Agriculture Reference
In-Depth Information
The spatially contagious nature of fire and issues of habitat context mean that
the scope for tight correspondence between flammable attributes of habitat
patches and in situ fire regimes is highly variable. There may be scope for widely
diverging fire regimes within habitat types, forced by varying combinations of
in situ and ex situ influences. Exploration of the variability in these patterns is
required to understand the level to which in situ flammable feedback may control
functional type composition.
Fire and the Maintenance of MTV
The mix of communities in Australian MTV can be regarded as comprising a
diverse, sclerophyll fire world . Such an entity is largely self-reinforcing via the
coupled effects of fire weather and habitats that emerge from the transitional
range of temperate climates in southern Australia. Strong evidence of fire in
organizing community distributions and boundaries via differential flammability
within MTV is, however, lacking. One possibility is that differences in flammabil-
ity among functional types are relatively small and largely overwhelmed by the
relatively frequent occurrence of severe fire weather across MTV environments
(see above). Additionally, the ubiquity of eucalypts results in competitive domin-
ation of vegetation structure, composition and fire regimes. The exceptional resili-
ence of eucalypts throughout MTV may also restrict the ability of more flammable
functional types to eliminate them. Thus vegetation boundaries and community
diversity appear to be primarily determined by major edaphic variations, in turn
influenced by moisture. However, the scope for fire to interact with these influ-
ences is poorly explored. Little is known of the extent of potential niches of major
functional types and the way these are mediated by fire and competition, as
demonstrated for arid shrub and grass combinations characteristic of alternative
habitats by Nano & Clarke ( 2010 ).
Plausible alternative dominants to eucalypts and sclerophyllous shrubs in MTV
communities are restricted to fragments in the landscape (e.g. rainforest patches in
the east, Bowman 2000 ), or scattered, low density populations (e.g. Callitris spp.)
within MTV. These alternatives, with inherently lower flammability, persist in this
tenuous manner due to adverse fire regimes that emerge from the characteristic
fire weather and wide habitat availability of more flammable competitors under
MTV climates in mainland, southern Australia.
The switch to dominance by Callitris spp. in sandy, southeastern MTV environ-
ments under cooler Holocene climates (Thomas et al. 2001 ) indicates the potential
for at least a shift in fire weather, such as a reduction in number of days conducive
to fire spread, to alter dominance and composition. Rainforest patches in the
continental southeast may also represent fire refugia (e.g. moist gullies, Bowman
2000 ) where effects of adverse fire regimes are ameliorated through a reduction in
conditions conducive to frequent and intense fire (i.e. higher fuel moisture, lower
wind speed and exposure to the sun). Patches of this kind in the southeast may
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