Agriculture Reference
In-Depth Information
In the eastern part of the basin, a good colonizer of old-fields is the thorny
dwarf shrub
Sarcopoterium spinosum
, which can form large and continuous mono-
specific formations, especially in overgrazed areas. It has clonal growth and a
strong postfire resprouting capacity, and recruits profusely, both after fire and in
the absence of fire (Henkin
et al.
1999
; Seligman & Henkin
2000
).
One of the early shrubs appearing in old-fields in the western Mediterranean
Basin is gorse or
Ulex parviflorus
, a very flammable shrub with fine fuels and
retaining a large proportion of dead biomass (
Fig. 4.5
; Baeza
et al.
2006, 2011
). It
is a non-resprouter and the density of this obligate seeder can be very high, making
the old-field a very flammable community that rapidly replaces itself after fire.
Other obligate seeder species may coexist with
Ulex parviflorus
, such as some
Cistus
species. Postfire recruitment of
Rosmarinus officinalis
is typically lower than
that of
Cistus
and
Ulex
, but it lives longer and may become abundant in later
stages of old-field succession or on colder inland sites.
Because most broadleaf evergreen shrubs are more shade tolerant and longer
lived than these small leaf, malacophyllous species, they are often functionally
late-successional species. Thus, with increasing time since abandonment, resprou-
ters and facultative seeders may colonize and become abundant. It is interesting
that resprouting species tend to appear earlier in abandoned tree crops (e.g. olive
or carob tree crops) than in herbaceous crops due to the fact that previous tree
crops act as perches for birds (Debussche
et al.
1982
; Pausas
et al.
2006a
) and
many resprouters have bird-dispersed fleshy fruits (
Table 4.3
; Pausas
et al.
2004b
)
and recruit in the absence of fire (see
Chapter 9
). Pines may also colonize these
old-fields, depending on the distance from a seed source tree.
Pines of the Mediterranean Basin
Pines (
Pinus
spp.) grow naturally in many places in the region, but they have also
been extensively planted (Pausas
et al.
2004a
,
2008
), and not always from local
provenances. Current pine communities are highly variable, and most understory
species are the same ones in surrounding shrublands and woodlands. Pines occur
at low or moderate densities, or they may form relatively dense monotypic forests.
They include pines from both crown fire regimes and surface fire regimes. They are
highly flammable and as a consequence of widespread planting have contributed
to large, high-intensity crown fires (Pausas
et al.
2008
). Comparing bark thickness
and bud tolerance to heating, they can be ranked from the most resistant to the
least resistant to fire as follows:
P. pinaster
,
P. pinea
,
P. nigra
,
P. halepensis
,
P. brutia
,
P. sylvestris
and
P. uncinata
(Fernandes
et al.
2008
).
Pinus halepensis
(Aleppo pine) and
P. brutia
(Turkish pine) are typical of pines in
crown fire regimes (Keeley & Zedler
1998
). They are thin barked with branches
from the base and are killed by most fires and do not resprout. Serotinous
cones open after fire and seed viability in the soil is short lived (Daskalakou &
Thanos
1996
;Pausas
et al.
2004a
); thus, they recruit profusely in the first
growing season (
Fig. 4.7
;Trabaud
et al.
1985
;Moravec
1990
; Thanos
et al.
1996
;
