PROSTORNA I VREMENSKA VARIJABILNOST CVJETANJA HRASTA LUŽNJAKA (Quercus robur L.)

Climate change, as well as biotic and abiotic stress environmental factors and the exploitation of oak forests have the greatest impact in reducing the pedunculate oak areas. These factors on one side reduce the pedunculate oak living area, while on the other side they create unfavorable conditions for its renewal. In the last decades, there has been an attempt to change this situation, primarily by planting appropriate provenances and more resistant varieties. Knowledge of the phenological variability is one of the essential elements useful in separation of genotypes better adapted to changing environmental conditions.One of the phenological studies of the pedunculate oak implied the analysis of the pollination time as one of the intermediate phase of the flowering phenophase. Observations were carried out in two populations at two locations in the area of Belgrade (Serbia), "Ada Ciganlija" and "Bojčinska šuma", a total of 58 trees (29 trees per location) in three consecutive years (2004, 2005, 2006). According to the ANOVA results differences between locations and years were statistically significantly (all p <0.0001). Time of pollination in the location of "Bojčinska šuma" was earlier compared to location "Ada Ciganlija" in all three years of observation. The obtained time difference gives rise to the assumption that there are different varieties of the pedunculate oak: the "early" and the "late" one. According to the phenological pattern of population, the majority of trees maintain the same trend from year to year, i.e. remain in the same phenological group (labeled as "early", "average" and "late"), or change it for one phenological level, suggesting the genetic influence on the expression of this trait. Since those populations are located in similar environmental conditions, obtained differences between them can be regarded as a consequence of intraspecific variability of the pedunculate oak and of the genetic structure of population.U radu je analizirana individualna i populacijska varijabilnost polinacije kao međufaze fenofaze cvjetanja lužnjaka. Istraživanja su obavljena na 58 stabala u dvije populacije lužnjaka na dva lokaliteta na području Beograda (Srbija) tijekom tri uzastopne godine (2004, 2005, 2006). Populacije se nalaze u oblasti umjereno-kontinentalne klime, na staništima koja odgovaraju lužnjaku, mješovite su strukture, raznodobne, vegetativnog i sjemenog porjekla, starosti 60–120 g. Promatranje je vršeno jedanput tjedno u travnju/svibnju. Lužnjak na analiziranim lokalitetima, uzimajući u obzir sva stabla i godine promatranja, počinje cvjetati najranije 7. travnja a najkasnije 2. svibnja. Cvjetanje na lokalitetu "Bojčinska šuma" događa se oko tjedan dana ranije u odnosu na lokalitet "Ada Ciganlija". Statističkom obradom potvrđen je značajan učinak lokaliteta, godine i individue. Prema fenološkom obrascu populacija i podeli u odnosu na vrijeme cvjetanja, većina stabala na lokalitetu "Bojčinska šuma" pripada fenološkoj grupi "rani" lužnjak, a na lokalitetu "Ada Ciganlija" grupi "kasni" lužnjak. Tijekom godina promatranja, najveći broj stabala ostajao je u istoj fenološkoj grupi ili se mijenjao samo za jednu razinu. S obzirom da se populacije nalaze u sličnim sredinama i stanišnim uvjetima, dobivene razlike mogu se smatrati posljedicom unutarvrsne varijabilnosti lužnjaka i genetičke strukture populacije. Genetička stabilnost fenofaze cvjetanja korisna je u odabiru "ranih" i "kasnih" formi lužnjaka u procesu individualne selekcije pod utjecajem promjene klimatskih čimbenika