XVI International Botanical Congess

Diameter changes of Zelkova serrata sapling stem had been continuously measured during two years using originally developed optoelectronic dendrometer. Annual thickening growth and daily shrinkage and swelling of stem corresponded with other reports. Fast shrinkage and/or swelling of stem were also detected. Fast diameter changes continued second to minute orders with more than 300um in amplitude, occurred frequently when shoots elongated vigorously and sporadically even in dormant period. Frequency and time of their occurrence were different among measuring sites of a sapling stem. Although unclear origin, the fast phenomena stronglysuggest dynamic morphological changes in the stem keeping with close relation to the phenological events.