Fire in Southern Australia - Fire in Mediterranean Ecosystems - page 224

Hammill & Bradstock 2006 ; Clarke et al. 2007 ). Anecdotal evidence of fine-scale
variation exists, with habitats such as dunes and rock outcrops having a lower
probability of burning than adjacent areas (Gill & Bradstock 1995 ; Bradstock &
Cohn 2002a ; Clarke 2002a ; Lamont et al. 2007 ; Burrows 2008 ). Such effects are
due to lower mass and continuity of fuel in these relatively drier habitats.
Clarke et al. ( 2005 ) posed a model where community flammability and fire
frequency was inversely related to moisture and productivity. This model,
developed for eastern, warm temperate vegetation, ranked rock outcrops as
having higher flammability than other neighboring communities such as dry
sclerophyll forest, wet heath and wet sclerophyll forests. The generality of this
model is debatable, as under some circumstances wet heaths may be more ignit-
able than forests. Rock outcrops often contain highly discontinuous fuel com-
pared with neighboring forests and may be less likely to sustain spreading fire than
surrounding vegetation (Clarke & Dorji 2008 ).
Such differences in probability of burning and its effects on fire frequency and
intensity may only partly depend on in situ fuel characteristics determined by
habitat. The spread of fire, a spatially contagious process, is determined by the
combination of fuel and ambient weather characteristics, as represented in fire
behavior models. Under severe fire weather, probability of burning in commu-
nities with relatively low flammability may increase, particularly if such commu-
nities are isolated within a more flammable matrix (e.g. rock outcrop communities
within an open forest matrix). Thus, relative flammability may be variable
according to weather conditions. In particular, differences in flammability may
diminish under extreme weather conditions, which may lessen the influence of fuel
characteristics on the probability and rate of spread of fire (Peters et al. 2004 ;
Bradstock et al. 2010 ).
Habitat, diversity and resprouting are linked (see discussion above). Hypothe-
sized causes for these links include competition for resources and selection via
alternative fire regimes, reflecting differential flammability among habitats
(Clarke & Knox 2002 ; Clarke et al. 2005 ). As noted, however, definitive evidence
of close correspondence between fire regime variations, particularly fire frequency,
is lacking, but limited data suggest confounded effects of habitats, fire regimes and
functional type selection.
An elegant example, involving the spatial partitioning of obligate seeder and
facultative seeding (resprouting) shrubs in kwongan heath, has been described by
Groeneveld et al. ( 2002 ) and Lamont et al. ( 2007 ). In this case, habitats and fire
interact spatially to segregate and confine species distributions within the wider
confines of their potential habitat range. Pausas & Bradstock ( 2007 ) showed that
increasing richness, abundance of obligate seeders and decreasing fire return
interval were correlated along a subcontinental scale gradient of MTV shrublands.
Clarke et al. ( 2005 ) postulated that habitat influences will have a substantial role in
shaping woody species richness and abundance of resprouters. They also predicted
that variations in fire regimes will also have a more limited selective influence on
these attributes.