Agriculture Reference
In-Depth Information
10 0 0 0
10 0 0 0
Quercus dumosa
Prunus ilicifolia
10 0 0
10 0 0
10 0
10 0
10
10
1
1
1
2345
10
15
20
1
2 3 4 5
10
15
20
25
30
Fig. 3.7
Density of seedlings and saplings in the understory of California chaparral unburned for
more than 50 years (Keeley
1992c
).
In these closed-canopy shrublands saplings generally
remain stunted and represent “advanced reproduction” capable of progressing into the canopy
only after resprouting following fires.
reproduction. This is a pyrocentric perspective because obligate resprouters do
have a sexual cycle with seedling recruitment; however, they have not opted for a
strategy of delaying reproduction to a single pulse of recruitment immediately
after fire. Obligate resprouting shrubs (Table
3.1
) reproduce sporadically during
fire-free periods and are best described as having
fire-independent reproduction
(Keeley
1998
; Garcı´ a-Fayos & Verdu´
1998
). In stark contrast to postfire seeders
these all have propagules designed for widespread dispersal, including animal-
dispersed meaty or fleshy fruits and wind-dispersed plumes (Keeley
1992d
; see also
Chapter 9
). Recruitment is largely restricted to the understory of the shrub canopy
and on sites free of fire for extended periods of time (Williams
et al.
1991
; Keeley
1992c
) or in gaps of adjacent woodlands (Keeley
1990b
). Recruitment appears to
be tied to years of high precipitation and in most cases saplings remain stunted in
the understory for extended periods of time (
Fig. 3.7
). In some respects this
represents advanced reproduction or seedling bank, as these stunted saplings
resprout and grow rapidly after fire, and in some taxa there is a level of fire
dependency for successful recruitment into the canopy.
In many forest types there are canopy species that regularly recruit in the
understory in the absence of fire. Typically these taxa are more shade tolerant
than taxa that specialize in recruitment in gaps after fires. Such species also are
important components in some fire-prone landscapes, particularly
Abies
(Pinaceae) in the northern hemisphere and
Eucalyptus
(Myrtaceae) in the south-
ern hemisphere. Some taxa have very flexible recruitment requirements with
respect to fire. For example, the North American white fir,
Abies concolor
,
dominates forests with a surface fire regime. It regularly recruits in the shady
understory between fires but it also capitalizes on postfire environments with
massive recruitment (
Fig. 3.6
). These taxa illustrate that the often-used general-
ization that species with shade-tolerant understory recruitment are
fire sensitive
is clearly not always true.
