Nature calendar: "green spring" has come
The first phenological sub-season of spring (snowy spring), which began in Polistovye on the 10th of March, was quite extended and contrasting. Its average temperature was -1.8°C. On the 15th of March, frosts returned, and on the 17th of March the temperature dropped to -18°C, but on the 18th of March, spring began to come into force again, although it occasionally missed the initiative.
Frosts were almost every night, sometimes night temperatures fell to -7°C -13°C, and on the 21st of March, even the daytime temperature did not rise above 0 degrees. Several times there was a light snow. The maximum temperature during this period was observed on the 25th of March (+ 6,3°C). This not steady weather did not prevent the arrival of birds. At the beginning of the third decade of March, the first starlings were sighted in the vicinity of Polistovsky Reserve, and wagtails - at the end of the month.
On the 1st of April, the average daily temperatures steadily moved 0 degrees upwards, which means that the next spring sub-season, the "motley spring", has come. At the very beginning of April, the first storks arrived, and on the 4th the cranes were met for the first time after the wintering. This sub-season was short and almost merged with "revival of spring" sub-season, the thermal criterion of which is the transition of daily temperatures through + 5°C, which happened on the 5th of April. From that day the speed of phenological phenomena began to increase every day. The most massive arrival of wintering birds also occurs at this sub-season.
Incomplete chronicle of the events of the "revival of spring":
April 5 - snow covered less than 1/2 of the land surface оn a meadow;
April 6 - meeting of the male newt;
April 7 - the first butterflies were met, pollen spreading of male inflorescences of hazel and gray alder, the arrival of swans;
April 8 - the snow completely melted оn the meadow, less than 1/2 of land surface is covered with snow in the forest;
April 10 - bloom of female inflorescences of , liverwort and coltsfoot;
April 11 - black alder bloom;
April 12 - mass bloom of the hazel, the first grass frogs appeared;
April 13 - the hairy wood-rush has blossomed;
April 15 - mass movement of grass frogs, the appearance of toads and Aedes mosquitoes;
April 16 - willow and aspen bloom.
During the period from the 1st to the 16th April, the average air temperature was +6,2°C, night temperatures fell below 0 degrees eight times, the minimum (-4,8°C) was recorded by the meteorological station of Polistovsky Reserve on the 13th of April. The maximum daily temperature (+21°C) was observed on the 9th and the 16th of April.
On the 17th of April, with the transition of dialy temperatures through + 10°C upwards, the next spring sub-season began, the "green spring". On this day, the blossom of the windflower and the leatherleaf started, and the next day the bird cherry tree turned green - the tips of its leaves, which had emerged from the kidneys, became clearly visible. At this stage, the arrival of birds is ending; soon male cuckoo singing, annoying creaky "trills" of corncrake and night serenades of nightingales will be heard.