BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Encelia farinosa | Brittle Bush 



GENERAL BOTANICAL CHARACTERISTICS : 
Brittle bush is a native, drought-deciduous, perennial shrub
[7,8,21,28].  It grows to about 5 feet (1.5 m).  It has a woody base and
is rounded and much-branched in form.  Thick branches support an
umbrella of leaves with few stems beneath [7].  The leaves are 0.7 to 2
inches (2-5 cm) long and 0.6 to 1 inch (1.5-2.5 cm) broad.  They are
mostly located toward the end of branches [35].  The flowering heads are
loosely clustered on long naked branchlets [1,35].  Brittle bush is
short lived.  On permanent plots in the Sonoran Desert, the maximum
observed longevity was 32 years [54].

Brittle bush generally has shallow roots [27].  One study found that the
root system of brittle bush on a north-facing slope was composed of a
stout taproot and numerous laterals.  All laterals bore groups of
filamentous roots [8].


RAUNKIAER LIFE FORM : 
   Phanerophyte


REGENERATION PROCESSES : 
Sexual reproduction - Brittle bush reproduces almost exclusively by seed
[7,45].  Seeds are dispersed long distances by wind.  Brittle bush often
germinates prolifically after heavy winter rains [7].  Plants are not
frost tolerant, and frost may damage leaves and stems [39].

Reproduction may be reduced by interspecific competition.  Growth and
productivity of brittle bush is limited by the low precipitation in its
native habitat.  Neighboring brittle bush further decrease water availability,
reducing brittle bush productivity [51].

Vegetative reproduction - Brittle bush can sprout from the root crown
[7,26].

Brittle bush is allelopathic.  The leaves produce a toxic, water-soluble
substance that inhibits the growth of several winter annuals [24].


SITE CHARACTERISTICS : 
Brittle bush is commonly found on dry, rocky or gravelly slopes and
mesas [1].  In the Sonoran Desert brittle bush is common on
south-facing, granitic slopes, volcanic slopes, upland flats, and
alluvial flats [44].  In coastal sage scrub brittle bush grows on soils
derived from alluvial deposits, sandstone, granite and diorite [44].  It
also grows on desert pavement [33].  Brittle bush grows poorly on clay
soils [16].  It occurs at elevations up to 3,000 feet (915 m)
[38,46,47].

Brittle bush is restricted to climates with long periods of limited
moisture.  The total amount of precipitation in these areas is quite
variable.  The seasonal pattern of rainfall is also variable, with some
brittle bush areas receiving most of the rain in winter, and other areas
receiving mostly summer rain [50].


SUCCESSIONAL STATUS : 
Facultative Seral Species

Brittle bush usually occurs in initial and early seres [7,31,34,42]. It
is an early colonizer of disturbed sites, often replacing long-lived
perennials in postfire communities [7,31,34,40].  An open brittle bush
community may persist for decades [7].  In permanent plots in the
Sonoran Desert, brittle bush density and cover was more or less stable
over 72 years.  However, only 17 percent of seedlings survived to the
seventh year [54].


SEASONAL DEVELOPMENT : 
Brittle bush leaves and flowers are formed whenever the water relations
are favorable [8].  This can occur any time from November through May
[35].  Under extreme drought conditions brittle bush becomes dormant and
the leaves are shed [21,50].  Brittle bush also shows seasonal variation
in leaf density and thickness.  During times of available water, leaves
expand more, are less pubescent, are less capable of reducing water
loss, and have lower resistance to carbon dioxide flux.  These
characteristics are reversed as soil water decreases and the more
mesophytic leaves abscise [50].

Related categories for Species: Encelia farinosa | Brittle Bush