BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Bromus tectorum | Cheatgrass 



GENERAL BOTANICAL CHARACTERISTICS : 
Cheatgrass is an exotic, annual, or occasionally biennial grass
dominating millions of acres in the western United States.  It is
particularly prevalent in the the palouse prairie and sagebrush
grassland of the Intermountain region and the Pacific Northwest.  It is
an invasive species, favored by disturbances such as overgrazing,
cultivation, or frequent fire.  Cheatgrass effectively outcompetes
native vegetation when cover of these species has been reduced.  Its
rapid growth and its ability to utilize most of the available upper soil
moisture enables it to exclude seedlings of other species [10,24].


RAUNKIAER LIFE FORM : 
   Therophyte


REGENERATION PROCESSES : 
Cheatgrass seed may germinate from fall through spring, depending on
moisture conditions.  Seeds are inhibited by high light intensities and
high temperatures.  This is particularly true for recently shed seed.
After 3 months of afterripening the impact of these factors lessens.
This inhibition prevents germination during the hot, dry summer months.
If the summer is unusually cool and wet, germination can take place.

Root elongation is rapid after germination and continues throughout the
winter in spite of low temperatures.  By spring, roots are well
developed and and able to use available soil moisture more efficiently
than native species, which develop at a slower pace.

Stature and seed production is strongly influenced by site conditions.
On good sites without strong competition, robust plants with many
flowering culms develop.  In unusually moist years (early summer rains),
a second seed crop may be produced [10].

Litter and rough microtopography aid the establishment of cheatgrass by
providing moderated temperatures and humidities for seeds [28].  Due to
germination, predation, and decomposition, fewer than 13 percent of seed
may survive until the following winter [17].  However, seeds stored
under dry conditions have germinated after more than 11 years [12].


SITE CHARACTERISTICS : 
Cheatgrass is able to establish on a variety of soils and is
particularly favored by conditions of disturbance, such as those
produced by fire, overgrazing, or cultivation.  It generally grows in
the 6 to 22 inch (15-56 cm) precipitation zone [13] but may also be
found in somewhat moister or drier conditions [12,14].  Although not
exacting in its requirements, cheatgrass appears to avoid areas of
extremely low precipitation or those with saline soils.  It is a
shade-intolerant plant and obtains its best growth in foothill or
grassland conditions in the Intermountain region [14].

Elevational ranges for cheatgrass in several western states are as
follows [6]:

          from 4,100 to 8,000 feet (1,250-2,450 m) in Utah
               4,000 to 9,500 feet (1,220-2,900 m) in Colorado 
               3,700 to 8,500 feet (1,130-2,600 m) in Wyoming 
               3,200 to 6,300 feet (  980-1,920 m) in Montan 


SUCCESSIONAL STATUS : 
Facultative Seral Species

Cheatgrass acts as both an early seral invader and a climax dominant on
many sites that historically supported a perennial grass and forb
understory.  Cheatgrass invades sites soon after disturbance.  It can
dominate by the 2nd year after fire and has been observed to retain its
position for at least 4 or 5 decades [3,4].  Site potential does not
seem to influence the success of cheatgrass.  With an adequate seed
source it is able to overtake native vegetation throughout the range of
sagebrush communities.  The overriding consideration in gauging its
potential success is the presence of rough microtopography and litter.
[25,28].


SEASONAL DEVELOPMENT : 
Cheatgrass generally germinates in the fall and grows rapidly until cold
temperatures set in.  When fall moisture is inadequate, it acts as a
spring annual.  After germination in the fall, vegetative growth may be
as much as 2 to 4 inches (5-10 cm).  For this degree of development, 2
inches (5 cm) or more of precipitation must accumulate.  These
conditions occur about 1 in 5 years in southeastern Idaho and 1 in 8
years in southwestern Idaho.

Spring production may be substantial, but plants are generally dry by
early June.  The stage of plant maturity is indicated by a change in
color.  Plants change from green to purple to tan as they cure. The
purple stage may be induced by a sudden drop in temperature or droughty
conditions.

Seeds become viable while plants are still mostly green and before they
are disseminated.  They ripen from late spring to early summer [10].

Cheatgrass phenology in Idaho has been documented as follows [14]:

Place    Year  Boot  Full  Anthesis  Soft  Purple  Brown Ovary  Seed
                     head            dough               dry    falls

Lewiston 1950  ----   3/6     5/6     5/27   6/3    6/10  6/10   ----
Boise    1957  4/23   4/29    5/6     ----   5/6    6/14  ----   6/14
Boise    1958  4/30   5/6     ----    5/17   5/17   6/10  6/10   7/18
Boise    1960  4/21   5/6     5/13    5/20   5/20   ----  5/26   6/2 

Related categories for Species: Bromus tectorum | Cheatgrass