Predicting the intensity of the birch pollen season

We present a model for the prediction of the magnitude ofBetula flowering and pollen dispersal which may be used in the management of birch pollinosis and in the planning of clinical trials. The pollen sum during the flowering season is regressed on the temperature sum from May 1st to July 20th during the initiation year, the pollen sum of the initiation year, and the temperature sum during the main pollen season in the flowering year. We suggest that the fluctuating flowering pattern inBetula alba-species is primarily determined by the availability of assimilation products during inflorescence initiation and development during the spring one year before anthesis. When inflorescences, which are initiated during the previous year, elongate in the beginning of anthesis, they act as strong sinks to stored carbohydrates, and thus compete with developing leaves and shoots. The result is an initially reduced photosynthetic capacity in years with intense flowering, and a limited potential for the initiation of new inflorescences for the following year. The ambient temperature during catkin initiation affects assimilation efficiency and is a determinant of about equal importance to flowering intensity as is the magnitude of the flowering in the initiation year. The amount of pollen dispersed is also dependent on the weather during anthesis, which is not possible to predict until about one month in advance. The two other independent variables are available during the previous summer, making it possible to give a sufficiently valid prediction to allergologists about the magnitude of the next birch pollen season, according to its botanical determinants. We suggest that the varying reproductive output inBetula alba should not be described as true masting. A more parsimonious explanation to the flowering pattern is that an individual continually maximizes reproductive effort, according to what is possible, but that reproduction is often constrained by the environment.     

Birch pollen abundance in Reykjavík,Iceland

A ten-year birch pollen record for Reykjavík, Iceland, has been analyzed with respect to fluctuations in the annual pollen sum, the starting date, and the duration of the birch pollen season. A three-year cycle is observed for the annual birch pollen sum, which could be of value in predicting the severity of the next birch pollen season. The annual birch pollen sum is regressed on six climatic variables, only one of which turned out to be statistically significant. The number of days with temperatures above +7.5°C in the year of inflorescence initiation shows a significant correlation with the annual birch pollen sum of the following flowering year (P =0.009). For the starting date of the birch pollen season the accumulated thermal sum on May 15 is shown to have the best predictive value, estimating it to within one week. The mean duration of the birch pollen season in southwestern Iceland is 17 days, starting May 29 and ending June 14.     

Birch pollen production,transport and deposition for the period 1984–1993 at Kevo,northernmost Finland

Summary Betula pollen production and flowering, pollen transport and pollen deposition are considered for the mountain birch region of northern Finland for the ten-year period 1984–1993. The most abundant flowering year was 1989 and, after that, 1985. In these years the highest values were also recorded for pollen in the air. There is a significant correlation between the amount of pollen released and the thermal sum of the previous year. In terms of pollen deposition the peak years were 1989 and 1986. The correlation between the amount of pollen in the air and that being deposited on the ground is also statisticaly significant. It is evident that some birch pollen is already present in the air before local flowering begins and that, in some years, this non-local pollen can account for more than 20% of the yearly total. This preflowering proportion was highest in 1985 and 1993, the latter being a prolific flowering year in the south of the country. There is a clear relationship between the proportion of the non-local pollen in the air and the proportion ofBetula pubescens/pendula type pollen deposited on the ground and, conversely, there is a significant correlation between the amount of local pollen in the air and the amount ofBetula tortuosa plusB. nana type pollen being deposited on the ground. The questions both of the viability of this long-distance pollen and of its ability to cause allergic reactions are considered. An assessment is also made of the degree to which fossil birch pollen assemblages can be realistically interpreted in terms of local vegetation if a varying proportion of the same pollen type is non-local.     

Prevention of the flowering of a tree,silver birch

Genetic modification of trees presents great advantages but it is hampered by the possible spread of introduced genes to native populations. However, the spread would be prevented if the modified trees would be sterile. We have previously shown that the induction of sterility by the prevention of flowering is possible in tobacco and Arabidopsis by introducing a gene construct composed of the ribonuclease gene BARNASE ligated to the flower-specific promoter of the birch gene BpMADS1. In the present study, we test this gene construct in silver birch (Betula pendula Roth). When this gene construct was introduced into very early-flowering birch clones, 81 kanamycin resistant lines were obtained. In 38 lines, the vegetative development was disturbed, e.g., the leaves were small and the plants were short and bushy or the growth of plants was weak. More importantly, in 7 other lines no male inflorescences formed or they aborted early. If male inflorescences were formed, they did not contain any stamens. The initial growth of these lines was similar to the non-transgenic control lines. Later, however, the growth of the non-flowering lines differed from that of the controls in showing some dichotomic branching and a reduced number of branches. Preliminary results showed that the gene construct can prevent the development of female inflorescences as well. The results show clearly that BpMADS1::BARNASE can prevent the flowering in a tree but the prevention of flowering may cause some side effects. Studies with ordinary birch clones will show whether the side effects are a property of the early flowering clones or all birches.     

The start of the birch pollen season in Finnish Lapland: separating non‐local from local birch pollen and the implication for allergy sufferers

Determining the start of the birch pollen season requires the reliable separation of non‐local from locally produced birch pollen. The research was undertaken close to the latitudinal birch tree line at the Kevo Subarctic Research Institute (69°45′N 27°01′E) in northern Finland. By comparing phenological and aerobiological observations, the proportion of birch pollen present in the air before local anthesis commences can be delimited. We coupled this with data of pollen deposition monitored by means of a modified Tauber trap. The dominant birch species at Kevo is the mountain birch Betula pubescens ssp. czerepanovii, whereas B. pubescens ssp. pubescens is very rare, hence we consider the proportion of the southerly B. pubescens‐type pollen deposited in the pollen trap to be non‐local in origin.

We did not observe any trend towards an earlier start of the phenologically observed mountain birch anthesis at Kevo as predicted from work elsewhere. Moreover, the fixed 2.5% threshold method for determining the birch pollen season proved not to be applicable since in many years this threshold was reached before the end of continuous snow cover. The results indicate that in some years non‐local birch pollen contributes considerably to the allergen load in Lapland with up to 57% of the total birch pollen sum being recorded before the day on which local anthesis commenced, and up to 70% of the annual birch pollen deposited being of the southerly birch type.     

Pollination biology and sexual differentiation ofOsyris alba (Santalaceae) in the Mediterranean region

Osyris alba L. is a widespread dioecious hemiparasitic shrub of S Europe, N Africa, and SW Asia. Male inflorescences are multiflowered whereas each female inflorescence is reduced to a single flower with persistent enlarged bracts. Pollination is a prerequisite for fruit and seed development and wind is unlikely to be an effective means of pollen spread. In southern Italy pollen is transported by small unspecialized flies and beetles. Both male and female flowers produce an indistinguishable sweet odour. Male flowers are produced in large numbers and over a larger period than the females and provide pollen, nectar, and staminal hairs as rewards for pollinators. The presence and function of staminal hairs with tip cells inOsyris alba has been reported for the first time. Female flowers are rewardless, producing neither mature pollen, nectar nor staminal hairs, but possess three modified yellow indehiscent anthers containing no viable pollen which may provide a strong visual feeding stimulus for pollinators. It is suggested that pollinators are attracted by deceit to female flowers by mimicry of the males and the floral mimicry is, therefore, intraspecific and intersexual. The floral characteristics and flowering phenology of male and female plants are consistent with this kind of mimicry. The female flower possesses a tricarpellary ovary with three ovules of which only one develops. The single seed, containing a small embryo and a large, rich endosperm, is borne in a red fleshy bird-dispersed fruit. The reduction in seed number per flower to one highly nutrient-invested seed, together with a reduction of the multiflowered inflorescence to a solitary flower and the sequential production of ripe fruits over an extended fruiting season, suggest that the female function is markedly resource-limited. It is suggested that, although all the reproductive characteristics present inOsyris alba, as well as hemiparasitism, had probably evolved before the end of the tropical Tertiary, they are of adaptive advantage in the nutrient and water-limited environment of the Mediterranean maquis.     

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.     

Prediction of birch airborne pollen counts by examining male catkin numbers in Hokkaido,northern Japan

Birch pollen is a very common cause of pollinosis in Hokkaido, northern Japan. Birch airborne pollen concentrations vary each year; hence, the development of a method for predicting annual airborne pollen concentration is very important in preventing widespread symptoms of pollinosis. In the current study, we investigated airborne pollen counts and male catkin numbers (male flower index) of birch in four cities of Hokkaido between 2002 and 2008. Airborne pollen surveys were conducted using Durham’s sampler, and male catkin numbers determined for three major birch species (Betula platyphylla var. japonica, B. emanii, and B. maximowicziana). We found an annual variation in male flower index for all the three birch species investigated. This variation worked in combination with the amount of precipitation during the pollen season to influence total birch pollen counts. In conclusion, the male catkin numbers of three major birch species reliably predict airborne pollen counts in Hokkaido, but only when the effect of precipitation during pollen season is considered.     

A satellite-based map of onset of birch (<Emphasis Type="Italic">Betula</Emphasis>) flowering in Norway

Birch (Betula pubescens L.) is by far the most common deciduous tree in Norway and birch forests define the forest line both northwards and upwards. Because of its mountainous topography, long fjords, and long length from north to south, Norway is climatically and ecologically very diverse. Therefore, developing pollen forecasts in Norway is a challenging task. In this study we use MODIS-NDVI (normalized difference vegetation index) satellite data with 250 m spatial resolution and 16-days time resolution for the period 2000–2007, and birch pollen counts from ten Burkad traps distributed throughout Norway, to characterize the onset of birch flowering in Norway. Four of the seven trap stations with long-term series show significant values at the 5% level or better between the MODIS-NDVI defined onset and the date when the annual accumulated birch pollen sum reaches 2.5% of the annual total. A map of Norway that shows the eight-year mean (2000–2007) onset of birch flowering was produced. It reveals large differences in the timing of the onset of birch flowering along the north–south and altitude gradients. The map provides useful general information that can be utilized by the Norwegian pollen forecast service. This study shows that remote sensing is a useful tool for not only characterizing the onset of the birch pollen season but also revealing regional differences not easily detected by pollen stations alone.     

Overexpression of BpAP1 induces early flowering and produces dwarfism in Betula platyphylla × Betula pendula

The involvement of APETALA1 (AP1) in the flowering transition has been the focus of much research. Here, we produced Betula platyphylla × Betula pendula (birch) lines that overexpressed BpAP1 using Agrobacterium‐mediated transformation; we obtained five independent 35S::BpAP1 transgenic lines. Polymerase chain reaction (PCR), Southern, northern and western analyses were used to identify the transformants. As determined by quantitative real‐time PCR (qRT‐PCR), BpAP1 expression in roots, shoots, leaves and terminal buds of 35S::BpAP1 transgenic lines was significantly higher than that in the wild type (WT, P < 0.01). The average height of 2‐year‐old 35S::BpAP1 plants was significantly lower (41.17%) than that of non‐transgenic plants. In the 35S::BpAP1 lines, inflorescences emerged successively beginning 2 months after transplanting. In addition, the length–diameter ratio of fully developed male and female inflorescences were both significantly less than those of the WT (P < 0.05), i.e. the morphological characteristic was stubby. The male inflorescences emerged early, with empty, draped anthers, and pollen was rarely produced, whereas the female floret structure was not different from WT. The pistils developed normally and could accept pollen, leading to the production of hybrid progeny (F₁). F₁ plants completed flowering within only 1 year after sowing. We demonstrate that BpAP1 can be inherited through sexual reproduction. Overexpression of BpAP1 caused early flowering and dwarfism; these lines had an obviously shortened juvenile phase. These results greatly increase our understanding of the mechanisms underlying the flowering transition and enhance genetic studies of birch traits, and they open up new possibilities for the breeding of birch and other woody plants.     

A long-term study of winter and early spring tree pollen in the Tulsa, Oklahoma atmosphere

Since 1986 the atmosphere in Tulsa, Oklahoma has been monitored for airborne pollen and spores with a Burkard 7-day spore trap situated on the roof of a building at The University of Tulsa. The present study specifically examined the early spring tree pollen season for several local taxa and the occurrence of pre-season pollen during December and January. Knowledge of the local pollen season will help identify the presence of out-of-season pollen and possible long distance transport (LDT) events. Average daily concentrations of airborne pollen for species ofBetula, Quercus, Ulmus, and Cupressaceae were determined for each year from 1987 to 1996. The data showed that during the early spring the precise pollination periods for these allergenic tree species are highly variable. There were considerable variations in start date, season length, peak concentration, date of peak, and cumulative season total. The start dates forUlmus, Betula, andQuercus varied by 30 days or more, while the early spring Cupressaceae pollen showed the least variation in start date (only 23 days). More research is needed to understand the mechanisms which govern the onset and magnitude of pollen release. Although several reports have documented episodes of long distance transport (LDT) of pollen, the actual contribution of out-of-season or out-of-region pollen to local air spora is poorly known. The current study also re-examined the LDT ofJuniperus ashei pollen in Oklahoma.Juniperus pollen appeared in the Tulsa atmosphere on 40% of the days in December and January with concentrations as high as 2400 pollen grains/m³ of air; however, no local populations ofJuniperus pollinate at this time of the year. High concentrations occurred on days with southerly winds suggesting thatJuniperus ashei populations in southern Oklahoma and Texas were the pollen source. Since no local pollen is present in the Tulsa atmosphere in December and January, this example of LDT has been easy to document.     

Modelling the Masting Behaviour of Betula platyphylla var. japonica using the Resource Budget Model

A masting model of Betula platyphylla var. japonica, a majorwind-pollinated tree in Hokkaido, northern Japan, was constructedfrom the perspective of the resource budget model. An 11-yeardata series of pollen dispersal by birch showed marked annualfluctuations in flowering. Although flowering fluctuated widelyamong years, a reciprocal relationship was observed betweentwo consecutive years; very little flowering occurred aftera mast year. This suggests that there is a negative relationshipbetween current fruiting and flower bud induction. There wasa significant positive relationship in flowering between regions,which suggests that weather conditions regulate flowering inbirch. A model that included weather variables and resourceallocation systems among years explained 94·5% of theobserved annual fluctuations in flowering. In the model, warmspring conditions from bud burst to flower bud development andlittle flowering in the previous year (t-1) resulted in increasedflowering in the current year (t), whereas abundant floweringin year t-2 resulted in a decrease in flowering in the currentyear (t). The latter indicates that flowering in year t-2 affectsresource storage after overwintering; the balance is carriedforward to year t-1 and affects the initiation of flower primordiabefore bud burst. In the model, fluctuating weather conditionsin the previous spring strongly affected the masting behaviourof birch. Copyright 2001 Annals of Botany Company Betula platyphylla var. japonica, flowering, masting, modelling, pollen dispersal, resource allocation, resource budget model, weather conditions     

Factors that determine the severity of <Emphasis Type="Italic">Betula</Emphasis> spp. pollen seasons in Poland (Poznań and Krakow) and the United Kingdom (Worcester and London)

The aim of this paper is to analyse variations in the severity of Betula pollen seasons, particularly in relation to meteorological parameters at four sites, Poznań and Krakow in Poland, and Worcester and London in the United Kingdom. Results show that there is a significant relationship between Betula pollen season severity and weather conditions both in the year before pollination and in the same year that pollen is released from the plant. Furthermore, it is likely that the magnitude of birch pollen seasons in Poznań, Worcester and London is linked in some way to different phases of the North Atlantic Oscillation (NAO). Significant positive relationships exist between birch pollen counts at Poznań and temperatures, rainfall and averages of the NAO in the year before pollination. An opposite relationship is evident at the two sites studied in the United Kingdom. There were significant positive correlations between the severity of birch pollen seasons recorded at Worcester and temperatures and averages of the NAO during the winter and spring in the year of pollination, and negative correlations at both Worcester and London with similar variables from the previous year. In addition, Betula pollen seasons in Krakow do not appear to be influenced by the NAO, which is probably the result of Krakow having a more continental climate.     

The importance of hornbeam (Carpinus sp.) pollen hypersensitivity in spring allergies

Hornbeam (Carpinus sp.) flowering occurs generallysimultaneously with birch anthesis. While birch pollenis known as the major tree-allergen in central andnorthern Europe, the quantitative and qualitative roleof hornbeam pollen in allergy has not been evaluated.In some regions of Switzerland, the annual ratiohornbeam SPI / birch SPI reaches 20–30% on average,and 50–180% some years. The relative importance ofhornbeam pollen hypersensitivity has been evaluated inmore than 200 patients suffering from spring allergiesto pollen during the last five years (1993–1997) inthe region of Geneva. Among symptomatic patientsduring the March-April period, 73.5% werehypersensitive to Betulaceae pollen. Overall, 71.7%of the patients allergic to Betulaceae pollen werefound to be sensitive to hornbeam, and 12.5% of thesame group of patients were sensitive to hornbeampollen only. Among this last group, half of thepatients, besides allergic rhino-conjunctivitis, werealso suffering from asthma. Hornbeam pollen isabundant and appears to have a significativeimportance in spring allergies. In some cases,specific immunotherapy to hornbeam pollen shouldperhaps be considered.     

Male-biased sex ratio and promiscuous pollination in the dioecious island treeLaurus azorica (Lauraceae)

Pollination ofLaurus azorica (Lauraceae), a dioecious Macaronesian tree, was studied. Male and female trees had the same size distribution. The population had 2.5 times as many male trees as females. In addition, males produced more flowers, and their inflorescences lasted longer. Individual flower lifetime and length of flowering season were the same in both sexes. Between the years of observation, one tree changed sex. Pollinators wereHalictinae bees and the flyTachina canariensis. The bees collected pollen and nectar and the fly collected nectar from both sexes. Both species visited other plants as well. The evolution of breeding systems inLauraceae is discussed.     

Pollination of Bactris (Palmae) in an Amazon forest

Phenology, inflorescence behavior, and pollination of 10 sympatric taxa ofBactris were studied in a lowland Amazon forest. Taxa flowered over an eight month period during the rainy season and early dry season, but individual taxa flowered for one to a few months. Related taxa had mostly non-overlapping flowering periods. Inflorescence behavior was similar for all taxa, with nocturnal pistillate anthesis and temperature elevation, followed 24 hours later by rapid, nocturnal staminate anthesis. Pollinators of all taxa were small weevilsPhyllotrox (Curculionidae) and nitidulidsColopterus (Nitidulidae), although various other insect visitors were recorded. Large numbers ofPhyllotrox were recorded on inflorescences, but weevil sex ratios were highly skewed.     

Integration of flowering dates in phenology and pollen counts in aerobiology: analysis of their spatial and temporal coherence in Germany (1992–1999)

We studied the possibility of integrating flowering dates in phenology and pollen counts in aerobiology in Germany. Data were analyzed for three pollen types (Betula, Poaceae, Artemisia) at 51 stations with pollen traps, and corresponding phenological flowering dates for 400 adjacent stations (< 25 km) for the years 1992–1993 and 1997–1999. The spatial and temporal coherence of these data sets was investigated by comparing start and peak of the pollen season with local minima and means of plant flowering. Our study revealed that start of birch pollen season occurred on average 5.7 days earlier than local birch flowering. For mugwort and grass, the pollen season started on average after local flowering was observed; mugwort pollen was found 4.8 days later and grass pollen season started almost on the same day (0.6 days later) as local flowering. Whereas the peak of the birch pollen season coincided with the mean flowering dates (0.4 days later), the pollen peaks of the other two species took place much later. On average, the peak of mugwort pollen occurred 15.4 days later than mean local flowering, the peak of grass pollen catches followed 22.6 days after local flowering. The study revealed a great temporal divergence between pollen and flowering dates with an irregular spatial pattern across Germany. Not all pollen catches could be explained by local vegetation flowering. Possible reasons include long-distance transport, pollen contributions of other than phenologically observed species and methodological constraints. The results suggest that further research is needed before using flowering dates in phenology to extrapolate pollen counts.     

Variations and trends of birch pollen seasons during 15 years (1996–2010) in relation to weather conditions in Poznań (western Poland)

Birch (Betula) pollen seasons were examined in relation to meteorological conditions in Poznań (1996–2010). Birch pollen grains were collected using a volumetric spore trap. An alternate biennial cycle of birch pollen season intensity was noticed in Poznań. The main factors influencing birch pollen season intensity were average daily minimum temperatures during the second fortnight of May and the month of June one year before pollination as well as the intensity of the pollen season of the previous year. Most of the pollen grains are recorded during the first week of the season; the number of pollen grains recorded at this time is positively correlated with mean maximum temperature and negatively correlated with daily rainfall. The significant effect of rainfall in reducing the season pollen index was noticed only during weak pollen seasons (season pollen index <?mean). In addition, mean daily maximum temperature during the first two weeks of the birch pollen season markedly influences its duration. No significant trends in duration and intensity of the pollen season were recorded, however, a slight tendency towards early pollination was observed (?0.4 days/year, p?=?0.310).     

Airborne birch pollen in Neuchâtel (Switzerland): onset, peak and daily patterns

An accurate forecast of the starting point of thebirch pollen season in Neuchâtel can be made byadding the positive daily average air temperature fromFebruary 1st onward until the figure 270 is reached.At this point, the birch trees are ready to bloom.After that, the daily average temperature has toexceed 10 °C to allow pollen release.Today, the birch pollen season starts some 19 daysearlier in the year than in the 1980's, a consequenceof a recent climate change.The daily patterns of airborne birch pollen isirregular. Moreover, pollen concentrations frequentlyexceed the threshold of the appearance of allergicsymptoms, except during rainfall. Therefore, the onlybehavioral recommendation that can be given to peopleallergic to birch pollen is to shorten as much aspossible the contact with outdoor air during the mainbirch pollen season.     

Impact of plant flowering phenology on the cost/benefit balance in a nursery pollination mutualism,with honest males and cheating females

This study documents the flowering phenology and its potential consequences on a nursery pollination mutualism between a dioecious plant, in which honest male plants, but not cheating females, allow the specific pollinator to reproduce within inflorescences. Very few pollinators were found to emerge during plant anthesis, leading to a low (if any) potential benefit through pollen dispersal. This opens the question why male plants do not also cheat their pollinators. Female plants flowered late in the season, when many males had just achieved their own anthesis, which increased the efficiency of pollen transfer. Finally, some late‐flowering males reached their anthesis simultaneously with females, which open the possibility for pollinator to choose between honest males and cheating females. Nevertheless, female plants were found to produce fruits, even though fruit production was limited by pollen (and pollinator) supply, meaning that cheating was not entirely retaliated by the mutualistic partner.