Environmental Engineering Reference
In-Depth Information
climate and accuracy of the works. However, visual
impact and modification of the soil profile are strong
reasons for limiting the use of this technique nowadays,
despite the emotional attachment - or nostalgia - that
many people still have for Mediterranean terraces.
35
control
treeshelter
30
25
20
Soil fertility and amendments
15
Forest soils of the Mediterranean Basin are frequently
poor in soil organic matter and low in phosphorus
availability (Vallejo
et al.
1998). Furthermore, land uses
and disturbances such as wildfire or erosion commonly
result in decreased soil fertility (Bottner
et al.
1995,
Vallejo
et al.
1998). To what extent soil nutrient
impoverishment is hampering restoration is a matter
of discussion. Soil organic matter intervenes in many
soil processes affecting plant growth, but especially
in soil structure (i.e. stability versus soil crusting
and erosion, and water-holding capacity) and soil
fertility. A soil organic matter concentration of 1.7%
has been used to identify soils in a predesertified stage
(Montanarella 2002). Seedling establishment does not
seem to be related to soil organic matter content at
levels between 2 and 4% (Maestre
et al.
2003b).
Further research on potential threshold values in
organic-matter content and other soil properties
could be of great help in optimizing restoration
practices.
Response to resource additions is considered an in-
dicator of limitation. Introduced seedlings commonly
respond to inorganic and organic fertilizers (Roldán
et al.
1996, Valdecantos
et al.
1996, 2002). Negative
and null responses are being associated with metal
toxicity, salinity and increased above- and below-
ground competition (Valdecantos 2001, Valdecantos
et al.
2002). There is a wide range of organic residues
available for improving soil fertility. They have tradi-
tionally been used for the restoration of old quarries
(Bradshaw & Chadwick 1980, Sort & Alcañiz 1996),
but they can be applied in other contexts (Roldán
et al.
1996, Valdecantos
et al.
1996, Navas
et al.
1999).
10
5
0
Seedling
Seed
Pre-germinated
Fig. 14.7
Effect of tree shelters on growth of
Quercus
ilex
ssp.
ballota
4.5 years after planting in eastern
Spain using three different techniques: standard
1-year-old seedlings (Seedling), directly sown acorns
(Seed) and acorns pre-germinated 1 week prior to
planting (Pre-germinated). Source: J.P. Seva,
unpublished results.
improve overall seedling performance (Bergez &
Dupraz 1997, Bellot
et al.
2002). The use of tree shel-
ters has gradually increased, being readily adopted by
practitioners. Tree shelters provide protection against
herbivory and extreme climatic conditions. Ventilated
tree shelters help to avoid excessive warming. They
can improve seedling survival and growth (Carreras
et al.
1997, Bellot
et al.
2002; Fig. 14.7), but the use
of this technique alone does not guarantee plantation
success (Oliet & Artero 1993, Navarro & Martínez 1997,
Peñuelas
et al.
1997, Grantz
et al.
1998). The root-
to-shoot ratio of protected seedlings is often lower
than in unprotected seedlings. Thanks to the slow
growth rates, Mediterranean seedlings growing inside
tree shelters may gradually acclimatize to adverse
climatic conditions outside the shelter and improve
shoot growth. When this does not happen, unbalanced
growth in stem height may occur. Still, a reduced root-
to-shoot ratio could negatively affect seedling poten-
tial to withstand drought.
Tree shelters
Bird-mediated restoration
Tree shelters or protective tubes are used to modify
the physical environment of the planted seedling
(acting as mini-greenhouses). If designed conveni-
ently, they can help to reduce evaporative demand and
The role of plant-animal mutualisms has been sug-
gested for cost-efficient restoration plans (Handel
1997). Bird-mediated restoration is based on the
