Agriculture Reference
In-Depth Information
Seed retention in canopy storage is variable within species, between congeneric
species and across families (Cowling & Lamont
1987
; Lamont
et al.
1991
; Enright
et al.
1998
; Lamont & Groom
1998
). For example, high rates of retention are
prominent in Proteaceae (see
Box 7.1
) and Casuarinacae but not in Myrtaceae
(Pannell & Myerscough
1993
; Gill
1997
; Lamont & Groom
1998
; Lamont
et al.
2007
). There is evidence within
Hakea
and
Banksia
of linkages between moisture
availability and levels of retention, with high rates of retention favored in drier
habitats (Cowling & Lamont
1998
; Lamont & Groom
1998
; Lamont
et al.
2007
).
This may reflect more restricted establishment opportunities or in facultative
seeders higher propensity for fires of lethal intensity.
Accumulation of soil seedbanks is less well known than for canopy storage, but
modeling studies based on inputs and losses indicate a tendency for an increase
and eventual decline with time since fire for
Acacia suaveolens
(Auld
1987
) and
Grevillea caleyii
(Regan
et al.
2003
). However, Wills & Read (
2007
) found that the
richness and density of the seed pool did not change significantly up to 26 yrs
postfire in a chronosequence study in southeastern Australia. Thus, soil seedbanks
of many species may be long lived (
30 yrs) and longevity of soil seed pools of
some taxa, most notably hard-seeded perennial plants, may significantly exceed
that of established plants (Auld
et al.
2000
; Wills & Read
2007
).
A substantial number of species persist after fire solely by resprouting but utilize
the subsequent postfire years for seedling recruitment. This group of pyrogenic
flowering plants (up to 25% of species in heathlands) resprout, flower and set seed
in the first year and establish seedlings in the second year and subsequent years
after fire (Bell
et al.
1984
; Keith
et al.
2002
). This life history is found in many
geophytes and other perennial herbs as well as some shrubs and the arborescent
monocot
Xanthorrhoea
(Dixon & Barrett
2003
; Auld & Denham
2006
; Lamont
et al.
2004b
). A resprouting gymnosperm
Podocarpus drouynianus
in Western
Australian MTC forests exhibits such a pyrogenic cone production life history
(Chalwell & Ladd
2005
).
>
Inhibition of Establishment
In most MTV, seedling recruitment is inhibited in unburned vegetation and occurs
in a pulse after fire. Fire-stimulated germination and establishment occur across a
wide range of taxa of many different growth forms (Bell
1999
; Dixon & Barrett
2003
; Merritt
et al.
2007
; Auld & Ooi
2008
). Heat and smoke break dormancy in
soil-stored seedbanks and typically species respond to one or the other of these
triggers (Bell
1999
; Auld & Ooi
2008
). For some species germination is affected by
interactions between heat and smoke but these effects are complex and only
partially understood (Thomas
et al.
2007
; Auld & Ooi
2008
). See
Chapters 3
and
9
for a detailed discussion of heat-stimulated and smoke-stimulated germination.
Effects of heat on subsequent seed germination are complex, given that tem-
peratures in the soil profile are mediated by patterns of fuel structure and fuel
consumption. For heat-stimulated species germination is positively correlated
with fire intensity, which is correlated with the level of surface fuel consumption
