FIRE EFFECTS
SPECIES: Adenostoma fasciculatum | Chamise 



IMMEDIATE FIRE EFFECT ON PLANT : 
Chamise is a fire-sensitive species [136], and mortality may be
substantial following fire [54,74,105].  Perennating buds are located
just beneath the soil surface and are quite susceptible to fire damage
[3,136].  Mortality patterns are related to season of fire, fire
intensity and severity, and fire frequency [125].

Season of burning:  Season of fire affects chamise lignotuber survival.
Spring or summer fires may kill up to 50 percent of plants, while fall
fires result in relatively little mortality [3,74,124].  Differential
mortality is related to seasonal flucuations in the carbohydrate
reserves of lignotuber and large roots.  High starch concentrations are
apparently necessary for the onset of sprouting [89,119].  Starch
concentrations may be insufficient to ensure sprouting when chamise is
burned in the late spring or summer, since carbohydrate reserves have
been depleted during spring growth [61,81].  Over the summer months,
however, starch reserves are recharged as carbohydrates are translocated
to the lignotuber, and most plants sprout following fall fires.  In dry
years, major carbohydrate mobilization does not take place; under these
conditions, spring or summer fires might produce lower level mortality
than in more "normal" years [116].

Fire intensity:  Mortality increases with increasing fire intensity.
Following low-, moderate-, and high-intensity June fires in old-growth
chamise in Sequoia National Park, approximately 46, 64, and 80 percent
of chamise plants died, respectively.  Seasonal patterns of fire
mortality are further accentuated by differences in fire severity
associated with spring/summer versus fall fires.  Early season fires
move slowly through a stand and the downward heat pulse is greater than
that produced by rapidly carrying, fall fires.  As a result, fall fires
are generally less severe than spring/early summer fires and produce
less mortality.  In one case, a moderately intense spring (June) fire
resulted in 64 percent chamise mortality, whereas a moderately intense
fall (October) fire resulted in only 14 percent mortality [116].

Fire frequency:  Chamise is extremely susceptible to short-interval
fires.  High mortality of both seedlings and sprouts is likely when
fires recur on burns seeded to annual grasses.  Chamise density
(seedlings and sprouted individuals) was reduced up to 97 percent
following a grass fire on a 1-year-old burn [136].  Chamise seedlings
are more sensitive to frequent fire than sprouted plants [136].  In
northern California, Hedrick [48] reburned 1-, 2-, and 3-year-old burn
sites which had been seeded to grass and mustard.  Mortality of
established chamise was 77 percent on the 1-year-old burns, 24 percent
on the 2-year-old burns, and 34 percent on the 3-year-old burns.
Seedling mortality was 99, 98, and 100 percent on the 1-, 2-, and
3-year-old burns, respectively.  Fires occurring at very short intervals
may completely eradicate postfire seedling reproduction if the soil seed
reserve is not well established and reproductive maturity has not been
reached [58,136].  Although sprouts are generally capable of heavy seed
production by the second year after fire [65], chamise seeds exhibit
poor viability.  A number of years are required to build up the
seedbank.

Seedbanks:  Chamise seed is sensitive to high temperatures [16,40,130].
Depending on fire intensity and seed position in the soil, a large
portion of the seedbank may be destroyed as the soil temperature rises
during burning [111].  While abundant seed is present beneath the shrub
canopy and in gaps between shrubs, burning modifies the seedbank by
concentrating readily germinable seed in the shrub interspaces.  Soil
temperatures during burning are lower in the shrub interspaces, and more
seeds survive fire in these interspaces than below the canopy [23].
Fire sensitivity is increased if seeds have imbibed water [23,99], and
seed mortality is high following spring fires, which are often severe
[111].  Reduced seed mortalities can be expected when fires occur under
dry soil conditions associated with late summer and fall.


DISCUSSION AND QUALIFICATION OF FIRE EFFECT : 
Small plants with a prefire biomass between 2 and 11 pounds (1 and 5 kg)
are particularly prone to fire mortality [3] because of their shallow
lignotubers and presumably smaller carbohydrate reserves [3,116].
Individuals with larger lignotubers are generally more fire tolerant,
although large shrubs which have survived previous fires may have more
dead material in their crowns, making them more prone to fire mortality
[124].  Fire susceptibility of larger plants also increases in older
stands where high fuel loads produce severe fires [74].  Mean lignotuber
area of fire-killed plants in a 90-year-old stand was 35 square inches
(227 sq cm) compared to 12 square inches (79 sq cm) for plants in a
23-year-old stand [74].  Very large chamise lignotubers tend to rot in
the center and are less capable of sprouting after fire [60].  While
young seedlings are readily killed by most fires, fire tolerance
increases with age.  In southern California, large numbers of 4-year-old
chamise sprouted following intense summer grassfires [58,136].


PLANT RESPONSE TO FIRE : 
Postfire regeneration in chamise involves a combination of sprout
regeneration and seedling recruitment [48,54,69,120].

Vegetative regeneration:  Although considerable plant mortality may
occur following fire, at least some percentage of the chamise population
survives and sprouts [39,42,61,120].  Residual plants typically sprout
within 6 weeks of fire regardless of season [108].  On sites in southern
California, chamise along moist ravines sprouted within 10 days of a hot
July wildfire [105].  Sprouts originate on the lignotuber from a narrow
band of tissue located 0.2 to 1 inch (0.5-2.5 cm) below the soil surface
[109].  Perennating buds along the periphery of the lignotuber are the
first to initiate sprouts, followed by buds near the base of charred
stems [6].  Sprout production varies by lignotuber size.  Large plants
usually possess large lignotubers which produce as many as 500 sprouts
[6].  During the first year sprout numbers are drastically reduced as
larger stems gain dominance [6,111].

Sprouts use stored carbohydrate reserves to achieve rapid growth
[109,111].  Rapid shoot elongation typically occurs during the first
spring following fire [60,108].  After fires in northern California,
sprouts averaged 20 inches (50 cm) by the end of the first postfire
growing season [9].  Shrubs with a large prefire biomass typically
produce the most vigorous sprouts and can be expected to dominate the
postfire community [124].  Baker and others [3] indicated that sprout
biomass of residual plants at the end of postfire year 1 is positively
correlated with prefire biomass.  Stem growth slows during postfire
years 2 and 3 [54,108], and growth during subsequent years declines
until it is almost neglibible by 20 years after fire [54,108].  Horton
and Kraebel [54] reported that 5-year-old sprouts reached an average
height of 33.6 inches (84 cm), while 20-year-old sprouts were only 40.4
inches (101 cm) tall [54].

The pattern of postfire sprout growth usually follows that of mature
plants.  Time of fire, however, may alter the initial pattern of
postfire shoot growth.  On sites in the southern Sierra Nevada, plants
burned in late June or early August produced sprouts that grew
continuously until the second postfire summer [108].  The reduced leaf
area of sprouted plants limited transpiration losses and resulted in
higher shoot water potentials, permitting shoot growth through the
summer drought period [46,47].  While summer fires (at a time of reduced
carbohydrate reserves) initially resulted in significantly shorter
plants, shoot heights of plants burned in different seasons were similar
by the end of the second postfire year [108].

Seedling regeneration:  Chamise produces an abundant crop of seedlings
from soil-stored seed [17,39,45].  While a flush of initial seedling
establishment may occur immediately following fire, subsequent mortality
is quite high [59,73,85].  On sites in southern California, seedling
densities in March ranged from 91,427 to 180,383 seedlings per acre
(37,000-73,000 seedlings/ha) but dropped to 29,652 to 34,594 pere acre
(12,000-14,000/ha) by June [73].  The degree to which seedlings
contribute to the postfire recovery of chamise is quite variable and
appears related to site conditions, amount of fire-induced adult
mortality, and stand age [39,58].  On sites where the majority of plants
survive fire, prefire shrub density is maintained and little seedling
establishment occurs.  Conversely, seedling establishment is often
substantial and critically important in regaining prefire levels on
sites where adult survival is low [3,66].

Recovery:  Because of hot, dry site conditions, postfire growth of
chamise chaparral is slow compared to other chaparral types [53,100].
Initial sprouting response may be substantially reduced following
intense summer fires, since more of the meristematic tissue in the
lignotuber is killed [116].  Four months after a July wildfire in
southern California, chamise plants produced up to 12 sprouts per plant,
but sprouts rarely exceeded 12 inches (30 cm) in length [105].  In
southern California chamise communities, chamise rapidly dominates the
postfire community and commonly comprises at least 33 percent of the
vegetation on 10-year-old burns.  In stands 22 to 40 years of age, it
reaches a maximum of approximately 50 percent of the total vegetative
cover [39].


DISCUSSION AND QUALIFICATION OF PLANT RESPONSE : 
Since chamise sprouts following fire, reproduction from seed is
generally considered facultative [43,68].  Chamise relies primarily on
vegetative reproduction for postfire establishment on foothill sites in
the southern Sierra Nevada [116,118].  Although as many as 2.73 million
seedlings per hectare may emerge following fire, they are usually
outcompeted by faster growing sprouts [117].  Likewise, vegetative
reproduction is the predominant mode of postfire regeneration at higher
elevations in southern California mountains [71,73,129].

As chaparral sites become increasingly arid, however, sprouting tends to
be less successful and seedling recruitment more prevalent following
fire [39,136].  On droughty, low elevation sites in southern California,
chamise depends to a large degree on successful seedling establishment
for population replacement after fire [56,58,71,72,136].  Howe and
Carothers [58] found that chamise seedlings grew vigorously and
contributed significantly to postfire stands at elevations between 1,312
and 1,968 feet (400-600 m) near Newhall, California, in Los Angeles
County.  Chamise seedlings comprised approximately 86 percent of the
chamise population on 6- to 9-year-old-burn sites.  Although seedlings
grew more slowly than sprouts during the first few postfire seasons,
they reached heights equal to that of sprouted plants within 8 to 9
years.  On 6-year-old, north-facing burns, however, vegetative
reproduction was the predominant mode of regeneration [58].  Hanes [39]
indicated that altitude also influences mode of postfire reproduction.
He found that seedlings comprised a higher proportion of the postfire
vegetation on burn sites between 1,000 and 2,000 feet (300-600 m) than
between 2,000 and 4,000 feet (600-1,200 m).


FIRE MANAGEMENT CONSIDERATIONS : 
Fire frequency:  Chamise is adapted to a fire cycle range from 10 to 100
years.  It can regenerate after fire intervals of over 100 years,
however [68,74,90,116].  Its capacity for canopy rejuvenation without
fire allows chamise to persist through long fire-free intervals.
Stohlgren and Rundel [125] suggested 30 to 80 years as a "typical" fire
frequency for chamise chaparral communities in Sequoia National Park.

Influence of ryegrass seedings:  Ryegrass (Lolium multiflorum) is often
seeded onto recently burned chaparral as a means of emergency
revegetation [4].  Ryegrass, however, inhibits growth and development of
chamise seedlings [33], and ryegrass substantially reduces postfire
chamise seedling establishment [4,33].  On seeded burns in southern
California, almost no chamise seedlings established where first-year
ryegrass cover ranged between 40 and 90 percent [19].

Ryegrass seedings also produce an easily ignitable fuel bed that
increases the likelihood of an early reburn.  Fires occurring at short
intervals have the potential to cause significant changes in species
density and composition within chamise chaparral [4].  Not only do
frequent fires produce high mortality of sprouted plants [136], but
postfire seedlings (derived from the previously dormant seedbank) are
also killed, thereby depleting the on-site seed reserve [66,136].
Consequently, chamise is unable to reestablish, and gaps in the shrub
matrix are subject to invasion by coastal sage scrub species such as
black sage, California sagebrush, and California buckwheat.  The site
may be dominated by coastal sage scrub species for 100 years or more
[4].

Deer browse:  Deer use of chamise is often extensive immediately
following fire [9,113,121].  Browse value of sprouts lasts for only 2 to
3 years because plants quickly mature to less nutritious stages or die
from overuse [96].  To enhance deer use of sprouts, cattle access to
burns should be restricted during the first postfire season [113].
Because of the lack of adequate escape cover, only the periphery of large
burns receive extensive deer use prior to the second postfire season.
The center of large burns are rarely if ever utilized during the first
several seasons [96].  Close utilization within the first year may kill
chamise, and mortalities of up to 64 percent are possible under intense
browsing pressure [10].

Late winter or early spring fires are most favorable for production of
deer browse because succulent sprouts with a high nutrient value are
produced almost immediately, and subsequent sprout growth is rapid
during the spring growth period [76]. If fires are conducted after
mid-September in northern California, sprouting may not be profuse until
the following spring [9].  Fires resulting in total plant consumption
produce the most usable browse, since deer tend to avoid burned chamise
with main scaffold branches remaining [9,24].

Related categories for Species: Adenostoma fasciculatum | Chamise