The length of the day, or more specifically the shortening of the day and first of all the lengthening of the night at the same time in autumn have an important role in the timing of overwintering of northern plants (compare with the time of autumnal colours later!). The accumulation of temperature sum as such is not enough to explain the whole event of overwintering but the plants react also to some other signals in the environment in autumn. When a certain amount of temperature has accumulated in the habitat, the inner clock of the plant recognises the situation and changes the rhythm towards overwintering: the growth comes to an end, buds complete, and winter stores are gathered up. Sarvas claimed that this rhythm is taken care of by the inner clock of a plant, which is synchronised by the accumulation of temperature sum in particular. Furthermore, the genes of a species/individual direct overwintering: thus, what kind of environment it has adapted to in the course of years.Ī Finnish professor Risto Sarvas has described the annual developmental rhythm of trees in three phases: active stage, autumn dormancy, and winter dormancy. Special changes in the environment synchronise overwintering: Temperature sum accumulates, night lengthens, and temperature falls the plants have to acclimatize to all this. All this preparation is called overwintering. for overwintering, begins in late summer at the end of growth when the hibernacula are completed, some parts of the plant die, and various changes take place on the cell level. Preparation for the changes in tolerance (resistance), i.e. Some northern plant species demand an experience of winter.įor plants, winter means first and foremost the tolerance of cold and dryness.On the level of cells, many changes take place in the autumn.The soil has some effects on overwintering, too.Autumn colds club the plants into dormancy.The shortening of day and clear autumn weather brings the blaze of autumn colors.The increase in the temperature sum leads to beginning of overvintering.

Autumn trees at night