated as the difference between preburn and

postburn weight. In 1980, preburn fuel sampling was

conducted in blocks 1 and 2 on March 11,14, a,“d 25 (for

treatment 1 plots, treatment 2 plots, and treatment 3

plots respectively), and postburn sampling was conducted on March 18, March 25, and April 21. Preburn

sampling dates in 1981 for blocks 3 and 4 were March 10,

March 19, and April 9; postburn sampling dates for

blocks 3 and 4 were March 24, April 8, and May 4 for

treatments 1, 2, and 3 respectively.

In 1980, the prescribed phenological stages were observed on March 9, March 18, and April 10, and the

block-l and block-2 plots were burned on March 11,

March 19, and April 16. In 1981, the three phenological

stages were observed on March 16, March 30, and April

20. Burn dates were March 23, April 2, and April 29 for

block 3 and May 1 for block 4. Burning conditions for

each plot were documented. Fireline intensity was estimated from average observed flame lengths using

relationships reported by Nelson (1980).

An analysis of variance was used to determine the

significance of the effects of burning treatment on

recorded study variables. Each year’s results were

analyzed separately. The analysis of variance was of the

form:

Source Df

Block

Treatment

Error

lbtal

1

2

14

17

Duncan’s multiple range test was used to separate treatment means when treatment effects were significant.

RESULTS

Summer Burns

HLU&V~~~ Damage.-The first summer fire was very

effective in destroying the live crowns of upland

hardwoods. Dogwoods suffered an average defoliation of

99 percent, while oaks and blackgums had defoliation

averages of 89 and 91 percent, respectively.

Following the second summer fire (1978), 25 percent

of the upland hardwoods had been completely killed, and

an additional 15 percent had suffered complete top-kill

but had sprouted (table 2). Complete kill ranged from 20

percent for dogwoods to 32 percent for blackgums.

Seventy-nine percent of upland-hardwood mortality occurred after the second fire, mostly among trees with

complete top-kill from the first fire. It appears that a

second fire is needed to “finish off” trees with complete

top-kill from an earlier fire and that a low-intensity burn

is adequate for this purpose. Surviving hardwoods had

damaged crowns. By May of 1979, average crown

3
Table 2.-Fire damage to hardwoods following two summer fires

First fire Second fire

Complete Complete Crown

Site and species Tkees Mean d.b.h. kill Top-kill kill Top-kill recovety’

Number Inches _______________________ - ________ percent _____________ - _________________

Upland

Dogwood 89 2.4 0 2 1 20 18 46

Oaks 75 3.2 9 20 20 1 1 53

Blackgum 19 2.5 1 6 2 1 1 6 16 47

Persimmon 4 3.2 0 2 5 25 25 50

Streambottom

Titi 52 1.9 29 58 2 1 44 3

Red maple 17 1.6 0 100 53 47 0

Gallberry 1 1 1.2 0 100 36 64 0

Sweetbay 3 6.8 100 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Sweetleaf 4 2.2 0 100 0 100 0

Cherry 3 0.7 0 100 100 . . . . . . . . .

*Percentage of preburn live crown,

recovery (sprouts excluded), ranged from 46 percent for

dogwoods to 53 percent for the oaks as a group. Unless

burning continues, however, damaged hardwoods will

recover and outgrow susceptibility to fire-kill.

Streambottom hardwoods were much more susceptible to fire-kill than the upland hardwoods. Fifty percent

of all streambottom hardwoods were killed outright, and

an additional 47 percent suffered from complete top-kill.

Again, most of the trees killed by the second fire had

suffered from complete top-kill after the first fire.

Percentage of upland hardwoods killed, suffering

from complete top-kill, or showing at least partial crown

recovery following two successive summer burns, by

diameter class, are given in table 3. Mortality and damage

declined as tree diameter increased; crown recovery increased with increasing tree diameter.

The degree of crown reduction persisting to the year

following the second summer burn was associated,

through regression analyses, with variables such as

species or species group, tree d.b.h., and densities (basal

areas) for pines, hardwoods, and the stand as a whole at

each sample point. Crown reduction was strongly associated with d.b.h., as expected. This effect was greatest

for blackgums and least for streambottom species as a

group. Increases in pine density were associated with

significantly increased crown-kill in the oaks and streambottom species, but not in dogwoods or blackgums. Increases in hardwood density were associated with

significantly reduced crown-kill in dogwoods, while increases in total stand density were associated with significantly reduced crown-kill in blackgums. Hardwood

leaf litter fuels burn with difficulty, if at all, under conditions in which other fuels burn very well (Lotti and others

1960). Dogwood leaf litter burns very poorly, and it

seems clear that heavy leaf litter in dogwood thickets

helps protect dogwood stems from surface fires. Longleaf

pine needle litter, on the other hand, creates more intense fires than oak leaf litter (Williamson and Black

1981) and other surface fuels, and this may explain the

increasing damage to oaks and streambottom hardwoods

with increasing density of pine overstory.

Pine Damage.-Summer burns killed both small and

large longleaf pines. Fifty-three percent of all pines in the

l-inch d.b.h. class and 28 percent of those in the ‘L-inch

d.b.h. class were killed by the first burn (table 4). Neither

Table 4.-Grown scorch and mortality ofpines after summer bums

Average crown scorch

Table 3.-Fate of upland hardwoods, by diameter class

Diameter class Killed Top-killed Crown recovery

Inches ________________________ percent ________-_______.-. _._-.--.-

1 58 22 20

2 1 5 20 65

3 13 6 8 1

4 7 7 86

L =5 4 0 96

D.b.h. class Trees 1st fire 2nd. fire mortality

Inches Number __________...________ Percent______..._________.---

1 162 81 10 53

2 106 43 5 28

3 43 18 2 5

4 22 13 0 5

5-6 14 14 0 0

7-9 18 1 1 1 0

10-12 22 10 1 0

13-15 55 4 0 0

16-18 77 7 0 12

19-21 30 8 0 13

22+ 8 3 0 25

4
burn killed any pines in the 5- to B-inch d.b.h. classes.

However, 13 percent of the pines larger than 15.5 inches

in d.b.h. were killed, and 80 percent of this mortality

resulted from the first burn. Pine mortality amounted to

8 percent of all sawlog-size trees (those with d.b.h. B9.5

inches). This is much higher than long-term mortality

rates observed for a number of mature longleaf pine

stands distributed throughout the Southeastern United

States, which ranged from 0 to 2.6 percent and averaged

0.9 percent annually (Boyer 1979). Lightning, a major

cause of mortality for large longleaf pines, was not a

factor during this study. The first summer fire was much

more intense than the second and resulted in greater

crown scorch (table 4). Even so, for all the larger pines

(d.b.h. >12.5 inches), crown scorch averaged less than 10

percent in the first fire and did not occur in the second.

L. E. Chaiken (Langdon 1971) observed that summer

burns in stands of mature loblolly pines sometimes

resulted in cambial kill at the groundline, where the bark

becomes extremely thin as it joins the roots. Accumulations of dead bark and needle litter at this vulnerable

point might possibly fuel fires hot enough to kill large

trees.

Spring Burns

The Fires.-Fuel loads (dry weight) averaged about

5,200 pounds per acre for the two blocks burned in 1980

and 6,600 pounds per acre for the two blocks burned in

1981. The 1980 burn was preceded by a prescribed burn

in the winter of 1978, and the 1981 burn was preceded by

a prescribed burn in the spring of 1979. Fuel composition

was predominantly cured and green herbaceous vegetation. The proportion of green to cured fuel increased

with later burning dates. Estimated preburn fuel weights,

proportion of green fuel, amount of fuel consumed by the

fire, and average fireline intensity are given in table 5 for

Table 5.-Fuel weights and fire intensity for each treatment and vear

&rrn date Total fuel

1980 Burns

3111

3119

4116

1981 Burns

3123

4102

4129

Poundslacre

4784 17 30 171

6933 19 67 170

3893 23 64 110’

7010 6 14 112

8777 14 18 132

4152 29 1 1 29

Fuel Fireline

Green fuel consumed intensity

- ---..____ percent _______-___ BTLJift/sec

Table 6.-Effect fire treatments on hardwood fate, crown reductioq

and sprouting

Crown

Treatment Fate * reduction*

Mean sprout

Sprouts/stem length

Percent Number Inches

1980 Burns

First year after treatment

1 3.7a* 40a 5a 1Oa

2 3.4a 47a 6a 10a

3 3.3a 53a 5a 9a

Second year after treatment

1 4.0a 32a 6a 18a

2 3.7a 40a 6a 20a

3 3.6a 44a 5a 18a

1981 Burns

First year after treatment

1 4.5a 9c lb 3b

2 2.5c 82a 5a 21a

3 3.9b 34b 2b 4b

Second year after treatment

1 4.9a 4c lb 4b

2 2.6~ 77a 5a 29a

3 4.3b 24b 2b 6b

*Average degree of damage scale, from l=dead to 5=no effect.

‘As percent age of preburn live crown.

‘Treatment means in the same column (by year of burn and

postburn remeasurement) followed by same letter are not significantly

different at the 0.05 level.

each treatment each year. All plots were burned with

headfires.

Hardwood Damage.-Timing of the 1980 spring

burns did not significantly affect fate of hardwoods (relative damage), average crown reduction, or number or size

of sprouts at the end of the first or second growing season

after burning (table 6). Crown reduction for all three

treatments averaged 47 percent at the end of the first year

after burning and fell to 39 percent at the end of the

second. Fires completely killed only 5 of the 537 sample

trees burned in 1980. Three of the five dead trees were in

treatment 3. Fires resulted in the top-kill of 131 more

trees, all of which sprouted from the roots or the rootcollar. Fifty-three of these trees were in treatment 3 plots

and 51 in treatment 2 plots.

Timing of the 1981 spring burns significantly affected

fate, or average degree of injury, crown reduction, and

sprouting (table 6). Treatment 2 resulted in a higher

average crown reduction, 82 percent, than either of the

other two treatments, or any of the 1980 treatments, and

also resulted in more and larger sprouts. Crown recovery

between 1 and 2 years after burning was slower in treatment 2 plots than in others. Treatment 3 produced the

lowest recorded fire intensity but still resulted in significantly greater hardwood damage than treatment 1.

Only 12 of the 526 sample hardwoods burned in 1981

were killed outright, 9 by treatment 2, and 3 by treatment

3. An additional 144 trees suffered complete top-kill but

5
sprouted. Of these, 117 were in treatment 2 plots and 23

were in treatment 3 plots.

This study suggests that the burn at full leaf might

have’ been more effective than either of the earlier two

burns-and would certainly have been more effective

than the first burn-if fire intensities had been equal.

The third 1980 burn resulted in somewhat greater crown

reduction than the first two 1980 burns, even though its

estimated fire intensity was lower. The third burn in 1981

was significantly more effective than the first 1981 burn,

even though the third burn had the lowest estimated fire

intensity.

Species Susceptibility to Fire.-Upland hardwood

species differed in their susceptibility to fire damage.

Fate, percent age of crown reduction, and mean diameter

(at 6 inches above groundline) for these species are given

in table 7.

The species most resistant to fire injurywere bluejack

and turkey oak, common associates of longleaf pine on

dry, sandy upland sites historically subject to frequent

fires.

CONCLUSIONS

A single hot summer fire did not cause much upland

hardwood mortality. A second summer fire 2 years later

resulted in most of the mortality in both upland and

bottomland hardwoods, even though it was not a very

intense fire. Mortality occurred mainly among trees that

had suffered complete top-kill after the first fire. Among

upland hardwoods, only these in the l-inch d.b.h. class

suffered over 50-percent mortality, and damage to

hardwoods in the 4-inch and larger d.b.h. classes was

negligible. The presence of pine needle-litter fuels was

apparently conducive to increased fire damage to some

upland hardwood species, as degree of damage increased

with increasing pine density. Results of other studies

suggest that a second summer fire 1 year rather than 2

years after the first might have caused greater damage, as

the trees would not have had a full growing season to

recover from the first burn.

Prescribed summer fires have the potential of causing

unacceptable levels of damage to longleaf pines. In the

Table I.--Species susceptibility to fire damage

Soecies Fate* Crown reduction Mean diameter’

Water oak 3.0

Dogwood 3.5

Red oak 3.5

Post oak 3.6

Bluejack oak 3.9

Percent Inches

68 1.6

52 1.5

5 1 1.8

45 1.5

29 1.7

Brkey oak 4.1 23 1.8

*Average degree of damage scale, from 1 =dead to 5=no effect.

‘Measured 6 inches above groundline.

present case, a single hot summer fire was more destructive to pines than to hardwoods. Mortality among pines

in the l- through 4-inch d.b.h. classes following the single

summer burn was as great as mortality among hardwoods

of the same size following two summer fires. In these size

classes, all pine mortality resulted from the first fire.

While there was no mortality among pines in d.b.h. classes from 5 to 15 inches, significant mortality occurred

among pines in the 16-inch and larger d.b.h. classes.

Eighty percent of this mortality also followed the first

burn.

No conclusive evidence was obtained from this study

that the timing of spring burns, based on phenological

stage of development of target species, had a significant

impact on the degree of hardwood crown reduction. Mortality was minimal, as it usually is, with just one burn. Fire

intensities differed among the three burning treatments

but could not be accurately estimated. It may be much

more important to burn when conditions will support hot

fires, with phenological stage of hardwood development

being only a secondary consideration.

The results reported here suggest that if all other

factors are equal, hardwood damage in terms of complete

top-kill or crown reduction may increase with later burning dates in the spring. Spring burns, especially when

conducted later in the spring, may be effective chiefly

because they result in depletion of hardwood root reserves and thus increase the effectiveness of subsequent

growing season fires. This possibility should be investigated further.

LITERATURE CITED

Boyer, William D. 1979. Mortality among seed trees in

longleaf pine shelterwood stand. Southern Journal of

Applied Forestry. 3(4): 165-167.

Brender, Ernst V; Cooper, Robert W. 1968. Prescribed

burning in Georgia’s Piedmont loblolly pine stands.

Journal of Forestry. 66(l): 31-36.

Chaiken, L.E. 1952. Annual summer fires kill hardwood

root stocks. Res. Note SE-19. Asheville, NC: U.S.

Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station. 1 p.

Chen, Ming-Yih; Hodgkins, Earl J.; Watson, W.J. 1975.

Prescribed burning for improving pine production and

wildlife habitat in the hilly coastal plain of Alabama.

Bull. 473. Auburn University, AL: Alabama Agricultural Experiment Station. 19 p.

Ferguson, Edwin R. 1961. Effects of prescribed fires on

understory stems in pine-hardwood stands of Texas.

Journal of Forestry. 59(4): 356-359.

Grano, Charles X. 1970. Eradicating understory

hardwoods by repeated prescribed burning. Res. Pap.

SO-56. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 11 p.

6
Grelen, Harold E. 1975. Vegetative response to twelve

years of seasonal burning on a Louisiana longleaf pine

site. Res. Note SO-192. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest

Experiment Station. 4 p.

Grelen, Harold E. 1983. May burning favors survival and

early height growth of longleaf pine seedlings. Southern

Journal of Applied Forestry. 7(l): 16-20.

Harrington, TA.; Stephenson, G.K. 1955. Repeat burns

reduce small stems in Texas Big Thicket. Journal of

Forestry. 53(11): 847.

Hodgkins, Earl J. 1958. Effects of fire on undergrowth

vegetation in upland southern pine forests. Ecology.

39(l): 34-46.

Langdon, 0. Gordon. 1971. Effects of prescribed burning

on timber species in the southeastern Coastal Plain. In:

Proceedings, prescribed burning symposium; 1971

April 14-16; Charleston, SC. Asheville, NC: U.S.

Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station: 34-45.

Lotti, Thomas; Klawitter, Ralph A.; LeGrand, W.F? 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 p.

Maple, William R. 1977. Spring burn aids longleaf pine

seedling height growth. Res. Note SO-228. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station. 2 p.

Nelson, Ralph M., Jr. 1980. Flame characteristics for fires

in southern fuels. Res. Pap. SE-205. Asheville, NC: U.S.

Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station; 14 p.

Riebold, R. J. 1955. Summer burns for hardwood control

in loblolly pine. Fire Control Notes. Washington,DC:

U.S. Department of Agriculture, Forest Service. 16(l):

34-36.

Trousdell, Kenneth B. 1970. Disking and prescribed

burning: sixth-year residual effects on loblolly pine and

competing vegetation. Res. Note SE-133. Asheville,

NC: U.S. Department of Agriculture, Forest Service,

Southeastern Forest Experiment Station. 6 p.

Waldrop, Thomas A.; Van Lear, David H.; Lloyd, E

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 p.

Williamson, G. Bruce; Black, Edwin M. 1981. High

temperature of forest fires under pines as a selective

advantage over oaks. Nature. 293: 643-644.

Wood, Frank W. 1955. Control of woody weeds: some

physiological aspects. Oct. Pap. 143. New Orleans, LA:

U.S. Department of Agriculture, Forest Service,

Southern Forest Experiment Station. 50 p.
Persons of any race, color, national origin, sex, age, religion, or with any

handicapping condition are welcome to use and enjoy all facilities, programs, and

services of the USDA. Discrimination in any form is strictly against agency policy,

and should be reported to the Secretary of Agriculture, Washington, DC 20250.
Boyer, William D. 1990. Growing season burns for control of hardwoods in

longleaf pine stands. Res. Pap. SO-256. New Orleans, LA: U.S. Department of Agriculture, Forest Service, Southern Forest Experiment Station.

7P.

Summer fires in existing longleaf pine stands carry undue risk of pine

mortality. One summer fire caused as much mortality among pines in the

l- through 4-inch d.b.h. classes as two successive summer fires among

hardwoods of the same size. Mortality among mature pines was also

excessive. Hardwood top-kill following a spring fire seemed affected more

by fire intensity than by timing of the fire.

Keywords: Hardwood control, Pinus palustris Mill., prescribed fire.