Hanna Ranta

A numerical model of birch pollen emission and dispersion in the atmosphere. Description of the emission module

A birch pollen emission model is described and its main features are discussed. The development of the model is based on a double-threshold temperature sum model that describes the propagation of the flowering season and naturally links to the thermal time models to predict the onset and duration of flowering. For the flowering season, the emission model considers ambient humidity and precipitation rate, both of which suppress the pollen release, as well as wind speed and turbulence intensity, which promote it. These dependencies are qualitatively evaluated using the aerobiological observations. Reflecting the probabilistic character of the flowering of an individual tree in a population, the model introduces relaxation functions at the start and end of the season. The physical basis of the suggested birch pollen emission model is compared with another comprehensive emission module reported in literature. The emission model has been implemented in the SILAM dispersion modelling system, the results of which are evaluated in a companion paper.

A numerical model of birch pollen emission and dispersion in the atmosphere. Model evaluation and sensitivity analysis

An evaluation of performance of the System for Integrated modeLling of Atmospheric coMposition (SILAM) in application to birch pollen dispersion is presented. The system is described in a companion paper whereas the current study evaluates the model sensitivity to details of the pollen emission module parameterisation and to the meteorological input data. The most important parameters are highlighted. The reference year considered for the analysis is 2006. It is shown that the model is capable of predicting about two-thirds of allergenic alerts, with the odds ratio exceeding 12 for the best setup. Several other statistics corroborate with these estimations. Low-pollen concentration days are also predicted correctly in more than two-thirds of cases. The model experiences certain difficulties only with intermediate pollen concentrations. It is demonstrated that the most important input parameter is the near-surface temperature, the bias of which can easily jeopardise the results. The model sensitivity to random fluctuations of temperature is much lower. Other parameters important at various stages of pollen development, release, and dispersion are precipitation and ambient humidity, as well as wind direction.

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.

Analysis of Airborne Betula Pollen in Finland; a 31-Year Perspective

In this 31-year retrospective study, we examined the influence of meteorology on airborne Betula spp. (birch) pollen concentrations in Turku, Finland. The seasonal incidence of airborne birch pollen in Turku occurred over a brief period each year during spring (April 30 – May 31). Mean peak concentrations were restricted to May (May 5 to 13). Statistically significant increases in the annual accumulated birch pollen sum and daily maximum values were observed over the study period. Birch pollen counts collected in April were retrospectively shown to increase over the duration of the study. Increases in April temperature values were also significantly associated with the earlier onset of the birch pollen season. Furthermore, the number of days where daily birch pollen concentrations exceeded 10 and 1,000 grains/m3 also increased throughout the study period. These data demonstrate that increases in temperature, especially during months preceding the onset of the birch pollen season, favor preseason phenological development and pollen dispersal. Birch pollen derived from other geographical locations may also contribute to the aerospora of Turku, Finland. To date, the public health burden associated with personal exposure to elevated birch pollen loads remains unclear and is the focus of future epidemiological research.

Performance of the cyclic autumnal moth, Epirrita autumnata, in relation to birch mast seeding

The mast depression hypothesis has been put forward to explain the 9- to 10-year population cycle of the autumnal moth (Epirrita autumnata; Lepidoptera: Geometridae) in northern Fennoscandia. We analysed long-term data from Finnish Lapland in order to evaluate the critical assumption of the mast depression hypothesis: that better individual performance of herbivores, followed by high annual growth rate of populations, occurs in the year following mast seeding of the host, the mountain birch (Betula pubescens ssp. czerepanovii). Since mast seeding has been suggested to occur at the expense of chemical defence against herbivores, we bioassayed the quality of birch leaves from the same trees by means of yearly growth trials with autumnal moth larvae. We also measured the size of wild adults as a determinant of potential fecundity of the species in different years. The relative growth rate of larvae was poorer in post-mast years compared to other years, rather than better as assumed by the hypothesis. Conversely, a slight indication of the increase in potential fecundity was observed due to the somewhat larger adult size in post-mast years. Population growth rate estimates, however, showed that the increase in fecundity would have to be much higher to facilitate population increase towards a cyclic peak with outbreak density. Accordingly, our two data sets do not support the assumption of a higher annual growth rate in autumnal moth populations subsequent to mast seeding of the host, thereby contradicting the predictions of the mast depression hypothesis. Temperatures, when indexed by the North Atlantic Oscillation and accumulated thermal sums, were observed to correlate with the abundance or rate of population change of the autumnal moth. The factors underlying the regular population cycles of the autumnal moth, however, remain unidentified. Overall, we suggest that the causal agents in cyclic insect population dynamics should be clarified by field experimentation, since trophic interactions are complex and are further modified by abiotic factors such as climate.

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.

How do airborne and deposition pollen samplers reflect the atmospheric dispersal of different pollen types? An example from northern Finland

We compared two >20 year long data sets of airborne and deposited pollen from northern Finnish Lapland (Kevo) and the middle boreal forest zone (Oulu) in terms of the plant taxa represented and their annual pollen quantities. Tree pollen (Betula spp., Pinus sylvestris) made up 92.8% of the total annual pollen in the air samples at Kevo, while in the ground‐level deposition samples the tree pollen fraction was 61.5%; the remaining 38.5% comprising pollen of ground and field level plants (Ericaceae, Cyperaceae and others). In Oulu, the proportion of tree pollen in the air and deposition samples was 90.6% and 89.0%, respectively. The annual fluctuations in the quantity of total pollen and tree pollen in both sampling systems were correlated, but no such correlation was detected for the low growing plants, except in the case of Urticaceae at Kevo. This suggests that pollen of these low‐growing plants mainly reflects the vegetation of the sampling site. Because tree pollen rises well into the atmosphere, it reflects pollen production from a larger area. Long‐range transported Betula spp. pollen recorded in the atmosphere prior to local flowering comprised a considerable part of the Betula spp. pollen at Kevo and was collected by both sampling systems.

An Approach to Simulation of Long-Range Atmospheric Transport of Natural Allergens: An Example of Birch Pollen

Diseases of the respiratory system due to aeroallergens, such as rhinitis and asthma, are major causes of a demand for healthcare, loss of productivity and an increased rate of morbidity. The overall prevalence of seasonal allergic rhinitis (allergic reactions in the upper respiratory system) in Europe is approximately 15 %; the asthma rates vary from 2.5% 10 %; etc. Pollenosis accounts for 12 45 % of all allergy cases. The sensitisation to pollen allergens is increasing in most European regions. The adverse health effects of allergens can be reduced by pre-emptive medical measures. However, their planning requires reliable forecasts of start time of high pollen concentrations in air, as well their levels and durations (Rantio-Lehtimaki, 1994; RantioLehtimaki and Matikainen, 2002). The currently available forecasts are based solely on local observations and do not consider the pollen transport from other regions or countries (Frosig and Rasmussen, 2003). However, there is a convincing evidence that long-range transport of pollen can significantly modify pollinating seasons (first of all, the start time and duration of high atmospheric pollen concentrations) in many European regions (Corden et al., 2002; Malgorzata et al., 2002; Hjelmroos, 1992). This transport causes unforeseen and sudden increases of concentrations of pollen that can occur up to a month before the start of the local pollen season. The long-range transport can substantially increase the concentrations of allergenic pollen also during the local flowering season. This is an important problem for Northern Europe and especially for Finland, where the flowering takes place later in spring. The most important pollinating species in respect to long-range transport are the birch ones, and Finland is neighbored by the Baltic

Susceptibility of Six Scots Pine Clones to the Pathogenic Fungus Gremmeniella abietina

Genotypic variation in susceptibility to Gremmeniella abietina, an economically important fungal pathogen of conifers, was studied by artificially inoculating 23 - yr - old grafted plants of six Scots pine (Pinus sylvestris L.) clones in a seed orchard. Two fungal isolates were used. The mycelium was inserted into the current year shoots in late winter and the length of the necrotic lesion caused by the fungus was measured the next spring. The growth and male flower production of the experimental shoots were also measured. The development of symptoms did not vary among the clones, but the location of the grafts within the orchard statistically significantly affected the length of necrosis. The clones differed significantly in regard to height and the production of male and female flowers. Differences in flowering intensity among the clones were not connected with the development of G. abietina. At the level of the single shoot, the production of male flowers correlated positively with the length of necrosis. The length of necrosis correlated negatively with the length of current and previous year shoots. The ability of the two fungal isolates to cause necrosis differed significantly.

Interactions during in vitro germination of Scots pine pollen

Pre-zygotic pollen competition is believed to play an important role in nonrandom mating, i.e., the unequal success of different pollen donors. We studied pollen–pollen interactions of Scots pine in vitro using multiwell plates with freely permeable inserts. Six genotypes were included in our experiments: three from northern Finland and three from southern Finland. We conducted control experiments by placing pollen of each genotype in both the well and its insert. In competition experiments each southern genotype was incubated in insert with each northern genotype in well, and vice-versa. Samples for the germinability observations were taken from inserts. The mean germination percentage of northern genotypes was lower when incubating with southern genotypes in competition experiments than in control experiments. In one case, a northern genotype showed lower mean germination percentage in competition experiment than in control experiment and in another case a southern genotype showed a higher value. Our results suggest a chemically mediated interaction between pollen from different genotypes and one which can vary among genotypes.