Effects of environmental factors on pollen production in anemophilous woody species

The aim of this study was to estimate the amount of pollen produced by anemophilous woody taxa with allergenic properties and with considerable contribution in the concentration of pollen in the air of a Mediterranean city (Thessaloniki, Greece). The taxa selected are Corylus avellana, Cupressus sempervirens var. horizontalis and var. pyramidalis, Olea europaea and Platanus orientalis; each was studied in more than one sampling stations differing in elevation, direction or both. O. europaea produced the highest number of pollen grains per flower (1.3 × 10⁵ ± 0.1 × 10⁵) and P. orientalis the highest per inflorescence (3.3 × 10⁶ ± 0.2 × 10⁶). At the level of crown, pollen grains produced were of the order of 10⁹ per surface/volume unit for O. europaea and the two C. sempervirens varieties; for the other two taxa, they were of the order of 10⁶. Pollen production was lower at higher elevation and northern direction and depended on the size of the floral unit sampled (flower for O. europaea, inflorescence for all other species): the bigger the floral unit, the more pollen it contained. Our results and reports from other areas, where C. sempervirens and O. europaea grow, show that these two Mediterranean species produce comparable amounts of pollen at the levels of inflorescence or flower, respectively, wherever they occur.