FIRE EFFECTS
SPECIES: Lithocarpus densiflora | Tanoak 



IMMEDIATE FIRE EFFECT ON PLANT : 
Tanoak is a fire-sensitive species.  Aboveground portions are extremely
susceptible to fire mortality [53,54].  The thin bark provides little
insulation from radiant heat which usually kills the cambium around the
base of the stem [30].  As a result, low-intensity ground fires readily
top-kill tanoak seedlings and sapling-sized stems [1,48,49].  Larger,
thicker barked trees occassionally survive light underburning [42].
Bark thickness of mature trees may range from from 1 to 3 inches
(2.5-7.5 cm), sometimes reaching 4 to 5 inches (1-12.5 cm).  Bole
injuries usually result following ground fires, however, and vertical
wounds 4 to 10 feet (1.2-3 m) long are common [31,42].  Many older tanoak
trees may initially survive light burns, but bole wounds facilitate the
entry of insects, and disease and most injured trees eventually die
[42].

Long-term survival is most likely in young, vigorous trees where bole
wounds tend to heal over rapidly [42].  In virgin redwood stands in
Redwood National Park, Veirs [54] found the oldest tanoak trees occupying
sites where frequent underburning by indigenous peoples reduced fuel
loadings to the point where only light-intensity ground fires occurred.
Crown fires kill the aerial portions of all tanoak, regardless of age or
size [36,42].



DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Tanoak is more susceptible to fire mortality when it occurs beneath a
mature conifer overstory.  Plants under these conditions are subject to
increased stress and are less able to survive fires than when growing in
a more open environment.  Understory tanoak exhibited significantly
lower predawn water potentials than those growing in adjacent open areas
[18].  Late spring (June), high duff consumption underburns
significantly (P<.05) reduced tanoak plant densities in the understory
of mixed conifer stands on sites in the Sierra Nevada [18].  (See fire
case study for more details.)


PLANT RESPONSE TO FIRE : 
After fire or cutting, tanoak resprouts from adventitious buds located
on a burl or lignotuber [16,31,42,48].  Most buds are located at or
beneath the ground surface [42].  Unless fires are particularly severe,
nearly all tanoak resprout to some extent during the first postburn
growing season [31].

Tanoak initiates a rapid postburn recovery and is an aggressive
competitor during the early stages of postburn succession [1].  Compared
to the slow growth of suppressed tanoak understories, tanoak sprout
development is dynamic in the postburn environment.  Sprout clumps
(aggregation of sprouts originating from a single tanoak individual) are
characterized by large numbers of resprouts and resprouts grow rapidly,
increasing greatly in both height and crown width [14].  If abundant in
the preburn community, tanoak often dominates the initial postburn
vegetation within 3 to 6 years, forming a dense cover which may exceed
49,400 stems/acre (20,000 stems/ha) [49].  Tanoak sprout development on
logged and burned sites in northern California is presented below [42].


   # of years after     Average sprout           Average # of 
    disturbance            height              sprouts per clump
                       (tallest in clump)
                            ft (m)

         2                 5.2  (1.6)               27
         3                 6.8  (2.1)               12
         4                 7.9  (2.4)               10
         5                 9.3  (2.8)               10
         6                10.3  (3.1)                9

The essentially pure, dense, even-aged sprout stands which frequently
result following fire provide the mutual shading necessary for optimal
tanoak development.  Where crowns maintain codominance with one another,
height growth is most rapid and tanoak avoids overtopping by associated
species.  Within approximately 20 years of burning, 60 to 90 percent of
the resprouts per sprout clump die as growth is concentrated into
multiple, dominant stems [31].  As succession progresses, preburn stand
density becomes a significant factor influencing both the growth and
continued dominance of tanoak [31].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Postburn sprouting potential of tanoak is strongly correlated with size
and vigor of the parent tree [42,48,49].  Site quality apparently has
almost no influence on sprout-clump development for at least 6 years
after disturbance [31,48].

Since burl size increases as tanoaks grow, larger stemmed tanoak (> 0.8
inches [2 cm] d.b.h.) usually possess larger burls with increased
numbers of dormant buds [49].  Trees greater than 12 inches (30 cm)
d.b.h. typically support abundant resprouts.  Sprout production by
vigorous, large diameter trees is impressive, with as many as 100
resprouts observed on some tanoak individuals.  Sprout growth is
intially fueled by portions of the residual root system.  Sprout growth
is related to parent tree diameter [31].  On sites in southwestern
Oregon, tanoaks 1 to 4 inches (2 to 10 cm) d.b.h. produced sprout clumps
measuring 4.9 feet (1.5 m) tall and 3.6 feet (1.1 m) wide within 6 years
of logging [48,49].  Trees 8.3 to 11.8 inches (21-30 cm) d.b.h.
produced clumps 7.2 feet (2.2 m) tall with crown widths equalling 8.5
feet (2.6 m).  Previous fires and the subsequent entry of pathogens can
substantially reduce the sprouting potential of parent trees greater
than 16 inches (40 cm) d.b.h. [14].  Sprout numbers also tend to be
reduced in older trees where dormant buds are covered by thick bark and
where logging debris is piled against tanoak stumps following
clearcutting [31].

Although tanoak is able to sprout at a very young age, sprouting
potential develops slowly.  Younger, smaller stemmed tanoak (< 0.8
inches [2 cm] d.b.h.) sprout much less vigorously than older
individuals.  Whereas stems in this smaller size class are usually
destroyed during fire, sprouting potential is related to burl diameter
[49].  Sprouting potential is enhanced as small tanoak age.  Older
individuals with larger burls generally produce the most vigorous
sprouts [31].  On sites in southwestern Oregon, small tanoak produced the
following pattern of development within 5 to 6 years after fire or
cutting [48]:

                average         average       average       average 
    age           burl          sprout       number of       clump
                diameter        height        sprouts      diameter
                 (mm)         inches (cm)                 inches (cm)

 14 - 20       5 - 25         11.2 (28)          4         6.2 (15.6)
 28 - 36      26 - 50         25.6 (64)          5        13.9 (34.8)
 40 - 52      51 - 75         28.4 (71)          7        14.6 (36.5)


FIRE MANAGEMENT CONSIDERATIONS : 
Broadcast burning:  Where conifer regeneration is a primary management
concern, broadcast burning is generally an ineffective site preparation
tool following clearcutting in conifer-tanoak stands [30].  Even though
burning delays the recovery of tanoak for approximately one growing
season, removal of logging debris promotes resprouting by exposing basal
buds to solar heating and permits sprouts to grow unimpeded [15,31].
Sites which are particularly prone to the rapid development of a dense
tanoak understory are those where the preburn vegetation consists of low
conifer stocking combined with high tanoak densities [49].

Preharvest underburning:  Tanoak sprouting may be more effectively
controlled by preharvest underburning treatments [18,19,49].
Preliminary research indicates that preharvest underburns are effective
in killing at least a portion of the tanoak understory when conducted in
late spring (June) under conditions which result in high duff
consumption [18,19].

Fires aimed at suppressing the tanoak understory can be expected to most
effective when conducted in 30 to 75 year old conifer stands.
Harvesting conifer-tanoak stands over 70 years of age typically results
in a dense cover of tanoak resprouts.  On many sites, resprouts from
delayed seedling regeneration are often responsible for high
postdisturbance tanoak coverages [49].  This younger, shrublike
component of the tanoak understory is an abundant (commonly exceeding
3,000 per/ha) but inconspicuous component of many stands prior to
disturbance.  Resprouting capabilities are greatly enhanced as
suppressed seedlings increase in age.  When released from dense shade,
suppressed tanoak over 70 years of age commonly produce more than 30
sprouts per plant; these typically reach heights of from 3.2 to 6.6 feet
(1 to 2 m) within three years.  By comparison, most 40 to 50 year old
tanoak produce an average of only five resprouts ranging from 12 to 27
inches (30 to 68 cm) in height 3 years after burning.  Furthermore,
development of a tanoak understory capable of vigorous, postdisturbance
sprouting may take upwards of 100 to 137 years [31].  The sprouting
potential of tanoak develops slowly and substantial tanoak seedling
establishment is often delayed until conifer stands are 20 to 35 years
old.  These factors suggest that on sites with 60 to 80 year conifer
rotations, one, well-timed, effective underburn can eliminate tanoak as
a competitor to conifer regeneration for two rotations.  Subsequent
tanoak seedling establishment must be controlled in order to realize the
full benefits of burn treatments; resprouted individuals can produce
acorns within at least 9 to 13 years of clearcutting and burning [49].

Hardwood management:  Burning should not be utilized as a method of
slash disposal in partially cut hardwood stands where tanoak is managed
for timber production.  Instead, logging debris should be lopped and
scattered or piled and burned [30].

Related categories for Species: Lithocarpus densiflora | Tanoak