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



IMMEDIATE FIRE EFFECT ON PLANT : 
The effect of fire on Our Lord's candle probably varies according to
such factors as fire intensity and severity, climate, site
characteristics, and genetic makeup of a particular subspecies or
population.  Although major differences between subspecies have been
documented with respect to botanical characteristics and regenerative
strategies, little is known about the effect of fire on each subspecies.
Few researchers have identified plants to subspecies when reporting fire
effects.  Consequently the literature appears variable and highly
contradictory.  Some researchers have observed low postfire mortality of
Our Lord's candle (< 25%) [37,38], while others have reported low
survival (10%) [19,20].  Much of the variability in fire effects is
probably due to genetically based differences in growth habit and
regenerative strategies.

Postfire mortality is probably high in semelparous, monocarpic
subspecies such as whipplei and parashii.  A fire which consumes
aboveground vegetation would presumably kill the plant, although some
individuals might survive if the foliage was only lightly damaged.

The effects of fire on iteroparous subspecies such as caespitosa and
intermedia are largely unknown.  However, survival is probably somewhat
more likely that in monocarpic subspecies, since they have the ability
to survive and regrow if portions of the dense clump or clone reamin
undamaged.  Subspecies intermedia froms new secondary rosettes from
underground portions of older plants; fires which occur after the
formation of these buds but prior to emergence may have little effect on
the buds themselves.  Thus, season of burn may be particularly important
in determining the effect of fire on this subspecies.

Postfire mortality is presubably low in ssp. percursa because the
rhizomes are afforded some protection from heat by overlying soil,
allowing the plant to survive even when aboveground vegetation is
consumed by fire.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
NO-ENTRY


PLANT RESPONSE TO FIRE : 
Postfire response of Our Lord's candle is extremely variable.  Each
subspecies presumably exhibits a characteristics response to fire, but
this diverse species shows extreme variability and many growth forms can
be observed in a single population.  The entire suite of postfire
responses by subspecies has not been well documented.  More research is
clearly needed to sort out the complex interrelationships between
genetic and environmental factors which influence postfire regenerative
strategies.

Postfire response of Our Lord's candle may be rapid.  Sprouts or
seedlings appeared within 2 years after a September fire removed all
aboveground vegetation [8].  Sprouting, when it occurs, can be vigorous.
As many as 262 to 1,690 sprouts per hectare were observed only 1 year
after a July wildfire in a chaparral-desert ecotone of southern
California [37,38].  On certain sites which had a prefire density of 27
per hectare, resprout densities were averaged 20 per hectare.  Each
plant produced an average of 18 to 85 sprouts [37,38], suggesting
increased density in burned stands.  Basal sprouting appears to be most
likely when foliage is not "severely burned" [9].  Limited evidence
suggests that where Our Lord's candle is capable of resprouting, this
mode of regeneration allows for much more rapid and complete recovery
than would be expected in populations which regenerate through seed
alone [27].  In many instances, Our Lord's candle appears to be capable
of surviving and resuming growth if only slightly damaged by fire
[9,19,48].  Some lightly burned stands produce an abundance of flowers
within 1 or 2 years after fire [9].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Recovery:  Vegetative regeneration of Our Lord's candle through
resprouting apparently permits a much more rapid and vigorous postfire
recovery than is possible through seedling establishment.  Specific
documentation of recovery following a fall fire of variable intensity in
a California coastal sage community is as follows [27]:

site #            % cover (#/ha)             mean size (cm sq)
             resprout     seedling        resprout      seedling
  1             4.3          --           2,344           156
  3            12.1          0.1          1,875           156
  4             8.8          0            1,562           469
  5             4.3          --             937           --
  6            10.8          0            1,719           156

Postfire recovery of Our Lord's candle cover through seed alone may take
more than 4 years in many southern California chaparral communities
[19].

Although evidence is lacking, the likelihood of vegetative regeneration
in subspecies or individuals capable of such a response may depend
largely on fire severity.  Conrad [9] reports that basal sprouting can
occur only if plants are not severely burned.


FIRE MANAGEMENT CONSIDERATIONS : 
One year after a summer wildfire in a California chaparral-desert shrub
ecotones, postburn productivity ranged from 0.05 pounds per acre (57
g/hectare) in winter to 11 pounds per acre (1,196 g/hectare) in spring
[37,38].

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