Agriculture Reference
In-Depth Information
(Bradstock & Auld
1995
; Tozer & Auld
2006
). Species responses are also variable,
with differing optima for release from dormancy apparent among closely related
taxa (Auld & O'Connell
1991
; Bell
1999
; Auld
et al.
2000
; Thomas
et al.
2007
).
Some taxa, such as Ericaceae, form dormant soil seedbanks that are sensitive to
seasonal temperature fluctuations (Ooi
et al.
2006
; Auld & Ooi
2008
). Release
from dormancy is therefore seasonal and not directly related to fire, though the
subsequent fate of emergents may be strongly dependent on fire-created gaps.
Autumn release from dormancy may be advantageous under a MTC rainfall
regime, where timing of germination will regularly coincide with rainfall. Under
an aseasonal rainfall regime in the southeast, such a response may be less advan-
tageous (Ooi
et al.
2006
; Auld & Ooi
2008
).
Fire releases seeds from canopy storage, either through direct heating or else
indirectly through mortality of stems. Many taxa with canopy storage have non-
dormant seeds that are available for germination upon release (Merritt
et al.
2007
).
In some cases (e.g.
Kunzea
, Myrtaceae) there is evidence of the need for further
fire-related cues, such as smoke following incorporation of released seeds into the
soil (Merritt
et al.
2007
). The widespread occurrence of serotinous taxa (including
both facultative and obligate seeder) across MTV communities (Gill & Catling
2002
; Keith
et al.
2002
; Burrows & Wardell-Johnson
2003
; Pausas
et al.
2004b
)
reflects the degree of inhibition to recruitment in the absence of fire, and the
regularity of fire in the environment. Serotiny functions to overcome inhibition of
establishment in unburned conditions and is favored by decadal intervals of fire
with low variance (Lamont
et al.
1991
; Enright
et al.
1998
; Pausas
et al.
2004b
).
Rates of seed release and establishment of seedlings of canopy-stored species are
positively related to fire intensity (Zammit & Westoby
1988
; Enright & Lamont
1989a
; Bradstock
1990
). There is limited evidence that fire intensity may have
negative effects on canopy storage of seeds (Bradstock
et al.
1994
; Burrows &
Wardell-Johnson
2003
) but instances of widespread recruitment failure due to
mortality of canopy-retained seedbanks are lacking.
Notwithstanding these variations among seedbank types and the nature of
mechanisms, the net effects of fire stimuli are positive. Establishment in unburned
conditions is infrequent (Gill & McMahon
1986
; Whelan
et al.
1998
; Yates
et al.
2003a
; Lamont
et al.
2007
). Germination and establishment may be ongoing in
species that lack dormancy but are limited by other factors in unburned condi-
tions. In some species with soil storage there is evidence of significant fractions
of seeds without dormancy, which correlates with lower probability of fire
(Bradstock
1989
; Pausas & Bradstock
2007
). Clarke & Dorji (
2008
) found a
greater proportion of fire-cued ephemerals in rock outcrops compared with neigh-
boring forests. This was assumed to reflect reduced postfire competition in rock
outcrops due to the lower cover of woody resprouters in outcrops than in forests.
Bond & Ladd (
2001
) noted similar trends across a broader range of taxa in
kwongan shrublands and woodlands.
Continous leakage of seeds from serotinous (Lamont & Groom
1998
; Lamont
et al.
2007
) and non-serotinous species such as eucalypts in the absence of fire may