In the last six years the North-East Italian plains were intensively studied for air pollution monitoring with lichen biodiversity measures. To date, more than 3,500 relevés of epiphytic lichen vegetation, based on a standard methodology, were carried out in this area. The present study fills a gap in the exploration of the area, presenting the results relative 10 the province of Gorizia. The study is based on 335 relevés in 104 stations. The relevés are frequency counts of all lichen species in a sampling grid subdivided into ten rectangles. The sum of the frequencies of all species is the Biodiversity index of each relevé. The average values of Biodiversity Indices of all relevés taken in the same station is the Index of Atmospheric Purity (IAP) of the station, following a slightly modified approach proposed by Swiss authors. The matrices of the 60 lichen species found in the survey area, and of the relevés/stations were submitted to multivariate analysis (classification and ordination): the results show a predominance of nitrophytic Xanthorion-species and a transition from Parmelion (prevalent in less anthropized areas) to Xanthorion vegetation (favoured by agriculture and more resistant to air pollution). Distribution maps showing presence and abundance of eight selected species (Candelaria concolor, Hyperphyscia adglutinata, Parmelia caperata, P. sulcata, P. subrudecta, Plzyscia adscendens, Phaeophyscia orbicularis, Xanthoria parietina) are presented and discussed. Automatic mapping programs were also used to map the distribution of the weighed averages of ecological indices associated to each species in each station of the survey area: a map of eutrophication and one of air humidity are presented and discussed. The IAP map of the province is discussed in terms of air quality levels: no extensive lichen desert does occur and IAP values are generally high, but a few restricted areas show some symptoms of air quality worsening, and would be worthy being monitored by instrumental recording.
