Fire in Southern Australia - Fire in Mediterranean Ecosystems - page 210

The role of fire as an ecological and evolutionary driver of vegetation transition
in the Tertiary is difficult to determine, given the paucity of appropriate paleoeco-
logical data (Bowman 2000 ; Kershaw et al. 2002 ). Reviews (e.g. Kershaw et al.
2002 ; Hill 2004 ; Hopper & Gioia 2004 ) highlight the prominence of climate,
particularly the transition from warm, wet to seasonally dry (and often cool)
climatic regimes, as a driver of change. The argument is that fire has followed
the effects of climatic-induced changes that result in the opening up of plant cover
due to rising aridity (e.g. Kershaw et al. 2002 ). The other putative driver is
nutrients because sclerophyllous vegetation is inherently adapted to exploit the
low-nutrient soils that typify soils in many parts of southern Australia. Tertiary
climates may have contributed to the ongoing impoverishment of soils (Beadle
1981 ; Barlow 1994 ; Hopper & Gioia 2004 ), thus expanding sclerophyll habitat.
Fire then accompanied these changes owing to the highly flammable character of
evergreen sclerophylls resulting from the high carbon to nitrogen ratio of leaves
engendered in dry, infertile habitats (Orians & Milewski 2007 ).
In this model, fire is seen as being an emergent property of sclerophyll vegeta-
tion, rather than a force promoting its emergence (Martin 1994 ). For example,
Cowling et al. ( 1996 ) attribute the diversification of species in kwongan plant
communities of southwestern Australia to fire regimes, whereas others contend it
is a direct result of soils and landscape heterogeneity with an uncertain role
for fire (Hopper 2003 ;Lambers et al. 2008 ). However, in reality the roles of
fire and resources (climate, moisture and nutrients) in shaping (drivers of evolu-
tion) and maintaining (ecological sorting) of MTV plant diversity are con-
founded. The influence of a drying climate or nutrient limitations on a plant
community assembly may not be readily disentangled from a resultant increase
in fire activity.
Patterns of diversity are commonly perceived to be a function of variations in
soil moisture and nutrients. Specht & Specht ( 1999 ) linked diversity, structure and
cover to indices of evaporative potential at a continental scale. In particular they
hypothesized that in moist environments, where cover in the dominant stratum
will be dense, diversity will be relatively low due to competitive effects on the
composition of subdominant strata. Measures of diversity have been correlated
with a host of edaphic factors such as nutrients, cations, pH, texture, at both inter-
and intra-community scales (e.g. Beadle 1962 , 1981 ; Adam et al. 1989 ; van der
Moezel & Bell 1989 ; Keith & Myerscough 1993 ; Hahs et al. 1999 ; Le Brocque &
Buckney 2003 ; Clarke et al. 2005 ; Wills & Clarke 2008 ). The species complement is
related to the productive potential of the habitat, with greater numbers of species
more likely in less productive than wetter and/or drier MTV habitats (Huston
2003 ; Pausas & Bradstock 2007 ). Competitive effects and/or selective influences
on functional types are commonly invoked to explain these patterns.
Measures of fire are not usually incorporated into correlative analyses of
resources and diversity at intra- and inter-community scales (Le Brocque &
Buckney 2003 ). Enright et al. ( 1994 ) included time since last fire in their study of
MTV plant communities in western Victoria, finding little effect on trends