Agriculture Reference
In-Depth Information
ignitions in the lower foothill shrublands to a substantial proportion of
lightning-ignited fires in the higher montane sites. Southern California is noted
for its autumn Santa Ana winds (
Box 1.3
) and when they coincide with ignitions
the result is firestorms that cover vast areas in a brief period of time.
The MTC region of central Chile occurs from roughly 30
to 40
S and closely
matches the California landscape with a north-south trending central valley
between lower coastal ranges and the much higher interior Andes (Mooney
1977a
; Arroyo
et al
.
1995
; Dallman
1998
). As in California, lower-stature matorral
shrublands with many drought-deciduous species are found near the coast, with
evergreen sclerophylls dominating sites further inland (
Fig. 1.6d
). Much of this
landscape has experienced widespread human disturbance and forms an open
mosaic of shrubland and alien-dominated annual grassland. There is a much
greater overlap with plant families in the northern hemisphere than with other
MTC regions in the southern hemisphere (
Table 1.2
), perhaps reflecting the early
breakup of Gondwana continents (see
Chapter 10
). As in the previously discussed
regions, geophytes and annuals comprise an important part of these ecosystems.
Broadleaf evergreen woodlands of
Cryptocarya alba
in the laurel family occupy
moister sites up to 1400 m, and in valley bottoms, and extending to higher
elevations are forests dominated by winter-deciduous
Nothofagus obliqua
. Unlike
those in California, evergreen conifer forests do not dominate at elevations above
these evergreen and deciduous woodlands, however; further south and still within
the MTC are patches of the very distinctive fire-adapted conifer
Araucaria
araucana
(Aagesen
2004
).
Most fires are started by humans and are generally small due to the mosaic of
shrublands with grasslands that are intensively grazed and exploited for firewood,
reducing fuel continuity (Zunino & Riveros
1990
). Lightning-ignited fires are rare
because there are few summer thunderstorms due to the massive Andes escarp-
ment that blocks monsoonal air masses from penetrating into Chile (Aschmann &
Bahre
1977
). Despite the apparent lack of a predictable natural source of fires,
sclerophyll shrublands are highly resilient to fire and most all-woody taxa resprout
after fire, some from basal lignotubers, but few recruit seedlings after fire.
In South Africa the MTC is concentrated in the southwestern portion of the
country known as the Cape region or botanically as the Cape Floristic Region.
Vegetation is largely one of two evergreen shrublands,
fynbos
(
Fig. 1.6e
) and the
lower stature
renosterveld
(Cowling
et al
.
1997a
). The former dominates on
quartzites and other substrates producing very coarse-textured oligotrophic or
low-nutrient soils (
Fig. 1.5
), whereas renosterveld is restricted to more fine-
grained and more fertile soils derived from shales. Floristically these vegetation
types are markedly different, with fynbos dominated by sclerophyllous-leaved
southern hemisphere families such as the Proteaceae and Restionaceae, and
renosterveld by more cosmopolitan plant families (
Table 1.2
). Small patches
of broadleaf evergreen woodlands and forests persist in isolated riparian areas
or steep cliffs known as kloofs. These sites are considered refugia where these
fire-sensitive forests have persisted (Moll
et al
.
1980
; Manders
1991
; Geldenhuys
