Seed-rich year for trees has covered Estonia in yellow pollen
This year, more pollen than usual can be seen across Estonia: the yellow dust has covered bodies of water, forests and car roofs alike. Dendrologists Urmas Roht and Ivar Sibul assess the phenomenon stems from trees having a seed-rich year.
Dendrologist and Räpina School of Horticulture (Räpina Aianduskool) educational institution head Urmas Roht said the amount of pollen stems from a good year for cones. "Conifer cone years come around every five to seven years. This year is likely a year when both spruce and pine flower and that is why there is more pollen. This time, deciduous trees have also bloomed well."
Estonian Environmental Research Centre air monitoring expert Mart Vill said the amount of pine pollen in the air might be higher than previous years by the end of the year.
"In total, the amount of pine pollen is similar to the total amount over previous years but the flowering period has not ended yet. Daily levels are significantly higher and by the end of the flowering period, the yearly amount will likely be significantly higher than in earlier years," Vill said.
He added that the long rain-free period has also affected the amount of pollen in the air. "I think one of the reasons might be this long dry period, since rain clears the air and also washes off pollen," the expert said.
Environmental Research Centre air quality and climate department head Erik Teinemaa said the amount of alder and birch dust has also increased this year.
Estonian University of Life Sciences dendrology docent Ivar Sibul explained the process of pollen development. "Coniferous and deciduous trees do not generate the same amount of seeds each year. There are seed years and gap years. A pine might produce seeds every 3-4 years, a spruce every 4-6 years and a silver birch every year or two. There are both female and male inflorescences in gap years and there are fewer seeds and cones, which is why there is less pollination in the spring," Sibul said.
He added that noticeable pollen in the spring comes from wind-pollinating trees such as spruces and pines. Deciduous trees that wind-pollinate are birches, alders and hawthorns.
More allergens in the air this year than normal
Data from the Estonian Environmental Research Centre and the Estonian Allergy and Asthma Federation shows that alder and birch have stronger allergens than pine and spruce. The greater amount of birch and alder pollen can therefore produce strong inconveniences for people with allergic tendencies.
Mart Vill explained that birches are blooming throughout the year. The last year there was this much birch dust was in 2019, which means there is more pollen than usual, based on the trees' natural development process.
Stable climate favors abundance of pollen
Ivar Sibul said temperature swings also affect tree growth and their blooming in spring. "The best factor for tree development is stable temperature, both during the vegetation period and the winter rest period. Trees are negatively affected by temperature swings and extreme climate conditions, such as droughts and frost," Sibul explained.
"Last summer and fall was warm and wet enough and the winter had stable snow coverage and temperature. It certainly suited forest trees. Wind-pollinating flowering plants already form male inflorescences by the end of the summer prior to next year's bloom, meaning catkins must also survive the winter. This is the reason last year's conditions and winter conditions are very important," he added.
The spring-summer blooming period is far from done and soon grasses wil begin to flower, as well, likely to last from the end of May until mid-September.
For more details on ambient air quality in Estonia, visit the Estonian Environmental Research Centre's air monitoring page here.
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Editor: Kristjan Kallaste