Agriculture Reference
In-Depth Information
(some species of
Fumana
,
Helianthemum
and
Cistus
), and aromatic Lamiaceae
(species of
Rosmarinus
,
Thymus
,
Lavandula
and
Salvia
). The germination of Faba-
ceae and Cistaceae is primarily stimulated by heat, whereas the germination cue
for Lamiaceae and Ericaceae is mainly smoke (Moreira
et al.
2010
;
Table 4.2
).
Resprouting is variable as some are non-resprouting obligate seeders and others
have the capacity to both resprout and recruit after fire (facultative seeders).
There is a tendency for non-resprouters to have seeds with a greater heat tolerance
and a greater heat-stimulated germination than facultative seeders have (Paula &
Pausas
2008
).
These communities are highly flammable because communities have a large
proportion of their biomass in fine fuels with high risk of ignition. Also, some
species are highly aromatic containing flammable oils, plus many are relatively
short lived and due to site aridity they accumulate a lot of dead standing biomass.
Thus, these communities tend to burn more readily than shrublands dominated
by broadleaf plants (Ojeda
et al.
2010
). However, at the drier end of the moisture
gradient or where sites have been overgrazed, fuel loads are low and discontinu-
ous, which inhibits fire spread. The regeneration of these communities is often
very dependent on the seedbank, and thus theymay be more sensitive to the length
of the inter-fire period than the shrublands dominated by postfire resprouting
shrubs.
Erica
is one of the common genera forming small-leaved shrublands. Its center
of diversity is in the Cape region of South Africa (see
Chapter 7
), where most are
postfire obligate seeders (Ojeda
1998
). In contrast, most species in fire-prone
ecosystems of the Mediterranean Basin resprout from lignotubers after fire or
clipping (e.g.
E. arborea
,
E. multiflora
,
E. australis
,
E. scoparia
; Canadell
et al.
1991
;
Lloret & Lo´ pez-Soria
1993
;Vil` & Terradas
1995
; Cruz & Moreno
2001a
) and
very few do not (e.g.
E. umbellata
; Quintana
et al.
2004
). Many of these
Erica
species have dormant seedbanks stimulated to germinate by smoke and thus they
recruit well after fire (
Table 4.2
; Moreira
et al.
2010
).
Another fine-leaved resprouter in the western part of the Basin is the tussock
grass
Ampelodesmos mauritanica.
This species accumulates large amounts of fine,
dead fuel (Vila`
et al.
2001
) in a loose airy structure that is very susceptible to
burning. Fire does not penetrate the tightly packed base of the tussock, which
survives and the fuel quickly regenerates. Furthermore, this species flowers and
produces abundant seeds after fire, resulting in heavy recruitment in subsequent
postfire years (Lloret
et al.
2003
).
The mediterranean old-field includes a range of vegetation combinations that
depend on environmental conditions: age since abandonment, previous crop and
interactions with grazing (Debussche
et al.
1996
; Bonet & Pausas
2004
,
2007
).
Recently abandoned fields are quickly occupied by herbaceous vegetation.
A dominant perennial grass in many old-fields is the rhizomatous
Brachypodium
retusum
, which resprouts quickly after fire. This species appears inmost western plant
communities (woodlands, shrublands, and in semi-arid conditions) but it shows its
maximum occurrence in early stages of old-field succession (Caturla
et al.
2000
).
