Environmental Engineering Reference
In-Depth Information
11.1
INTRODUCTION
In spite of the similarities in climate, many striking
differences can be found among MCRs, in addition
to fi re regime. As mentioned, historical differences in
land use
practices, including the time span of degrada-
tion processes, socio-economic dependence on local
resources and cultural perceptions of the relationship
between humans and nature, all have great impact on
biota and ecosystem dynamics. The Mediterranean
Basin is the only MCR in the so-called Old World, where
humans have practised agriculture for as long as 13
millennia in some areas (Purugganan & Fuller 2009).
The process, initiated in the Near East, is thought to
have spread to the entire Mediterranean region over
the course of about three millennia (Zeder 2008). In
the process, people consumed resources and trans-
formed, or ' resculpted ' natural
landscapes
and
eco-
systems
to their own ends (Blondel
et al
. 2010 ).
Therefore, environmental
degradation
in the region
is ancient (Thirgood 1981). However, the intentional
fi res, herbivory by domestic livestock, agroforestry
practices and constant trade of wild and domestic
species of plants and animals fi rst developed in the
Mediterranean Basin itself, are now common practices
there, and indeed in most of the MCRs (Armesto
et al
.
2007). They cannot be described simply as environ-
mental destruction. Instead, in more neutral terms, we
may refer to the profound transformation of the 'origi-
nal' or pre-Holocene landscapes (Blondel
et al
. 2010 ).
Certainly, the combination of the great diversity of
physical conditions (geology, topography and soils) and
of land use histories, and fi nally the large number of
possible pathways and stages of succession occurring
after various disturbances all give to Mediterranean
landscapes a particular patchwork pattern and kalei-
doscopic quality that Blondel and Aronson (1999)
called a 'moving mosaic'. Both the interpretation of
these landscapes, and the procedures for carrying out
ecological restoration there, are highly complex.
In the four MCRs other than the Mediterranean
Basin, intentional anthropogenic transformation of
landscapes was less intense and extensive until very
recently. However, the indigenous cultures of each four
of those regions also have a long history of landscape
modifi cation, mostly through the intentional use of
fi re. Natural fi re regimes were often altered, affecting
ecosystems dynamics, landscape structure and biodi-
versity in the process (Pausas & Keeley 2009).
Of course, urbanization, industrialization and
'metropolization', and the globalization of commodity
and service markets, are driving current land uses and
There are only fi ve Mediterranean - climate regions
(MCRs) on Earth - the Mediterranean Basin, most of
California, central Chile, southern South Africa and
south - central and south - western Australia. They all
have cool, or cold and relatively wet winters alternat-
ing with long, hot and dry summers. Spring and
autumn seasons are ephemeral in comparison, and
highly variable. During much of the year, droughts
lasting weeks or even months are frequent, with grave
consequences on all biota, since water is the key limit-
ing factor for growth and well-being of all organisms,
including humans. Yet, biodiversity is unusually high
in all fi ve MCRs. Well-adapted woodlands and shrub-
lands, which are the subject of this chapter, are nu-
merous and noteworthy, in ecological, cultural and
socio - economic terms.
Climate, geology and evolutionary biogeography of
MCRs have all contributed to alpha, beta and gamma
biodiversity of these regions. In the Mediterranean
Basin, California and Chile, the predominantly young,
orogenic systems produce intense geomorphologic
dynamics with poorly developed, shallow soils (Brad-
bury 1981). The uneven relief with steep slopes in
large parts of the territory and spreading of unconsoli-
dated and soft substrata increase the risk of soil degra-
dation. In sharp contrast, MCR landscapes in South
Africa and Australia are ancient and stable; as a result,
they have highly weathered and leached soils that are
very poor in nutrients (Rundel 1998). Human land use
histories have also contributed to ecological diversity in
all fi ve regions, and must be taken into account when
contemplating or undertaking ecological restoration.
Natural
wildfi res
are common in most of the fi ve
MCRs, owing to the high accumulation of fuels leading
to enhanced fl ammability in summer, the frequency of
lightning storms and, in some areas, periodic but
intense, hot and dry winds such as the Santa Ana in
California and the Mistral in southern France. An
exception is central Chile where the Andean Cordillera
protects the MCR area from summer storms and light-
ning (Rundel 1998). As a result, central Chilean scle-
rophyllous vegetation is ill adapted to frequent fi res,
never having had selective pressure from this form of
disturbance over evolutionary time. Nonetheless, in
recent decades anthropogenic fi res have become much
more common, and this is causing profound changes
in the characteristic features of central Chilean land-
scapes (Armesto
et al
. 2009 ).
