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Changes in flowering of birch in the Czech Republic in recent 25 years (1991–2015) in connection with meteorological variables

Hajkova, Lenka, Kožnarová, Věra, Možný, Martin, Bartošová, Lenka
Acta agrobotanica 2015 v.68 no.4 pp. 285-302
Betula pendula, air, altitude, atmospheric precipitation, flowering, interphase, pollen, temperature, Central European region, Czech Republic
The paper presents the results of long-term phenological observations of silver birch (Betula pendula) during the years 1991–2015 across the phenological network of the Czech Hydrometeorological Institute (CHMI – Český hydrometeorologický ústav). The data assembled over this period were used for identification of timing of generative phenophases associated with pollen release into the air: inflorescence emergence 10%, beginning of flowering 10%, beginning of flowering 50%, beginning of flowering 100%, and end of flowering. The stations are situated at altitudes from 155 m (Doksany) to 1102 m (Modrava). The average timing of beginning of flowering 10% was 8th April (Lednice = lowland station) and 14th May (Modrava = mountain station); the average timing of beginning of flowering 50% was 12th April (Lednice) and 20th May (Modrava); the average timing of beginning of flowering 100% was 18th April (Lednice) and 22nd May (Modrava), and the average timing of end of flowering was 26th April (Lednice) and 28th May (Modrava).The totals of effective temperatures above 5°C (TS5) and sums of daily precipitation were used as a bio-climatological criterion for assessment of the dependence of phenological phases on meteorological variables. The average sums of TS5 and the average sums of daily precipitation total were as follows: 61.0–80.8°C, 82.8–327.4 mm (inflorescence emergence); 105.2–106.4°C, 85.9–365.2 mm (beginning of flowering 10%); 124.8–130.8°C, 89.8–385.9 mm (beginning of flowering 50%); 144.7–158.6°C, 95.2–390.7 mm (beginning of flowering 100%); and 181.6–223.8°C, 104.7–427.4 mm (end of flowering).Synoptic situations occurring during interphase intervals were obtained – the most often found synoptic situations were B (stationary trough over Central Europe), Bp (east travelling trough), NEa (northeast anticyclonic situation), Sa (south anticyclonic situation) and SWc2 (southwest cyclonic situation moving northeast to eastwards).The period of occurrence of birch pollen in the air lasts 52 days on average and the highest concentration was recorded on 23rd April, 2003 – 2606 pollen grains/m3.