Agriculture Reference
In-Depth Information
Persistence
Resprouting is common in species in most fire-prone environments, in most
growth forms and most taxonomic groupings. Australia stands out amongst
MTC regions in having the greatest diversity of shrubs with lignotubers (see
Fig. 3.1
and
Table 3.2
). In MTC Australian shrublands many of the shrub
dominants resprout and most also recruit seedlings after fire and are termed
facultative seeders. In some MTC communities there are woody species that lack
the capacity to resprout and so postfire recovery is entirely dependent on seedling
recruitment (see
Table 3.4
). This life history mode is termed obligate seeding and it
is particularly prominent in genera that are dominants of shrublands or as
understory shrubs in woodlands and forests: e.g.
Allocasuarina
,
Banksia
,
Dryandra
,
Grevillea
and
Hakea
(Bell
2001
). Tree species such as
Eucalyptus
,
Corymbia
,
Angophora
and
Allocasuarina
are usually resprouters (Gill
1997
; Burrows & Wardell-
Johnson
2003
; Nicolle
2006
). There are exceptions: for example, low-stature, obligate
seeder eucalypts known as mallees occur in some dry southwestern environments.
Graminoids and herbs exhibit varying degrees of resprouting. In Restionaceae
(e.g. see
Fig. 7.6
) there are higher proportions of obligate seeders in the MTC
southwest than in the aseasonal climate of the southeast (Bell
et al.
1984
; Pate
et al.
1991
; Clarke
et al.
1996
; Benwell
1998
; Bradstock
et al.
1997
; Keith
et al.
2007
).
Most resprouters have high resprouting success, although high fire intensities
may elevate mortality in some resprouters (Bradstock & Myerscough
1988
;
Burrows & Wardell-Johnson
2003
; Vivian
et al.
2008
). Woody obligate seeders
uniformly die when burned and for most species this is not a variable response,
as suggested by Vesk & Westoby (
2004
). A few obligate seeders with a tall
growth form and thick bark may survive low-intensity fires, such as some
Alloca-
suarina
and
Callitris
species (Morrison
1995
; Bell & Williams
1997
; Bradstock &
Cohn
2002b
).
There is an overall trend toward higher proportions of resprouters (woody and
herbaceous) in moist environments (up to 75%) and lower proportions (
~
50%) in
dry environments (Lamont & Markey
1995
; Groeneveld
et al.
2002
; Keith
et al.
2002
; Burrows & Wardell-Johnson
2003
; Clarke
et al.
2005
; Keith
et al.
2007
;
Pausas & Bradstock
2007
), a pattern also seen in Californian MTC ecosystems
(see
Chapter 5
). Such a pattern could reflect effects of productivity on availability
of space. In moist or more fertile environments, resprouting graminoids and
shrubs usurp space soon after fire, thus disadvantaging seedling recruitment by
obligate seeders (Yates
et al.
2003a
; Clarke
2002b
; Clarke
et al.
2005
; Enright
et al.
2007
; Pausas & Bradstock
2007
).
Obligate seeder shrubs dominate at the drier end of the moisture gradient
and this life history is commonly associated with narrow or needle leaves
that, due to the low surface area to volume ratio, enhance water use efficiency in
these habitats (Lamont & Groom
1998
; Bell
2001
; Pausas
et al.
2004b
; Lamont
et al.
2007
). Obligate seeder shrubs tend to be taller with fewer stems than closely
related resprouting taxa, which appear to be allocating more resources to
basal
lignotubers and other root regenerative structures (Lamont & Markey
