Pollen season trends in winter flowering trees in South Spain

The present work has studied the trends in pollen seasons of winter flowering trees (Alnus, Cupressaceae, Fraxinus, Populus and Ulmus) in Córdoba, Granada and Málaga (Andalusia, Spain) over the years 1994–2017. The influence of meteorological parameters on the seasonal airborne pollen has been also analyzed. Pollen concentrations were recorded using Hirst-type volumetric spore traps, following the standardized methodology of the Spanish Aerobiology Network and the European Aerobiology Society. The nonparametric Mann–Kendall test and the nonparametric Sen’s method have been used to study linear trends for pollen season timing and intensity, and for temperature and rainfall. Significance was determined using the F-test. Spearman analyses were applied to test for correlations between pollen season parameters and weather-related factors before and over the pollen season. The results obtained suggest that flowering has delayed over recent years, especially for trees with a bloom closer to spring (poplar and elm). Earlier flowering species are more influenced by the meteorological parameters before the flowering. However, species blooming later are more influenced by the meteorological parameters during the pollen season. Meteorological parameters affect more the interior cities than the coastal city.