BOTANICAL AND ECOLOGICAL CHARACTERISTICS
SPECIES: Bromus japonicus | Japanese Brome 



GENERAL BOTANICAL CHARACTERISTICS : 
Japanese brome is an introduced, cool-season, annual grass from 8 to 48
inches (20-120 cm) tall.  It sheaths are hairy; the blades are glabrous
to hairy. The inflorescence is an open panicle bearing 6 to 13 caryopses
[34,36,38,43,68].  Roots may be shallow [61], or surprisingly deep for
an annual.  Roots of plants in Lewistown, Montana, reached depths of 5
feet (150 cm), with most roots concentrated between 2.7 and 4.7 feet (80
and 140 cm) below ground.  Japanese brome root density surpassed that of
five other annual bromes also occurring at the site [40].


RAUNKIAER LIFE FORM : 
   Therophyte


REGENERATION PROCESSES : 
Japanese brome reproduces entirely from seeds.  The seeds require a
moist substrate for germination.  A heavy thatch or litter layer
improves germination rates by retaining moisture [5].  Seeds germinate
over a broad temperature range:  from just above freezing to over 95
degrees Fanrenheit (35 deg C) [5,25].  Under laboratory conditions a
majority (67%) of fresh seed was immediately germinable, but under
natural conditions most seeds are retained on the parent plant until
late fall or winter, which delays germination [5].  Some seeds are
dispersed off-site in animal hides or dung:  The majority of seeds found
in bison chips on the Wichita Mountains Wildlife Refuge, Oklahoma, were
Japanese brome [11].  Other seeds fall near the parent plant [4,5].
Seeds are probably not deeply buried.  In Wind Cave National Park, South
Dakota, Whisenant [71] found few Japanese brome seeds deeper than 1.2
inches (3 cm) below ground.  Late fall- and winter-dispersed seeds
undergo dormancy and need a period of afterripening the following summer
before germination occurs.  Most seeds therefore germinate in fall and
are from the previous year's crop [5].  Fall precipitation increases
successful germination, and above-average precipitation is critical when
the litter layer is sparse to absent [70].  Whisenant [71] reported that
Japanese brome density in Wind Cave National Park was much greater in
summers that followed heavy fall rains.  Winter and spring precipitation
did not greatly affect Japanese brome density.  A minority of seeds
germinate in spring; plants growing from these seeds tend to flower
later in the year, if at all [5,22,40].  Japanese brome is a prodigious
seed producer [4].  The long-term viability of Japanese brome seeds is
unknown, but seeds remain viable for at least several years.  Soil from
north-central Kentucky, collected after the germination period had passed,
still contained an average concentration of 2,325 viable Japanese brome
seeds per square meter [5].

Seedlings overwinter in a rosettelike growth form [5].


SITE CHARACTERISTICS : 
Japanese brome invades disturbed and undisturbed sites.  It dominates
disturbed areas in the Jackson Hole Wildlife Park, Wyoming, where it
occurs on bridle paths, roadsides, gravel pits, and heavily used or
burned picnic sites [55].  In other areas it is reported from
site-prepared plantations [53], old prairie dog mounds [50], moderately
to heavily grazed rangelands [56], and undisturbed mixed-grass prairie
[72].

Japanese brome grows on soils of various textures including sand [8],
silt [9], clay [7], and claypan [35].  It usually occurs on mesic sites
[28,49,75].  Fine-textured soils with good litter cover promote best
growth [70].  It is apparently intolerant of alkaline soils [64].


SUCCESSIONAL STATUS : 
Japanese brome colonizes disturbed sites [4,19].  It sometimes decreases
with succession:  Four years following elimination of disturbance
(logging and ranching) on the University of Kansas Natural History
Reserve, Japanese brome had 7.4 percent cover.  Twelve years later it
was present only in trace amounts.  Twenty-seven years later it was
absent from the community [24].  Japanese brome may persist or even
dominate some late seres or climax communities, however [40,42].
Huschle and Hironaka [42] listed a Japanese brome phase of the bluebunch
wheatgrass-Sandberg bluegrass (Agropyron spicatum-Poa sandbergii
[Pseudoroegneria spicata-Poa secunda]) habitat type by the middle and
lower Snake River, Idaho.


SEASONAL DEVELOPMENT : 
Japanese brome usually germinates in fall.  It shows some fall
vegetative growth, winter dormancy, vigorous spring vegetative growth,
and late spring flowering.  It fruits and dies in summer, and seeds
disperse from the dead plants in fall and winter [4,5,22,71].
Overwintering Japanese brome seedlings are among the first grasses to
resume growth in spring [29].  A minority of seeds germinate in spring,
and flowering occurs in late summer in these plants.  Spring-germinating
plants in northern latitudes are usually killed by frost before seeds
are ripe [71,75].

Baskin and Baskin [5] reported that in north-central Kentucky,
germination occurs from early September to mid-October; flowering begins
in early May; seeds ripen and plants die from late June to early July;
and seeds disperse from late October until March.

Frequency (%) of occurrence of phenological stages in central Oklahoma
was reported as follows [2]:

          germinating    vegetative    
           seedling        growth      anthesis    fruiting    dissemination

winter       45.8           ----          5.0        9.2           9.2
spring       ----           51.7         13.3       ----          ----
summer       ----           15.6          4.4       43.3          42.2
autumn        1.5           ----         ----       32.3          32.3

Related categories for Species: Bromus japonicus | Japanese Brome