Agriculture Reference
In-Depth Information
Box 3.1 Smoke and Charred Wood Stimulated Seed Germination
In many MTC ecosystems there are species with seedling recruitment restricted
to the immediate postfire years from soil-stored seedbanks that are triggered to
germinate by fire. Historically it was thought these were stimulated by intense
heat and indeed many species are, but for a substantial proportion of postfire
recruiting species, heat does not trigger germination; rather it is cued by
chemicals produced by biomass combustion. These chemicals are present in
smoke and charred wood, or can even be generated by heating wood to 175
C
(Keeley & Nitzberg
1984
; S. Keeley & Pizzorno
1986
). Because of the ease of
generation most experimental work has used smoke and so for convenience we
will refer to this phenomenon as
smoke-stimulated germination
(Brown
1993
;
Keeley & Fotheringham
1998
).
Perhaps the first to recognize this phenomenon were the California Indians
who routinely sowed native tobacco (
Nicotiana
spp.) seeds in postfire ash beds
(Harrington
1932
). Under natural conditions
Nicotiana attenuata
and
N. quad-
rivalvis
are known to recruit primarily after fire and germination is triggered
almost exclusively by charred wood or smoke (Baldwin
et al.
1994
; Keeley &
Fotheringham unpublished data). The first scientific report of this phenom-
enon was by Wicklow (
1977
) who demonstrated that germination of the post-
fire annual
Emmenanthe penduliflora
was dependent on charred wood.
Subsequent studies demonstrated that many other California annuals and
perennials that restrict recruitment to recently burned sites were triggered to
germinate by chemicals produced during the combustion of biomass and not
by heat shock (Keeley
1987
; Keeley & Keeley
1987
). The first demonstration
that smoke could trigger germination was made on a South African fynbos
species by de Lange & Boucher (
1990
).
This “smoke”-stimulated germination is now known from many postfire
recruiting species in South Africa (Brown
1993
), Western Australia (Dixon
et al.
1995
), California (Keeley & Fotheringham
2000
) and the Mediterranean
Basin (Moreira
et al.
2010
). Many of these species could be described as having
smoke-dependent germination
, as the only environmental cue that will trigger
germination is smoke. Some species from the matorral in Chile exhibit some
enhanced germination in response to smoke but these are not species that
typically recruit seedlings after fire (Go´ mez-Gonza´ lez
et al.
2008
). Smoke-
dependent germination in postfire recruiting species is now known from hun-
dreds of species. The plant families (Table
B3.1.1
) where it has been most
convincingly demonstrated are rather different in the northern and southern
hemispheres and present an apparent example of convergent evolution
(Keeley & Bond
1997
; see also
Chapter 9
). Enhanced germination in response
to smoke also has been found in some non-MTC species that recruit seedlings
after fire (Jefferson
et al.
2008
; Lindon & Menges
2008
; Abella
2009
).
Continued
