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ŠUMARSKI LIST 7-8/2014 str. 18     <-- 18 -->        PDF

or extinction of certain species (Alberto et al., 2011). Therefore, maintaining high genetic variability is a valuable resource for the adaptation of species that takes place through the process of conservation of genes and the process of mating (Baliuckas and Pliura, 2003; Aitken et al., 2008).
Global warming and climate change was recorded in the area of ​​Serbia as well (Figure 1). In the period 1971 - 2000. there has been registered an upward trend in the mean annual temperatures that caused an average shift of the beginning of the spring and summer by 2.5 days per decade (Popović et al., 2009). Changing the time of the beginning of seasons directly affects the phenophase of flowering, and therefore it is important to study this phenophase as a part of the reproductive biology of species (Gomez-Casero et al., 2007). The change of environmental factors also influence the variability of phenophase occurrence (start, end and duration), at a population level and an individual level as well. Individual variability in the beginning of the occurrence of certain phenophases, or their duration, is useful for the selection of plants for resistance to temperature extremes (Gološin et al., 2005), and to pathogen impact (Klaper et al., 2001), and it makes species more potential to adapt to new climate change and thus contribute to its survival. Uniformity of flowering time between the selected individuals is one of the conditions that guarantee the production of seeds of genetically better quality which should be taken into account in the establishment of seed plantations (Franjić et al., 2011). Beside selection, practical importance of the phenological research is to make prediction models of expected changes for the needs of urban ecology, allergology and agrometeorology (Richardson et al., 2006; Šestan, 2012).
The beginning and duration of phenophases largely depend on the temperature, and then on the photoperiod, precipitation, radiations, CO2 increase, etc. (Kremer, 2002; Hájková et al., 2010; Hanousková, 2010). According to the model predictions of climate change if at the end of the 21st century there was a duplication of CO2 in the air, the oak pollen season would begin a month earlier (Garcia-Mozo et al., 2006). Phenological rhythm also depends on the local changes in the weeks right before the activation of a phenophase (Badeck et al., 2004; Bednorz and Urbaniak, 2004).
The aim of this research was to define the pattern of all three flowering phenophases among and within analyzed locations i.e. populations, as well as the monitoring of changes during three successive years. In this context, there has been searched for the answers to the following questions: Is there a difference in pollination as a part of flowering phenophase among locations for each of the years analyzed; Is there a difference among years for each of the locations analyzed; What is the phenological pattern of the analyzed populations compared to the percentage presence of trees with different flowering time; And whether the trees remain in the same group ("early", "average", "late") each year or they change it?
Materijal i metode
Species – Vrsta
Pedunculate oak (Quercus robur L.) belongs to a very numerous and important genus Quercus, family Fagaceae (Nixon, 1993). It is one of the most respected forest tree species, whose areas have been significantly reduced in the last century (Thomas et al., 2003; Balboa-Murias et al., 2006; Broshtilov, 2006; Helama et al., 2009; Tikvić et al., 2011). It occurs in the temperate zone of the northern hemisphere, in almost all of Europe. In Serbia, the largest areas under