FIRE EFFECTS
SPECIES: Quercus marilandica | Blackjack Oak



IMMEDIATE FIRE EFFECT ON PLANT : 
In general, low-severity fires top-kill small blackjack oaks, and more
severe fires top-kill larger trees and may kill rootstocks as well.  In
the New Jersey Pine Plains, where flame heights are high enough to
ignite and sustain a crown fire, nearly all stems smaller than 9.8 to 13
feet (3-4 m) tall are top-killed [58].

Acorns on the ground surface are usually killed by surface fires [11].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Blackjack oak associated with eastern redcedar is more likely to be
top-killed by fire because eastern redcedar is highly flammable and
fires tend to be hot.  A severe fire in a post oak-eastern redcedar
community in the Wichita Mountains of Oklahoma top-killed 92 percent of
all trees (post oak, blackjack oak, and eastern redcedar) greater than 3
inches (7.6 cm) in d.b.h.; only 13.5 percent of the top-killed blackjack
oaks and post oaks sprouted.  In the adjacent post oak-blackjack oak
forest, only 66 percent of trees greater than 3 inches (7.6 cm) were
top-killed by the fire, and 70 percent of these sprouted [40].

There is disagreement in the literature as to whether blackjack oak is
more susceptible to fire in a savanna or in a forest.  A March fire in a
central Oklahoma oak savanna top-killed most oaks smaller than 1.6
inches (4 cm) in d.b.h. and top-killed or severely damaged some trees up
to 3.5 inches (9 cm) in d.b.h.  In the adjacent post oak-blackjack oak
forest, however, few woody stems larger than 1 inch (2.5 cm) in d.b.h.
were top-killed.  In the savanna, all litter was consumed, whereas only
45 percent of the litter in the adjacent forest burned.  The authors
suggest that lack of grass under a closed-canopy forest results in a
much cooler fire [23].

However, an investigation of the effects of a prescribed fire in March
in a savanna and adjacent blackjack oak-black hickory forest in central
Illinois showed the opposite effect:  savanna blackjack oaks were less
affected by fire than blackjack oaks in the adjacent closed-canopy
forest.  Patterns of fuel consumption around isolated mature blackjack
oaks in the savanna showed that fire never reached the base of the
trees.  A few trees had slightly scorched lower branches, but all trees
survived the fire.  In the closed-canopy forest, mortality of trees
[stems larger than 3.5 inches (9 cm) in d.b.h.] was high.  Three years
after the fire, the density of blackjack oak had decreased from a
prefire density of 179 trees per acre (443 trees/ha) to 74 trees per
acre (183 trees/ha).  In essence, the fire converted the closed-canopy
forest to an open-canopy forest.  Seventy-five percent of top-killed
trees had basal sprouts 1 year after the fire [2].

The difference in fire effects on blackjack oak in the Illinois savanna
and forest was attributed to the difference in fuel load.  Estimated
average fuel load was 2.5 ounces per square foot (840 g/m sq) in the
savanna and 8.0 ounces per square foot (2,671 g/m sq) in the forest.  In
the savanna, fuel load was further reduced under mature blackjack oaks
because grass growth was less in the shade created by the down-sweeping
branches, and the wind removed excess leaf litter.  In the closed-canopy
forest, understory fuels built up over time [3].

The results of these two studies indicate that the effect of fire on
blackjack oak is dependent on surface fuel load.


PLANT RESPONSE TO FIRE : 
If top-killed by fire, blackjack oak sprouts vigorously from the root
crown [59].  

Because of sprouting, fire tends to increase the number of understory
blackjack oak stems.  Eight annual fires in Tennessee resulted in 470
stems per acre (1160 stems/ha) compared to 20 stems per acre (49
stems/ha) in the control.  Two periodic fires separated by 5 years
resulted in 70 stems per acre (173 stems/ha) [53].

Frequent fire in the Pine Plains of New Jersey has resulted in
multistemmed blackjack oaks.  Two months after a May wildfire, there
were to 3,949 genetically defined blackjack oak and bear oak individuals
per acre (9,750 genets/ha) and 50,422 sprouts per acre (124,500
sprouts/ha).  Oaks averaged 13 sprouts per root crown [8].

In a study in Oklahoma, blackjack oak seedlings were more prevalent in
recently burned areas, suggesting blackjack oak seedlings may increase
after fire.  The authors did not speculate on whether the acorns were
buried on-site before the fire or were disseminated postfire by off-site
sources [13].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Many present-day post oak-blackjack oak stands were former savannas.  In
the Wichita Forest Reserve in Oklahoma, the average age of stands
coincides with the advent of fire suppression in the reserve [13].
Forests may or may not revert back to savannas with prescribed burning
[23,58].  Prescibed fire, in conjunction with herbicides, may be
effective at eliminating blackjack oak [52].  Prescribed fire in 4-year
rotations may be effective at preventing blackjack oak expansion into
prairies [59].

Related categories for Species: Quercus marilandica | Blackjack Oak