178
6.3.6 Human Use and Cultivar Availability (Hypotheses 7 and 8)
Hypotheses 7 and 8 (Table 6.2 ) state that species that are used for hay, forage, and
revegetation are more likely to be invasive than those that are not and that develop-
ment of named cultivars is associated with invasiveness. The logistic regressions
showed human use and cultivar availability to be signifi cantly correlated with both
wide introduction and weediness (Table 6.3 ).
Sections Bromopsis and Ceratochloa contain species that are widely used for
hay, forage, and revegetation (Fig. 6.6 ). Bromus inermis , in section Bromopsis , is
widely cultivated and has been used extensively for hay and forage and for reveg-
etation of roadsides, ditches, mine tailings, old logging trails, overgrazed rangeland,
and other disturbed areas in North America (Sampson 1913 ; Weintraub 1953 ;
Otfi nowski et al. 2007 ). Many cultivars are available. These are typically grouped
into northern meadow types based on strains introduced from relatively wet temper-
ate regions in Eastern Europe and Russia, southern steppe types based on strains
probably introduced from Hungary, and intermediate types (Williams et al. 2011 ;
Smoliak et al. 1990 ). Cultivar “Polar” is a hybrid of B. inermis and B. pumpellianus
(Walsh 1994 ). Bromus pumpellianus is native across both North America and Asia
and is sometimes considered a subspecies of B. inermis. For this reason, B. inermis
is often listed as native in North America. However, B. inermis ( Bromus inermis
ssp. inermis) was introduced from Eurasia in the 1880s and has interbred with and
often replaced B. pumpellianus (Elliot 1949 ). Bromus inermis has invaded natural
grasslands, shrublands, and forests in western North America. It often forms
monocultures and can exclude other species (Otfi nowski et al. 2007 ; Sumners and
Archibold 2007 ; Dillemuth et al. 2009 ; United States Geological Survey 2013 ).
Bromus erectus , a Eurasian Bromopsis species, is used for pasture and hay in
Europe (Jongepierova et al. 2007 ). It now grows in disturbed areas in eastern North
America and is listed as a crop and environmental weed in Australia (Barkworth
et al. 2007 ; Randall 2007 ). Two other species in section Bromopsis , the closely
related (or conspecifi c) B. riparius and Bromus biebersteinii Roem. & Schult.
(meadow brome), have also been introduced into North America for hay and forage
and are only occasionally reported as being weedy (Lass and Prather 2007 ; Williams
et al. 2011 ). Bromus riparius is sometimes used as a less aggressive alternative to
B. inermis , and the two species hybridize (Williams et al. 2011 ). Other species in
section Bromopsis , including Bromus leptoclados Nees in Africa and B. auleticus i n
South America, are used for hay or forage, but have not been widely introduced into
new regions (Stewart 1996 ; Iannone et al. 2012 ).
Cultivars of South American Ceratochloa species B. catharticus (rescue brome)
are used for forage and hay in North America, Australia, New Zealand, and Europe
(Stewart 1996 ; Williams et al. 2011 ). The taxonomy of B. catharticus is diffi cult,
and a number of Ceratochloa grasses formerly listed as species are now considered
to be conspecifi c with B. catharticus. Grasses in the B. catharticus complex have
S.Y. Atkinson and C.S. Brown