The effect of urban green areas on pollen concentrations at ground level: a study in the city of Florence (Italy)

Urban green areas can improve people's quality of life, although airborne pollen may provoke allergic disease. The record of the pollen rain in different sites within a city can be useful to understand the distance reached by the pollen of different plants and its amount. Moss cushions are natural gravimetric pollen traps and represent a useful and economic tool for this kind of survey. Moss samples were collected from 16 sites in Florence at the distance of a decade. To test the effects of urban green areas on pollen records, the land cover was analyzed in buffers drawn around each sampling site. Pollen frequencies were correlated with the extension of the green spaces and with the number of trees inside the buffers. Pollen concentration maps were drawn to plot the pollen deposition at the different sites of the city center. The pollen records at ground level displayed an uneven concentration across the city and a strong prevalence of arboreal pollen. The greatest statistical correlation between pollen frequencies and arboreal land cover was shown for the larger buffers. The influence of Cupressaceae and Quercus was noteworthy at great distances. Some of the common ornamental trees growing along the main roads, such as Celtis and Tilia, showed a strictly local influence on pollen rain. The results of the study highlight the utility of a network of records inside cities for evaluating the actual contributions of the plants to pollen accumulation at the height where people walk. They may provide a useful indication for the planning of urban green areas in order to reduce health risks for citizens.