| Fig. 4.1.33. Vegetative period (phenological phases) for meadow plants (oat grass - Arrhenatherum - in Poland), for trees and herbs in a mixed oak forest in northern Germany (with comparison of Ranunculus ficaria to those in Russia and England), and also for plant species from cold regions (high mountains, arctic regions) and from semiarid and arid regions (steppe, deserts). After Larcher (1994). 1 Time required for complete leaf cover; 2 death due to drought; 3 flower buds visible; 4 flowering period; 5 fruit ripening and seed dispersal

There are also short-term periodic or episodic events which cannot be explained by the usual phenological characteristics, but determine the dynamics of these communities decisively. These include regularly occurring floods in river basins, requiring particular adaptations to the extreme water supply, and problems of root respiration and perhaps mechanical disturbance (Fig. 4.1.32 A, B). Another example is the stress caused by avalanches, with the subsequent characteristic vegetation patterns in the Alpine belt. Regularly repeated human influences are important, e.g. mowing once or twice a year and grazing with different numbers or species of animals.

Other growth processes also occur in phases, e.g. of shoots or roots, but this may not always be visible (Fig. 4.1.34).

Phases of activity and dormancy are characteristic for all regions with a seasonal climate. A distinction is made between phases or periods of stronger activity of vegetative and reproductive growth. Occasionally, several vegetative pulses of growth occur; for example, in late summer some tree species rapidly form very distinct new shoots. Seasons may be determined by temperature or from water supply. In the latter case, seasonally changing water supply is the most important regulatory factor for short-term dynamics of vegetation. Even under Mediterranean conditions, for example, summer annuals of temperate zones are replaced by winter annuals, flowering periods shift into autumn. In the tropics with seasonal precipitation the flowering phase is induced by the onset of the rains.

Leaf unfolding

Shoot growth

Root growth

Growth in diameter

Assimilate accumulation

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