Environmental Engineering Reference
In-Depth Information
observation of succession of abandoned woody crops,
as olive trees, carob trees, almond trees and vineyards.
In these conditions, the natural succession is signi-
ficantly faster than in non-woody crops thanks to the
role of the trees as perch sites for frugivorous birds.
These birds defecate seeds of late-successional, bird-
dispersed species that germinate around the perching
tree forming a nucleus of advanced succession (Verdú
& García-Fayos 1996). Furthermore, the perch tree may
also create a favourable microsite for germination
and survival. Dead trees may also be used by birds
as caches (e.g. for acorns; Mosandl & Kleinert 1998).
These bird-mediated facilitation processes inspired a
restoration technique based on providing bird perches
(e.g. dead trees, artificial woody structures) in old-field
sites to accelerate colonization rates and ecosystem
restoration. Although being an attractive and inex-
pensive technique to help succession, it has seldom
been applied to Mediterranean ecosystems and most
examples come from elsewhere, mainly from tropical
ecosystems (e.g. McClanahan & Wolfe 1993). Because
in many areas of extensive old-fields there is a very
low seed availability of late-successional species, this
technique could be appropriate. A potential limitation
for the use of these techniques may be the lack of
suitable dispersers (Alcántara et al. 1997) and of a close
source of target species seeds; however, its applica-
tion clearly needs to be explored and tested under
Mediterranean conditions.
Thus, landscape-restoration programmes should be
diverse, adaptive, self-organizing and able to face the
ecological realities of change (Whisenant 1999, 2002).
The selection of the species (often a combination of
species) for each part of the landscape, and the
arrangement of the restoration patches at the differ-
ent scales may determine the sustainability of the
restoration and the self-sustaining recovery process.
14.4.2 Evaluation and monitoring
In order to improve our understanding of the success
or failure of restoration actions, there is a need for
long-term monitoring and evaluation of restoration
actions in Mediterranean landscapes. Evaluating
ecological restoration success on the ecosystem and
landscape scales can be performed using indicators
(e.g. Tongway & Hindley 1995, Aronson & Le Floc'h
1996a, Whisenant 1999), although widely accepted
standard protocols are not yet available.
14.4.3 Extreme and unpredictable dry
conditions
Restoration techniques for Mediterranean conditions
have greatly improved in recent decades, thanks to the
inputs from disciplines such as community ecology,
ecophysiology and soil science. However, we still
lack well-tested and reliable techniques for restoring
degraded ecosystems in arid or semi-arid regions, and
thus further research is needed in this context. More-
over, nursery production needs to be diversified in order
to provide high-quality seedlings for different purposes
and conditions.
14.4 Concluding remarks
Several critical issues in ecological restoration for
Mediterranean ecosystems deserve further development
in the near future.
14.4.1 A landscape approach
14.4.4 Economics
In many Mediterranean systems, and due to the large
and long-standing human impacts, degradation pro-
cesses are not local and large heterogeneous areas need
to be restored. Restoration needs to be viewed and
approached at the landscape (and/or regional) scale.
Different combinations of the above-mentioned re-
storation techniques may be required for different
purposes, but also for different parts of the landscape.
The benefits of restoration projects are indirect and
long-term, and thus they do not have a market value
under prevailing economic systems. For this reason,
restoration actions in the Mediterranean are strongly
dependent on subsidies - mostly from the European
Union - and changes in the existing subsidy policies
could have strong impacts on our landscapes.
 
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