Bioclimatic cyclicality and its influence on woody plants at Saint-Petersburg

In conditions of the warming of climate the observations on indicators of Nature Calendar at Peter the Great Botanic Garden (Saint-Petersburg, Russia) in 1980-2021 let us give the phenological estimation of short periodical oscillations of climate. The cyclicality of climate develops in the change of early-warm (EW) and late-cold (LC) years which reflects on winter hardiness and reproductive ability of woody plants. All severe and unfavorable winters happens to occur in LC years. In EW years the winter months are considerably warmer (in February on 7,2 oC, in January on 4,4 oC). There is rather large difference on spring, from its beginning till June inclusive. It means that conditions for wintering of plants are better in early-warm years. The duration of winter is shorter on 52 days, and the spring and the summer seasons are longer, consequently. According to USDA Hardiness Zones of woody plants, in late-cold years with average minimum temperature -26,5 oС St.-Petersburg is situated at 5a zone. And at early-warm years with temperature -19,3 oC it transfers to warmer zone 6b.