BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Adenostoma fasciculatum | Chamise 



GENERAL BOTANICAL CHARACTERISTICS : 
Chamise is a diffusely branched, resinous, native shrub [25,91,121] from
2 and 12 feet (0.6-3.5 m) tall [91].  Plants are unarmed, spreading, and
branch very close to the ground [91,128].  The many slender stems are
erect and generally lack permanent branches [38].  Young stems have
reddish bark; bark becomes gray and shreddy with age [38,91].  Linear,
needlelike leaves occur in alternate fascicles along the stem [18,121].
Leaves are 0.25 inch (0.6 cm) long, sharp-pointed, heavily sclerified,
and evergreen [18,38,65].  The inconspicuous, bisexual flowers are white
and occur in showy, 1- to 4-inch-long (2.5-10 cm) terminal clusters
[22,121].  The fruit is an achene [91,128].

Although rooting habit is variable [79,84], roots are usually deeply
penetrating, much branched, and widespreading [38,49].  The root system
is extensive in relation to the crown [78,79].  Chamise typically
develops several taproots which penetrate fractured rock to depths of 10
to 12 feet (3.0-3.7 m) [38]; extensive laterals originate from the
lignotuber [49].  Longevity of chamise is estimated at 100 to 200 years
[52,66,116].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Chamise reproduces sexually and vegetatively.  Since chamise seed
germinates at high rates only after fire, seedling recruitment and
population expansion are fire dependent [68,69].  Canopy rejuvenation
through the production of new basal sprouts occurs with or without the
influence of fire [68,70].

Reproduction by seed:  Onset of seed production occurs early in chamise,
often by 3 years of age [27].  Seed production does not appear to
decrease with age.  Ninety-year-old shrubs generally produce
substantially greater quantities of seed than those 20 years of age
[66].  Seeds are dispersed during the summer [69].  Because the small
achenes are not highly specialized for wind disperal, most seeds fall
near the parent plant [69].  Although the seed crop is abundant, the
majority of seeds are not filled and viability is quite low, in some
cases 0 to 4 percent [38,69,88,126].  Maximum seed production occurs
following winters with above-average rainfall [3,38].

Chamise produces a dimorphic seed population composed of dormant as well
as readily germinable seeds [16,126].  Dormancy is imposed by a more or
less impermeable seedcoat.  Heat from fire scarifies the seedcoat and
stimulates germination [16,69,126].  Christensen and Muller [16] found
that germination was enhanced when seeds were exposed to temperatures of
160 to 180 degrees Fahrenheit (71-82 deg C) for 15 minutes.  Keeley [69]
suggested that heat shock from fire and the presence of charate (charred
wood) may act synergistically to stimulate germination.  In laboratory
studies, Keeley found that addition of charate significantly increased
germination (11%) relative to controls (4%).  Maximum germination (18%),
however, occurred when heat-treated seeds were incubated in the presence
of charred wood [69].  Black sage (Salvia mellifera) apparently inhibits
chamise germination [131].

Under natural conditions, dormant seeds accumulate in the soil until
stimulated by fire to germinate [66,126].  Chamise seeds are unpalatable
and seedbanks apparently are not subject to heavy predation [111].
Consequently, chamise seed densities increase over time [133].  Seed
density in the seedbank beneath 9-year-old stands was estimated at 2,000
seeds per square meter while in 85-year-old stands, seed density was
approximately 21,000 seeds per square meter [132].  Abundant germination
from soil-stored seed occurs during the first rainy season after fire;
germination during the second year is uncommon [54,67,111].  Although
emergent seedling populations are quite high [45], mortality is
substantial during the first several years [39,54,120].  On sites in
southern California, approximately 90 percent of the seedlings that
germinated during March and April died within the first year [80].
Drought stress during late spring and summer is a major cause of
first-year seedling mortality [59,86].  By the end of the second growing
season, drought-induced mortality decreases as seedlings develop
sufficient root biomass [87].  Taproots of newly germinated seedlings
are barely 2 inches (5 cm) long by July, whereas taproots of 2-year-old
seedlings range between 8 and 12 inches (20-30 cm) [80].  Small mammal
herbivory contributes significantly to mortality [17], particularly in
the fall [85].  First-year mortality due to rabbits may be as high as 25
percent [85].  Failure to establish may also be due to lack of suitable
microsites and competitive interference [43,86].  On southern California
burns, survival of first-year seedlings was not affected by the presence
of residual shrubs or herbaceous perennials; annuals, however,
significantly reduced seedling growth [80].

Many chamise plants die during subsequent years [48,120], but some
survive [48,54].  Twenty-five years after a fire in central California,
chamise resulting from seed were still growing and had reached an
average height of 31.9 inches (80 cm) [54].

A portion of chamise seed germinates without fire scarification under
favorable moisture and temperature conditions [126,133].  A study of the
seedbank beneath an 85-year-old stand of chamise indicated that 20
percent of the chamise seedbank (density averaged 9,500 chamise seeds/sq
m) was readily germinable [133].  Although initial establishment
sometimes occurs without the influence of fire [35,54,101], seedling
survival beyond the first year is extremely low and usually limited to
areas recovering from human disturbance or overgrazing [135].  In mature
chaparral, seedlings occasionally establish in canopy gaps, but
successful establishment almost never occurs directly beneath the canopy
[17,38,69,70,72,134].

Vegetative regeneration:  Chamise rejuvenates its crown by continually
producing new sprouts from an established lignotuber [48,69,70].
Following disturbances such as fire or cutting, chamise sprouts
vigorously from surviving adventitious buds on the lignotuber [57,120].


SITE CHARACTERISTICS : 
Chamise is the most common chaparral species throughout the foothills
and coastal mountains of California [13,38,39].  It is present in
approximately 70 percent of California chaparral [13,39].  It is most
often associated with hot, xeric sites [43] over a wide range of
elevations, soils, latitudes, and distances from the coast [44].  In
southern California it is a ubiquitious dominant on outwash plains,
mesas, ridges, and dry, south- and west-facing slopes at elevations up to
6,000 feet (1,800 m) [18,35,38,52,91,100,121].

Sites supporting chamise commonly receive between 10 and 40 inches (250
and 1,000 mm) of annual precipitation, and have a temperature range from
32 to 100 degrees Fahrenheit (0-38 deg C) [48].  In the southern Coast
Ranges, where average annual rainfall ranges from 16 and 20 inches
(400-500 mm), chamise occurs abundantly on all slopes and exposures and
grows on deep, fertile soils as well as shallow, rocky ones [48,121].
As precipitation increases farther northward, chamise is largely
restricted to the poorer soils and the drier, more exposed sites
[48,120].

Chamise occurs in both pure and mixed stands [38,39,120].  Nearly pure
(>80%) stands of chamise are impenetrable and are referred to as
"chamisal" [20,25,43].  Such stands usually have shallow, rocky soils
with a southern aspect [35,53].



SUCCESSIONAL STATUS : 
Facultative Seral Species

Chamise is a long-lived, shade-intolerant shrub [66] which dominates
lower elevation chaparral throughout much of California [20,42].
Disagreement exists over whether its dominance is a reflection of a
climatic climax [5,20] or is a fire-induced subclimax [42].  Hanes
[43,44] stated that chamise chaparral is unable to perpetuate itself in
a vigorous condition without recurrent fire and terms it a true
"fire-type vegetation".  Chamise stands older than 60 years of age are
sometimes termed " decadent" [39,48].  Old stands have low species
diversity and produce little annual growth, with dead stem biomass far
exceeding live stem biomass [40,43].  Stand stagnation has been
attributed to the accummulation of biochemicals in the the soil that
inhibit decompostion, humification, and nitrification [40,94,131].
Limited nutrient availability, especially of nitrogen, may partially
contribute to the decline of chamise chaparral [119].  Fire rejuvenates
stagnant stands by removing phytotoxic substances from the soil,
increasing the concentration of available nutrients, and stimulating
sprouting of adults and germination of dormant seed [44].

Chamise is present soon after fire and remains present in all stages of
succession.  It achieves initial postfire dominance through vigorous
sprout production and establishment of large numbers of seedlings
[9,74,120].  Typical vegetal cover on 1-year-old chamise chaparral burns
also includes a high percentage of herbaceous vegetation and the
seedlings and sprouts of associated shrubs and subshrubs.  As chamise
seedlings and sprouts grow during the first postfire decade, herbaceous
vegetation rapidly declines; likewise, subshrubs and short-lived shrubs
are restricted to smaller and smaller openings [29,45].  A dense stand
of chamise typically develops within approximately 8 to 10 years [42],
with chamise frequently comprising one-third of total cover [39].
Stands often exhibit complete canopy closure by 22 years of age [116].
In pure stands of chamise in southern California, chamise may reach 25
percent, 50 percent, and 55 percent cover within 10, 40, and 70 years of
fire, respectively [53].

Short-lived shrubs and herbaceous cover are largely lacking from
undisturbed stands of chamise chaparral [116].  Chamise probably
produces allelopathic toxins which inhibit germination and growth of
other species [16,17].  During summer drought, chamise leaves accumulate
water-soluble phenolics as a result of normal metabolic activity; fog
drip and rain transport the toxins into the soil [43,83].  Competition
for light may also be a factor controlling seed germination beneath
mature stands [67,69].

Although chamise has only a limited ability to colonize disturbed areas
[135], it is capable of pioneering broken rock surfaces and alluvial
washes [43].  Chamise may invade woodlands where grass cover is sparse
and sometimes invades productive soils following fire [48].  On sites
with relatively deep soils, decadent chamise may be replaced by annual
grasses [35].


SEASONAL DEVELOPMENT : 
Stem elongation occurs from February through May [2,130].  Shoot
organization in chamise consists of short and long shoots and has been
described by Jow and others [62].  New leaves appear in late January or
February and continue to develop as shoots elongate [2].  New foliage is
not limited to the current season's growth; short shoots remain active
and produce leaves on 2- to 8-year-old branches [62].  Leaves are
retained for two growing seasons [118].

Chamise produces nearly twice the amount of reproductive tissue as it
does new stems and leaves [89].  In Sequioa National Park, flowers
develop on the current year's growth in June followed by fruit
development in July [2].  Fruit ripening and dispersal is completed by
August.  At this time, inflorescences die back and new growth becomes
woody [2].  Although flower bud development and flowering occur at a
time of decreasing water potential, reproductive growth is somewhat
resistant to summer drought conditions.  Water stored in the lignotuber
allows chamise to maintain reproductive growth despite low water
potentials [2].  Ample rainfall during the season directly preceeding
major growth activity increases the quantity of reproductive as well as
vegetative growth [2,38].

Root growth:  The period of root growth lasts considerably longer than
the seasonal flush of shoot growth [78].  Fine roots may grow for 5 to 7
months [78].

Carbohydrate reserves:  Onset of shoot growth is preceeded by
carbohydrate mobilization to the shoot apex and correlated with a
decrease in the starch concentration of the roots and lignotuber [108].
Demand for nutrients during canopy and reproductive growth is quite high
and by the end of the spring growth season, carbohydrate reserves in the
roots and lignotuber are largely depleted [61].  During the summer,
water stress-induced suppression of photosynthesis results in a
reduction in carbohydrate availability at the shoot apex, and shoot
growth ceases [1,5,38,108].  Cessation of growth is followed by a
gradual increase in root starch reserves over fall and winter [61,81].

Related categories for Species: Adenostoma fasciculatum | Chamise