The onset and duration of vegetative phenological stages in European beech (Fagus sylvatica L.) under changing conditions of the environment

A phenological study on the onset and duration of particular phenological stages of European beech (Fagus sylvatica L.) was carried out using sample trees growing in a research area of the Faculty of Fo­res­try and Wood Technology, MENDELU Brno for a period of 17 years (1991–2007). The paper describes the onset and duration of particular phenological stages depending on effective temperatures. In spring phenological stages, the high dependence was proved on air temperatures. To evaluate temperature requirements of studied species the cumulative sum of temperatures which activated the beginning of a respective phenological stage was used. It is evident that the onset and the course of particular phenological stages were very variable being subject to the effect of temperature changes, particularly in the spring season. In recent years, the earlier onset is noted of spring phenological stages and the length of their duration shortens. Effects of temperature on the onset and duration of the stage of budbreak and the beginning of foliage became evident in European beech most mar­ked­ly. 2007 was a very extreme year from the aspect of the early onset of spring vegetative phenological stages. In that year, a marked shift was noted in the onset of particular staged as compared to previous years. To specify phenological observations, records of phenological data of a camera placed in the central part of a crown were used. Results obtained show that some spring phenological stages take only several hours, which corresponds with higher temperatures during spring months in last years. In the area described, higher temperatures were measured even in autumnal months as compared with a long-term average. Owing to high temperatures in the pre-dormancy period, the extension of a growing season occurs and thus also shortening the dormancy playing an irreplaceable role in forest trees. Shortening the dormancy can result in the disturbance of physiological processes and subsequently the decline of trees.