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conceptual framework that can be used to evaluate the relative potential for invasion
and ecological impact of the dominant exotic annual Bromus species in the western
United States.
Keywords Fire • Resilience • Resistance • Management • Moisture regime •
Temperature regime
2.1 Introduction
Numerous Bromus species occupy a wide range of ecosystems around the globe
(Atkinson and Brown 2015 ; Clayton et al. 2006 ), including 58 species within North
America (Clayton et al. 2006 ), approximately half of which are exotic species that are
nonnative to the continent (Pavlik 1995 ). Exotic annual Bromus ( Bromus hereafter)
are of signifi cant concern to ecologists and land managers alike (Brooks and Pyke
2001 ). Much of what has been reported about the environmental and ecological con-
trols on Bromus and their interactions with land uses and disturbance regimes have
focused on the Cold Deserts ecoregion of the western United States (Fig. 2.1 ) and on
Bromus tectorum L. (cheatgrass) in particular. This chapter reaches beyond that spe-
cifi c ecoregion and individual species to examine the invasion potential, ecosystem
threats, and management strategies for the dominant Bromus species within each of
fi ve major ecoregions of the western United States (Table 2.1 ; Fig. 2.1 ). Other chapters
within this book that are relevant to the topics in this chapter include Chambers et al.
( 2015 ), Germino et al. ( 2015 ), Monaco et al. ( 2015 ), and Pyke et al. ( 2015 ).
2.1.1 Resistance and Resilience to Bromus Invasions
The invasion potential, ecosystem threats, and management strategies for Bromus
all vary based on ecosystem resistance to invasion and resilience to disturbance.
Resistant ecosystems have the capacity to retain their fundamental structure,
processes, and functioning (or remain largely unchanged) despite stressors, distur-
bances, or invasive species (Folke et al. 2004 ). Resilient ecosystems have the capac-
ity to regain their fundamental structure, processes, and functioning following
stessors like drought and disturbances like wildfi re and then reorganize without
crossing thresholds to alternative ecosystem states (Holling 1973 ; Walker et al.
2004 ). We use resistance and resilience as explanatory concepts throughout this
chapter, along with temperature and precipitation gradients which are key factors
affecting resistance and resilience (Brooks and Chambers 2011 ; Chambers et al.
2014a , b ; Fig. 1.1 ).
Resistance to invasion is particularly important in the context of this chapter and
is related to abiotic and biotic attributes and ecological processes that limit the pop-
ulation growth of invading species (D’Antonio and Thomsen 2004 ). Ecosystem
resistance to invading species is a function of both the fundamental niche, which
is largely related to climate suitability, and the realized niche, which is related
M.L. Brooks et al.