Spatio-temporal investigation of flowering dates and pollen counts in the topographically complex Zugspitze area on the German-Austrian border

Flowering behavior of the major allergenic species Betula pendula Roth (silver birch), Dactylis glomerata L. (cocksfoot) and Alopecurus pratensis L. (meadow foxtail), was examined by phenological observations in 2009 along an altitudinal gradient (from 700 m up to 1,700 m a.s.l.) in the topographically complex Zugspitze area on the German-Austrian border. The results were compared with pollen counts derived from pollen traps located at different altitudes (720 m, 1,503 m, 2,650 m a.s.l.). Phenological onset dates showed a great dependence on altitude and on exposition. Altitudinal gradients of the two grass species showed a delay of between 6 and 7 days (100 m) ^-1 and can be interpreted as a temperature response rate varying between -9 and -10 days (1 °C) ^-1. For birch phenophases, the altitudinal gradients were ca. 3 days (100 m) ^-1, corresponding to temperature response rates of circa -7 days (1 °C) ^-1. Northern and western exposed birch trees at the same altitude showed large differences in flowering dates (5-7 days). A comparison of phenological and aerobiological data in the phenological survey area revealed good agreement in the start of season dates, especially at lower altitude. Therefore, it was local pollen emissions, not long- or medium-range pollen transport that accounted for the timing of the aerobiological start of the season. Pollen counts at the highest and vegetation-free site were particularly affected by medium-range transport. More pronounced responses to altitude and therefore to temperature for the analyzed grass species indicate a greater temperature sensitivity. This suggests that further temperature increase could result in a remarkably earlier grass pollen season and, in turn, lead to major consequences for human health. Particular wind patterns can contribute to high and medically relevant pollen concentrations even at high elevation sites, implying less favourable conditions for those people allergic to pollen.