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

BEDNAŘOVA, E. , KUCERA, J., MERKLOVA, L. : The onset and duration of vegetative phenological stages in European beech (Fagus sylvatica L.) under changing conditions of the environment. Acta univ. agric. et silvic. Mendel. Brun. , 2010, LVIII, No. 4, pp. 23–30 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 Fores try 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 eff ective 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 eff ect 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. Eff ects of temperature on the onset and duration of the stage of budbreak and the beginning of foliage became evident in European beech most marked ly. 2007 was a very extreme year from the aspect of the early onset of spring vegetative phenological stages. In that year, a marked shi 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. phenological stages, climatic changes, weather, temperature sum, vegetative period, European beech, forest tree species A period of the onset and duration of phenological stages of forest trees is to a great extent de pen dent, except genetic factors, on outside conditions, particularly on meteorological factors. The beginning of fl ushing, leaf unfolding, bud developing and fl owering is usually possible when the air and soil temperature exceeds a certain critical point characteristic of every life stage of the plant cycle (LARCHER, 1995; BEDNAŘOVA, KUCERA, 2002). “Temperature sum” is the accumulated temperature above a certain threshold value from a certain starting date calculated by the progressive addition of mean daily temperatures. For the calculation of temperature sums, most commonly a threshold value is used, which defi nes the beginning of the thermal growing season, usually 5 °C. The temperature sum during the growing season is referred to as an eff ective temperature sum (LAPPALAINEN, 1994; DIEKMANN, 24 E. Bednařova, J. Kucera, L. Merklova 1996; BAGAR, NEKOVAŘ, 2007). Phenological observations can characterize a climatic region with a mean length of the growing season taking into account ecological properties of forest trees (LUKNAROVA, 2000). Depending on changes of weather under given climatic conditions we can evaluate also trends in changes of climate on the basis of monitored changes in phonological stages. Expected climatic changes and related negative factors can aff ect the course of basic life phenomena of plants, par ticu lar ly of forest ecosystems (KRAMER, 2000; LUKNAROVA, 2002; SKVARENINOVA, 2005). With respect to possible climatic changes, it is necessary to obtain further more detailed information on growth processes of forest trees both existing and those, which were autochthonous on the given site. Thus, with respect to monitoring the microclimate and phenology of a stand to contribute to explain ecophysiological factors (BAGAR et al., 2001). The moni to ring of phenological stages of cultivated and wild plants and their evaluation can provide the signalling of ingoing climatic changes. Due to warming, changes in the development of forest trees and herbs can also occur. Thus, plants can be con si dered as bioclimatic indicators and phenological observations can be used for assessing eff ects of potential climatic changes (KOCH et al., 2005; SKVARENINOVA et al., 2006). Conditions of the successful use of phenology in problems of the evaluation of climatic changes consist in long time series and possibilities to compare various localities and the knowled ge of relationships between temperature and a similar change in a corresponding temperature series in the course of time KOCH et al., 2005). MATERIAL AND METHODS Monitoring the phenology of European beech (Fagus sylvatica L.) is carried out at this locality since 1991. To specify data obtained, the study was completed (in 2007) by data aimed at monitoring spring phenological stages using a camera system. The research area is situated on the NE to E slope of a watershed ridge at an altitude of 625 m, the Drahanska vrchovina Upland geographical unit. The research area is determined by coordinates 16° 41 30 E long. and 49° 26 31 N lat. Climatically, the area is characterized as slightly warm and slightly humid with a long-term annual temperature 6.6 °C and 683 mm annual precipitation (KOLEKTIV, 1992). The actual situation of the locality is characterized on a Fig. 1. Phenological observations were carried out according to adapted methods of the CHMU (Czech Hydro-Meteorological Institute) (1987) in nine selected sample trees. During the spring season (March to June), phenological observations are carried out 3 times a week. In the summer and autumnal season, once a week. To a date of particular phenological stages, an ordinal number was assigned of a day from the beginning of a calendar year. To each of the phenological stages, sums of mean daily air temperatures were calculated at a threshold value of 0 °C and 5 °C (TS 0 °C, TS 5 °C) and sums of the soil temperature at a threshold value of 0 °C and 3 °C (TSp 0 °C and TSp 3 °C). In the monitored stand, sensors are installed to measure air temperature (Datalogger Minikin T) on the lower limit of the tree crown. The soil temperature at depth of 25 cm (Microlog SP), are another measured characteristic. Parameters of the environment are characterized using instruments of the Environmental Measuring System, Brno (EMS Brno). Camera – a programmable photographic modu le used for the detailed monitoring of pheno400 500 600 700 800 90