19appear in lower elevation areas with locally higher soil moisture such as riparian
zones and roadsides (Brooks 2009 ), it only occurs as a dominant Bromus species at
higher elevations, such as those within the upper blackbrush ecotone, sagebrush,
piñon–juniper, and interior chaparral (Fig. 2.4b ) (Klinger et al. 2011a ). Bromus trinii
Desv. (Chilean chess) has also been reported from some locations, generally within
the same ecological range as B. rubens ( http://www.calfl ora.org , accessed 8 Apr 2014),
but its relative dominance is typically very low (Brooks 2009 ; exception is Brooks
1999 ). Bromus diandrus can also be found in the Warm Deserts ( http://www.calfl ora.org ,
accessed 8 Apr 2014), but almost always in localized areas of higher soil moisture
such as along roadsides, in riparian areas, or associated with agricultural or urban
developments (Dudley 2009 ; M. Brooks, pers. obs.).
2.2.1 Invasion Potential of Warm Deserts by Bromus
The lowest elevation ecosystems of the Warm Deserts are characterized by hyper-
thermic, typic aridic soils (Fig. 2.3c ) and sparse cover of creosote bush scrub
or saltbush scrub. Creosote bush scrub is dominated by the type species, Larrea
tridentata (DC.) Coville (creosote bush), and is the most widespread vegetation
Fig. 2.4 Hypothetical ( a ) resistance to common Bromus species and ( b ) resilience to historical
and altered fi re regimes for the Warm Deserts ecoregion (primary altered regime characteristic
labeled in gray )
2 Exotic Annual Bromus Invasions: Comparisons Among Species and Ecoregions...