BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Flourensia cernua | Tarbush 



GENERAL BOTANICAL CHARACTERISTICS : 
Tarbush is a much-branched, densely leafy shrub.  It grow from less than
1 foot (0.30 m) to 3 to 7 feet (1-2 m) tall.  This native perennial
produces a tarlike odor, hence its common name [8,16,26].

Tarbush leaves are alternate, simple, and elliptical, and are covered
with small black glands..  The sticky leaves grow up to 1 incg (2.5 cm)
long.  The scaly stem appears white because of hairs and dried resin
[16,20,26].

The composite flower heads are small, solitary, and inconspicuous.  The
disked flower heads lack ray flowers and are pendant [8,16,26].  The
fruit is an achene.  Densely hairy, relatively motile seeds are produced
in small pendant clusters [2,5].


RAUNKIAER LIFE FORM : 
   Phanerophyte
   Therophyte


REGENERATION PROCESSES : 
Tarbush grows at a slow rate and can spread vegetatively.  This shrub
produces a relatively motile seed that can be dispersed by wind [5,6].


SITE CHARACTERISTICS : 
Tarbush thickets inhabit deserts, and dry soils of valleys, mesas,
flats, and foothills [16,26].  It reaches its best development in heavy
clay loam soils with some gravel near the surface on sites that receive
some flood water.  It is often found in limestone or calcareous soils.
Although it grows intermixed with creosotebush, it prefers soils that
are deeper (24 inches [60 cm]) than those in areas where creosotebush
dominates.  It also grows into fringe areas of tobosa swales
[5,7,16,20].  Although only 1 foot (0.30 m) tall or less in dry areas,
tarbush may reach heights of 6 feet (1.8 m) or more on favorable sites
[16].

Elevations range from 3,000 to 6,500 feet (1,067-1,981m) [16].

Primarily an inhabitant of the Chihuahuan Desert, tarbush is adapted to
an average annual precipitation of 9.4 inches (24 cm), 70 percent of
which falls in the summer when desert plants tend to be dormant and only
20 percent of which falls in the winter [2].  Temperatures are extreme;
June has an average high of 97 degrees F (36 deg C), January averages a
high of 56 degrees F (13 deg C).  Temperatures exceeding 89 degrees F
(32 deg C) can occur on 115 or more days in a year, but temperatures can
also fall below 32 degrees F (0 deg C) on 66 days [2,22].


SUCCESSIONAL STATUS : 
Tarbush occurs in the desert shrub ecosystem, a system which may fall
outside traditional ideas of succession.  Extreme events or
"disturbances" of the classical deciduous forest model of succession do
not necessarily produces changes in species composition in the desert.
The desert may be "autosuccessional" in this regard.  In addition, if
species composition does change, no predictable sequence of successional
events can be made.  The concept of climax as the final phase in a
predictable, relatively unidirectional sequence of change in species
composition may not be a valid element of desert succession [32].

Disturbance, even to the point of total destruction of aboveground
vegetation, does not drastically alter soil or water conditions in the
desert.  The "climax" or stable vegetation type is well adapted to the
extremes of desert climate whether a site is bare or vegetated, unlike
mesic counterparts.  However, if long-term disturbance has led to
species composition change, this may not be reversed by a simple
cessation of disturbance.  Reinvasion by species of the original
community may necessitate unusual and extreme conditions.  Because the
pace of regrowth is slow in deserts, successional stages may appear to
occur, but these may not be necessary for establishment of the stable
community that will emerge over time [19].

Campbell [6] considered tarbush to be characteristic of the late seral
stage on clay soils and of climax on gravelly clay loams in southern New
Mexico.  Muller [21] stated that no seral stages occurred in
creosotebush-tarbush climax types since disturbance did not result in
invasion of new species.  Such communities did not develop along
classical successional lines.

Tarbush is part of the desert grassland disclimax in which shrubs invade
the herbaceous community following grazing.  Tarbush primarily invades
tobosa grasslands.  Quickly reinvading, this shrub frustrates attempts
to convert such rangeland back to grassland [22,27].


SEASONAL DEVELOPMENT : 
Tarbush is a rather unusual desert shrub because new growth occurs in
midsummer and flowers appear in late fall.  Fruit matures from January
to March [26].

Related categories for Species: Flourensia cernua | Tarbush