A calendar for tree pollen in London

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Abstract
Data from a pollen monitoring network in Islington, North London, are used to construct tree pollen calendars for the tree seasons 1987 to 1989 inclusive. Annual variations in the pollen abundance and length of flowering season are investigated for individual species in relation to meteorological factors and the inherent biological rhythms of trees. Results indicate clear relationships between seasonal variations in pollen abundance and the weather, both in the prevailing season and also in the preceeding year during the time of pollen formation. Annual variations evident in the pollen records for Betula and Quercus support the theory of inherent biennial cycles for these species. Patterns for other trees do not show clear trends within the period sampled. Insufficient information is available to determine the concentration thresholds of allergic response for most tree pollens, but evidence from Finland is used to identify the timing and duration of periods which exceed the response thresholds for Betula.