BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Bromus inermis | Smooth Brome 



GENERAL BOTANICAL CHARACTERISTICS : 
Smooth brome is an exotic, cool-season grass from 1.3 to 3.2 feet
(0.4-1.0 m) tall.  Blades are flat.  The inflorescence is an open
panicle from 2.4 to 6.8 inches (6-17 cm) long bearing 6 to 11-flowered
spikelets.  Lemmas have short awns (<2 mm) or are unawned [53,54,61].

Two principle types of smooth brome are recognized, the northern and
southern.  The northern type is weakly rhizomatous, with leaves well up
on the stem and short glumes.  A few northern cultivars are actually
bunchgrasses.  The southern type is strongly rhizomatous, with leaves
near the base of the stem and long glumes.  Other notable differences
are earlier spring growth of the southern type and more even growth of
the northern type through the growing season [55].

In a meadow in West Viriginia on shallow silty loam, smooth brome roots
grew to a depth of 18 inches (46 cm), with most of the root biomass
occurring in the first 3 inches (7.6) of soil.  (Average root
productivity was 717.7 lbs/acre inch at 0-3 inches below ground [52].)
Witte [127] found roots as long as 9.4 feet (2.87 m).

Due to cloning, smooth brome is a long-lived species.  Plantings have
persisted for at least 60 years [98].


RAUNKIAER LIFE FORM : 
   hemicryptophyte


REGENERATION PROCESSES : 
Smooth brome reproduces by seed, rhizomes, and tillers.  Spread by seed
has been rated moderate, and vegetative spread has been rated good [97].

Smooth brome is usually cross-pollinated [72,86], although it may
self-fertilize from different spikelets of the same plant [86].  McKone
[72] found that seed set was significantly lower in smooth brome than in
other brome species.  Insect herbivory has been cited as a factor
reducing seed set in smooth brome [86,91].  Seed yield of smooth brome
broadcast-planted in Michigan 174 pounds per acre when grown with
alfalfa and 121 pounds per acre when grown alone [122].  Seed has
remained viable for 22 months to over 14 years [49,55].  Seed stored in
a shed for 19 years showed 20 percent germination [66].  Seed requires
stratification to germinate.  Germinative capacity of fresh, stratified
seed has varied from 83 to above 95 percent in the laboratory [49].
Optimal temperatures for germination in the greenhouse were from 68 to
86 degrees Fahrenheit (20-30 deg C) [49].  Like all cool-season species,
however, smooth brome can germinate at lower temperatures.  Bleak [17]
reported that smooth brome seed sown in late fall to early winter in
central Utah germinated and produced roots and shoots under deep snow
cover.  Light enhances germination but is not required [49].

Seedling growth is rapid [56,59].  Knobloch [72], who described
germination and seedling development in detail, reported that 54 days
after sowing, greenhouse-grown seedlings had 150-millimeter-long roots,
five leaves, and had begun tillering.  Baker and Jung [9] found that
under greenhouse conditions, the optimal day temperature for growth was
between 64.9 and 76.8 degrees Fahrenheit (18.3-24.9 deg C), and that food
reserves were depleted less with low night temperatures than with warm
night temperatures.  Cultivars differ in rate of growth and drought
tolerance [30].


SITE CHARACTERISTICS : 
Smooth brome is widely adapted to a variety of sites.  It is common in
riparian zones, valley bottoms, and dryland sites.  [48,56,119].  It is
adapted to all soil textures [49,55,90], although it may not thrive on
sand or heavy clay [119].  Smooth brome tolerates acid soils; it
comprised the dominant cover on a coal spoil of pH 4.5 in British
Columbia [56].  It does not grow on soils that are more than moderately
alkaline [55].  It is fairly saline tolerant [56].  Smooth brome grows
best on moist, well-drained soils [49], but tolerates poorly drained
soils [32].  Smooth brome is best adapted to regions receiving more than
15 inches (380 mm) of annual precipitation [98,119].  Eleven inches (280
mm) of annual precipitation is the minimum that will support smooth
brome without irrigation [98].

Some cultivars of smooth brome are adapted to northern latitudes and
high elevations [60,102].  Smooth brome persists to about 9,000 feet
(2,743 m) elevation in the northern Rocky Mountains [24,119] and to
about 11,000 feet (3,300 m) in the central and southern Rocky Mountains
[119].  General elevational ranges in several states are:

     from 7,000 to 10,000 feet (2,134-3,048 m) in Arizona [69]
     below 8,900 feet (2,700 m) in California [61]
     from 4,500 to 10,000 feet (1,372-3,048 m) in Colorado [57]
     from 4,096 to 10,352 feet (1,280-3,235 m) in Utah [121]


SUCCESSIONAL STATUS : 
Smooth brome generally invades after disturbance and persists
[19,20,37].  It is a common invader of disturbed prairie throughout the
Great Plains [112,125,126].  In Yellowstone National Park, Wyoming,
smooth brome cover was similar in young eastern cottonwood (Populus
deltoides), mature eastern cottonwood, and grassland areas [19].  Boggs
and Weaver [20] reported that along the Yellowstone River, moderate
grazing increased the occurrance of shrubs in mature eastern cottonwood,
and severe grazing converted the area to smooth brome, timothy (Phleum
pratense), and Kentucky bluegrass (Poa pratensis).

Smooth brome tolerates moderate shade to full sun [49,56]


SEASONAL DEVELOPMENT : 
Smooth brome undergoes fall green-up.  Inflorescences are initiated
during cool, short fall days [90].  In colder climates, smooth brome is
dormant in winter.  It may remain green year-round in southern climates
[76].  Spring growth begins early in the season [110,107].  Lengthening
culms expose the panicles in late spring to early summer [90], and
smooth brome flowers in summer.  In Minnesota, flowering occurred from
early to late June [80,86].  It occurred in late May or early June in
Ames, Iowa, with later, sporadic flowering [72].  Phenology is delayed
in northern latitudes and high elevations.  Smooth brome on the Wasatch
Plateau of Utah flowers 85 to 102 days after snowmelt [44].  Seed
matures in early to late summer [49].  Smooth brome grows throughout the
growing season when soil water is adequate.  Under dry soil conditions
it becomes dormant, but it resumes growth when soils moisten [16].

Related categories for Species: Bromus inermis | Smooth Brome