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ŠUMARSKI LIST 7-8/2014 str. 22     <-- 22 -->        PDF

for two levels (0.0 %). In the location of "Bojčinska šuma" also most of the trees changed the group for one level (62.1 %), whereas significantly fewer trees changed the group for two levels (37.9%), and there were no trees without the group change (0.0 %). According to total results, in the location of "Ada Ciganlija" all trees (100.0 %) kept the same trend from year to year, or they changed in only for one level. In the location of "Bojčinska šuma" all of trees (100.0 %) changed its group for one or two levels (Figure 4b).
Among those trees that, over the years of observation, have not changed phenological group in the "Ada Ciganlija" location (41.4 %), there have been mostly late flowering trees (70.0 %), early flowering have been 20.0 %, and 10.0 % of the intermediate ones. In the "Bojčinska šuma" location there have been no trees that, over the years of observation, showed stability and remained in the same phenological group.
According to the Annual Report of Republic Hydrometeorological Service of Serbia there has evidently been a slight rise in temperature in Belgrade area during the last 110 years. Also, the abrupt and sudden changes typical for the amount of precipitation have been noticeable (Table 1). Analyzed period of phenological observation in this paper (2004, 2005, and 2006) fits the average of it (110 years), and there have not been any sudden changes to reflect on the phenological cycle.
Flowering time mostly depends on the species and areas in which it develops, and also on the climate, mostly temperature and precipitation (Bednorz and Urbaniak, 2004; Figueiredo Goulart et al., 2005; Gomez-Casero et al., 2007; Franjić et al., 2011). The impact of latitude on an oak flowering is best illustrated by the following examples. Flowering of several oak species in the area of Spain (37° 26´ N) takes place from 26th February till 17th April (Quercus sp., Garcia-Mozo et al., 2000), or in the second half of March (42° 15´ N), and in the area of Italy (43° 06´ N) during the last two weeks of April (Quercus robur, Q. suber, Q. ilex, Q. pyrenaica, Q. pubescens, Rodríguez-Rajo et al., 2003). In northern areas, in Slovakia (48° 38´ N) oak flowering occurs about 10th May (Quercus robur, Škvareninová et al., 2008), and even more in the north, in the area of Germany (53° 39´ N) it happens even later, from 8th till 20th May (Quercus robur, Schueler et al., 2005). According to results presented here, oak flowering (Quercus robur) in Serbia (44° 49´ N) occurs between 7th April and 2nd May, which compared to the literature data corresponds to the coordinates of the study area.
There is not much data about oak flowering in natural populations in the area of Serbia. According to Erdeši (1971), in south-western Srem oak flowering occurs between 8th April and 23rd May, with a difference among individual trees of 2–6 weeks on which basis has been allocated 4 varieties: var. robustissima: 8.04.–30.04.; var. typica: 11.04.–5.05.; var. tardiflora: 25.04.–9.05. and var. tardissima 10.05.–23.05. Compared to the above mentioned literature data and results presented here, analyzed pedunculate oak in the Belgrade area would belong to the earliest flowering forms of var. robustissima. However, it should be also taken into account that recorded slight rise in temperature since the beginning of the last century, certainly had an impact on a certain shift and earlier beginning of the pedunculate oak vegetation. Climate data (Popovic et al., 2009) and the value of the rain factor for the analyzed area in the last decade compared to data for the period of half a century ago (Radulović, 1982) point to climate change in the direction of increased aridity. Bearing in mind above mentioned constatation about the trend of moving vegetation forward, comparing with early and late phenological forms should be taken with some caution. From this point of view it would have been very useful and interesting to make a review of the pedunculate oak phenology in the same populations in which Erdeši (1971) conducted observations 40 years ago.
Analyzed pedunculate oak expressed an individual variability of flowering. A significant difference between trees with the earliest and the latest flowering in the location of "Ada Ciganlija" confirms this statement, as well as that it was more pronounced in this location. In the location "Ada Ciganlija"