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according to the air quality of the chosen site, as they can emit high quantity of VOC; this is
the case of holm oak whose use should be limited to areas far from sources of pollutants
precursors, because it could tend to facilitate formation of pollutants of secondary origin such
as ozone. In peri-urban environment it can be also used the cork oak (
Q. suber
), less suitable
in strictly urban environment;
•
elms (
Ulmus minor
and
U. montana
), long-lived trees, tall with dense and large foliage,
therefore suitable for mitigation of both noise and atmospheric pollution. Both species are
used as ornamental trees in urban green; in Rome the first is indigenous;
•
lindens (
Tilia cordata, T. platyphyllos, T. x vulgaris
), which in addition to being generally
large and long-lived, have dense foliage, all suitable for mitigation of air and acoustic
pollution. In Rome grow well even if they are not indigenous and are mainly suitable for the
realization of street trees and buffer areas. Furthermore, often their leaves present sticky
secretions which can improve the efficiency of holding suspended atmospheric particular
matter;
•
hackberry (
Celtis australis
), long-lived species, with large and wide canopy, widespread for
tree-lined rows and urban green areas thanks to its adaptability and resistance to pollution and
large and dense crown which produces shade;
•
various conifers, for the reasons above-mentioned (evergreen individuals, greater leaf area,
etc.). In the Mediterranean environment species of the genus
Pinus
(e.g. pine
P. pinea
,
although it is a species that can cause allergies and not suitable for tree-lined rows because of
shallow roots), species of the genus
Cupressus
(such as cypress,
C. sempervirens
), species of
the genus
Cedrus
(such as Atlas cedar,
C. atlantica
, ornamental species but of exotic origin).
It is important to remind that although conifers are efficient for air and noise pollution
mitigation, thanks to their dense and complex crown, however, they are species which suffer
of high levels of environmental pollution and, therefore, they should not be placed in
environment characterized, for example, by high anthropic emissions;
•
among the shrubs, the most common are the heather (
Erica arborea
) and the viburnum
(
Viburnum tinus
), both evergreen. They are appropriate for both noise absorbing function and
atmospheric pollutants abatement, thanks to their habit which make them suitable for the
realization of green belts near the ground, as a support of tree species, such as conifers, which
often are characterized by “empty” portions or lacking foliage in the proximity of the ground.
1.4.3 Criteria for the selection of species to increase animal biodiversity
Each animal species has specific ecological requirements, therefore there are not vegetal species
more suitable than other for increasing biodiversity. However, it is possible to provide some general
criteria, which enable to realize forestry interventions which can contribute to the increase of
biodiversity, even if their main function is different (such as capture CO
2
, mitigation pollution, etc.).
In detail:
•
to favour a mixture of species (avoiding monospecific interventions of forestation) and of
various sizes: this helps to create a more diverse habitat for wildlife and permits greater
stability and resistance of the plant community (and greater plant biodiversity). The layering
of natural forests can be reproduced using appropriate shrub species (e.g.
Cytisus
sp.,
Crataegus
sp.,
Ligustrum vulgare
). Even in the case of tree-lined street, can be functional for
the fauna designing multi-species rows. The variety of species can also facilitate the
colonization by soil organisms (bacteria, fungi, invertebrates), essential to maintain over time
the new plants;
•
to prioritize a variety of planting patterns. In fact, the nature of the arrangement of trees and
shrubs is not regular, thus planting new individuals in a way to create a more varied habitat as
close to natural conditions;
•
to favour native species, so as to contribute to increase even plant biodiversity;
•
select also species with flowers and fruits. The presence of flowers helps to increase insect
records, which in turn represents a trophic resource for other species (birds, mammals,
reptiles). Trees with flowers also have an aesthetic function. Even the fruits (berries, drupes,
apples) are a trophic resource for many species, especially birds. The use of trees that produce
fruits superseded and/or cones must however be evaluated in situations, as the vicinity of
roads, where their fall may represent a security risk The conservation of rare cultivar of fruit
tree in the urban park can give an implementation to the conservation of germoplasm. In urban
areas interesting interventions of high conservation value and protection of genetic diversity