No abstract

Masting, the intermittent production of large crops of flowers by a plant population, is a common feature among trees in boreal and temperate forests. The pollen of many broadleaved trees causes allergic diseases, which are major causes of increasing health-care costs in industrialised countries. As the prevalence and severity of allergic diseases are connected with the concentrations of airborne pollen, an universal model predicting the intensity of the coming flowering would be a valuable tool for pollen information services, and ultimately for allergic people and allergologists. We investigated whether a resource budget model created in Japan explains the fluctuations in the annual pollen sums of Betula-species in north European data sets (10-12 years at 4 sites, 20 years at 10 sites). Using the shorter data sets, the model explained 76-92% of the annual fluctuations at five study sites. Using the 20-year data set, the percentage for southern Finland was much lower, only 48%, compared with the 85% of the 12-year data set. The annual pollen sums have been higher during the 1990s than in the 1980s, which may explain the ineffectiveness of the model, while applied to the 20-year data set. Our results support the resource budget model: the masting of birch species is regulated by weather factors together with the system of resource allocation among years. The model can serve pollen information service. However, only the 10 most recent years should be used to avoid interference from trends in changing vegetation and/or climate.

No abstract

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)(1998)(1999)(2000)(2001)(2002)(2003)(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 23 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 (pv0.05; Student-NewmanKeuls 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.