By means of a Burkard Seven Day Recording Volumetric Spore Trap located in central Stockhom, about 20 m above ground level, pollen was sampled between March and August for eight consecutive years (1973#x2013;1980). The pollen spectra with special reference to trees, in particularBetulaandPinus, were compared as to amount and distribution of taxa. No co-variation between the two latter genera was noted.Betulashowed a #xB1; distinct biennial periodicity. The main pollen season is defined.BetulaandPinusshowed slightly different patterns regarding beginning and duration of the pollen season; mean intensity is compared.
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