13.06.2014 change 13.06.2014

We know what to plant in the cities to help people with allergies

Due to the strong heating of the city centres, plants growing in the city sensitise more strongly and over longer periods. People with allergies will cope better with pollination season in cities if we plant acacia trees, maples and conifers instead of birch and hazel, advises scientist from Łódź.

In the cities it is best to plant acacia trees, hornbeams, maple, lilac, spruces, pines and jasmines, whose pollen sensitises much less - recommend experts from the Nofer Institute of Occupational Medicine in Łódź. They developed recommendations for planting plants that are safe for allergy sufferers in cities in the international project UHI (Urban Heat Islands).

According to Dr. Wojciech Dudek of the Institute of Occupational Medicine, female poplar, willow, ash are also safe because they do not produce pollen at all. All of these plants can be safely used in newly built housing estates and restored squares and urban parks - explained Dudek during the seminar "Why is it warmer in than out of the city?", organized by the Institute of Geography and Spatial Organization PAS in Warsaw.

Recommended trees also include chestnuts, rowan, firs, larches. When it comes to shrubs, people with allergies well not complain about the presence cotoneaster, boxwood, dogwood, forsythia, quince, barberry and hawthorn. Among climbing plants, useful in the design of green facades, recommended plants include common ivy, Virginia creeper and silvervine fleeceflower.

Plants that should be absolutely avoided include birch, alder and hazel, which are the biggest problem for people allergic to pollen. Only a slightly better in this respect are poplar, elm, willow, beech, oak, sycamore, ash, linden and ragweed - said Dr. Dudek.

The researchers grouped the plants according to their allergenic potential after examining 1,189 plants from almost a hundred species growing in three neighborhoods, which are pilot areas of the UHI project in Warsaw. "Plants that cause allergy constituted more than 10 percent. This does not seem much, but they can produce a lot of pollen" - said Dr. Dudek.

He explained that a single inflorescence of birch, containing up to 350 flowers, can produce approximately 14 million pollen, enough to "contaminate" of about 300 thousand cubic meters of air. Birch can have few hundred to a few thousand inflorescences. For people with seasonal allergies to pollen this is a big problem - explained Dudek. More over, when it comes to allergenic potential, plants in the cities have slightly different properties than outside the cities.

The difference is the result of warmer climatic conditions in the cities due to the so-called urban heat island (UHI) effect. According to Prof. Krzysztof Błażejczyk from the Institute of Geography and Spatial Organization PAS, asphalt, reinforced concrete and concrete facades of buildings that dominate in the cities get very hot on summer days, and at night transfer all the heat to their surroundings. Consequently, in urban centres the air temperature is higher (mostly at night and early in the morning) than in the undeveloped, on average by 1-2 degrees Celsius.

This does not seem like much, but it can affect the physiology of plants - emphasised Dr. Dudek. He added that several factors cause the fact that plants in the city are more dangerous for people with allergies. "In the warmer urban conditions, plants produce more pollen, and the period of pollination is prolonged: the plants begin to shed pollen earlier and pollinate for a long time" - he explained.

Pollen from the city plants also contains more allergens - proteins that sensitise people. Without these proteins, pollen does not "recognize" the flower on which it can sprout.

Allergies are also promoted by pollutants present in cities that irritate the mucous membranes of the respiratory tract, allowing allergens to more easily pass into the respiratory tract. Very fine particles of dust help allergens penetrate the remotest parts of the respiratory tract, extending their time of contact with the organism, and the mucosal surface they affect - explained the expert from Łódź.

He emphasised that in order to cool the city, people bring more and newer types of plants (for example to create "green roofs", green facades and expand the surface of green areas). "Selection of plants should not be, however, random or dictated purely by aesthetics" - he warned.

"Wrong selection of vegetation will beautifully alleviate the urban heat island effect. It may, however, cause a drastic decline in the quality of life of people with pollen allergies. They may experience worse symptoms of allergic rhinitis and conjunctivitis or asthma. We should be careful with the plants we introduce in the city - he noted - Instead of moving out of the city, you can remodel the city greenery and to remove the most sensitising plants from urban areas". (PAP)

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