FIRE EFFECTS
SPECIES: Eucalyptus globulus
IMMEDIATE FIRE EFFECT ON PLANT :
Crown fire's effect upon bluegum eucalyptus varies. Because the stringy
outer bark is highly flammable and bark thickness is readily reduced by
fire, past fire frequency largely determines the relative protection
bark offers. Repeated fire damage to bark before bark thickness has
been restored may result in top-kill, or at times, tree mortality. If
bark is sufficiently thick, bluegum eucalyptus branches survive crown
fire and send out epicormic sprouts [50]. No studies quantifying bark
thickness with tree survival were found.
DISCUSSION AND QUALIFICATION OF FIRE EFFECT :
NO-ENTRY
PLANT RESPONSE TO FIRE :
Bluegum eucalyptus recovers well from fire [3]. Epicormic sprouting is
common in trees only scorched by fire. It is also common in trees where
crown fire occurred but bark was thick enough to protect dormant branch
buds. Heat-damaged bark is shed, and sprouting proceeds rapidly [50].
Top-killed trees sprout from the lignotuber. Vigorous sprouting is
supported by food reserves stored in the root system and lignotuber [3].
Bluegum eucalyptus also establishes from seed after fire. Some seed is
already stored in the seedbank. Release of crown-stored seed is
triggered by shoot death, and crown-stored seeds are rapidly
disseminated after fire [50].
In 1929, a catastrophic fire burned a bluegum eucalyptus stand in
California. The forest regenerated to a fully stocked condition. In
November 1946, a second fire burned much of the same area. Again, the
forest regenerated. By 1983, it was a very dense uneven-aged stand [33].
DISCUSSION AND QUALIFICATION OF PLANT RESPONSE :
NO-ENTRY
FIRE MANAGEMENT CONSIDERATIONS :
Fuel buildup occurs very rapidly in unmanaged bluegum eucalyptus stands
in California [1,33]. Fuel reduction programs can reduce wildfire
hazard, as can the establishment of fuelbreaks [1,31].
In December, 1972, the San Francisco Bay Area experienced a severe cold
snap, resulting in extensive frost damage to bluegum eucalyptus trees
[6,18]. Frost-killed leaves and twigs increased bluegum eucalyptus
litter ten-fold. By early 1973, following a particularly hot, dry
summer and autumn, the litter combined with standing dead and damaged
bluegums constituted a major fire hazard [1,6,18]. Several fuel
reduction methods were proposed: mechanical removal of trees, thinning
of present stands, and prescribed fire. The first two alternatives are
commonly applied now in freeze-killed or damaged stands. Broadcast
fires have been used with success in undisturbed areas under reasonably
moist (13-19% fuel moisture) weather conditions. Spring fires have
reduced fuel loads up to 87 to 96 percent without damage to overstory
trees. Prescribed burning has been widely applied to eucalyptus forests
in Australia to reduce fuel loads and prevent wildfires [1].
|
