Guidelines suistainable urban forestry ROMA_Eng

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SOx, O 3, PM10, PM2.5) both directly (removal by leaves trough stomata uptake for atmospheric
pollutants and/or dry deposition on the cuticle) and indirectly changing natural air streams (thus
changing local concentration of atmospheric pollutants).
All plants are able to remove pollutants from air, but some species can be more efficient due to
their morphological, functional and specie-specific features such as: leaf structure (thickness, shape,
stomata density and morphology) and their seasonal persistence on the plant. In general, at the same
environmental conditions, the efficiency in absorbing atmospheric pollutants is better in presence of
high stomata density and high cuticle thickness. Referring to dusts (PM10, PM2,5, suspended
particles, smoke, aerosol), some specie-specific characteristics can contribute to a more efficient
removal of pollutants such as leaf surface micromorphology (presence of hair, wax, roughness, etc.),
total leaf surface and complexity of leaf morphology. In general, trees are more efficient than shrubs,
and among these conifers are better than deciduous trees due to an higher leaf surface and a more
complex and well-structured phyllotaxis and crown morphology.
Although the role of vegetation for improve air quality is undeniabl , it is important to specify
that is still controversial the quantification of effective contribute of single species in atmospheric
pollutants removal, net to complex plant-atmosphere interactions. Furthermore, it is to remind that
some species, particularly those characteristics of Mediterranean area, can emit considerable quantity
of Volatile Organic Compounds (so-called VOCs, such as isoprene and terpenes) which in urban
areas, especially in presence of high concentrations of NOx, can induce the increase of tropospheric
ozone concentration.
Therefore, in forestry interventions aimed to atmospheric pollutants abatement it is crucial to select
the best species association according to their eco-physiolocial and functional features (such as species
with a lower ozone formation potential, like turkey oak, cherry-tree, manna ash, field maple, etc.), and
considering the surrounding environment.
Vegetation, and in general green areas, is involved also in water cycle, through the so-called
“phytopurification”. Thus, many species are able to efficaciously absorb pollutants in the soil, storing
inside their tissues. For example, Salix caprea is efficient in the phytoextraction of zinc, arsenic,
cadmium, lead and other heavy metals which are often common in soils around disused industrial
areas in suburbs.
In very anthropic areas, significant presence of woodlands, both natural and artificial, contributes to
rhizodegradation, phytodegradation, phytoextraction, phytostabilization processes, reducing impacts
of soil pollutants. However, it is necessary to pay attention to phytovolatilization events, which consist
in the absorption, chemical transformation and consecutive release of pollutants in the atmosphere
through evapotranspiration (such as mercury, selenium, silver, arsenic, solvents, ethers) .
Vegetation, furthermore, can contribute to noise reduction, thanks both to leaves (which redirect
acoustic waves and absorb sound energy converting it in heat) and to structural changes of the soil by
roots. It is necessary to consider many variables during the planning of a forestry intervention aimed to
noise mitigation: in fact, size of noise reduction depends on species (leaf shape and dimension, soil
coverage, etc.). In brief, it was observed that abatement of noise levels occurs mainly at high
frequencies (Bullen, Fricke, 1982) . Moreover in a place delimited by buildings completely covered
by vegetation, it is estimated an average reduction of sound pressure levels of about 4-5 dB, at 125 Hz,
and of about 8-9 dB at 4000 Hz (Smyrnova et al. 2011 .
1.1.3 Biodiversity conservation
Urban green areas, being a suitable habitat for different animal and plant species, can contribute to
biodiversity conservation and safeguard both at local and broad scale. The same Convention on
Biological Diversity recognizes the importance of urban biodiversity protection for the achievement of
their objectives, with particular reference to urban green areas and urban protected areas.
9 For example a study realized in London revealed that rough leaves of linden showed an higher particulate load respect to other broad-leaved
species characterized by a smooth leaf surface ., 2013. L’impianto, la gestione e la valorizzazione multifunzionale dei boschi
periurbani : interventi forestali non produttivi per la valorizzazione dei boschi - Supporti tecnici alla Legge regionale forestale della
Toscana; 9).
10 For example see a recent study in the city of Barcellona on PM 10 e NO2. F. Baró, L. Chaparro, E. Gómez-Baggethun, J. Langemeyer, D. J.
Nowak J., Terradas, 2014. Contribution of Ecosystem Services to Air Quality and Climate Change Mitigation Policies: The Case of Urban
Forests in Barcelona, Spain. In AMBIO A Journal of the Human Environment. 43: 466-479.
11 Consiglio Nazionale delle Ricerche, IBAF, Istituto di Biologia Agro-Ambientale e Forestale. “Le piante per il fitorimedio”.
12 Bullen, R., Fricke F. 1982. Sound propagation through vegetation. Journal of Sound and Vibration Volume 80, Issue 1, 8 January
13 Smyrnova Y., Kang J., Cheal C., Hong-Seok Yang 2011. Numerical simulation of the effects of vegetation on sound fields in urban spaces.
Forum Acusticum.