The variation of the onset of Betula pendula (Roth.) flowering in Rzeszów, SE Poland: fluctuation or trend?

Abstract

The global rise in air temperature has major implications for ecosystems, populations, ecology of many living organisms, public health as well as economy. Plants, like silver birch (Betula pendula Roth.), strongly respond to the climatic variation. Therefore, the species is a good indicator of the global climate change, especially warming. The phenological observation was undertaken to verify the hypothesis on an acceleration of the start of Betula pendula pollen release in the season. The investigations were carried out in 2000–2015 (16 years) in the Rzeszów area, SE Poland. On average, Betula pendula started to pollinate in the middle of April; the difference between the earliest and latest dates was nearly 1 month. The full pollination started on 18 April, on average. The timing of pollination strongly depended on the course of weather in February and March. The most crucial was temperature in the first half of March. Considering the synergistic impact of meteorological parameters, the most important were temperature and rainfall in January and February, rainfall in March and temperature just before the pollination. It was found that North Atlantic Circulation influenced pollen release in Betula pendula. The positive North Atlantic Oscillation in March and in December–March periods resulted in pollination onset. Tendency towards warmer average annual temperature was recorded, however the timing of phenophases did not follow it. Despite the strong relationship with temperature there was no acceleration of Betula pendula pollination. Probably, the climate warming effect on the onset and duration in Betula pendula phenophases would be detectable in longer than a 16-year period.