Frost periods and beginning of the ash (Fraxinus excelsior L.) pollen season in Basel (Switzerland)

In order to be able to forecast the beginning of the ash pollen season, several meteorological factors have been considered. During these research activities it appeared that the ash pollen release is closely linked to frost periods happening during the months of February and March. For 24 years over a period of 29 consecutive years, a daily concentration of 30 ash pollen grains/m³/day has been reached when the cumulated mean daily temperatures starting on the last day when the absolute minimum temperature is lower or equal to −2 °C amounts on average to 214 °C – admitting a variation of plus or minus 42 °C. As for the five remaining years, rain is three times responsible for the delay of the pollen release. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cumulative temperatures for prediction of the beginning of ash (Fraxinus excelsior L.) pollen season

The aim of this study is the analysis of the meteorological conditions leading to the release of ash pollen in order to predict the beginning of the pollen season in Zurich, Switzerland. For 12 years over a period of 14 consecutive years, it appears that ash pollen release begins when the cumulated mean daily temperatures starting on January 1 reach 220.7°C, admitting a variation of ±30°C that more or less corresponds to 3 consecutive days at 10°C.     

The influence of the hot and dry summer 2003 on the pollen season in Switzerland

A record-breaking heat wave affected the European continent in summer 2003. In Switzerland, the temperature in June, July and August exceeded the 1961–1990 mean by about 5 °C. These extreme temperatures had significant effects on the pollen production and on the airborne pollen loads. Especially affected was the grass pollen season, which started 1–2 weeks earlier than in the mean. During May and the first part of June the grass pollen production and dispersion was favoured by the warm and dry weather and many days with high pollen concentrations were registered. First water deficiencies occurred in June so that the grasses ceased to grow. The grass pollen season ended 7–33 days earlier than normal. For many of our stations of the Swiss pollen network this had never occurred as early as in 2003. The other herbaceous plants were not affected as much as the grasses. We measured very high Chenopodium and Plantago pollen concentrations, about normal concentrations of Urtica and Rumex and slightly lower Artemisia pollen concentrations than normal. The summer 2003 was exceptional and its reoccurrence is at the moment statistically extremely unlikely. But models of climatologists show that in the future, climate variations will increase and that in the period 2071–2100 about every second summer could be as warm or warmer and as dry or dryer than 2003.     

Prediction of the beginning of the olive full pollen season in south-west Spain

Given the clinical and agricultural importance of the olive in SW Spain, we have carried out a study to predict the starting date of its full pollen season. The study covers 6 years of meteorological and palynological observations — the latter using a Cour sampler installed in Huelva (SW Spain). The results obtained show that olive full pollination begins when the plant has accumulated 731C of daily temperature above 5C from the end of its dormant period. The mean duration of this accumulation was 83 days. A positive relationship has been found between mean temperature of the months before the pollen season (February and March) and the date when the season starts (April). From the data available, rainfall registered between 1 September and 31 March (both before pollination), does not affect the starting date of the full pollen season, but can affect total pollen production, particularly in years with prolonged drought.     

Prediction of the beginning of the olive full pollen season in south-west Spain

Given the clinical and agricultural importance of the olive in SW Spain, we have carried out a study to predict the starting date of its full pollen season. The study covers 6 years of meteorological and palynological observations — the latter using a Cour sampler installed in Huelva (SW Spain). The results obtained show that olive full pollination begins when the plant has accumulated 731°C of daily temperature above 5°C from the end of its dormant period. The mean duration of this accumulation was 83 days. A positive relationship has been found between mean temperature of the months before the pollen season (February and March) and the date when the season starts (April). From the data available, rainfall registered between 1 September and 31 March (both before pollination), does not affect the starting date of the full pollen season, but can affect total pollen production, particularly in years with prolonged drought.     

A study of Gramineae and Urticaceae pollen in the Derby area

Summary Gramineae and Urticaceae seasonal variations and diurnal rhythms for Derby in 1986, 1987 and 1988 are shown and discussed.The time of highest hourly concentration of Gramineae for Derby in June was 1900 hours. Maximum hourly counts for June of Urticaceae pollen occurred between 1400 and 1600 hours.Urticaceae has a second period of high concentration in August. Gramineae and Urticaceae pollens from 1969–1990 show no significant long term trends.     

Long distance pollen transport cause problems for determining the timing of birch pollen season in Fennoscandia by using phenological observations

The male flowering and leaf bud burst of birch take place almost simultaneously, suggesting that the observations of leaf bud burst could be used to determine the timing of birch pollen release. However, long‐distance transport of birch pollen before the onset of local flowering may complicate the utilization of phenological observations in pollen forecasting.

We compared the timing of leaf bud burst of silver birch with the timing of the stages of birch pollen season during an eight year period (1997–2004) at five sites in Finland. The stages of the birch pollen season were defined using four different thresholds: 1) the first date of the earliest three‐day period with airborne birch pollen counts exceeding 10 grains m^?3 air; and the dates when the accumulated pollen sum reaches 2) 5%; 3) 50% and 4) 95% of the annual total. Atmospheric modelling was used to determine the source areas for the observed long‐distance transported pollen, and the exploitability of phenological observations in pollen forecasting was evaluated.

Pair‐wise comparisons of means indicate that the timing of leaf bud burst fell closest to the date when the accumulated pollen sum reached 5% of the annual total, and did not differ significantly from it at any site (p<0.05; Student‐Newman‐Keuls test). It was found that the timing of leaf bud burst of silver birch overlaps with the first half of the main birch pollen season. However, phenological observations alone do not suffice to determine the timing of the main birch pollen season because of long‐distance transport of birch pollen.     

Production of total and stainable pollen grains in Olea europaea L

The production of the total and stainable number of pollen grains per flower and per inflorescence of 13 olive cultivars (Olea europaea L.) has been investigated. Grains stainability was evaluated by using the acetic carmine staining method whereas the production of pollen grains was calculated by using a Bürker haemocytometer. All pollen characteristics taken into account varied significantly among the cultivars. The number of flowers per inflorescence ranged from a maximum of 31.3 (‘Cipressino’) to a minimum of 13.0 (‘Leccino’), the number of pollen grains per anther ranged from 123?346 (‘Arbequina’) to 40?975 (‘Sant'Agostino’), and the pollen stainability from 97.6% (‘Cipressino’) to 48.0% (‘Cellina di Nardò’). The number of stainable pollen grains per inflorescence averaged 2?559?512, ranging from a maximum of 3?913?678 (‘Nociara’) to a minimum of 940?143 (‘Sant'Agostino’). All parameters were positively correlated, whereas a linear negative correlation was found between stainability and total pollen grains both per anther and per inflorescence.     

Poaceae pollen in Galicia (N.W. Spain): characterisation and recent trends in atmospheric pollen season

Airborne Poaceae pollen counts are greatly influenced by weather-related parameters, but may also be governed by other factors. Poaceae pollen is responsible for most allergic reactions in the pollen-sensitive population of Galicia (Spain), and it is therefore essential to determine the risk posed by airborne pollen counts. The global climate change recorded over recent years may prompt changes in the atmospheric pollen season (APS). This survey used airborne Poaceae pollen data recorded for four Galician cities since 1993, in order to characterise the APS and note any trends in its onset, length and severity. Pollen sampling was performed using Hirst-type volumetric traps; data were subjected to Spearman’s correlation test and regression models, in order to detect possible correlations between different parameters and trends. The APS was calculated using ten different methods, in order to assess the influence of each on survey results. Finally, trends detected for the major weather-related parameters influencing pollen counts over the study period were compared with those recorded over the last 30 years. All four cities displayed a trend towards lower annual total Poaceae pollen counts, lower peak values and a smaller number of days on which counts exceeded 30, 50 and 100 pollen grains/m³. Moreover, the survey noted a trend towards delayed onset and shorter duration of the APS, although differences were observed depending on the criteria used to define the first and the last day of the APS.     

A predictive study of cupressaceae pollen season onset, severity, maximum value and maximum value date

In this paper Cupressaceae pollen season onset, severity, maximum value and maximum value date, have been studied for 15 consecutive years (1982–1996). The data set was obtained using a Hirst spore-trap (Burkard Manufacturing). In order to determine the influence of the previous months’ meteorological variables on Cupressaceae season’s parameters, the sums of maximum, average and minimum temperatures, and total rainfall for the months of October, November and December were used as independent variables in predictive formulae built by multiple regression analyses. The variance explained percentage by regression analyses varied between 60 and 87%. Total rainfall in the months prior to anthesis and temperature (particularly minimum temperature) are important factors to consider in forecasting models of Cupressaceae pollen season parameters, but meteorological conditions at the time of pollen production are also important and can modify the pre-established potential of pollination.     

The effect of the meteorological factors on the Alnus pollen season in Lublin (Poland)

Alder pollen seasons and the effect of meteorological conditions on daily average pollen counts in the air of Lublin (Poland) were analysed. Alnus pollen grains reach very high concentrations in the atmosphere of this city during the early spring period and the parameters of pollen seasons were very different in the particular years studied. The pollen season lasted on average one month. The highest variation was observed for the peak value and the Seasonal Pollen Index (SPI). The pollen seasons, which started later, had shorter duration. Peak daily average pollen counts and SPI value were higher during the shorter seasons. Similarities in the stages of pollen seasons designated by the percentage method depended on the start date of the pollen season. Season parameters were mainly correlated with thermal conditions at the beginning of the year. Regression analysis was used to predict certain characteristics of the alder pollen season. The highest level of explanation of the variation in Alnus pollen season start and peak dates was obtained in the model using mean temperature in February. The obtained regression models may predict 82% of the variation in the pollen season start date, 73% of the variation in the duration, and 62% in the peak date.     

Climate change and extension of the Ginkgo biloba L. growing season in Japan

To understand the effects of climate change on the growing season of plants in Japan, we conducted trend analysis of phenological phases and examined the relationship between phenology and air temperatures. We used phenological data for Ginkgo biloba L., collected from 1953 to 2000. We defined the beginning and the end of the growing season (BGS and EGS) as the dates of budding and leaf fall, respectively. Changes in the air temperature in the 45 days before the date of BGS affected annual variation in BGS. The annual variation in air temperature over the 85 days before EGS affected the date of EGS. The average annual air temperature in Japan has increased by 1.3°C over the last four decades (1961–2000), and this increase has caused changes in ginkgo phenology. In the last five decades (1953–2000), BGS has occurred approximately 4 days earlier than previously, and EGS has occurred about 8 days later. Consequently, since 1953 the length of the growing season (LGS) has been extended by 12 days. Since around 1970, LGS and air temperatures have shown increasing trends. Although many researchers have stated that phenological events are not affected by the air temperature in the fall, we found high correlations not only between budding dates and air temperatures in spring but also between leaf‐fall dates and air temperatures in autumn. If the mean annual air temperature increases by 1°C, LGS could be extended by 10 days. We also examined the spatial distribution of the rate of LGS extension, but we did not find an obvious relationship between LGS extension and latitude.     

Forecasting the onset of the grass pollen season in Melbourne (Australia)

In Melbourne, a southern hemisphere city with a cool temperate climate, the grass pollen season has been monitored using a Burkard spore trap for 12 years (11 pollen seasons, which extend from October through January). The onset of the grass pollen season (OGPS) has been defined in various ways using both arbitrary cumulative scores (Sum 75, Sum 100) and percentages (10% Pollen Fly). OGPS, based on the forecast model of pollen season devised by Lejoly-Gabriel (Acta Geogr. Lovan., 13 (1978) 1–260) has been most widely used in efforts to forecast the beginning of the pollen season. OGPS occurred in Melbourne between 20 October to 24 November (average 6 November), a difference of 35 days. Duration of the pollen season ranged from 46 to 81 days, with a mean of 55 days, one of the longest reported. The relationships between onset and various weather parameters for July have enabled us to modify a model, using linear regression analysis, to predict onset. The prediction model is based on a negative correlation between date of onset and the sum of rainfall for July (a winter month). The error of prediction (Ep) is 24% and predicted day of OGPS was precisely predicted on 2 occasions, and on others with a range of accuracy of 3 to 14 days.     

A study of Quercus pollen in the Derby area, UK

The major allergenic pollen prevalent in the Derby air in May is Quercus pollen which has been monitored volumetrically from 1970–1997. Quercus pollen levels in Derby are increasing, showing an established long term trend, with 1995 being an exceptionally high year. There is now an earlier start date and a longer seasonal duration. The mean Quercus diurnal periodicity for 1991–1997 shows a peak at 15.00 hours.A detailed study of the 1990–1997 seasons established that a maximum temperature of 20 °C or above, at the usual time of flowering, occasions the start of the Quercus pollen season. Average May temperature and drought in the previous June and July are important factors in determining Quercus pollen totals. Predictions for the forthcoming seasons were produced which compared favourably with the actual pollen totals.     

The effects of climate change on the birch pollen season in Denmark

During the last two decades the climate inDenmark has become warmer and in climatescenarios (IPCC, 2001) it is foreseen that thetemperature will increase in the comingdecades. This predicted future increase intemperature will probably affect both theflowering of plants and the dispersion ofpollen in the air. In this study the alreadyobserved effects on the birch pollen season arestudied.Trend analyses of the birch pollen seasonfor two stations in Denmark more than 200 kmapart give similar results. In Copenhagen thereis a marked shift to an earlier season – itstarts about 14 days earlier in year 2000 thanin 1977, the peak-date is 17 days earlier andthe season-end is 9 days earlier. For Viborgthe trend to an earlier season is in generalthe same, but slightly smaller.During the same period there has also beena distinct rise in the annual-total amount ofbirch pollen, peak-values and days withconcentrations above zero.Rising mean temperatures during winter andspring can explain the calculated trends towardearlier pollen season. Models for estimation ofthe starting date based on Growing Degree Hours(GDH's) give very fine results with acorrelation coefficient around 0.90 and rmserror around 4.2 days.For annual-total there is a significantpositive correlation with the mean temperaturein the growing season the previous year.     

Concentration of airborne pollen of Vitisvinifera L. and yield forecast: a case study at S.Michele all'Adige,Trento, Italy

The possibility of creating a forecast model for grapeproduction using airborne pollen concentrations ofVitis vinifera L. was investigated. The studyarea is located in the province of Trento (46°11,11°08), North Italy. Because of its prestigious wineproduction, the area is quite important on a nationalscale.Airborne pollen concentration data (P/m³) werecollected for a five year period (1993–1997) with aHirst type sampler (VPPS 2000 – Lanzoni) following thestandard methodology proposed by the ItalianAeroallergen Network. For the same five-year period,grape production data (kg/ha) from vineyards adjacentto the pollen sampler were used along with provincialdata. Regression lines were constructed using the Lnof the annual sum of daily pollen concentrations (Ip)as the independent variable and grape productionvalues as the dependent variable. Correlations betweenpollen data (pollen index, beginning and duration ofmain pollen season) and meteorological data(temperature and rainfall) are shown.     

The role of temperature in the onset of the Olea europaea L. pollen season in southwestern Spain

Temperature is one of the main factors affecting the flowering of Mediterranean trees. In the case of Olea europaea L., a low-temperature period prior to bud development is essential to interrupt dormancy. After that, and once a base temperature is reached, the plant accumulates heat until flowering starts. Different methods of obtaining the best-forecast model for the onset date of the O. europaea pollen season, using temperature as the predictive parameter, are proposed in this paper. An 18-year pollen and climatic data series (1982–1999) from Cordoba (Spain) was used to perform the study. First a multiple-regression analysis using 15-day average temperatures from the period prior to flowering time was tested. Second, three heat-summation methods were used, determining the the quantities heat units (HU): accumulated daily mean temperature after deducting a threshold, growing degree-days (GDD): proposed by Snyder [J Agric Meteorol 35:353–358 (1985)] as a measure of physiological time, and accumulated maximum temperature. In the first two, the optimum base temperature selected for heat accumulation was 12.5°C. The multiple-regression equation for 1999 gives a 7-day delay from the observed date. The most accurate results were obtained with the GDD method, with a difference of only 4.7 days between predicted and observed dates. The average heat accumulation expressed as GDD was 209.9°C days. The HU method also gives good results, with no significant statistical differences between predictions and observations. Received: 18 April 2000 / Revised: 14 September 2000 / Accepted: 19 September 2000     

Airborne Pinus pollen in the atmosphere of Brisbane, Australia and relationships with meteorological parameters

Relationships between weather parameters andairborne pollen loads of Pinus inBrisbane, Australia have been investigated overthe five-year period, June 1994–May 1999.Pinus pollen accounts for 4.5% of the annualairborne pollen load in Brisbane where thePinus season is confined to the winter months,July–early September. During the samplingperiod loads of 11–>100 grains m³ wererecorded on 24 days and 1–10 grains m³ on204 days. The onset and peak dates wereconsistent across each season, whereas the enddates varied. The onset of the Pinuspollen season coincided with the coolestaverage monthly temperatures (< 22°C),lowest rainfall (< 7mm), and four weeks afterdaily minimum temperatures fell to 5–9°Cin late autumn. Correlations obtained betweendaily airborne Pinus pollen counts andtemperature/rainfall parameters show thatdensities of airborne Pinus pollen arenegatively correlated with maximum temperature(p < 0.0001), minimum temperature (p < 0.0001)and rainfall (p < 0.05) during the mainpollination period. The mean duration of eachpollen season was 52 days; longer seasons wereshown to be directly related to lower averageseasonal maximum temperatures (r² = 0.85,p = 0.025). These results signify that maximumand minimum temperatures are the majorparameters that influence the onset andduration of the Pinus pollen season inthe environs of Brisbane. Respiratory allergyis an important health issue in Brisbane,Australia, but it remains unknown whether ornot airborne Pinus pollen is acontributing factor.     

Heat requirement for the onset of the Olea europaea L. pollen season in several sites in Andalusia and the effect of the expected future climate change

Olives are one of the largest crops in the Mediterranean region, especially in Andalusia, in southern Spain. A thermal model has been developed for forecasting the start of the olive tree pollen season at five localities in Andalusia: Cordoba, Priego, Jaen, Granada and Malaga using airborne pollen and meteorological data from 1982 to 2001. Threshold temperatures varied between 5°C and 12.5°C depending on bio-geographical characteristics. The external validity of the results was tested using the data for the year 2002 as an independent variable and it confirmed the models accuracy with only a few days difference from predicted values. All the localities had increasingly earlier start dates during the study period. This could confirm that olive flower phenology can be considered as a sensitive indicator of the effects of climate fluctuations in the Mediterranean area. The theoretical impact of the predicted climatic warming on the olives flowering phenology at the end of the century is also proposed by applying Regional Climate Model data. A general advance, from 1 to 3 weeks could be expected, although this advance will be more pronounced in mid-altitude inland areas.