Agriculture Reference
In-Depth Information
conditions they are known as
pyro-endemics
; others are more opportunistic and
are most abundant after fire but persist long after fire in gaps and other disturb-
ances. A few annuals and herbaceous perennials seem to thrive best in low
numbers in mature chaparral.
Annuals dominate the postfire flora, typically comprising more than 50% of the
cover and diversity in the first few postfire years. The dormant seedbanks of these
species are triggered by either intense heat shock or combustion products
from smoke or charred wood (Keeley
1991
; Keeley & Fotheringham
1998
).
Heat-stimulated germination is found in hard-seeded species that have water-
impermeable seeds until the outer seed coat is scarified and include families such
as Fabaceae and Convolvulaceae. Chemically stimulated species have water-
permeable seeds that imbibe water but remain dormant until cued by combustion
products from smoke or charred wood (see
Box 3.1
). These species include
members of the Hydrophyllaceae, Lamiaceae, Polemoniaceae, and Scrophularia-
ceae, among others (Keeley & Fotheringham
2000
).
Shrub Canopy Recovery
Postfire regeneration of the shrub dominants is by either resprouting and/or
seedling recruitment, and the relative importance of each is a function of (1)
innate characteristics of species, (2) fire intensity and (3) postfire drought.
The majority of shrub taxa have the capacity to resprout from adventitious
the lignotuber is an ontogenetic stage of development that is evident by the first
year of growth (see
Table 3.2
). These include
Adenostoma fasciculatum
(Rosaceae),
and many species in the two largest shrub genera,
Arctostaphylos
(Ericaceae) and
Ceanothus
(Rhamnaceae). Others, such as species of
Quercus
(Fagaceae) will
produce basal swellings following repeated decapitation from fire or browsing.
Most other resprouters generally lack any sort of basal burl.
A postfire pulse of seedling recruitment is observed in some taxa but not all.
Adenostoma fasciculatum
, and all species of
Arctostaphylos
and
Ceanothus
, produce
seeds on an annual to biennial basis and the bulk remain dormant in the soil for
decades or even centuries until germination is triggered by fire. These postfire
recruiters are most common on more xeric sites, such as low elevations and south-
facing exposures (Keeley
1986
; Meentemeyer & Moody
2002
).
Many species resprout after fire and lack seedling recruitment from dormant
seedbanks. These postfire obligate resprouters have not been selected to delay
reproduction to a single postfire pulse of recruitment, rather they recruit in the
inter-fire interval (see
Table 3.1
). These include species of
Prunus
,
Quercus
,
Rham-
nus
, and
Cercocarpus
. Other vigorous resprouters that have a low level of recruit-
ment after fire include
Fremontodendron
spp.,
Rhus
spp. and
Garrya
spp. It has
been hypothesized that these different fire responses are tied to character syn-
dromes that include drought tolerance response, dispersal and past history (see
Table 9.1
).
