Environmental Engineering Reference
In-Depth Information
Quercus ilex
Pinus halepensis
marls
100
limestone
Fig. 14.4
Survival of
Quercus ilex
ssp.
ballota
and
Pinus halepensis
seedlings planted in the same year
(1992) and on different bedrocks:
marl colluvium (
) and limestones
(•); different sets of the same
symbol type refer to different plots.
Data from CEAM (Fundación
Centro de Estudios Ambientales
del Mediterráneo; Mediterranean
Centre for Environmental Studies)
experimental plots in eastern Spain.
80
60
40
20
0
0
2
4
6
8
0
2
4
6
8
Time (yr)
Mediterranean ecosystems. The mixing, adaptation
and application of these techniques will of course vary
from one context to another. Restoration projects are
expensive and usually cannot be justified by direct
production benefits. Economic justification relies on
indirect benefits, mostly services to the society (i.e.
external factors). Restoration investments must be
kept as reduced as possible, but this is highly depend-
ent on the specific socio-economic and cultural con-
text. For example, irrigation is seldom used in
restoration projects of southern European countries
because the scarce water available is prioritized for
other uses (mostly agriculture and tourism). However,
irrigation is not unusual under semi-arid and arid con-
ditions elsewhere (Allen 1995, Lovich & Bainbridge
1999, Bainbridge 2002), and it is commonly applied
for seedling establishment in northern Africa.
To ensure sustainability, selection of woody species
for restoration should be based, as much as possible,
on the natural late-successional vegetation of the
area, and on the environmental characteristics of the
site. Traditionally pines were planted in many areas
in the Mediterranean Basin for catchment protection
and sand-dune fixation. Pines have high survival
and growth rates, allowing a relatively quick re-
vegetation success. However, extensive pine planta-
tions provide an excellent fuel bed for large,
devastating fires. Furthermore, pine woodlands com-
monly show low resilience to recurrent fires because
Mediterranean pines do not resprout after fire. Early
attempts to introduce broad-leaved resprouting species
(e.g.
Quercus
species; Fig. 14.4) met with high mor-
tality (Mesón & Montoya 1993) and, until recently,
techniques for introducing broad-leaved or evergreen,
late-successional resprouting species in Mediterranean
conditions were poorly developed. A relevant research
question concerns whether it is possible to artificially
skip stages in natural succession in this fashion, as
suggested in Fig. 14.2.
As mentioned already, water-use efficiency is a key
factor affecting plant survival and growth in Med-
iterranean conditions (Fig. 14.5). Water availability
and plant water-use efficiency may be manipulated
by different restoration techniques, such as seedling
preconditioning, soil preparation, fertilization, pro-
tection by tree shelters and use of nurse plants. In short,
Mediterranean restoration efforts generally aim at
maximizing water-use efficiency and water avail-
ability (Table 14.2). Furthermore, other techniques
based on the recognition and use of the ecological site
diversity may also be applied, such as microsite
selection and bird-mediated restoration. Each species
ensemble and technique should be applied to the
different landscape parts as appropriate. Restoration
strategies should optimize the available resources and
processes of the degraded site in its current state and
context.
As many woody late-successional species do not form
a permanent seed bank, seeding woody species is an
attractive technique to re-introduce target species
