Changes in the pollen seasons of the early flowering trees Alnus spp. and Corylus spp. in Worcester, United Kingdom, 1996–2005

Abstract

Previous work on Betula spp. (birch) in the UK and at five sites in Europe has shown that pollen seasons for this taxon have tended to become earlier by about 5-10 days per decade in most regions investigated over the last 30 years. This pattern has been linked to the trend to warmer winters and springs in recent years. However, little work has been done to investigate the changes in the pollen seasons for the early flowering trees. Several of these, such as Alnus spp. and Corylus spp., have allergens, which cross-react with those of Betula spp., and so have a priming effect on allergic people. This paper investigates pollen seasons for Alnus spp. and Corylus spp. for the years 1996-2005 at Worcester, in the West Midlands, United Kingdom. Pollen data for daily average counts were collected using a Burkard volumetric trap sited on the exposed roof of a three-story building. The climate is western maritime. Meteorological data for daily temperatures (maximum and minimum) and rainfall were obtained from the local monitoring sites. The local area up to approximately 10 km surrounding the site is mostly level terrain with some undulating hills and valleys. The local vegetation is mixed farmland and deciduous woodland. The pollen seasons for the two taxa investigated are typically late December or early January to late March. Various ways of defining the start and end of the pollen seasons were considered for these taxa, but the most useful was the 1% method whereby the season is deemed to have started when 1% of the total catch is achieved and to have ended when 99% is reached. The cumulative catches (in grains/m(3)) for Alnus spp. varied from 698 (2001) to 3,467 (2004). For Corylus spp., they varied from 65 (2001) to 4,933 (2004). The start dates for Alnus spp. showed 39 days difference in the 10 years (earliest 2000 day 21, latest 1996 day 60). The end dates differed by 26 days and the length of season differed by 15 days. The last 4 years in the set had notably higher cumulative counts than the first 2, but there was no trend towards earlier starts. For Corylus spp. start days also differed by 39 days (earliest 1999 day 5, latest 1996 day 44). The end date differed by 35 days and length of season by 26 days. Cumulative counts and lengths of season showed a distinct pattern of alternative high (long) and low (short) years. There is some evidence of a synchronous pattern for Alnus spp.. These patterns show some significant correlations with temperature and rainfall through the autumn, winter and early spring, and some relationships with growth degree 4s and chill units, but the series is too short to discern trends. The analysis has provided insight to the variation in the seasons for these early flowering trees and will form a basis for future work on building predictive models for these taxa.

The effect of climate conditions on inter-annual flowering variability monitored by pollen traps below the canopy in Draved Forest, Denmark

“…For Corylus, pollen deposition is correlated with precipitation in February and in July of the flowering year. Emberlin et al (2007) found that rainfall had no impact on the start date of the pollen season for Corylus in England, but in Draved February rain seems to favour pollen dispersal. The correlation to July precipitation, which occurs after the flowering season, is most probably spurious.…”

The Onset, Course and Intensity of the Pollen Season

“…Different aerobiological studies, based on long historical databases, have shown earlier pollen seasons during recent years as a result of temperature increase, most of them related to spring fl owering trees (Garcia-Mozo et al 2006 ;Galán et al 2005 ;Emberlin et al 2007 ;Damialis et al 2007 ;Frei and Gassner 2008 ;Bono fi glio et al 2009 ;Orlandi et al 2009 ). The greater advances observed in earlier rather than later spring pollen seasons are probably due to the higher dependency on temperature of early spring tree species, such as hazel, alder and birch.…”

“…a moderate increase of temperature resulted in a delay in winter/early spring tree pollen season start (Emberlin et al 2007 ;Tedeschini et al 2006 ) . It also depends on regional characteristics Recio et al 2009 ) , what may confound patterns.…”

“…the longer the chilling period, the fewer days of heat accumulation are needed to start the fl owering (e.g. Rodriguez-Rajo et al 2004 ;Emberlin et al 2007 ) . However, the range of chilling and forcing intervals is not satisfactorily known , nor is it clari fi ed when and how chilling and forcing temperatures act on bud growth when they alternate.…”

Plants remember past weather: a study for atmospheric pollen concentrations of Ambrosia, Poaceae and Populus

“…Emberlin et al (1997) found a trend to earlier Betula pollen seasons that was related to an increase in cumulative temperatures over 5.5°C in January, February and March. Furthermore, they detected a significant positive relationship between the start dates of the Corylus pollen season and temperatures in October suggesting that lower temperatures in October result in an earlier onset, and vice versa (Emberlin et al 2007). They found a significant negative association between onset and December temperatures indicating that higher December temperatures will produce an earlier onset of Corylus flowering and vice versa (Emberlin et al 2007).…”