Bracken (Pteridium aquilinum, L.) is a fern which mostly reproduces vegetatively although it also produces large numbers of spores that are dispersed by wind. Spore production was monitored using a Burkard spore trap, operated continuously, from August to October 1990 and 1991, with the intake about 20 cm from a clump of bracken fronds. Changes in spore concentration with height were also measured using five rotorod samplers placed downwind of a stand of bracken at the edge of a Field of wheat stubble. Between 20th August and 20th October 1990 and between 30th September and 14th October in 1991, daily average spore concentrations often exceeded 750 spores m-3. Daily mean concentrations exceeding 1,750 spores m-3air were observed on 13th September 1990 and 1st October 1991. Spores were mostly dispersed singly and nearly half were released between 08.00 and 11.00 hrs GMT.
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