ARTIFICIAL DEFOLIATION, DECAPITATION OF THE TERMINAL BUD, AND REMOVALOF THE APICAL TIP OF THE SHOOT IN SESSILE OAK SEEDLINGS AND CONSEQUENCES ON SUBSEQUENT GROWTH

To simulate the damage caused by herbivores and fungi and study their effects on 1-year-old nursery-grown sessile oak (Quercus petraea (Matt .) Liebl.) seedlings, (1) the portion of stem produced during the firs t growth flush, referred to as the growth unit (GU), was artificially defoliated, decapitated, or both or (2) the apical part of the GU was removed in the period of apparent rest. In comparison to control seedl ings, defoliation, decapitation combined with defoliation, and apical part removal (1) caused earlier production of the GU in the second flu sh, (2) reduced length and number of leaves in the GU produced during the second flush, (3) consequently reduced the portion of stem produce d during the entire growing season (the annual GU), and (4) increased the number of branches of the CU damaged during the first flush. In co ntrast, decapitation caused later production of the GU of the second f lush and had apparently no effect on height growth components. In all treatments, the number of branches that developed on the GU produced d uring the first flush increased.