Agriculture Reference
In-Depth Information
Table 9.1 Character syndromes associated with postfire obligate resprouters and obligate seeders
in MTC shrublands
Obligate resprouters
(see
Table 3.1
)
Obligate seeders
(see
Table 3.4
)
Stresses or traits
Water stress mode
avoiders (anisohydric)
tolerators (isohydric)
Mechanism
morphological (deep
roots)
anatomical physiological
Potential drought-induced
mortality
Adults
very low
moderate
Seedlings
very high
moderate
Recruitment mode
disturbance free
disturbance dependent
Safe sites
under canopy
burned sites
Safe site availability
In time
annually
10-100 yr intervals
In space
limited
extensive
Seed dormancy
weak/no
deep
Seedbank
transient (
<
1 yr)
persistent (10-100 yrs)
Germination cues
a
none
heat shock or chemicals
from char or smoke
Dispersal strategy
spatial
temporal
Mode
vertebrates
passive or invertebrates
Shadow
wide
narrow
Season
autumn-winter
spring-summer
Seed size
large
small
Ecological niche width
wide
narrow
Biogeographical distribution
widespread
localized
Origin
early Tertiary
early Tertiary -
Quaternary
a
Many species from both life histories may have a cold stratification requirement.
Physiological, anatomical and morphological changes were thus likely an import-
ant part of evolutionary steps (ES) 1 and 2 in
Fig. 9.5
.
Coincident with these recruitment patterns is a suite of life history characteristics
(
Table 9.1
), many of which are related to reproduction (Garcı´ a-Fayos &Verdu´
1998
;
Keeley
1998
). This is particularly evident in dispersal mechanisms. Fire-dependent
reproduction has selected for seeds that fall near the parent plant and are
deeply dormant in order to disperse through time, from one fire cycle to the next.
Disturbance-independent recruitment requires fruits that are spatially dispersed in
order to seek out appropriate safe sites, and thus they are wind or animal dispersed
with limited seed dormancy. These dispersal strategies imply very different metapo-
pulation dynamics between these life history modes. These transient seedbanks have
the potential for recruiting annually between fires and are likely to be dependent on
years of extraordinary rainfall for successful establishment. The observation that the
seeds of this functional type are fire sensitive (e.g. French & Westoby
1996
) should
