FIRE ECOLOGY
SPECIES: Yucca whipplei | Our Lord's Candle 



FIRE ECOLOGY OR ADAPTATIONS : 
The specific fire adaptations of Our Lord's candle vary greatly
according to subspecies.  Even individuals within a given population may
exhibit varying adaptations to fire.  Typical regenerative strategies of
each subspecies may represent evolutionary adaptations to the fire
frequency most common in the habitat occupied by that taxon.  Genetic
variation present within populations may have allowed Our Lord's candle
to persist or spread despite climatic shifts leading to changes in fire
frequency or subsequent geographic isolation.

Our Lord's candle is generally well adapted to persist in fire-prone
environments, and is closely associated with chaparral types
(particularly ssp. whipplei and ssp. parashii) [43].  However, Our
Lord's candle often grows in openings within chaparral communities where
fuel levels are lower than those of surrounding areas [10].  This may
result in lighter fires and increased survival.  On some extremely
harsh, rocky sites occupied by the species, fire may be infrequent due
to insufficient fuels.

Large, densely packed leaf bases provide some protection from fire [36].
Fairly vigorous resprouting has been noted after many fires
[29,35,38,38], but in other instances, little if any resprouting has
occurred and high mortality has been observed [20].  Plants frequently
survive and resume growth if only lightly damaged [9,19,48].  Specific
plant morphology may largely dictate the probability of survival and
most typical mode of postfire response.  Conditions which favor
rhizomatous or caespitose forms of Our Lord's candle are generally not
conducive to seedling germination and establishment [18].  Subspecific
variation may be extremely important in explaining differences in fire
adaptations.  Thus, correct identification of subspecies is essential
when considering specific fire adaptations.

Of the five subspecies, ssp. whipplei and parashii are ones most closely
associated with the fire-prone chaparral.  They exhibit a larger leaf
area which may allow for more rapid growth rates in fire-free years, a
characterisdtic of selective value in fire-prone habitats [23].  Also,
although seed of Our Lord's candle is in general very sensitive to heat
damage, seeds of these two subspecies are more resistant to exposure to
high temperatures (up to 230 degrees Fahrenheit [110 deg C]) than are
seed of the other subspecies [23].  Reestablishment is probably through
surviving on-site or off-site wind-dispersed seed.

The rhizomes of ssp. percursa vary in depth, length, and thickness but
are probably well protected from fire by overlying soil.  This
subspecies is probably capable of resprouting rapidly after fire.  Many
of the populations of Our Lord's candle which have been observed to
resprout vigorously and rapdily, even after fires of high intensity, may
be representatives of this subspecies.  Postfire resprouting is much
more important than reestablishment through seed for this subspecies.

Subspecies caespitosa would probably be killed by fires that removed
aboveground vegetation, with reestablishment through off-site seed
likely.  However, its caespitose growth form may promote survival in
areas experiencing lighter fires.  Undamaged or slightly damaged
portions of the clump would survive and resume growth, permitting fairly
rapid reestablishment.  The seed of this subspecies is very sensitive to
fire [23].

Subspecies intermedia typically grows in a dense clump of rosettes with
secondary rosettes forming from underground portions of older plants
[17,45].  These underground plant parts are presumably protected from
the damaging effects of heat by overlying soil.  These adaptations
suggest that ssp. intermedia can survive and resume growth, particularly
after lighter fires.


POSTFIRE REGENERATION STRATEGY : 
   Secondary colonizer - off-site seed
   Rhizomatous shrub, rhizome in soil

Related categories for Species: Yucca whipplei | Our Lord's Candle