Alnus × spaethii pollen can cause allergies already at Christmas
Alnus × spaethii is a hybrid alder with the parent species A. japonica and A. subcordata. It is known for both its tolerance for urban climate conditions and enhanced air pollution concentrations and hence often figures on recommended tree guidance lists in towns. At the MeteoSwiss pollen station of Buchs (Switzerland), unusual early peaks of alder pollen already in December or January have been observed in the last 8 years. These peaks occurred several days to weeks earlier than at any other Swiss pollen station. As pollen source, an alley of Alnus × spaethii trees, planted in 1995–2000, 800 m south of the pollen trap could be identified. Phenological observations during this period in Buchs confirmed these pollen observations and showed that the trees were fully flowering on December 30, 2009, December 28, 2010 and 2011 and December 24, 2012. Due to the presence of Alnus × spaethii a very early, longer and more intense alder pollen season was observed in Buchs. As recently shown, these alder pollen can be also of clinical relevance. Thus, newly introduced plant species seem to be able to become a relevant allergen within a short time.