Prescribed fire is the best tool foresters have to regenerate oak forests. Periodic fire shaped the composition of the forest prior to fire exclusion over the last century. We can see that oak-dominated forest is now being overtaken by more shade-tolerant species, most of which are of lesser value to wildlife and not as valuable as shade intolerant species like oak and cherry.
Fire favors oak because it invests the first year of growth into its root system. The taproot can resprout vigorously after the tree is top-killed by a fire, while species such as maple and poplar do not. Oak doese not compete well with other species that grow quickly the first year and overtake them.
Fire can be used to create new growth that is palatable for deer and regenerate blueberry – new blueberry bushes bear far more fruit than old, decrepit bushes. When Mountain Laurel gets so thick, nothing else can grow and it is not proiving good cover, it should be burned and will resprout vigirously. The laurel/blueberry ecotype is fire adapted – it uses fire to out-compete other plants and is the first to show up after a fire. Sassafras is another species that responds well to a burn, but not as desireable as a wildlife plant.
Repeated fires every few years on rotation on your land can keep new vegetation constantly springing up and increase plant diversity tremendously which, in turn, improves the browse availability and bedding cover for deer.
I have included alink to a USFS article that is a very good one for information on fire in oak forests and talks about oak savanna: http://www.fs.fed.us/ne/newtown_square/publications/technical_reports/pdfs/2000/274%20papers/vanlear274.pdf
When I was in California working, I wandered through a lot of oak savanna ecotype out there. It was very beautiful and full of wildlife. Deer layed in the shade of oaks and quail were everywhere. I would like to try creating a grassland/oak habitat here in PA. If anyone would like to try it on their land, let me know.
There is a new video on my Youtube channel that I took of a fire site that was burned a month ago.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
Abstract
Fire is widely recognized as having been a major force
shaping the character of eastern hardwood forests.
Exclusion of periodic surface fires from mixed hardwood
stands for over 70 years has contributed to the gradual
succession of shade-tolerant species into the understory and
midstory of these stands. Following major disturbance to the
overstory, these shade-tolerant species or pioneer shade-
intolerant species are able to out-compete oak regeneration
and dominate the next stand. Because of fire exclusion for
many decades, regeneration of oak-dominated stands has
been a major silvicultural problem. Recent research indicates
that a shelterwood-burn technique, which mimics the natural
disturbance regime that historically favored oaks, can be
used on productive upland sites to enhance the competitive
position of oaks in the advance regeneration pool. This
paper presents silvicultural guidelines for applying the
technique and discusses several options to meet the
management objectives of different landowners.
Introduction
Regenerating oaks on good quality sites has been a difficult
problem throughout the eastern United States for many
decades. Oak regeneration failures have generally been
attributed to either poor initial establishment of oak seedlings
or the slow juvenile growth of oak advance regeneration
when it is present (Abrams 1992, Lorimer 1993, Loftis and
McGee 1993). In the dense shade of mature mixed-
hardwood stands, oak seedlings and seedling sprouts do not
develop into competitive stems. Overstory removal by either
partial or complete cuttings releases well-established shade
tolerant regeneration and facilitates establishment of fast-
growing shade intolerant seedlings. Subsequent stand
development is to a mixed mesophytic forest with oak as a
minor component or altogether absent (McGee 1979;
Abrams 1992; Lorimer et al. 1994). This successional trend
is a relatively recent phenomena, developing in the past 75
years, and is tied to the exclusion of fire from eastern
hardwood forests (Little 1974; Van Lear and Johnson 1983;
Lorimer 1993).
Fire research in hardwoods has lagged far behind that in
pines, although several studies suggested that oaks were
ecologically adapted to frequent burning (Swan 1970,
Niering et al. 1970, Thor and Nichols 1974, Waldrop et al.
1987, Augspurger et al. 1987). All of these studies noted that
oaks resisted root kill by fire to a greater extent than their
competitors. Numerous authors, based on literature reviews,
accounts of early explorers and settlers, observed vegetative
patterns and responses, and other evidence, have
concluded that fire played an important role in the
development and maintenance of oak forests in the eastern
United States (Little 1974; Van Lear and Johnson 1983;
Crow 1988; Van Lear and Waldrop 1989; Williams 1989;
Abrams 1992).
In this paper, we will discuss the use of fire as a silvicultural
tool to regenerate oaks. Particular emphasis is placed on a
new regeneration method that utilizes partial harvesting
followed by prescribed fire.
Interactions Between Fire and Oaks
With the arrival of Indians in the eastern United States as
early as 12,000 years ago, fire became a more frequent
disturbance that shaped forest composition and structure
(Pyne 1982; Williams 1989). Indians used fire for many
reasons, including hunting, facilitating travel, stimulating
berry production, clearing land for agricultural crops, and as
a defense against enemies. The frequent, widespread use of
fire by Indians and the European settlers that followed them
created an environment favorable for the establishment and
maintenance of oaks. In the early 1900s, fire-suppression
efforts of the U.S. Forest Service and state forestry
commissions began to be successful in reducing the
frequency, extent, and influence of this powerful
environmental force. The forest changed dramatically as fire
was largely removed from the Eastern forest ecosystem.
Shade-tolerant and fire-intolerant species began to dominate
forest understories, overstory densities increased, and fire-
sensitive species moved upslope from moist coves to xeric
slopes.
Frequent burning creates environments that favor oaks on
better-quality sites. Surface fires remove much of the mid-
and understory strata in mature mixed hardwood stands,
reducing shading. Spring fires are especially effective
(Barnes and Van Lear 1998). Fire reduces the thickness of
the forest floor, preparing a favorable seedbed for caching of
acorns by squirrels and jays by (Darley-Hill and Johnson
1981, Galford et al. 1989). Fire reduces surface soil moisture
which discourages establishment of mesophytic species
(Barnes and Van Lear 1998) and may control insect
predators of acorns and new seedlings (Galford et al. 1989).
The presence of oaks encourage surface fires because of
the nature of their litter. An oak stand adds about 4.5 Mgha
–
1
yr
-1
of leaf litter to the forest floor (Loomis 1975). This litter
remains curly, creating a porous fuelbed for surface fires.
Unlike leaf litter of mesophytic species which forms a flat mat
upon compaction and decays rapidly, oak leaf litter
undergoes little decay during the winter. In regions where
snowpacks are heavy, oak litter recurls after snowmelt, once
Using Prescribed Fire to Regenerate Oaks
D.H. Van Lear
1
,
P.H. Brose
2
,
and
P.D. Keyser
3
1
Bowen Professor of Forestry, Department of Forest Resources,
Clemson University, Clemson, SC 29634-1003
2
Research Forester, USDA Forest Service, Warren, PA 16365
3
Wildlife Biologist, Westvaco Corporation, Rupert, WV 25984
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
again creating a porous fuelbed capable of carrying a
surface fire during the spring fire season (Lorimer 1989).
Because of the complexity of forest ecosystems, effects of
fire in hardwood stands vary. Fires in stands of mixed
composition have occasionally created oak-dominated
stands (Roth and Hepting 1943; Carvell and Maxey 1969;
Ward and Stephens 1989), probably because intense fires
controlled competition and stimulated rapid growth of oak
reproduction (Johnson et al. 1989; Lorimer 1989). In other
cases, species composition in young stands has been
altered very little by fire (Johnson 1974; McGee 1979;
Waldrop et al. 1985; Augspurger et al. 1987).
Effects of fire vary because of differences in season of
burning and fire intensity. Season of burning affects
physiological condition of the plant and the ability of species
to resprout. Hardwoods have the greatest ability to sprout
when carbohydrate storage in their roots is high, i.e., in the
dormant season. In the growing season, root reserves are
lower and sprouting vigor is less. Fire intensity is critical
because certain species, such as the oaks, can survive
higher intensity fires than their competitors (Brose and Van
Lear 1998) because their sprouts originate deeper in the soil
than those of their competitors (Hane 1999).
Using Fire to Encourage
Oak Regeneration
Understory Burning
Fire exclusion for most of the past century has altered stand
structure and composition of eastern hardwood stands.
Shade-tolerant and fire-intolerant species have gradually
encroached into the understory of oak-dominated stands.
Now, in the absence of periodic fire, there is no growing
space for oak reproduction, which may or may not be
present in the advanced regeneration pool. Van Lear and
Watt (1993) developed a theoretical silvicultural prescription
to encourage oak regeneration by burning the understory of
mature mixed hardwood stands near the end of the rotation.
Barnes and Van Lear (1998) tested this hypothesis in the
Piedmont of South Carolina and found that one burn early in
the growing season when leaves were expanding was as
effective as three winter fires in reducing density of
understory and midstory stems (fig. 1). The number of oak
rootstocks in the regeneration layer was increased by
burning, root/shoot ratios of oaks were enhanced, and
competitive woody species decreased. There was little
visible damage to boles of overstory oaks from the fires,
especially in the larger size classes.
Although oak regeneration was increased by understory
burning, it remained small and generally ephemeral. It
appeared that burning would have to be continued for a
relatively long period, i.e., perhaps 10 years or so, before
sufficient oaks of competitive size would be present in the
advance regeneration. Such an approach is handicapped by
the expense and risks of multiple prescribed fires, making it
a rather unattractive option for landowners and managers.
Nevertheless, if no advance regeneration exists in a stand,
periodic understory burning may provide a means to
establish oak seedlings and seedling sprouts, which could
then be encouraged to begin vigorous growth by the
following technique.
Shelterwood Cutting Followed
by Prescribed Fire
The Shelterwood-Burn Method
Oak-dominated stands on better quality sites in the southern
Piedmont and mountains often have abundant but small and
non-competitive oak reproduction in the regeneration layer.
When such stands are harvested by either clearcutting or the
shelterwood method, oak reproduction cannot compete with
Figure 1.
—
Reduction of midstory/
understory densities following three
winter burns and one spring burn in
mixed hardwood stands in the South
Carolina Piedmont.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
rapidly growing shade-intolerant species and/or well-
established shade-tolerant species (Loftis 1983,
Abrams 1992, Schuler and Miller 1995).
A shelterwood-burn method (fig. 2) has recently been
developed in the Piedmont of the southeastern
United States to enhance the competitive position of
oak regeneration in such stands (Keyser et al. 1996;
Brose and Van Lear 1998; Brose et al. 1999a). This
method is based on the silvics and fire ecology of oak
and yellow-poplar regeneration and involves an initial
shelterwood harvest which removes roughly half of
the overstory basal area. All yellow-poplars are
removed in this first cut of the two-cut shelterwood
method, leaving the best dominant and codominant
oaks. Logging slash must be kept away from bases
of residual oaks by directional felling. This partial
harvest is followed by a 3- to 5-year waiting period,
after which a relatively hot growing-season
prescribed fire is run through the advance
regeneration.
Oak reproduction must be relatively vigorous and
free-to-grow to be competitive. We defined such oaks
as straight stems at least 1.3 m tall with no major
competitors within 3 m (Nix 1989). Oaks resist root
kill by fire better than yellow-poplar and other
competitors, especially as fire intensity increases (fig.
3) (Brose and Van Lear 1998). Density of free-to-
grow oaks exceeded 800 stems/ha and yellow-poplar
density was greatly reduced (up to 90%) in areas
burned in the spring with high intensity flames. In
contrast, winter burns provided little control of yellow-
poplar and, even with a high intensity fire, oaks
density did not reach 300 stems/ha. Summer fire
resulted in substantial numbers of free-to-grow oaks
in all fire intensity levels, but especially in the two
medium intensity levels. High intensity summer fires
killed many of the smaller oak seedlings while low
intensity summer fires failed to control competition.
Oak reproduction will not be uniform over the entire
burned area. If free-to-grow oaks exceed 370/ha and
60% or more of the stocking plots have at least one
free-to-grow oak, the stand can be considered regenerated
with the likelihood that oaks will be a dominant component of
the next stand. One burn may not be enough if oak
dominance is desired in the new stand. Decades of fire
exclusion have allowed oak competitors to become firmly
established. If more oaks are desired, additional fires may be
prescribed as dictated by leaf litter accumulation. We believe
that oak dominance of the advance regeneration will
continually increase with repetitive spring burning at about 2-
year intervals.
We believe that a shelterwood cut, rather than a clearcut, is
the essential first step in this technique. The shelterwood
continues to produce oak litter which creates the continuous
fine fuel bed necessary to carry the subsequent fire. If a
clearcut had been used, foliage from yellow-poplar, a poor
medium for carrying surface fires, would dominate the forest
floor. In addition, shading from the shelterwood prevents
yellow-poplar regeneration from growing so large during the
interval before burning that it could not be killed by fire (Hane
1999).
In the 3 to 5- year period following the initial cut, logging
slash settles and loses it
’
s foliage, minimizing the risk of bole
damage to residual trees caused by flareups in heavy fuels
(Brose and Van Lear 1998; Brose et al. 1999a). Although
yellow-poplar was removed in the initial shelterwood cut, its
seed remains viable in the duff for up to 10 years (McCarthy
1933). Most of this stored seed germinates during the
waiting period and those seedlings are killed in the
subsequent fire. The waiting period also allows residual
overstory trees to recover from the shock of the initial cut
before they will be stressed again by burning.
Figure 2.
—
Schematic diagram of the shelterwood-burn technique. A =
high quality oaks; B = hickories, poor quality oaks, and yellow-poplars; C
= American beech, flowering dogwood, and red maple; D = mixed
hardwood regeneration dominated by yellow-poplar; and E = mixed
hardwood regeneration dominated by oaks.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
Advantages of the
Shelterwood-burn Technique
The shelterwood-burn method is attractive to landowners
because the initial cut of the shelterwood method produces
immediate income. A small portion of the profit is then used
to pay for the prescribed burn. Careful planning, e.g.,
consider using skid trails for fire breaks, before timber
harvest can reduce later prescribed fire costs. Removal of
the shelterwood after burning is at least as profitable as the
initial cut because the best oaks were retained and some
probably increased in value during the intervening years
before final harvest.
If the landowner
’
s goal is to manage for wildlife, the
shelterwood-burn method can be used to sustain hard mast
production while providing a source of palatable browse
during the regeneration period. Landowners can maintain
indefinitely the classic structure of the shelterwood while
stockpiling oak regeneration with periodic burns (Brose et al.
1999b). Many upland game and non-game species utilize
the mast, browse, and cover in a regenerating shelterwood
(Brose et al. 1999b; Lanham et al. 2000). A note of caution
–
in areas where deer density is extremely high and early
successional habitat is relatively rare, the shelterwood-burn
method probably will not work because of over-browsing of
oak regeneration.
The shelterwood-burn system could be used to restore fire-
maintained ecosystems (Brose et al. 1999b). Frequent
growing season burns after the initial shelterwood cut would
gradually reduce woody regeneration (even the oaks) and
create a hardwood woodland or savannah, two habitats that
have become increasingly rare after decades of fire
exclusion (Buckner 1983; Pyne 1982; Van Lear and Waldrop
1989; Abrams 1992).
Research suggests that the shelterwood-burn technique may
be successful in other physiographic regions and on different
sites. Repeated burning in oak-pine communities on xeric
sites in the Cumberland Plateau reduced regeneration of red
maple and other non-oak species and promoted chestnut
oak regeneration (Arthur et al. 1998). On mesic sites in
Wisconsin, two spring burns reduced densities of sugar
maple and hophornbeam by 80%, while density of northern
red oak increased (Kruger 1992). Ward and Gluck (1999), in
Connecticut, observed that burning several years after a
shelterwood harvest favored oaks and reduced competition
from birch and shrubs. Hot fires in mountain laurel thickets in
the Northeastern United States that opened canopies, i.e., a
disturbance similar to a shelterwood harvest, allowed oak
reproduction to grow past the dense shrub layer (Moser et al.
1996).
Conclusions
Oak forests on good quality sites have been in decline in the
eastern United States for decades as more shade-tolerant
species gradually succeed oaks or shade-intolerant species
outgrew them after a major disturbance. Fire historically
played a major role in maintaining oak-dominated forests but
periodic surface fires have been excluded from these sites
for over 70 years.
Practical silvicultural prescriptions using fire for oak
regeneration have been lacking. Understory burning in
mature mixed hardwood stands creates environmental
conditions which should favor oak regeneration but
developing oak reproduction does not reach sufficient size to
be competitive when the overstory is removed.
A shelterwood-burn technique has recently been developed
which overcomes this major disadvantage. This technique
reduces the vigor of oaks
’
competitors, especially if growing
season burns of relatively high intensity are used, and
provides conditions (increased light and reduced growth of
competitors) which allow oak regeneration to vigorously
resprout following the subsequent burn. It mimics a
Figure 3.
—
Mortality (%) of hickory, oak, red maple,
and yellow-poplar advance regeneration as fire
intensity increases within spring prescribed burns
conducted in shelterwood stands.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
disturbance pattern (i.e., partial overstory disturbance
followed by fire) that has shaped the composition of eastern
forests for millennia. The shelterwood-burn method is also
economically attractive because the initial shelterwood cut
yields an immediate income and the prescribed burn is low
cost compared to alternative treatments.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
Abstract
Fire is widely recognized as having been a major force
shaping the character of eastern hardwood forests.
Exclusion of periodic surface fires from mixed hardwood
stands for over 70 years has contributed to the gradual
succession of shade-tolerant species into the understory and
midstory of these stands. Following major disturbance to the
overstory, these shade-tolerant species or pioneer shade-
intolerant species are able to out-compete oak regeneration
and dominate the next stand. Because of fire exclusion for
many decades, regeneration of oak-dominated stands has
been a major silvicultural problem. Recent research indicates
that a shelterwood-burn technique, which mimics the natural
disturbance regime that historically favored oaks, can be
used on productive upland sites to enhance the competitive
position of oaks in the advance regeneration pool. This
paper presents silvicultural guidelines for applying the
technique and discusses several options to meet the
management objectives of different landowners.
Introduction
Regenerating oaks on good quality sites has been a difficult
problem throughout the eastern United States for many
decades. Oak regeneration failures have generally been
attributed to either poor initial establishment of oak seedlings
or the slow juvenile growth of oak advance regeneration
when it is present (Abrams 1992, Lorimer 1993, Loftis and
McGee 1993). In the dense shade of mature mixed-
hardwood stands, oak seedlings and seedling sprouts do not
develop into competitive stems. Overstory removal by either
partial or complete cuttings releases well-established shade
tolerant regeneration and facilitates establishment of fast-
growing shade intolerant seedlings. Subsequent stand
development is to a mixed mesophytic forest with oak as a
minor component or altogether absent (McGee 1979;
Abrams 1992; Lorimer et al. 1994). This successional trend
is a relatively recent phenomena, developing in the past 75
years, and is tied to the exclusion of fire from eastern
hardwood forests (Little 1974; Van Lear and Johnson 1983;
Lorimer 1993).
Fire research in hardwoods has lagged far behind that in
pines, although several studies suggested that oaks were
ecologically adapted to frequent burning (Swan 1970,
Niering et al. 1970, Thor and Nichols 1974, Waldrop et al.
1987, Augspurger et al. 1987). All of these studies noted that
oaks resisted root kill by fire to a greater extent than their
competitors. Numerous authors, based on literature reviews,
accounts of early explorers and settlers, observed vegetative
patterns and responses, and other evidence, have
concluded that fire played an important role in the
development and maintenance of oak forests in the eastern
United States (Little 1974; Van Lear and Johnson 1983;
Crow 1988; Van Lear and Waldrop 1989; Williams 1989;
Abrams 1992).
In this paper, we will discuss the use of fire as a silvicultural
tool to regenerate oaks. Particular emphasis is placed on a
new regeneration method that utilizes partial harvesting
followed by prescribed fire.
Interactions Between Fire and Oaks
With the arrival of Indians in the eastern United States as
early as 12,000 years ago, fire became a more frequent
disturbance that shaped forest composition and structure
(Pyne 1982; Williams 1989). Indians used fire for many
reasons, including hunting, facilitating travel, stimulating
berry production, clearing land for agricultural crops, and as
a defense against enemies. The frequent, widespread use of
fire by Indians and the European settlers that followed them
created an environment favorable for the establishment and
maintenance of oaks. In the early 1900s, fire-suppression
efforts of the U.S. Forest Service and state forestry
commissions began to be successful in reducing the
frequency, extent, and influence of this powerful
environmental force. The forest changed dramatically as fire
was largely removed from the Eastern forest ecosystem.
Shade-tolerant and fire-intolerant species began to dominate
forest understories, overstory densities increased, and fire-
sensitive species moved upslope from moist coves to xeric
slopes.
Frequent burning creates environments that favor oaks on
better-quality sites. Surface fires remove much of the mid-
and understory strata in mature mixed hardwood stands,
reducing shading. Spring fires are especially effective
(Barnes and Van Lear 1998). Fire reduces the thickness of
the forest floor, preparing a favorable seedbed for caching of
acorns by squirrels and jays by (Darley-Hill and Johnson
1981, Galford et al. 1989). Fire reduces surface soil moisture
which discourages establishment of mesophytic species
(Barnes and Van Lear 1998) and may control insect
predators of acorns and new seedlings (Galford et al. 1989).
The presence of oaks encourage surface fires because of
the nature of their litter. An oak stand adds about 4.5 Mgha
–
1
yr
-1
of leaf litter to the forest floor (Loomis 1975). This litter
remains curly, creating a porous fuelbed for surface fires.
Unlike leaf litter of mesophytic species which forms a flat mat
upon compaction and decays rapidly, oak leaf litter
undergoes little decay during the winter. In regions where
snowpacks are heavy, oak litter recurls after snowmelt, once
Using Prescribed Fire to Regenerate Oaks
D.H. Van Lear
1
,
P.H. Brose
2
,
and
P.D. Keyser
3
1
Bowen Professor of Forestry, Department of Forest Resources,
Clemson University, Clemson, SC 29634-1003
2
Research Forester, USDA Forest Service, Warren, PA 16365
3
Wildlife Biologist, Westvaco Corporation, Rupert, WV 25984
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
again creating a porous fuelbed capable of carrying a
surface fire during the spring fire season (Lorimer 1989).
Because of the complexity of forest ecosystems, effects of
fire in hardwood stands vary. Fires in stands of mixed
composition have occasionally created oak-dominated
stands (Roth and Hepting 1943; Carvell and Maxey 1969;
Ward and Stephens 1989), probably because intense fires
controlled competition and stimulated rapid growth of oak
reproduction (Johnson et al. 1989; Lorimer 1989). In other
cases, species composition in young stands has been
altered very little by fire (Johnson 1974; McGee 1979;
Waldrop et al. 1985; Augspurger et al. 1987).
Effects of fire vary because of differences in season of
burning and fire intensity. Season of burning affects
physiological condition of the plant and the ability of species
to resprout. Hardwoods have the greatest ability to sprout
when carbohydrate storage in their roots is high, i.e., in the
dormant season. In the growing season, root reserves are
lower and sprouting vigor is less. Fire intensity is critical
because certain species, such as the oaks, can survive
higher intensity fires than their competitors (Brose and Van
Lear 1998) because their sprouts originate deeper in the soil
than those of their competitors (Hane 1999).
Using Fire to Encourage
Oak Regeneration
Understory Burning
Fire exclusion for most of the past century has altered stand
structure and composition of eastern hardwood stands.
Shade-tolerant and fire-intolerant species have gradually
encroached into the understory of oak-dominated stands.
Now, in the absence of periodic fire, there is no growing
space for oak reproduction, which may or may not be
present in the advanced regeneration pool. Van Lear and
Watt (1993) developed a theoretical silvicultural prescription
to encourage oak regeneration by burning the understory of
mature mixed hardwood stands near the end of the rotation.
Barnes and Van Lear (1998) tested this hypothesis in the
Piedmont of South Carolina and found that one burn early in
the growing season when leaves were expanding was as
effective as three winter fires in reducing density of
understory and midstory stems (fig. 1). The number of oak
rootstocks in the regeneration layer was increased by
burning, root/shoot ratios of oaks were enhanced, and
competitive woody species decreased. There was little
visible damage to boles of overstory oaks from the fires,
especially in the larger size classes.
Although oak regeneration was increased by understory
burning, it remained small and generally ephemeral. It
appeared that burning would have to be continued for a
relatively long period, i.e., perhaps 10 years or so, before
sufficient oaks of competitive size would be present in the
advance regeneration. Such an approach is handicapped by
the expense and risks of multiple prescribed fires, making it
a rather unattractive option for landowners and managers.
Nevertheless, if no advance regeneration exists in a stand,
periodic understory burning may provide a means to
establish oak seedlings and seedling sprouts, which could
then be encouraged to begin vigorous growth by the
following technique.
Shelterwood Cutting Followed
by Prescribed Fire
The Shelterwood-Burn Method
Oak-dominated stands on better quality sites in the southern
Piedmont and mountains often have abundant but small and
non-competitive oak reproduction in the regeneration layer.
When such stands are harvested by either clearcutting or the
shelterwood method, oak reproduction cannot compete with
Figure 1.
—
Reduction of midstory/
understory densities following three
winter burns and one spring burn in
mixed hardwood stands in the South
Carolina Piedmont.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
rapidly growing shade-intolerant species and/or well-
established shade-tolerant species (Loftis 1983,
Abrams 1992, Schuler and Miller 1995).
A shelterwood-burn method (fig. 2) has recently been
developed in the Piedmont of the southeastern
United States to enhance the competitive position of
oak regeneration in such stands (Keyser et al. 1996;
Brose and Van Lear 1998; Brose et al. 1999a). This
method is based on the silvics and fire ecology of oak
and yellow-poplar regeneration and involves an initial
shelterwood harvest which removes roughly half of
the overstory basal area. All yellow-poplars are
removed in this first cut of the two-cut shelterwood
method, leaving the best dominant and codominant
oaks. Logging slash must be kept away from bases
of residual oaks by directional felling. This partial
harvest is followed by a 3- to 5-year waiting period,
after which a relatively hot growing-season
prescribed fire is run through the advance
regeneration.
Oak reproduction must be relatively vigorous and
free-to-grow to be competitive. We defined such oaks
as straight stems at least 1.3 m tall with no major
competitors within 3 m (Nix 1989). Oaks resist root
kill by fire better than yellow-poplar and other
competitors, especially as fire intensity increases (fig.
3) (Brose and Van Lear 1998). Density of free-to-
grow oaks exceeded 800 stems/ha and yellow-poplar
density was greatly reduced (up to 90%) in areas
burned in the spring with high intensity flames. In
contrast, winter burns provided little control of yellow-
poplar and, even with a high intensity fire, oaks
density did not reach 300 stems/ha. Summer fire
resulted in substantial numbers of free-to-grow oaks
in all fire intensity levels, but especially in the two
medium intensity levels. High intensity summer fires
killed many of the smaller oak seedlings while low
intensity summer fires failed to control competition.
Oak reproduction will not be uniform over the entire
burned area. If free-to-grow oaks exceed 370/ha and
60% or more of the stocking plots have at least one
free-to-grow oak, the stand can be considered regenerated
with the likelihood that oaks will be a dominant component of
the next stand. One burn may not be enough if oak
dominance is desired in the new stand. Decades of fire
exclusion have allowed oak competitors to become firmly
established. If more oaks are desired, additional fires may be
prescribed as dictated by leaf litter accumulation. We believe
that oak dominance of the advance regeneration will
continually increase with repetitive spring burning at about 2-
year intervals.
We believe that a shelterwood cut, rather than a clearcut, is
the essential first step in this technique. The shelterwood
continues to produce oak litter which creates the continuous
fine fuel bed necessary to carry the subsequent fire. If a
clearcut had been used, foliage from yellow-poplar, a poor
medium for carrying surface fires, would dominate the forest
floor. In addition, shading from the shelterwood prevents
yellow-poplar regeneration from growing so large during the
interval before burning that it could not be killed by fire (Hane
1999).
In the 3 to 5- year period following the initial cut, logging
slash settles and loses it
’
s foliage, minimizing the risk of bole
damage to residual trees caused by flareups in heavy fuels
(Brose and Van Lear 1998; Brose et al. 1999a). Although
yellow-poplar was removed in the initial shelterwood cut, its
seed remains viable in the duff for up to 10 years (McCarthy
1933). Most of this stored seed germinates during the
waiting period and those seedlings are killed in the
subsequent fire. The waiting period also allows residual
overstory trees to recover from the shock of the initial cut
before they will be stressed again by burning.
Figure 2.
—
Schematic diagram of the shelterwood-burn technique. A =
high quality oaks; B = hickories, poor quality oaks, and yellow-poplars; C
= American beech, flowering dogwood, and red maple; D = mixed
hardwood regeneration dominated by yellow-poplar; and E = mixed
hardwood regeneration dominated by oaks.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
Advantages of the
Shelterwood-burn Technique
The shelterwood-burn method is attractive to landowners
because the initial cut of the shelterwood method produces
immediate income. A small portion of the profit is then used
to pay for the prescribed burn. Careful planning, e.g.,
consider using skid trails for fire breaks, before timber
harvest can reduce later prescribed fire costs. Removal of
the shelterwood after burning is at least as profitable as the
initial cut because the best oaks were retained and some
probably increased in value during the intervening years
before final harvest.
If the landowner
’
s goal is to manage for wildlife, the
shelterwood-burn method can be used to sustain hard mast
production while providing a source of palatable browse
during the regeneration period. Landowners can maintain
indefinitely the classic structure of the shelterwood while
stockpiling oak regeneration with periodic burns (Brose et al.
1999b). Many upland game and non-game species utilize
the mast, browse, and cover in a regenerating shelterwood
(Brose et al. 1999b; Lanham et al. 2000). A note of caution
–
in areas where deer density is extremely high and early
successional habitat is relatively rare, the shelterwood-burn
method probably will not work because of over-browsing of
oak regeneration.
The shelterwood-burn system could be used to restore fire-
maintained ecosystems (Brose et al. 1999b). Frequent
growing season burns after the initial shelterwood cut would
gradually reduce woody regeneration (even the oaks) and
create a hardwood woodland or savannah, two habitats that
have become increasingly rare after decades of fire
exclusion (Buckner 1983; Pyne 1982; Van Lear and Waldrop
1989; Abrams 1992).
Research suggests that the shelterwood-burn technique may
be successful in other physiographic regions and on different
sites. Repeated burning in oak-pine communities on xeric
sites in the Cumberland Plateau reduced regeneration of red
maple and other non-oak species and promoted chestnut
oak regeneration (Arthur et al. 1998). On mesic sites in
Wisconsin, two spring burns reduced densities of sugar
maple and hophornbeam by 80%, while density of northern
red oak increased (Kruger 1992). Ward and Gluck (1999), in
Connecticut, observed that burning several years after a
shelterwood harvest favored oaks and reduced competition
from birch and shrubs. Hot fires in mountain laurel thickets in
the Northeastern United States that opened canopies, i.e., a
disturbance similar to a shelterwood harvest, allowed oak
reproduction to grow past the dense shrub layer (Moser et al.
1996).
Conclusions
Oak forests on good quality sites have been in decline in the
eastern United States for decades as more shade-tolerant
species gradually succeed oaks or shade-intolerant species
outgrew them after a major disturbance. Fire historically
played a major role in maintaining oak-dominated forests but
periodic surface fires have been excluded from these sites
for over 70 years.
Practical silvicultural prescriptions using fire for oak
regeneration have been lacking. Understory burning in
mature mixed hardwood stands creates environmental
conditions which should favor oak regeneration but
developing oak reproduction does not reach sufficient size to
be competitive when the overstory is removed.
A shelterwood-burn technique has recently been developed
which overcomes this major disadvantage. This technique
reduces the vigor of oaks
’
competitors, especially if growing
season burns of relatively high intensity are used, and
provides conditions (increased light and reduced growth of
competitors) which allow oak regeneration to vigorously
resprout following the subsequent burn. It mimics a
Figure 3.
—
Mortality (%) of hickory, oak, red maple,
and yellow-poplar advance regeneration as fire
intensity increases within spring prescribed burns
conducted in shelterwood stands.
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Proceedings: Workshop on Fire, People, and the Central Hardwoods Landscape GTR-NE-274
disturbance pattern (i.e., partial overstory disturbance
followed by fire) that has shaped the composition of eastern
forests for millennia. The shelterwood-burn method is also
economically attractive because the initial shelterwood cut
yields an immediate income and the prescribed burn is low
cost compared to alternative treatments.
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