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cues to produce seedling cohorts after a fire, including fire-stimulated flowering,
heat- or smoke-stimulated seed germination or seed release from serotinous cones
(see
Chapter 3
). Fire-stimulated flowering is particularly common in geophytes
and graminoids, including grasses. Flowering is also stimulated by fire in many
resprouting shrubs. Keeley (
1993b
) showed that flowering in
Cyrtanthus
, a fynbos
geophyte, is smoke stimulated, but for many species, the cue may be increased
resources in the postburn environment rather than specific fire-related cues (e.g.
Verboom
et al.
2002
for
Ehrharta calycina
, a grass). Fire stimulates seed germin-
ation by physical or chemical cues. In fynbos, heat shock stimulates germination
in members of several families including Fabaceae, Rhamnaceae (
Phylica
) and
Sterculiaceae (
Hermannia
). Brits
et al.
(
1993
) described a novel cue, heat desicca-
tion, for ant-dispersed (myrmecochorous) seeds of several Proteaceae. In Califor-
nia chaparral Wicklow (
1977
) first reported that chemicals leached from charred
wood triggered germination of fire-dependent species and later smoke was found
to do the same (see
Box 3.1
). Smoke-stimulated germination was first reported for a
fynbos species by de Lange &Boucher (
1990
) for
Audoinia
, amember of the endemic
family Bruniaceae. Smoke-stimulated seed germination has since been reported
for many fynbos species in diverse families (reviewed by Brown
et al.
2003
).
Keeley & Bond (
1997
) noted that fire-stimulated germination cues of heat or
chemicals from charred wood and smoke were convergent traits in chaparral and
fynbos and that different cues were associated with different growth forms.
Annuals were most commonly smoke stimulated whereas shrubs were relatively
evenly spread among smoke and heat-shock stimuli. Species with non-refractory
seeds were quite common in both systems, strikingly so in plants with other modes
of postfire regeneration. Thus geophytes, most of which have fire-stimulated
flowering, had non-refractory seeds, as do serotinous species, which release seeds
en masse after the plant is burned (Keeley & Bond
1997
; Brown
et al.
2003
).
Although the discovery of smoke-stimulated germination in fynbos species led to
an explosion of new plants for horticulture (Brown
et al.
1995
), it is less certain
how many fynbos species have an obligate dependence on smoke. Smoke stimu-
lates germination in a wide variety of plants from diverse biomes (Pierce
et al.
1995
; Brown
et al.
2003
) and qualitative or quantitative differences in response in
species from fire-prone vs. fire-resistant ecosystems have seldom been explored.
Pierce
et al.
(
1995
) found that smoke stimulated germination in members of the
Mesembryanthemaceae from both fire-resistant succulent shrublands and fire-
prone fynbos and suggested that their results cast some doubt on the ecological
significance of smoke as a fire-related cue. While constituents of smoke may be a
general germination cue in angiosperms, the specific importance of smoke as a
germination cue for plants sharing similar fire life histories has been shown in
comparative studies of seed germination in Californian chaparral (Keeley &
Fotheringham
1998
), Mediterranean Basin matorral (Moreira
et al.
2010
) and
fynbos (Keeley & Bond
1997
).
Fire-stimulated seed release from serotinous cones is common in many fynbos
and Australian flowering shrubs (see
Fig. 3.5a
-d), as well as a few coniferous
