Year seasons duration and arboreal plants at Saint-Petersburg

The uninterrupted phenological monitoring has been carried out at Peter the Great Botanic Garden of the Komarov Botanical Institute (Saint-Petersburg, Russia) since 1980. The analysis of the dates of seasons beginning and duration during 42 years of observations (1980-2021) has shown that the duration of winter period has decreased from 32 % to 29 % comparing with 1953-1981, if we compare the period of the past 20 years - from 32 % to 26 %. The summer season has enlarged since 19 % till 24 %. The spring season has the tendency to shortening (from 23 % till 22 %). In condition of the warming of the climate of Saint-Petersburg at the 21 century there is the tendency of enlarging of the autumn season, especially of its second half. In such conditions those woody plants which had the forced end of vegetation, nowadays have the possibility to finish it successfully and to prepare for wintering. Warm winters promote to widen the cultural habitat of warm-loving exotic trees and shrubs. The observations on indicators of the Calendar of Nature let us give the phenological estimation of short periodically oscillations of climate and of its modern warming, using the long years dendrophenological and meteorological information.