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escaped from cultivation in a number of regions and have become ruderal and
environmental weeds (Randall 2007 ; Wu et al. 2009 ). North American native
Ceratochloa species Bromus carinatus Hook. & Arn. (California brome) and closely
related (or conspecifi c) Bromus marginatus Nees ex Steud. (mountain brome) are
also used for hay, forage, and revegetation, and cultivars are available (Darris 2007 ;
Tilley et al. 2006 ; United States Department of Agriculture Natural Conservation
Service Lockeford Plant Materials Center 2012 ).
Annual Bromu s grasses used by humans include species that have already
invaded many parts of North America such as B. tectorum , which is used exten-
sively for early season forage (Upadhyaya et al. 1986 ). A few cultivars of annual
Bromus species have been developed, but are less widely used than those of peren-
nial species. B. rubens “Panoche” was developed in California for soil stabilization.
A cultivar of Bromus mollis L. (syn. B. hordeaceus ) , also developed in California,
is used as a cover crop and for range reseeding and burn rehabilitation. Bromus
arvensis L. (fi eld brome) “Dos” is a Russian cultivar (Williams et al. 2011 ).
B. rubens , B. hordeaceus , and B. arvensis are all considered to be invasive both in
North America and in other parts of the world, although B. arvensis has become less
common in some parts of Europe (Ainouche and Bayer 1997 ; Stace et al. 2005 ).
6.3.7 Temperature and Precipitation (Hypotheses 9, 10, 11 and 12)
We hypothesized that species that are widely distributed and weedy would be able
to grow in both hot and cold regions and also in arid regions. Our results showed
that low minimum temperature, high maximum temperature, wide temperature
range, low minimum precipitation, high maximum precipitation, and wide precipi-
tation range are all signifi cantly correlated with both wide introduction and with all
three categories of weediness (Tables 6.3 and 6.4 ) (Figs. 6.7 and 6.8 ).
Introduced and weedy Bromus species tended to occur in relatively warm and
both wetter and drier climates compared to the overall distribution of Bromus spe-
cies. Some invasive species, including B. tectorum and B. inermis , are also able to
survive cold temperatures. A number of Bromus grasses are native to the
Mediterranean region where rainfall occurs primarily in the winter and are winter
annuals that can germinate in the fall, survive the winter, and resume growth in early
spring (Jackson 1985 ; Sales 1994 ; Salo 2005 ). This type of life cycle can give
annual Bromus species a competitive advantage over native species in western
North America (DeFalco et al. 2003 ; Norton et al. 2007 ). Winter annuals often pro-
duce seed and die in early to mid summer. Their dried foliage then provides fuel for
fi res (Brooks et al. 2015 ; Germino et al. 2015 ). Two highly invasive species,
B. tectorum and B. rubens , are associated with an increase in fi re frequency that has
seriously damaged natural habitats (Melgoza et al. 1990 ; Melgoza and Nowak 1991 ;
Zouhar 2003 ; Salo 2004 , 2005 ; Brooks 2012 ). Some Bromus species grow at high
elevations in South America and Central Asia. These species tend to have restricted
ranges, and relatively little information about them is available.
S.Y. Atkinson and C.S. Brown