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44
1.5 Selection of the propagation stock
Selection of the propagation stock
is another important aspect to take in account for a successful
forestry intervention: in fact it is necessary to choose carefully arboreal individuals for guaranteeing
quality, health (no injuries and/or plant diseases) and, when possible, genetic state. It is important that
vegetal material to use was in compliance with declared species and varieties, exempt from structural
flaws, injuries and infections, provided with a normal and healthy root apparatus. It has to be
examined also breeding manner, choosing between root ball or containe
r 47, as naked root involves
problems of taking root, resulting in a fail of planting.
Better results from an ecological and functional point of view are obtained through the breeding of
spontaneous species, present in the residual vegetal associations inside urban pattern or in their
surroundings.
Unfortunately, plants supply often represents a problem, because, currently a real planning of
forestry interventions at National scale is missing. Therefore, very often it is requested to nursery
gardens propagation stock that is not immediately available, with resulting delays and/or changes in
species selection. Instead, a propagation material of quality reduces the risk of a scarce implants
survival and allows a successful forestry intervention. In particular, when choosing trees, it is
opportune to assess the following aspects:
•
trunk structure, that should be upright and without injuries/alterations, especially on root
collar (which is the portion of the tree between the trunk and the root, at ground-level);
•
the shape of the crow, that should be symmetrical and display a regular branching, without
drastic cuts;
•
the correct proportion between height and diamete
r 48;
•
a healthy root apparatus, well structured and with an adequate number of roots. In
particular it is necessary to verify the possibly presence of circling and/or spiral roots,
which during growing could cause problems to plants. Moreover for plants in clod, it is
necessary to control that the root ball is of dimensions appropriate to those of the plant;
•
age and dimensions, to select also in relation to planting pattern. As general rule, it should
be expedient prefer young individuals, which start to grow again quicker and stronger
respect to plants of greater dimensions (and age).
It is advisable that these characteristics are assessed by experts, both in the nursery garden and in
the installation site (to control that plants did not be subjected to damages during handling).
While the majority of tree species is available on the market, some difficulties can be found for
shrubs, for which the offer of the market is reduced (with considerable lack for some species of genus
Salix
,
Cytisus
etc.) (Cornelini et al., 2002)
49. In particular in Mediterranean area, due to limiting
factors above-mentioned (cf 1.4), it could be more difficult to find suitable species, because common
autochthonous species available in nursery garden not always are consistent with the Mediterranean
vegetation succession
(AA.VV., 2010
) 50.
47
In Italy, the use of root balls (clods) is widespread, as it allows plants to grow on substratum similar to those of destination. In this case,
however, it is fundamental to realize transplantations in the nursery garden to allow a correct roots development. Moreover plants in clods
are much expensive. Plants in container are generally lighter and do not depend on soil seasonality, as the substratum can be prepared on the
basis of specific needs. However it is necessary to pay more attention during both the repotting and the bedding out, to avoid spiral or
damaged roots. Generally, naked root are not used, except in shifts among nursery gardens.
48
For example at a diameter of 20-25 cm should correspond an height of 5,5-6 meters; for a plant with a trunk circumference of 40-45 cm,
height has to be about 8 - 10 meters.
49
Cornelini P., Palmeri F., Sauli G., 2002.
Le specie autoctone da impiegare negli interventi di ingegneria naturalistica
. Acer n.6.
50
AA.VV., 2010.
Analisi e progettazione botanica per gli interventi di mitigazione degli impatti delle infrastrutture lineari
. ISPRA Manuali
e linee guida 65.3/2010.