Airborne pollen calendar for Trieste (Italy), 1990-2004

Daily airborne pollen grains were collected in Trieste (1990–2004) using a Hirst-type trap. A large quantity of pollen grains was found, the mean annual total being 48 082 grains. Daily counts were particularly high between March and June, the highest values being recorded between April and May. A total of 123 different pollen taxa from 80 families were identified. Almost half of the total pollen content came from introduced trees and shrubs, one fifth from natural woodlands, and one quarter from herbaceous taxa. This composition reflects the ornamental and ruderal flora of the town, as well as the natural vegetation surrounding the urban area. The pollen richness of both mesophilous and thermophilous taxa reflects the complexity of this zone, considered a ‘‘crossroad’’ of species of different chorological types. Total daily pollen concentrations were positively correlated with temperatures only in the pre-peak period. The main taxa, except for Urticaceae, Pinus and Gramineae, displayed positive correlations with temperatures both in the main pollen season and in the pre-peak period. The annual pollen sum of Ostrya was negatively correlated with total rainfall of the previous summer, and that of Pinus was negatively correlated with the winter severity.