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more so in some communities than in others and species with fire-adaptive traits
such as lignotubers and dormant seedbanks that delay reproduction to a single
pulse of recruitment can capitalize on these fire-induced changes in resources.
Landscape variation in substrates can also alter community structure, which
affects the extent to which closed-canopy shrublands develop and thus affects
fire-driven diversity patterns (Cowling
et al.
1989
; Carrington & Keeley
1999
;
Safford & Harrison
2004
).
In addition to these deterministic factors, there are also stochastic effects that
control diversity in fire-prone communities. Event-dependent factors such as fire
intensity or the coincidence of high rainfall after fires can play key roles in postfire
diversity patterns, as demonstrated in both southern and northern hemisphere
MTC regions (Yeaton & Bond
1991
; Richardson
et al.
1995
; Keeley
et al.
2005c
).
Elevated fire intensity works through diminishing seedbanks and resprouter sur-
vivorship, both of which contribute to postfire cover and species richness.
Drought years after fire reduce soil moisture and thus diversity, and the impact
of postfire drought years may vary with landscape location. Long-term studies of
diversity in fire-prone Cape fynbos suggest that other stochastic factors are
important determinants of community diversity (Thuiller
et al.
2007
).
A model illustrating how landscape variation in plant communities and fire
history affect community diversity patterns in California shrublands is illustrated
in
Fig. 11.6
. In this model distance from the coast influences growth-form domin-
ance, which in turn affects community heterogeneity and site-specific abiotic
conditions. Both of these contribute to local richness. Fires in this region vary in
frequency relative to distance from the coast and create different landscape
mosaics of stand age. Older stands have a greater amount of dead fuels and alter
local fire intensity, which in turn affects postfire cover and richness.
Fire and Regional Diversity
Different processes appear to determine plant diversity at different spatial scales
(Crawley & Harral
2001
). Fire, however, is one of those ecosystem processes that
can affect diversity at most spatial scales, including communities, landscapes and
region. Common metrics include
beta
,
gamma
and
delta
diversities, terms that have
been applied inconsistently by numerous authors (Tuomisto
2010
).
Landscape mosaics of different fuel structure will contribute to heterogeneous
fire regimes and provide diverse habitats that affect both floral and faunal diver-
sity at the landscape scale (Romme
1982
). Even for landscapes with the same fire
regime, mosaics in fuels can lead to a patchwork of different stand ages that
contribute to landscape diversity (Clark
et al.
2002
; Uys
et al.
2004
). Such pattern-
ing is less likely in shrubland-dominated crown fire regimes where fire spread is
dependent on sufficient canopy fuels or strong winds, and these factors contribute
to large landscape-scale fires. In forest types where fires are spread by surface
fuels, patchiness in fuels or different seasons of burning can create a patchwork of
