FIRE EFFECTS
SPECIES: Pinus taeda | Loblolly Pine 



IMMEDIATE FIRE EFFECT ON PLANT : 
Loblolly pines less than 5 feet (1.5 m) tall are usually killed by light
fire [37,59].  Saplings up to 2 inches (5 cm) in diameter are usually
killed by moderate-severity fire, and trees up to 4 inches (10 cm) in
diameter are usually killed by high-severity fire.  Trees greater than 4
inches d.b.h. are rarely killed by moderate-severity fire [17].
Shade-grown saplings are susceptible to mortality from light fire
because of retarded bark and height growth [59].  In general, suppressed
small trees are more susceptible to fire damage and mortality than are
vigorous, large trees [1,39,45,54].  Summer fires kill more trees than
do winter fires [22].

Crown damage:  Crown damage generally results in more fatality than
basal damage does [17,22,54,61].  Following a low-severity winter fire
in a 4-year-old stand that averaged 7.3 feet (2.2 m) in height,
mortality was low for seedlings that had less than 80 percent crown
scorch [61].  Older trees are not very susceptible to mortality from
crown scorch.  Only a small percentage of severely crown-scorched trees
greater than 8 inches (20 cm) in d.b.h. were killed by a high-severity
hot spot in a prescribed summer fire in Virginia [1].

Mortality is greatly increased if needles burn.  If there is 25 percent
or more needle consumption in loblolly pine younger than 9 years old ,
75 percent mortality can be expected [22].  If the buds are killed, the
tree will not recover [59].  Crown scorch is more serious in a summer
fire because there are no dormant vegetative buds [41].

Loblolly pine needles were killed instantly when immersed in water at
147 degrees Fahrenheit (64 deg C) but survived 13 minutes at 126 degrees
Fahrenheit (52 deg C) [10].

Roots are normally insulated by mineral soil, but if they are exposed
and burned, the tree can die [59].  Kayll [32] reported that heat
tolerance of seedling roots varied, but exposure to 129 degrees
Fahrenheit (54 deg C) for 5 minutes, 122 degrees F (50 deg C) for 30
minutes, or 118 degrees F (48 deg C) for 2 hours was generally lethal.

If a crown fire occurs, seeds inside cones can be destroyed.  In one
study [59], only 16 percent of seeds were viable in top-killed trees
compared to 70 percent in uninjured trees.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
A low-severity, slow-moving fire in thick litter can cause severe basal
scorch.  Such a fire in east Texas burned deep depressions in the bark
of merchantable-sized loblolly pine.  Ten percent of the stand died
directly from the fire or from insect infestation of fire wounds [24].


PLANT RESPONSE TO FIRE : 
The growth of young loblolly pine can be reduced by fire damage.
Lightly scorched 4-year-old seedlings showed a slight loss in height
growth but no loss in diameter growth [61].  In another study [39],
19-year-old loblolly pine showed no growth loss when lightly scorched,
and only completely scorched trees continued to have growth loss 3 years
after the fire [39].

Loblolly pine seeds will germinate on soil exposed by fire [3].  

If crown scorch occurs in the winter, foliage is usually replaced by
surviving dormant vegetative buds [41].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Contrary to other findings, growth after a prescribed fire in Louisiana
was greater in trees with one-third or less crown scorch than in trees
with no crown scorch [54].  In effect, the fire pruned the lower
branches, which have low photosynthetic efficiency.

Loblolly pine growth may be more sensitive to the amount of soil
moisture available early in the growing season than it is to fire damage
[41].


FIRE MANAGEMENT CONSIDERATIONS : 
Prescribed fire is used in loblolly pine stands for seedbed preparation,
hardwood control, fuel reduction, and thinning.  Unless thinning of
seedlings is desired, stands should not be burned before they are large
enough to withstand injury.  To avoid crown scorch, loblolly pine should
be 10 to 15 years old, 15 to 20 feet (4.6-6.1 m) tall, and have a bark
thickness of 0.3 to 0.4 inch (0.8-1.0 cm) before being burned for the
first time [2,7,41,37,59,65].  To avoid mortality but not crown scorch,
trees smaller than 8 feet (2.4 m) tall or less than 2 inches (5 cm) in
diameter at groundline should not be burned [11].  The first fire is
difficult because of excess fuel build-up and danger to young pines.  A
backfire should be used in cool weather and high moisture conditions.

Hardwood control:  Hardwoods smaller than 4 inches (10 cm) in diameter
can usually be controlled by frequent fire [62].  Hardwood recovery
takes 5 to 10 years, depending on the site quality.  Using prescribed
fire every 5 years or when 25 percent of the largest hardwood stems are
approaching 1 inch (2.5 cm) in diameter is recommended [41,42].

A single winter fire is effective at controlling 1-inch-diameter (2.5
cm) hardwoods [41]; periodic winter fires can control hardwoods up to 2
inches (5 cm) in diameter; and a summer fire can control hardwoods up to
4 inches (10 cm) in diameter [59].  Although prescribed burns are
usually conducted during winter to avoid injury to loblolly pine, summer
burning is a more effective control of hardwood competition [23].
Twenty years of annual summer burning completely eradicated hardwoods
from a loblolly pine forest in South Carolina [62,63].  However, a
series of annual winter fires will not eradicate hardwoods because root
stocks are not killed.  Three annual summer fires at mid-rotation,
followed by periodic winter fires may be an effective means of hardwood
control [42].  Infrequent low-severity surface fires may speed up
succession to hardwoods by increasing the number of hardwood sprouts
[14].

Seedbed preparation:  A low-severity summer prescribed fire,
approximately 1 month before seedfall, is the most effective seedbed
preparation [19,41,42,57].  If only a winter fire is used, hardwoods
have an entire growing season before loblolly pine seedfall [41,57].  A
winter fire 1 to 2 years prior to a summer fire is suggested to reduce
fuel buildup.  A winter fire, followed by three annual summer fires just
before harvest, was very effective [52].  Brown and burn treatments have
also proven effective [6].

Thinning:  Prescribed burning has been used successfully to thin young
loblolly pine stands.  However, the forest manager risks damaging the
entire stand and reducing the growth rate.  A prescribed fire in South
Carolina resulted in a 58 percent reduction in stems per acre and near 0
percent mortality in 1 inch (2.5 cm) diameter and larger saplings [61].
Thinning with fire should only be done in stands with a wide range of
diameters [45].

Disease and insects:  In the Coastal Plain, prescribed burning before
and after thinning reduced infection by root rot (Heterobasidion
annosum).  The fire destroyed litter which is associated with sporophore
development of H. annosum.  A fungal competitor (Trichloderma spp.)
increased in the soil after burning and may have contributed to the
reduced infection [25].

Fire wounds 4 to 6 inches (10-15 cm) wide and larger can result in cull
from fungi, insect action, or high amounts of resin [26].  The black
turpentine beetle (Dendroctonus terebrans) attacked trees with fire
wounds in east Texas [24].

Nutrients:  It is unclear whether prescribed fire on loblolly pine sites
will increase or decrease the available nitrogen.  Fire volatilizes
nitrogen in the soil, and repeated burning on infertile sites may limit
productivity [33].  However, decomposition of burned material increases
the available nitrogen content of soil.  Consequently, light prescribed
fire may be a low-cost alternative to fertilizer [50,64].

Related categories for Species: Pinus taeda | Loblolly Pine