Airborne pine (Pinus spp.) pollen in the atmosphere of Perugia (Central Italy): Behaviour of pollination in the two last decades

The phenology of many species, which grow intemperate climate, is principally regulated bythe temperature and the plants respond withvariations in the beginning, in the durationand in the intensity of the various phenophasestowards every climate change. We have analysedthe data of Pinus pollination in Perugia,Central Italy, during last 2 decades(1982–2001), in a period during which theannual mean temperature significantly increasedby about 0.8 °C.The pine pollination started, on average,between the end of March and mid-April andended in the last days of June, with a meanduration of 65 days. The start dates showed asignificant negative correlation with theaverage air temperature in March andsignificant trends towards an earlier beginningof pollination by 18 days (–0.9 day/year) and ashorter duration of the pollen season by 10days (–0.6 day/year) were found over thestudied period. Moreover, the trend of thedaily pollen counts showed, on average, analmost normal distribution, but the analysis ofeach yearly trend revealed significantdifferences correlated with the meantemperature during the pollen season. Theseobserved trends in pine pollination suggest theuse of aerobiological monitoring of thisairborne pollen as indicator of temperaturechange in Central Italy over a relatively longperiod.     

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.     

A predictive study on the beginning of the pollen season for Gramineae andolea europaea L.

Summary On the basis of the results of seven years (1982–1988) of pollen and meteorological monitoring in the atmosphere of Perugia and Ascoli Piceno (central Italy) beginning of pollen season forecasts for Gramineae and Olea europaea L. are reported. The beginning of the pollen season for grass varied between May 2 nd and May 27th while for Olea it varied between May 26 th and June 23rd. By a statistical analysis of these data several significant correlations were found between the onset of the principal period of pollination and the air temperature in the preceding months and the number of ?heat units? required to flower. Utilizing multiple regressions a predictive method of the beginning of pollen season for both the taxa is reported.     

A method to forecast the start of theBetula, Platanus andQuercus pollen seasons in North London

This paper attempts the prediction of the start of theBetula, Quercus andPlatanus pollen seasons in London, UK based on pollen sampling conducted over a 5-year period, 1987–1991. The times at which eight different thresholds of accumulated daily pollen counts (M⁻³) were passed were correlated against heat sums, chill units, accumulated sunshine hours, monthly meteorological parameters and the start dates of earlier pollen seasons to identify significant associations. Few meteorological parameters were significantly correlated with the start dates of the three pollen seasons, the exceptions being significant negative correlations between the average monthly air temperature in the months immediately preceding theBetula andPlatanus pollen season. However, significant relationships were identified between the start dates of theBetula, Quercus andPlatanus pollen seasons and the start of theCorylus, Taxus andPopulus pollen seasons with coefficients of determination as high as 98%. These indicator species were then used as predictors to forecast the start of theBetula, Quercus andPlatanus pollen seasons, both individually and in combination with one another, providing levels of explanation of up to 99%.     

Temperature requirements of Alnus pollen in Spain and Italy (1994-1998)

Woody plants in temperate regions, in order to prevent the water in their cells from freezing, interrupt their growth entering into a physiological state called "dormancy". Trees also have a heat requirement that must be fullfilled before actual growth is resumed and pollination occurs. The objective of this study is to ascertain the influence that a climatic parameter such as temperature exerts on Alnus, in order to identify the start of the dormancy period, its duration and the consequent heat requirement that triggers flowering in three European regions located at the same latitude. In this regard, we chose two areas in Spain (Vigo and Santiago de Compostela) and one in Italy (Perugia), since they have different temperature patterns, ranging from mild in the case of Vigo to cold in that of Perugia, including an intermediate temperature pattern (Santiago). Monitoring in the three stations was carried out by means of a 7-day Lanzoni VPPS 2000 pollen trap. Alnus began its pollen season between the second and third week of January in Spain, while in Italy it began during the first week of February. During the four years under study, in order to overcome the dormancy period, Perugia needed an average of 962 chilling hours (CH), Santiago 622 CH, and Vigo had the smallest chilling accumulation with only 460 CH. In the case of heat accumulation, we found that Perugia had the smallest requirement and Vigo the largest, thus Perugia needed an average of 42 (growth degree days) GDD, Santiago around 50 GDD and Vigo 62 GDD.     

Influence of meteorological parameters on Olea flowering date and airborne pollen concentration in four regions of Portugal

For calculating the total annual Olea pollen concentration, the onset of the main pollen season and the peak pollen concentration dates, using data from 1998 to 2004, predictive models were developed using multiple regression analysis. Four Portuguese regions were studied: Reguengos de Monsaraz, Valença do Douro, Braga and Elvas. The effect of some meteorological parameters such as temperature and precipitation on Olea spatial and temporal airborne pollen distribution was studied. The best correlations were found when only the pre‐peak period was used, with thermal parameters (maximum temperature) showing the highest correlation with airborne pollen distribution. Independent variables, selected by regression analysis for the predictive models, with the greatest influence on the Olea main pollen season features were accumulated number of days with rain and rainfall in the previous autumn, and temperatures (average and minimum) from January through March. The models predict 59 to 99% of the total airborne pollen concentration recorded and the initial and peak concentration dates of the main Olea pollen season.     

Trends in pollen season characteristics of Alnus,Poaceae and Artemisia allergenic taxa in Bratislava,central Europe

Over the period 2002–2019, air temperature and precipitation significantly increased regionally for Bratislava, which could lead to phenological changes in some plant species. This study aimed to analyse the changes in the intensity, timing, and duration of pollen seasons of three allergological important plant taxa (Alnus, Poaceae, Artemisia) in the study area over 18 years. The pollen sampling was performed using a Hirst-type sampler. Mann–Kendall tau test was used to determine trends in pollen season characteristics, while Spearman’s correlation analysis was used to identify the relationships between the characteristics of pollen seasons and both air temperature and precipitation trends. The notable changes in the pollen-season-related features were observed for all analysed taxa. The Alnus pollen season now reaches the peak earlier and its intensity is rising in line with the summer-autumn temperature increasing trend, while unexpectedly intensity and duration of the Artemisia pollen season are declining in line with the increased precipitation and/or temperature trends. On the other hand, the intensity of the Poaceae pollen season is also declining, however, without statistically significant correlations with recorded increases in meteorological parameters considered. This phenomenon is probably related to both the reduction of the area of grasslands due to urbanization and the implementation of effective maintenance of urban green areas (e.g., timely mowing preventing the repeatedly flowering of grasses).

     

Global warming and the earlier start of the Japanese-cedar (Cryptomeria japonica) pollen season in Toyama, Japan

Atmospheric pollen surveys were conducted in Toyama City, Japan over a 21-year period (1983–2003). Airborne pollen was collected by two methods, the gravimetric method and the volumetric method. The gravimetric method indicated that the start of the Cryptomeria japonica pollen season, as indicated by pollen dispersion, has advanced from day 73 (from January 1) in 1983 to day 47 in 2003. Measurements taken using the volumetric method confirmed this trend. There was a significant correlation between the start dates obtained by both methods. Meteorological data indicated that the most noticeable elevation in temperature during the experimental period occurred in February – an increase of 2.1°C. Significant correlations existed between the mean temperatures and the start dates of the pollen season. These results support the steadily increasing number of reports indicating a global warming trend. The temperature change in February in affecting the start dates of the C. japonica pollen season is particularly relevant in the context of human health. Further studies will be needed to clarify the effects of the global warming trend on the pollen season and human health in more detail.     

The influence of air temperature on the starting date of Quercus pollination in the South of Europe

In temperate zones the air temperature influences many aspects of the plant growth and also the time of flowering is often correlated with this environmental parameter. It is a generally accepted idea that higher temperatures in the period preceding ripening of the flowers determine earlier pollination. To verify if a correlation between the air temperature and the date of onset of the pollination period of Quercus spp. exists, a comparative study was carried out over 7 years (1995–2001) in two South-European towns: Vigo (Spain) and Perugia (Italy). Quercus pollen is released in the atmosphere of Perugia on average in the last two weeks of April while in the Spanish region the pollination occurs on average one month before.

In order to overcome the dormancy period Perugia requires 1110 Chilling Hours (CH)-884 Growth Degree-Days (GDD°C) and Vigo 709 CH-861 GDD°C. With the Ashcroft method Perugia needs 1075 CH-1000 GDD°C and Vigo 625 CH-1512 GDD°C. Heat accumulation from the end of winter dormancy to the onset of pollination, showed the highest significance when mean temperature in Perugia and maximum temperature in Vigo were used. Every year we have found that the colder station needed a lower heat accumulation: Perugia required a higher quantity of chilling and heat than Vigo. However, the correlation detected between temperature and flowering was, on average, less significant that those found in the same regions for other arboreal taxa that present winter pollination (e.g. Corylus, Alnus). This preliminary study suggests that there is an effect of air temperature on Quercus pollination, but other environmental factors, such as photoperiod, hours of light, rainfall, relative humidity, may be of great influence in determining the onset of pollination in plants with a spring flowering.     

The effect of air temperature on the starting dates of theUlmus, Platanus andOlea pollen seasons in the SE Iberian Peninsula

A study is made of the effect of air temperature on the start of the pollen seasons of three tree species—Ulmus, Platanus andOlea—in the southeastern Iberian Peninsula. These initial results are based on an aerobiological analysis performed over a 4-year period in the city of Granada, Spain. Sampling was carried out with a Burkard spore trap. The main aim of the present study was to use regression analysis to identify the preseasonal date when these species start to accumulate heat in their floral buds, enabling models to be created that indicate the onset of the pollen season for these taxa. ForUlmus there was no significant correlation between the onset of pollination and the mean temperature during the preceding period, whereasPlatanus presented a significant correlation with mean temperature during the month of January, andOlea with mean temperature during the second fortnight in February and the month of March. ForUlmus, the start of the pollen season ranged between 30 January and 8 February; forPlatanus, between 13 and 17 March; and forOlea, between 20 April and 13 May. The accumulated temperature needed to induce the onset of flowering ranged between 121 and 256°C forUlmus, with values of 428–607°C and 656–881°C forPlatanus andOlea, respectively.     

Alnus andBetula pollen content in the atmosphere of santiago de Compostela, North-Western Spain (1993–1995)

The present study analyzes the behaviour ofAlnus andBetula pollen in the atmosphere of the town of Santiago de Compostela (N.W. Spain) from January 1993 to December 1995. The main pollination period of both taxa is identified for each sampling year, which, in the case ofAlnus, took place in January and February and, forBetula, during April.Alnus andBetula pollen are found in very high quantities in the atmosphere of Santiago de Compostela, representing 5% and 12% respectively of the total annual pollen that was counted. We studied the correlation between pollen content each year for both taxa and the main meterological parameters (average, maximum and minimum temperatures, precipitation and hours of sunshine). Finally, we analyzed the diurnal behaviour model for each taxon. ForAlnus, the maximum concentrations were found around 20:00 h, while, in the case ofBetula, the main pollen concentration took place between 15:00 h and 20:00 h in 1993 and 1994, and at 00:00 h in 1995.     

Changes in the pollen seasons of the early flowering trees <Emphasis Type="Italic">Alnus</Emphasis> spp. and <Emphasis Type="Italic">Corylus</Emphasis> spp. in Worcester,United Kingdom, 1996–2005

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-storey 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/m³) 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.     

Correlation between large-scale atmospheric fields and the olive pollen season in Central Italy

Olives are one of the largest crops in the Mediterranean and in central and southern Italy. This work investigates the correlation of the Olea europaea L. pollen season in Perugia, the capital city of the region of Umbria in central Italy, with atmospheric parameters. The aim of the study is twofold. First, we study the correlation between the pollen season and the surface air temperature of the spring and late spring in Perugia. Second, the correlation between the pollen season and large-scale atmospheric patterns is investigated. The average surface temperature in the spring and late spring has a clear impact on the pollen season in Perugia. Years with higher average temperatures have an earlier onset of the pollen season. In particular, a 1°C higher (lower) average surface temperature corresponds to an earlier (later) start of the pollen season of about 1 week. The correlation between the pollen season and large-scale atmospheric patterns of sea level pressure and 500-hPa geopotential height shows that the cyclonic activity in the Mediterranean is unequivocally tied to the pollen season in Perugia. A larger than average cyclonic activity in the Mediterranean Basin corresponds to a later than average pollen season. Larger than average cyclonic activity in Northern Europe and Siberia corresponds to an earlier than average pollen season. A possible explanation of this correlation, that needs further investigation to be proven, is given. These results can have a practical application by using the seasonal forecast of atmospheric general circulation models.     

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.     

Influence of wind direction on pollen concentration in the atmosphere

The daily pollen concentration in the atmosphere of Badajoz (SW Spain) was analysed over a 6-year period (1993–1998) using a volumetric aerobiological trap. The results for the main pollination period are compared with the number of hours of wind each day in the four quadrants: 1 (NE), 2 (SE), 3 (SW) and 4 (NW). The pollen source distribution allowed 16 pollen types to be analysed as a function of their distribution in the four quadrants with respect to the location of the trap. Four of them correspond to species growing in an irrigated farmland environment (Amaranthaceae-Chenopodiaceae, Plantago, Scirpus, and Typha), five to riparian and woodland species (Salix, Fraxinus, Alnus, Populus, and Eucalyptus), four to urban ornamentals (Ulmus, Arecaceae, Cupressaceae, and Casuarina), and three which include the most frequent pollen grains of widely distributed species (Poaceae, Quercus, and Olea). The results show that the distribution of the sources and the wind direction play a very major role in determining the pollen concentration in the atmosphere when these sources are located in certain quadrants, and that the widely distributed pollen sources show no relationship with wind direction. In some years the values of the correlations were not maintained, which leads one to presume that, in order to draw significant conclusions and establish clear patterns of the influence of wind direction, a continuous and more prolonged study will be required. Received: 6 May 1999 / Revised: 30 March 2000 / Accepted: 31 March 2000     

Atmospheric pollen season in Zagreb (Croatia) and its relationship with temperature and precipitation

The number of individuals allergic to plant pollen has recently been on a constant increase, especially in large cities and industrial areas. Therefore, monitoring of airborne pollen types and concentrations during the pollen season is of the utmost medical importance. The research reported in this paper aims to determine the beginning, course and end of the pollen season for the plants in the City of Zagreb, to identify allergenic plants, and to assess the variation in airborne pollen concentration as a function of temperature and precipitation changes for the year 2002. A volumetric Hirst sampler was used for airborne pollen sampling. Qualitative and quantitative pollen analysis was performed under a light microscope (magnification ×400). In the Zagreb area, 12 groups of highly allergenic plants (alder, hazel, cypress, birch, ash, hornbeam, grasses, elder, nettles, sweet chestnut, artemisia and ambrosia) were identified. Birch pollen predominated in spring, the highest concentrations being recorded in February and March. Grass pollen prevailed in May and June, and pollen of herbaceous plants of the genus Urtica (nettle) and of ambrosia in July, August and September. Air temperature was mostly higher or considerably higher than the annual average in those months, which resulted in a many days with high and very high airborne pollen concentrations. The exception was April, when these concentrations were lower because of high levels of precipitation. This also held for the first half of August and the second half of September. Pollen-sensitive individuals were at high risk from February till October because of the high airborne pollen concentrations, which only showed a transient decrease when the temperature fell or there was precipitation.     

Airborne olive pollen in Vigo (Northwest Spain): a survey to forecast the onset and daily concentrations of the pollen season

Temperature is one of the main factors affecting the start of flowering in tree species that flower at the beginning of spring. Knowledge of the chilling and heat needs required by plants to overcome the period of dormancy enables us to determine the onset of pollination, which is of great importance to allergy sufferers. This study attempted to obtain behaviour models with a view to determining both the onset of the olive pollen season and daily pollen concentrations during the pollination period in Vigo. Monitoring was carried out using a Lanzoni VPPS 2000 pollen trap, from 1995 to 2002 inclusive.

Olea pollen is mainly detected during the spring, principally in May. Given the geographical location, the very limited presence of this tree in the study area and the low Olea pollen concentrations detected in northern Spain as a whole, the values recorded here in the atmosphere of Vigo are particularly striking. A strong correlation was observed between total quantity olive pollen collected over the season and rainfall recorded during the second fortnight in February. According to the proposed model, an average of 680 Chilling Hours (CH) are necessary to overcome the chill period and break the state of bud dormancy, and 481 Growth Degree Days (GDD) °C are needed to induce flowering. Models for predicting daily mean pollen concentrations combine temperature and the previous days' pollen concentrations as predictor variables to provide a high level of prediction.     

Synchronized inter‐annual fluctuation of flowering intensity affects the exposure to allergenic tree pollen in North Europe

Many anemophilous, early‐flowering tree genera include allergy plants of world‐wide significance. We studied the synchronisation of high and low pollen years in the genera Betula, Alnus, Corylus, Salix and Populus and the cumulative effects that an increasing number of taxa has on the number of days of exposure to different levels of allergenic pollen in North Europe. The proximal causes of the inter‐annual variations of airborne pollen loads were analysed with a multiple regression analysis. The annual fluctuations of airborne pollen sums were compared between genera and found to be positively correlated among all combinations of genera at the three study sites. Most correlations were statistically significant (p<0.05). The comparison between Betula and Alnus is discussed first. Betula pollen was clearly the most abundant airborne pollen type. The presence of Alnus pollen, however, significantly increased the predisposal to allergenic pollen. At all sites, the number of days per year when the Betula and Alnus pollen counts together exceeded 10 and 100?grains m^?3 of air, was found to be greater than the number of days when the Betula pollen counts alone exceeded 10 and 100?m^?3 of air. The difference was statistically significant. In Kuopio, the difference was found to be statistically significant even for grains per 1?000?m^?3 of air of Betula and Alnus together compared with the same count of Betula pollen alone. Betula, Alnus and Corylus belong to the order Fagales and have cross‐reacting main allergens. The flowering of Alder and Corylus culminate at the same time, two to four weeks earlier than that of Betula. Due to synchronization of high and low years and the mostly non‐overlapping flowering seasons, the time of exposure to pollen may be very long during the high years. Furthermore, Alnus and Corylus pollen may prime allergic people before the onset of the Betula season.     

A comparative study of different temperature accumulation methods for predicting the start of the Quercus pollen season in Cordoba (South West Spain)

The aim of the present paper is to study the influence of air temperature on the start of Quercus pollination in Córdoba (Andalusia, Spain). Sixteen years of pollen counts were used. The start date of the pollen season in this period varied between 26^th February and 7^th April. Chilling requirements and heat accumulation were taken into account although no significant correlation between chilling hours and the start date was observed. Five different predictive methods based on heat accumulation were compared in this paper: 1) Number of days over a threshold; 2) Heat Units (accumulated daily mean temperature after deducting a base temperature); 3) Growing Degrees Days (Snyder 1988), as a measure of physiological growing time; 4) Accumulated maximum temperatures; and 5) Mean maximum temperature. Results indicated that the optimum base temperature for heat accumulation was 11 C^o. This threshold was used in the first three methods mentioned above. Good statistical results were obtained with the five methods, yielding high levels of explanation (p～99%). Nevertheless, the most accurate method appeared to be the Growing Degree Days (GDD^o) method, which indicated that a mean of 127.3 GDD^o must be accumulated from the end of the chilling period up to the beginning of the Quercus pollen season in Córdoba (South West Spain). Results were tested for predicting start dates in 1999 and 2000. The predicted dates were only one day after the actual dates.     

Airborne pollen data of Platanaceae in Santiago de Compostela (Iberian Peninsula)

The pollen count of the Platanus genus in the atmosphere of Santiago de Compostela (Galicia, Spain) was carried out from 1993 to 1998, with the pollen of this taxon representing 6% of total identified pollen. The principal pollination period (P.P.P.) was centred on the months of March and April, with an average duration of 23 days.During the study period we obtained negative correlations with precipitation and humidity and positive ones with temperature and hours of sunshine, with a confidence index of more than 90%. On the basis of the six-year study period, we also calculated the average accumulated temperature required to trigger the onset of flowering, which oscillated between 330 and 456 °C, with this result being confirmed for 1999 (437 °C). We also observed that the values of maximum pollen concentration of this taxon in the last 7 years (1993–1999), were obtained on days during the P.P.P. with maximum temperatures above 18 °C. The model of intradiurnal variation reflects, for the majority of years, a greater representation during the central hours of the day.