Guidelines suistainable urban forestry ROMA_Eng

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Box 2 - Urban green spaces and allergies to pollens: recommendations
Pollens represent the male part (male microgametophyte) in the reproductive process of seed
plants. Pollen grains are characterized by a protective double wall: an external one (called exine)
and an inner one (called intine).
When the pollen is mature, it is released for pollination and can reach the female part of the flower
by wind (anemophilous plants) or by insects (entomophilous plants), water, birds and other
animal .
Generally, pollens that cause allergies:
• come from anemophilous plants ,
• contain certain substances called allergens that, in genetically susceptible people, stimulate
the immune system to produce antibodies,
• are produced in large amounts by plants very common in the are .
The external wall of the pollen grain contain specific proteins that help pollen grains to be
recognized by the female part of the flower. These proteins are responsible for allergic reactions in
sensitive people, and act as antigens, stimulating the immune system to produce antibodies (IgE).
When antibodies meet antigens, chemical mediators are produced, such as histamine, to trigger the
inflammatory process at the base of allergic symptoms (rhinitis , conjunctivitis, asthma etc.).
Pollen concentration in the air depends mostly on the presence and distribution of plants in the
area, and on weather-climatic variables such as wind, humidity, temperature and rainfall.
Climate change can affect pollens production: rising temperatures are associated with increase in
length and earlier beginning of pollen season, spread of invasive species and, in combination with
high CO2 concentrations, to an increased production of pollen.
The pollen allergenicity level, the ability and the extent of the pollen grain to induce allergic
reactions, has been estimated for many trees, shrubbery or herbaceous species in several studies.
This knowledge has been used by ARPA Emilia Romagna to organize botanical data sheet, where
four level of allergenicity are identified: low, moderate, high and very high .
The level of allergenicity of most common species are summarized in following Table. Must be
taken into account that the level of allergenicity may also change with different local climatic
pattern.
Furthermore, in urban areas the high concentration of air pollutants which will lay down on pollens
and carried by them, can amplify the allergenicity of pollens and make people more susceptible to
them.
In Italy, as well as in Europe, the increase of pollen-sensitive population requires certain safety
measures in the selection of species for green spaces that are suitable for recreational use (parks,
gardens, green school areas, etc.), among these measures is suggested:
• to use native species with low-allergenic pollen;
• to use female or sterile plants in the case of species with moderate-very high allergenic
pollen;
• to use plants with entomophilous pollination;
• to organize maintenance services of grassy meadows (e.g. mowing) before blooming
period to prevent pollen spread;
• to avoid the use of stinging or poisonous plant species (e.g. Gleditsia triacanthos L. -
honey locust - thorny locust; Robinia pseudoacacia L.- False acacia or black locust) or
toxic (e.g. Nerium oleander L. – Oleander; Taxus baccata L.- English yew, or European
yew; Laburnum anagyroides Meddik - Common Laburnum, Golden Chain or Golden
Rain).
In Italy some of these measures were also introduced in regional regulations, such as in the
Tuscany Region .
42 "Pollini". Edited by Arpa Umbria , University of Perugia - Faculty of Agriculture, Asl 1 Umbria .
43 Some entomophilous species, which produce lower amounts of pollen and rely on insects for pollination dispersion, may still be allergenic.
44 The anemophilous plants produce large amounts of pollen grains, invisible to the eye, and carried by the wind at long distances.
45 Tuscany Region - Regulations for the Construction Bio - Eco Sustainable ( RES ) 2nd edition , 2012.