Agriculture Reference
In-Depth Information
Mediterranean Basin
Shrubland diversity increases markedly after fire due to resprouts and seedlings from
species present prior to fire, coupled with a large ephemeral herbaceous flora arising
from dormant bulbs/corms and seeds. Herbaceous perennials comprise a large
portion of this diversity on many sites. On rare occasions annual plants disperse into
burned sites from surrounding disturbed sites (Bonnet & Tatoni
2004
). In garrigue
and maquis, diversity is typically low during the first year but increases during the
first decade as more species colonize from outside the burned area and persist until
canopy closure (Trabaud & Lepart
1980
). During early succession diversity is sensi-
tive to precipitation (Kutiel
1997
). As the canopy closes in, this ephemeral flora
diminishes but persists on open sites between shrubs or in grasslands. These shrubs
are core species widely abundant within sites andwidely distributed across landscapes
(Pa¨ rtel
et al.
2001
), as is evident in California shrublands (Keeley
et al.
2005c
).
Intensive land use, particularly grazing, has replaced fire in many of these shrub-
lands (Zohary
1962
; Naveh & Whittaker
1979
), and resulted in a mosaic of grass-
lands and shrublands often with very different species composition fromundisturbed
shrublands (Alados
et al.
2004
). These open unburned stands have substantially
higher diversity than burned sites (Verdu´
et al.
2000
; Keeley & Fotheringham
2003b
;deBello
et al.
2007
). At the more arid eastern end of the basin, on sites with
a history of intensive livestock grazing and fire, open shrublands produce some of the
highest plant diversities observed in any MTC region (
Table 11.2
). These sites often
average 125-150 species per 0.1-ha scale with or without recent fire, which is nearly
double the species richness observed in otherMTC ecosystems (
Table 11.2
), although
potentially comparable to the extraordinary diversity observed in mediterranean-
type vegetation (MTV) dominated by longleaf pine in the southeastern USA (Platt
et al.
2006
). In the eastern Mediterranean Basin these high levels of diversity persist
even in years of subnormal rainfall (Aronson & Shmida
1992
). It has been hypothe-
sized that this may arise from the much greater regional species pool to draw from
in this region at the confluence of floras from Europe, Asia and Africa (Keeley &
Fotheringham
2003b
). For example, Israel has nearly nine times greater density of
species than Spain (Danin
2001
).
California
California shrublands follow a pattern of diversity changes in response to fire that is
similar to the Mediterranean Basin. Following fire in closed-canopy shrublands there
is a large postfire flush of annual species from dormant seedbanks. However, postfire
herb succession inCalifornia differs in several respects.Most prominent is the fact that
a significant proportion of the annuals in the postfire flora are strict
pyro-endemics
,
which are generally not found on other disturbed sites as in the Mediterranean Basin.
These fire endemics are largely from families best developed in western North Amer-
ica, in particular the Hydrophyllaceae and Polemoniaceae (Keeley
et al.
2006b
).
This postfire endemic annual flora is fire dependent with strict smoke-
stimulated germination (Keeley & Fotheringham
2000
), but despite its disturb-
ance-dependent life history, persistence of these taxa is sensitive to invasion by
