Use of phenological and pollen-production data for interpreting atmospheric birch pollen curves

Although aerobiological data are frequently used as a fl owering sign in phenological research, airborne pollen counts are infl uenced by a number of factors affecting pollen curves. A study was made about the reproductive biology of birch and environmental factors infl uencing its pollen release and transport, in order to achieve a reliable interpretation of Betula pollen curves. Aerobiological data were recorded in 2002 and 2003 at two sites in NW Spain and phenological observations were carried out on 20 trees from four Betula populations (three Betula alba L. and one B. pendula Roth.). Pollen production was calculated for six Betula alba trees. Chilling and heat requirements for triggering development were calculated. Due to differences in the geographical location, budbreak and fl owering started fi rst in Betula pendula. The fl owering period lasted from 8-13 days. Reduced pollen output per anther and catkin in individual trees in 2003 prompted a marked decline in overall pollen production. Major differences observed in birch pollen curves were attributed to the infl uence both of weather conditions and pollen transport from areas where the fl owering occurs at a different time. Heat requirements calculated using phenological and aerobiological data were similar when the peak pollen- count date was used.