FIRE CASE STUDIES
SPECIES: Encelia farinosa | Brittle Bush 



CASE NAME : 
Fire in Creosotebush Scrub of the Sonoran Desert, California


REFERENCE : 
Brown, D. E.; Minnich, R. A. 1986 [7]


SEASON/SEVERITY CLASSIFICATION : 
Beginning in 1978, a series of fires spread through dried herbaceous
fuels into extensive areas of creosotebush (Larrea tridenta) scrub.  The
flames reduced the herb layer to a low stubble, indicative of
fast-moving, low-intensity fires.  Fires occurred in June, July, August,
or September.


STUDY LOCATION : 
Four sites, on Quaternary alluvial fans descending from the east scarp of
the San Jacinto Mountains at the end of the Coachella Valley near Palm
Springs, California, were chosen for study.  The four sites were located
at the fire boundaries on the Chino, Blaisdell, and Palm canyon alluvial
fans in order to compare burned vegetation with adjacent unburned
stands.

Fires occurred in the Chino Canyon fan (1,250 acres [500 ha], 1978),
Blaisdell and Chino canyons (6,900 acres [2800 ha], 1980), and the east
scarp and alluvial fans below 3,200 acres (1,300 m) from Chino Canyon to
Palm Canyon (15,000 acres [6,000 ha], 1980).  A 3,000 acre (1,200 ha)
fire in 1982 overlapped large areas burned in 1973 near Snow Creek.  In
1983, the first of three fires reburned portions of the Snow Creek area
and Blaisdell Canyon.  Two smaller fires also occurred along Snow Creek
road and Interstate 10.


PREFIRE VEGETATIVE COMMUNITY : 
Most of the Sonoran Desert is covered with creosotebush scrub consisting
of scattered low shrubs less than 6.6 feet (2 m).  Representative growth
forms include evergreen sclerophyllous and deciduous shrubs, subligneous
subshrubs, leaf and stem succulents, and annual herbs.  Bajadas and
adjacent mountainsides in the Coachella Valley are covered by
creosotebush, brittle bush (Encelia farinosa), big galleta (Hilaria
rigida), hedgehog cactus (Echinocereus engelmannii), and Grays ratany
(Krameria grayi).

Vegetation on the plains and lower bajadas, including the study sites,
is dominated by creosotebush, white bursage (Ambrosia dumosa), and
brittle bush, which may form 60 to 100 percent of total vegetation
cover.  Blue paloverde (Cercidium floridum), ironwood (Olynea tesota),
smoketree (Dalea spinosa), beloperone (Beloperone californica), and
desert lavender (Hyptis emoryi) are common along washes.  Succulents
such as Ferocactus acanthodes, hedgehog cactus, beavertail cactus
(Opuntia basilaris), teddy-bear cholla (O. bigelovii), and golden cholla
(O. echinocarpa) reach maximum densities on sandy hillsides and bajadas
with rocky, gravelly, or sandy substrates.


TARGET SPECIES PHENOLOGICAL STATE : 
The phenological state of brittle bush at the time of the fires is
unknown.  The areas were surveyed between April 25 and May 27 1983, when
brittle bush was in full growth or flower.


SITE DESCRIPTION : 
The climate of the Coachella Valley is extremely arid.  Average annual
rainfall at Palm Springs is 5.4 inches (138 mm).  Summers are hot and
dry, although there are occasional thunderstorms, mostly over the nearby
mountains.  Coarse-textured soils are well-drained and moderately
alkaline, with a minimum of organic matter.  No information was given as
to the specific topography, slope, and elevation of each site.


FIRE DESCRIPTION : 
The fires in creosotebush scrub characteristically spread during periods
when ambient temperatures averaged 95 to 104 degrees Fahrenheit (35-40
deg C) and relative humidity ranged from 10 to 25 percent.  High winds
were caused by the typical spring and early summer gravity acceleration
of descending coastal marine air spilling through San Gorgonio Pass.
Upcanyon winds and nocturnal air drainage promoted fire spread on the
eastern face of Mt. San Jacinto.  The flames reduced the herb layer to a
low stubble, indicative of fast-moving, low-intensity fires.


FIRE EFFECTS ON TARGET SPECIES : 
The vegetation was sampled three growing seasons after fires at
Blaisdell, Palm Canyon and Palm Indian sites and five growing seasons
after fire at the Chino site.  Brittle bush plants were mostly scorched.
Only leaves and branches near the ground burned, leaving foliage on
higher stems.  However, brittle bush suffered 93 percent mortality.

None of the severely burned brittle bush plants resprouted after fire;
16 percent of the scorched plants resprouted.  Brittle bush accounted
for most of the seedlings observed during the first growing season.  The
wet 1982-1983 season was followed by abundant reproduction of brittle
bush in both burned and unburned sites.  After 3 to 5 growing seasons,
the total cover in burned sites was about half that of unburned sites
and was composed mostly of brittle bush.

Density (D) and cover (C) of established (unburned) and resprouting
(burned) brittle bush at two sites in the Sonoran Desert, California,
are shown below.  Density is expressed in number of plants per 100
meters square.  Cover is expressed as percent ground covered.

                 unburned      burned
                  D     C      D    C    
Chino           11.5   9.2    1.5  2.0  
Palm Canyon     13.0  10.6    2.0  2.6
Palm Indian      3.0   1.4    2.5  3.5
Blaisdell        1.0   0.9    0.0  0.0

Brittle bush seedling density (number/ha) in initial and subsequent
growing seasons was:
        
        1980-1981    1981-1983

Burned   1,460         7,010  
Unburned    90         5,650 


FIRE MANAGEMENT IMPLICATIONS : 
Fires are infrequent in the Sonoran Desert owing to limited biomass,
wide spacing between shrubs and sparse ground cover.  Successional
studies in creosotebush scrub reveal postdisturbance recolonization by
long-lived species is very slow and may require hundreds of years.
Fires may have long-term impacts on the structure and composition of
this community.  Brittle bush is a good colonizer after fire.  Fires in
creosotebush scrub have resulted in an increase in brittle bush
frequency and density.  Recent fires have converted creosotebush scrub
at Palm Springs to brittle bush coastal sage scrub similar in
composition to the stands covering semiarid interior valleys around
Riverside, California.

Related categories for Species: Encelia farinosa | Brittle Bush