Recent trends in airborne pollen for tree species in Galicia, NW Spain

The global climate change recorded over recent years may prompt changes in phenological events. The present study sought to analyse the varying impact of changes in weather conditions at different times of the year on woody-plant flowering, by analysing recent trends in airborne count for 3 pollen types abundant in Galicia belonging to the Fagales order: Alnus, which flowers in early winter; Betula, in early spring; and Castanea, in early summer. Pollen sampling was performed using Hirst-type volumetric traps in Ourense, Santiago, Vigo and Lugo; data were subjected to regression models, applied using the SPSS 17.0 statistical software package. The atmospheric pollen season started later in Lugo; the lower winter minimum temperatures in Lugo compared to the other 3 cities over the study period would explain the higher chilling accumulation recorded. The trend towards increasing temperatures was more marked in the south of Galicia (Vigo and Ourense) than in more northern cities. Mainly, maximum temperatures in September or October displayed an increasing trend at Ourense, Vigo and Lugo, while summer temperatures showed significant increases in Ourense. The temperature increase detected, especially during spring and summer, could account for the slight trend towards an earlier pollen season onset in all 4 cities, and for the advance of the Castanea pollen-season end date observed in Ourense.