FIRE EFFECTS
SPECIES: Quercus chrysolepis | Canyon Live Oak 



IMMEDIATE FIRE EFFECT ON PLANT : 
Aboveground foliage of canyon live oak is sensitive to fire, and this
plant is generally top-killed by fires of even relatively low intensity
[26].  Light ground fires can seriously damage or girdle this oak or
produce fatal cambium injuries to the crown and trunk [58,59,73].  The
dead flaky outer bark is extremely flammable and can carry fire several
feet up the trunk [73].  The bark is relatively thin and offers little
protection when compared with other species of oak [58].  The trunk
appears to be sensitive to heat damage [70], which often extends up the
trunk, far above any obvious signs of charring [72].

The total effect of fire on oaks varies according to fire intensity and
severity, fire behavior, season of burn, and the size of the plants
[70,72].  Younger plants and those with smaller stems and lower crown
heights tend to be most vulnerable [70,72].  Trees with crown-to-ground
distances of 15 to 30 feet (5-10 m) or more tend to be most resistant to
damage [60].  Larger trees have relatively little dead fuel in the crown
since leaf fall occurs in early summer prior to the fire season.  The
thicker bark of larger oaks provides some additional protection as does
the greater living biomass which decreases overall flammability [60].
Trunks of oaks are, in general, more seriously damaged by slower moving,
lower intensity fires than those of higher intensity, but shorter
duration.  However, because of the presence of heat-sensitive leaves,
crowns tend to be more severely injured by fires of higher intensity,
but shorter duration.  Fires are generally more damaging as the growing
season proceeds, with winter fires the least damaging.  The 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 [72].

Stem and bark:  Young oak stems which have been damaged by heat
generally change from gray to reddish-gray in color.  The subsurface
layer of the bark changes from green to tan or brown, and the inner bark
appears yellow instead of the normal white or pink.  Damaged inner bark
often has a characteristic fermented aroma.  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 [72]:

              1) light  - spotty char or scorch, scattered
                          pitting of the bark
              2) medium - continuous charring, pronounced reductions areas 
                          of minor bark reduction
              3) heavy  - pronounced reductions in bark thickness, in
                          some areas the bark is burned through      
                          exposing the wood beneath

Basal scars produced by scorching can admit rot and disease and
frequently serve as a point of ignition in subsequent fires [70].

Crown:  Crown damage is variable in oaks and the degree of damage can
differ even within an individual crown].  Damage may range from
essentially none to total removal of the foliage.  Crown survival of
larger trees is somewhat variable.  Trees of 12 inches (30.5 cm) d.b.h.
have survived with wounds up to 20 feet (6.1m) in height [70].

Damage within a stand may be serious and widespread.  Up to 78 percent
of the stands in a given area may be defoliated by char or scorch in
bigcone Douglas-fir-canyon live oak forests of California [59].
Fire-related injuries can increase oak's susceptibility to attack by
insects, fungus, or windthrow [70].  Belowground portions of canyon live
oak generally survive even when the plant is top-killed by fire
[58,59,67,68].  However, plants may be killed if burned at too frequent
intervals [73].  Acorns of canyon live oak are sensitive to heat and are
generally destroyed by fire [24].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
The full effect of fire on oaks may not become obvious for some time.
It may be necessary to wait for at least one growing season, and
preferably three, before survival can be accurately determined.
Undamaged leaf crowns of seemingly girdled canyon live oaks may appear
alive for as long as 8 years after fire [72].  Plumb [70] noted that
when dense pure stands of canyon live oak 6 to 12 inches (15-31 cm)
d.b.h. were burned, initial damage appeared to be restricted to the
bottom 1 to 5 feet (0.3-1.5 m) of the trunk.  All trees 3 inches (7.6
cm) d.b.h. or smaller were top-killed within 18 months, but at least 55
percent of the larger trees appeared to be alive, although presumably
girdled at the base.  However, crowns of 50 percent of the remaining
trees turned brown and died by the 36th month after fire, and most of
the rest were expected to die within the next few years [70].

Various methods have been developed for assessing damage to oaks
including chemical, electrical, and visual techniques [70,72].


PLANT RESPONSE TO FIRE : 
Canyon live oak generally sprouts prolifically after fire [59,88,89].
Even seedlings are often capable of sprouting after disturbance [49],
and moderate to dense regrowth of sprouts is typical after fire [72].
Canyon live oak sprouts vigorously from the subsurface rootcrown even
when the upper canopy is only partially defoliated by burning or
scorching [60,70].  The rootcrown itself has been described as a "basal
woody mass" but does not appear to be lignotuberous [40,60].  Postfire
stump-sprouting occurs where portions of the stump remains intact
[37,49,67].  Under certain circumstances, some larger trees crown sprout
if only "marginally singed" [59].  However, this appears to be somewhat
unusual, with resprouting typically occurring from the base and not the
crown [57,58,68].  On occasion, plants may sprout from both the base and
the crown [P. McDonald pers. comm. 1990].

Postfire recovery:  Where sprouting occurs, recovery of canyon live oak
is generally rapid.  In some areas, sprouts are capable of reaching 3 to
6 feet (1-2 m) in height within only four 4 after fire.  On many sites
following lighter fires, canyon live oak frequently forms dense,
virtually impenetrable stands 3 to 10 feet (1-3 m) in height within 15
to 30 years after fire [59,60].  After 30 years, canyon live oak
generally grows in multistemmed clumps which form a closed canopy 15 to
30 feet (5-10 m) high [60].  Frequent fires favor shrublike growth forms
of canyon live oak which often dominates other species following several
fires at fairly close intervals [11].  Open woodlands of canyon live oak
are temporarily replaced by live oak chaparral after repeated burning
[57].  However, protection from fire favors the reestablishment of oak
woodlands as oak sprouts ultimately grow tall enough to outcompete other
associated plants [49].

Acorns:  In certain areas, some postfire establishment can occur through
the germination of canyon live oak acorns [88].  However, in most
locations, regeneration through seed is probably important only in years
of favorable precipitation [77].  Conditions created by fire are not
generally conducive to the germination of acorns, and most oaks seldom
establish through seed after fire [40,42].  The current year's acorns
are generally killed by fire and even acorns stored in the soil are
vulnerable to heat [41].  Animals may carry some viable seeds to the
site from adjacent unburned stands, and some on-site seeds, more deeply
buried in rodent caches, can germinate and contribute to postfire
reestablishment.


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Canyon live oak sprouts most prolifically on sites with deeper soils and
with higher soil moisture [38,69].  Sprouting varies according to
elevation as follows [69]:

                elevation               % sprouting
                2,100 ft                73
                4,100 ft                60
                total                   66


FIRE MANAGEMENT CONSIDERATIONS : 
Fuels and flammability:  Although the heat content of the outer bark of
canyon live oak is relatively low when compared with other California
oaks (Quercus spp.), its low density and flakiness contribute to heat
buildup around the trunk [72].  The heat content of canyon live oak has
been calculated as follows [70]:

                    density           heat content      moisture content
                    (lb/ft 3)         (lb/ft 3)         (%)

flaky outer bark       41                7175               11
outer bark             48                7525               --
inner bark             43                6575               65
wood                   45                7875               60


Prescribed fire:  Plumb [70] reports that "the use of prescribed fire in
the management of canyon live oak does not appear to be promising" where
primary goals include maintenance of oak woodlands.  Trees are
sufficiently sensitive to trunk girdling that even ground fires can kill
the trunk surface.  Prescribed fire can be used in stands of larger
trees where fuel loading is low, or where trunks are protected from the
direct effects of heat [70].  Repeated fires at frequent intervals can
maintain shrubby canyon live oak chaparral.

Postfire harvest:  A correct determination of the degree of damage is
essential before appropriate harvest recommendations can be made.  Plumb
and Gomez [72] suggest waiting at least one growing season, and if
possible three, before cutting larger, more valuable trees which have
uncertain potential for crown survival.  The following postfire harvest
guidelines have been developed for canyon live oak [70]:

                  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 or more 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 oaks larger than 6 inches (15.2 cm) d.b.h. [70].

Wildlife:  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].

Bigcone Douglas-fir communities:  Bigcone Douglas-fir forests with a
canyon live oak understory are susceptible to frequent ground fires
[62].  In certain areas, canyon live oak grows in tree-sized form with
bigcone Douglas-fir.  Here, the relatively nonflammable oak serves as a
buffer against fire [58].  Where burned at frequent intervals, bigcone
Douglas-fir forests may be replaced by a canyon live oak woodland or
chaparral dominated by multi-stemmed clumps of oak [55].  Conversion of
treelike canyon live oak to a shrublike growth form results in greater
cumulative damage to the bigcone Douglas-fir overstory [58].  Minnich
[13] notes that the "success of [bigcone Douglas-fir] seems dependent on
tree-sized canyon live oak escaping fire."

Regeneration of bigcone Douglas-fir appears best in shade provided by a
canyon live oak canopy [58,59].  However, with time, continuous shade
proves detrimental to the development of regenerating conifers [55].
The growth of bigcone Douglas-fir is often suppressed under the shade of
the canyon live oak canopy until pole-sized conifers grow above the oaks
[60].  Bigcone Douglas-fir may not regain dominance for several hundred
years [55] [see Successional Status].

Coulter pine stands:  Where canyon live oak occurs with Coulter pine,
the oak contributes to higher fuel levels which produce fires necessary
for the regeneration of this conifer [60].

California white oak savanna:  Certain higher elevation valley oak (Q.
lobata) savannas of California are currently being invaded by such
species as canyon live oak.  Fire suppression is frequently cited as a
probable cause of this vegetative change.  Frequent fires would
presumably kill many of the young canyon live oak sprouts and maintain a
California white oak savanna [27].

Related categories for Species: Quercus chrysolepis | Canyon Live Oak