Pollen season of European beech (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) and temperature trends at two German monitoring sites over a more than 30-year period

Although beech (Fagus) pollen are often disregarded, they play an allergological role. This study focused on pollen season (PS) of European beech (Fagus sylvatica L.) and mean yearly temperatures (T) at two climatically different sites (lowlands vs. Alps) in Germany. Pollen sampling was conducted with 7-day recording volumetric spore traps between 1982 and 2014. Both PS parameters (start, peak, length, annual pollen index PI]) and T were compared in two periods (1982–1991 and 1992–2014), and correlations between PS and T were analysed. At both sites, average PS occurred earlier in the second period. Statistically significant differences were proved at the alpine site in terms of start and peak of the season, and PI. On average, PS in the lowlands was shorter and occurred earlier than in the Alps. As is the case with a lot of temperate tree species, beeches show the masting phenomenon and PI differed greatly among the years. Mast years were much less frequent than non-mast years, and the differences between the pollen sums were significant. Average pollen counts at the alpine site were about three times higher than in the lowlands. At both sites, higher T was significantly correlated with an earlier start and peak of the season, and an increased PI. Trends of T over the years were significantly positive. Temperature increase as a part of climate change may contribute to an earlier occurrence of the flowering season of European beech and to higher airborne pollen concentrations.