Pollen season and climate: Is the timing of birch pollen release in the UK approaching its limit?
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In light of heightened interest in the response of pollen phenology to temperature, we investigated recent changes to the onset of Betula (birch) pollen seasons in central and southern England, including a test of predicted advancement of the Betula pollen season for London. We calculated onset of birch pollen seasons using daily airborne pollen data obtained at London, Plymouth and Worcester, determined trends in the start of the pollen season and compared timing of the birch pollen season with observed temperature patterns for the period 1995–2010. We found no overall change in the onset of birch pollen in the study period although there was evidence that the response to temperature was nonlinear and that a lower asymptotic start of the pollen season may exist. The start of the birch pollen season was strongly correlated with March mean temperature. These results reinforce previous findings showing that the timing of the birch pollen season in the UK is particularly sensitive to spring temperatures. The climate relationship shown here persists over both longer decadal-scale trends and shorter, seasonal trends as well as during periods of ‘sign-switching’ when cooler spring temperatures result in later start dates. These attributes, combined with the wide geographical coverage of airborne pollen monitoring sites, some with records extending back several decades, provide a powerful tool for the detection of climate change impacts, although local site factors and the requirement for winter chilling may be confounding factors.
KeywordsBetula pollen London Plymouth Worcester Phenology Climate change Vernalisation
This work was partly funded by the Copenhagen Global Change Initiative (www.cogci.dk) and the Villum-Kann Rasmussen Foundation through a Post Doc grant to Carsten Ambelas Skjøth and a Royal Society of New Zealand (ISAT) grant to Rewi Newnham. Tim Sparks acknowledges the support of the Technische Universität München – Institute for Advanced Study, funded by the German Excellence Initiative. The authors would like to thank the National Pollen and Aerobiology Research Unit at the University of Worcester who provided the pollen counts, particularly all those staff who are actively involved in producing pollen count data. The authors are also grateful to the Environmental and Public Protection offices, Islington, who operate the pollen trap in North London, to Martin Kent for insightful comments on the manuscript and to Tim Absolom for drafting Fig. 5. Data on birch leafing were kindly supplied by the Woodland Trust.
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