FIRE EFFECTS
SPECIES: Quercus wislizenii | Interior Live Oak 



IMMEDIATE FIRE EFFECT ON PLANT : 
Trunks and crowns of interior live oak are extremely sensitive to fire
[44,47].  However, because of this oak's ability to sprout after fire,
plants usually survive even when aboveground vegetation is consumed.
Interior live oak is generally top-killed whenever fuels burn around the
base of the tree [24].  The total effect of fire on oaks varies
according to fire intensity and severity, fire behavior, season of burn,
and size of the plants [45,47].  Generally, late season fires are more
damaging to oaks than those which occur in the spring.  Winter fires
appear to cause the least damage.  Slower moving, lower intensity fires
are typically more damaging to the trunk than fires of higher intensity
but shorter duration.  Crowns are most susceptible to fires of higher
intensity, even if they are of short duration.  Bark is typically less
severely damaged when burned at lower ambient air temperatures.  Oaks
less than 6 inches (15.2 cm) d.b.h. are generally top-killed by even low
intensity fires [47].

Younger trees, and those with smaller diameters and lower crown heights
tend to be most susceptible.  In comparison with other oaks, interior
live oak has a high ratio of inner to outer bark, but total bark
thickness is low and offers little protection.  Researchers observed
that even interior live oaks with a bark thickness of 1 inch (2.5 cm) or
more were girdled at the base after a fire of moderate intensity.  Most
California interior live oaks have a d.b.h. of less than 12 inches (30.5
cm) which further increases vulnerability to fire [45].

Stem and bark:  Young oak stems which have been damaged by heat
generally change from a gray to reddish-gray in color.  The subsurface
layer of the bark changes from a green to tan or brown, and inner bark
appears yellow instead of the normal white or pink.  Damaged inner bark
often develops a characteristic fermented aroma [47].  When the bark of
interior live oak is charred, cambium death is almost inevitable [45].
The cambium can be considered dead if the bark has been consumed, or if
it appears to be cracked and separated from the wood.  Trunk char may be
categorized as follows [47]:

         light charring  -   spotty char or scattered pitting of the bark.
         medium charring -   continuous charing, areas of minor bark         
                             reduction. 
         heavy charring  -   pronounced reductions in bark thickness, wood
                             sometimes exposed.

Crown:  Crown damage is variable in oaks and the degree of damage can
differ even within an individual crown [45].  The extent of damage may
range from none to total removal of the foliage.

The actual extent of damage is not always readily apparent in oaks.  A
period of several years may be required for the full extent of damage to
become evident.  [See Discussion and Qualification of Fire Effect].
Fire-related injuries can increase oak's susceptibility to attack by
insects, fungus, or windthrow [45].  Although portions of most interior
live oaks survive after plants are top-killed by fire, some are killed
if burned too frequently [48].  Acorns are extremely sensitive to heat
[45] and are generally killed even when buried in the soil, litter, or
duff.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
The full effect of fire on interior live oak may not become obvious for
some time.  It may be necessary to wait at least one growing season, and
preferably three, before the amount of injury can be accurately
determined.  Trees with bark as thick as 1.5 to 2.0 inches (3.8-5.1 cm)
can be girdled, although initial visual examination suggests that the
bark has received only minor charring.  The surface of even heavily
charred interior live oak remains smooth and often retains the original
furrow patterns.  As the bark dries, vertical cracks may appear,
exposing the damaged tissue beneath [47].  Various methods have been
developed for assessing damage to oaks including chemical, electrical,
and visual techniques [45,47].


PLANT RESPONSE TO FIRE : 
Interior live oak sprouts vigorously after the trunk or crown has been
damaged by fire [8,22,56,60].  This oak sprouts from the stump [10,15]
when remaining portions are sufficiently undamaged, and from the base or
root crown [44,47].  Root crown sprouting, after damage to the trunk and
crown, is generally vigorous [47].  Under some circumstances, postfire
regeneration from seed may also occur [10,69], although acorns are
vulnerable to heat [45].  Favorable weather conditions are necessary for
good germination, and sprouting appears to be the primary mode of
regeneration in most areas.  Repeated fires generally produce small
multistemmed trees [47].

Postfire recovery:  Initial sprout growth is slow [16, P. McDonald,
pers. comm. 1990], although Biswell and Gilman [8] reported that in the
western Sierra Nevada of northern California, sprouts reached 24.9
inches (63 cm) in height within 10 or 11 months after fire.  By the end
of the second growing season, maximum sprout heights of 78 inches (198
cm) were reported, and a few sprouts had grown to 95 inches (241 cm) in
height by the third summer.  Maximum sprout heights of 8 feet 9 inches
(267 cm) were observed by the fourth postfire growing season [1].  Oak
(Quercus spp.)  chaparral dominated by interior live oak (variety
frutescens) and Nuttall's scrub oak (Q. dumosa) develop impenetrable
cover within 5 to 10 years after fire [39].

Canopy cover of interior live oak is initially reduced by fire although
actual oak numbers typically increase.  Vogl [67] observed the following
response of interior live oak in a recently burned knobcone pine (Pinus
attenuata) forest of southern California:

           % cover            # plants per acre 

unburned      5.4                  88
burned        4.5                 173


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Fuels and flammability:  The heat content and flammability of interior
live oak has been calculated as follows [45]:

     (theoretical value for heat of combustion = 8,600 Btu/lb.)

                density (lb/cu ft)       heat content (Btu/lb)

  outer bark           62                      9,875
  inner bark           45                      7,700
  wood                 44                      7,925

Prescribed fire:  Plumb [45] reports "successful use of prescribed fire
in interior live oak management does not seem promising" where
maintenance of woodlands is a primary management goal.  Poor heat
resistance and easily damaged bark generally result in stem mortality or
damage producing high potential for decay [11, P. McDonald, pers. comm.
1990].  Large individual trees may feasibly be protected in small areas
[45].  Repeated fires may be used to maintain this oak as a small
multistemmed plant [47].

Postfire harvest:  A correct determination of the degree of damage is
essential before appropriate harvest recommendations can be made.  Plumb
and Gomez [47] suggest waiting at least one growing season, and if
possible three, before cutting larger valuable trees which have
uncertain potential for crown survival.  Once damage has been assessed,
the following guidelines may be used [45]:

                  tree size and degree of trunk char -

                    light      medium      heavy
  < 6 inches dbh    cut        cut         cut
  6-12 inches dbh   leave      cut         cut
  > 12 inches dbh   leave      cut         cut

Harvesting may be recommended if 75 percent of the trunk is girdled on
trees less than 6 inches (15.2 cm) d.b.h., or if more than 50 percent is
girdled on trees greater than 6 inches d.b.h. [45].

Valley oak savannas:  Certain higher elevation valley oak (Q. lobata)
savannas in the Santa Lucia Mountains of central coastal California, are
being invaded by species such as interior live oak.  Fire suppression is
frequently cited as a probable cause of this vegetative shift.  Although
seedlings of both oaks are eaten by herbivores, interior live oak
sprouts tend to be somewhat more browse-resistant.  Increased livestock
utilization may favor interior live oak.  Frequent fires presumably
killed many of the young interior live oak sprouts and helped to
maintain valley oak savanna [26].

Wildlife and livestock:  Sprouts are extremely vulnerable to herbivores
during the first few years after fire [22,25,56].  Domestic goats can
kill a large proportion of sprouts and seedlings during the first 3 to 5
years after fire.  Deer prefer oak sprouts and feed on them year-round
for at least the first 2 postfire years [56].  Fire in California oak
woodlands can create favorable, although transitory, habitat for birds
such as the flicker and hairy woodpecker which feed on insects present
in the branches of fire-killed trees [14].

Related categories for Species: Quercus wislizenii | Interior Live Oak