Agriculture Reference
In-Depth Information
not be interpreted to mean such taxa are maladapted to fire-prone environments;
rather they do not capitalize on fire for recruitment opportunities.
Thus, references to resprouters vs. seeders need to be qualified to emphasize
that this is in reference to their postfire response, since both have seedling recruit-
ment. In fire-prone ecosystems it is often assumed that there is a great advantage
to postfire seedling recruitment over recruitment between fire cycles. However,
recruitment by fire-independent recruiters has not been widely studied and the
relative costs and benefits of continuous recruitment between fires vs. delaying
reproduction to a single postfire pulse requires careful scrutiny (Gadgil & Bossert
1970
). A single snapshot in time for older stands shows seedling (and sapling) to
parent ratios within the range of values observed for the single pulse from postfire
seeders (
Table 9.2
).
Although these obligate resprouters all appear to have origins in the early
Tertiary, there is no reason to assume those landscapes were uniformly mesic
and it is hypothesized these taxa originated on sites at the arid end of the soil-
moisture gradient. The notion that these taxa were understory plants in mesic
forests is untenable considering the physiology of present-day sclerophylls. As
discussed in
Chapter 10
, those islands of suitable habitat were likely widely
Table 9.2 Seedling/parent ratios for fire cycles; fire-independent recruiter recruitment in long unburned
stands and fire-dependent recruiters for the first postfire year
These should not be thought of as species-specific values as they will be shaded by factors such as
stand age for fire-independent recruiters and stand age prior to the fire for fire-dependent recruiters.
Ratio
seedling/
parent
Functional
type
MTC
a
Source
b
Species
(# of sites)
Fire-Independent Recruiters (postfire obligate resprouters)
(total cumulative seedlings and saplings present in stands
>
50 yrs of age)
Heteromeles arbutifolia
Ca
(1)
77
9
Prunus ilicifolia
Ca
(2)
33
1
Quercus
spp.
Ca
(5)
5
1
Quercus suber
Me
(1)
5
16
Rhamnus crocea
Ca
(4)
3
1
Fire-Dependent Recruiters
(single postfire pulse of seedlings)
Soil-stored seedbanks - Facultative seeders
Adenostoma fasciculatum
Ca
(25)
64
3
Ceanothus spinosus
Ca
(10)
75
3
Fremontodendron
californicum
Ca
(62)
93
2
Malachothamnus
fasciculatus
Ca
(6)
546
3
Malosma laurina
Ca
(5)
194
3
Rhus ovata
Ca
(8)
80
3
Ribes
spp.
Ca
(8)
683
3
Trevoa trinervis
c
Ch
(2)
7
12
