FIRE EFFECTS
SPECIES: Quercus dumosa | Nuttall's Scrub Oak 



IMMEDIATE FIRE EFFECT ON PLANT : 
California scrub oak often occurs in highly flammable chaparral stands
which burn at relatively high frequency.  The total effect of fire on
oaks varies according to fire intensity and severity, fire behavior,
season of burn, and size of the plants.  Because most Nuttall's scrub
oak is relatively small (generally less than 8 inches [20.3 cm] d.b.h.)
and has thin, flaky bark, it is almost always top-killed by fire
[48,50].  Seedlings are almost always killed by fire [31].  Larger,
older Nuttall's scrub oaks with slightly thicker bark and higher crowns
tend to be somewhat more resistant to fires than smaller individuals
[48].  Stems of lightly charred trees with d.b.h.'s greater than 6
inches (15 cm) can occasionally survive fire [48,50].

Trunks of oaks are, in general, more seriously damaged by slower moving,
low intensity fires than those of shorter duration and high intensity.
However, the heat-sensitive crowns are generally seriously damaged by
high-intensity fires, even those of relatively short duration.  Greater
damage occurs as the growing season progresses, with least damage
produced by winter fires [50].  Oaks are usually less severely damaged
when burned at lower ambient air temperatures.

Stem and bark:  The full extent of bole damage may not become evident
for some time.  However, the trunks of most scrub oak exhibit medium to
heavy charring soon after fire.  Young oak stems 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 has a characteristic fermented aroma.  A pattern of vertical
cracks often develops in the charred bark of scrub oak, and the bark may
be burned through to the wood.  The loose, outer bark is generally
consumed if heavily burned.  The cambium can be considered dead, with
overall survival unlikely, if the bark has been consumed, or if it
appears to be cracked and separated from the wood.  Trunk char of oaks
may be categorized as follows [50]:

      light charring  - spotty char or scattered pitting of the bark
      medium charring - continuous charring, areas of minor reductions
                        in bark thickness
      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 [48].  The degree of damage may
range from essentially none to total removal of the foliage.

Oaks less than 6 inches (15.2 cm) d.b.h. are usually top-killed by even
low intensity fires [50].  However, underground portions of scrub oak
generally survive fire even though top-killed, and overall adult
mortality is often quite low [31,65].  Nearly 100 percent survival of
belowground or surface level regenerative structures has been documented
after spring or summer fires in southern California chaparral [39].
Mortality may be more likely after hot fires with the potential to
damage regenerative structures.  Some California oaks are killed if
burned at frequent intervals [52].
                  
Seed:  The heat-sensitive acorns of Nuttall's scrub oak are poorly
adapted to survive fire [74].  Most acorns still present on the trees
are killed readily by fire [73], as are the majority of those stored
on-site in the soil or litter [20,28,31].  Occasionally, acorns buried
in rodent caches are sufficiently protected from heat to survive and
germinate [73,74].


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
It may be necessary to wait for at least one growing season, and
preferably three, before the true potential for survival can be
accurately determined [50].  Fire-related injuries can increase oak's
susceptibility to attack by insects, fungus, or windthrow [48].  Various
methods have been developed for assessing damage to oaks including
chemical, electrical, and visual techniques [48,50].


PLANT RESPONSE TO FIRE : 
Nuttall's scrub oak typically sprouts prolifically after fire [6,27,36].
Stump-sprouting is commonly observed where portions of the stump remain
intact [18,39,44].  Nuttall's scrub oak also resprouts from the root
crown [9,50].  Older root crowns which have been burned repeatedly can
develop into large structures at, or below, the soil surface [20].
However, scrub oak "does not usually form a distinct burl" [31].
Establishment from seed does occur but appears to be less common than
sprouting [30,29,73].

Vegetative response:  Sprouting is generally both vigorous and rapid
[20].  Plants usually sprout by the first growing season after fire, but
delayed sprouting has also been observed [48,50].  Sprouts may emerge as
soon as 10 days after fire, or sprouting may be deferred for up to 2
years.  The ability to remain dormant for at least one growing season
prior to sprout production may enhance survival as sprouting is delayed
until a favorable moisture regime is encountered [47].  Speed of
recovery depends on such factors as topography, aspect, and weather
[30].  Sprouting appears to be unrelated to season of fire.  The
availability of soil moisture is probably the primary factor controlling
sprouting [47].  Sprouting of Nuttall's scrub oak is most common and
most rapid on deep, moist soil, particularly on north-facing slopes
[20,46,47].  Generally, fewer plants sprout on more xeric rocky sites,
and sprouting is often delayed until the following spring [46,47].

Seedling establishment:  Regneration by seed does occur but may be
limited to periods of abundant rainfall [30,74].  Many Nuttall's scrub
oak seedlings were observed in the spring following a December
prescribed fire during a period of unusually abundant rainfall.
However, because of the timing of dispersal, acorns are poorly adapted
to survive fire [74].  Seedbeds created by fire do not favor germination
or growth of Nuttall's scrub oak [31].  Rarely, seedlings buried in
rodent caches or in stands with unusually deep litter survive fire and
subsequently germinate [73].

Rate of postfire recovery:  Nuttall's scrub oak generally recovers
fairly rapidly after fire, particularly on better sites.  It, along with
ceanothus, commonly dominates southern California chaparral by the
fourth year after fire [30].  Impenetrable cover can develop in oak
chaparral within 5 to 10 years after fire [41].  In coastal sage
communities, Nuttall's scrub oak generally becomes dominant by the second
decade after fire [20].

Growth of sprouts is somewhat variable [46], but is generally rapid
during the first 3 years after fire [24].  Sprout heights of more than 2
feet (0.6 m) have been observed within only 2 months after fire [47].
Approximately 4 to 5 months after a July wildfire, some sprouts had
reached 2 to 3 feet (0.6-0.9 m) in height, and most were at least 12
inches (31 cm) tall [46].  Biswell and Gilman [6] observed that some
sprouts had reached 24.9 inches (63 cm) within 10 months after a
September wildfire, and maximum heights of 78 inches (198 cm) had been
reached by the end of the second growing season.  Maximum heights of 95
inches (236 cm) were recorded by the end of the third growing season,
and a few oaks had reached 8 feet 9 inches (236 cm) by the end of the
fourth growing season.

Sprouts tend to grow more rapidly than seedlings during the first few
years after fire.  Comparative heights of Nuttall's scrub oak seedlings
and sprouts by the end of the spring of the first postfire year were as
follows [30]:

           high elevation       mid. elevation       low elevation
resprouts        30 cm                47 cm              55 cm
seedlings        -----                12 cm               7 cm


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
NO-ENTRY


FIRE MANAGEMENT CONSIDERATIONS : 
Fuels and flammability:  Nuttall's scrub oak tends to be somewhat less
flammable than many other chaparral species.  Flammability is reduced
because of the relatively high fuel moisture of living plants, a lower
proportion of dead-to-live fuels, and fewer volatiles [18].  The volatile
content is approximately 3.7 percent, and leaf energy content averages
20.33 kJ -1 [18,46].  Heat content has been calculated as follows [48]:

                     density (lb/ft 3)        heat content (Btu/lb)
  flaky outer bark            37                   8350
  outer bark                  45                   8250
  inner bark                  63                   6750
  wood                        57                   8060

Nitrogen volatilization:  Approximately 25 percent of the aboveground
biomass and surface soil was volatilized in fires which consumed 60
percent of Nuttall's scrub oak biomass [55].

Prescribed fire:  Limited evidence suggests that burning may be
difficult in stands dominated by Nuttall's scrub oak [3,18].  In mature
chaparral stands with significant amounts of fine fuels, burning without
damaging oaks is often difficult [20].  Repeated fires can maintain
Nuttall's scrub oak as a small, multistemmed shrub [50].  Hot fires tend
to be most effective in reducing sprouters such as Nuttall's scrub oak.
Riggan and others [55] observed that low fuel moisture and winds
consistently greater than 5 to 8 miles per hour (8-12 km/hour) are
required to spread fire in Nuttall's scrub oak communities.  Flame
lengths of 20 to 33 feet (6-10 m) were produced by prescribed fires
which released just enough energy to achieve steady spread rates.  A
threshold for fire propagation in communities with little dead wood is
overridden by higher wind speeds which increase the efficiency of heat
transfer to unburned fuels.

Postfire harvest:  The degree of damage must be correctly determined
before appropriate harvest recommendations can be made.  Plumb and Gomez
[50] suggest waiting for at least 1, and if possible, 3 growing seasons
before cutting oaks in which crown survival is in doubt.  Once damage
has been accurately assessed [See Fire Effects], the following
guidelines may be used for Nuttall's scrub oak [48]:

                           plant size and degree of trunk char
                           light        medium       heavy
     < 6 inches d.b.h.     cut           cut         cut
     6-12 inches d.b.h.    leave         cut         cut

Harvesting of oaks is generally recommended if 75 percent of the trunk
is girdled on plants less than 6 inches (15.2 cm) d.b.h., or if more
than 50 percent is girdled on plants greater than 6 inches (15.2 cm)
d.b.h. [48].

Postfire productivity:  Total postfire production of Nuttall's scrub oak
has been reported at 2.5 pounds per acre (2.8 Mg/ha) in the first year
after fire.  Annual biomass production over a 35-year period was
estimated at 2.8 pounds per acre (3.2 Mg/ha), but foliar biomass
averaged .97 pounds per acre (1.1 Mg/ha) by the first postfire year
[55], suggesting rapid recovery after fire.

Wildlife considerations:  Tender Nuttall's scrub oak sprouts provide
wildlife browse after fire [66].  Following fires in southern California
chaparral, new sprouts are browsed by deer during late June through
early July.  An average of 20 percent of all shoots on 23 percent of the
plants were browsed by deer during this time period.  Small mammals such
as the brush rabbit browsed stump-sprouts most heavily during October
and November.  Postfire utilization of Nuttall's scrub oak by small
mammals in southern California chaparral was as follows [39]:

          year        % shrubs browsed       % shoots browsed per plant
          1982               20                          4.5
          1983               45                          8.0

Livestock:  Recently burned chaparral comprising Nuttall's scrub oak can
provide an adequate maintenance diet for domestic goats during the
spring and summer [62].

Related categories for Species: Quercus dumosa | Nuttall's Scrub Oak