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ŠUMARSKI LIST 5-6/2018 str. 40     <-- 40 -->        PDF

Dalmatia: Dundo forest on the island of Rab, on Mljet and in Blato on the island of Korčula (Hirc, 1903-1912; Trinajstić, 2006). Moreover, individuals of Q. pseudosuber (= Q. crenata) were historically reported from many sites across Istria and the Kvarner region (Šijana forest, Strobl, 1872; Pericin 2001, Veruda forest, Freyn, 1877; Dragonja, Tinjan, Pazin, Mirna river, Lovran and Volosko, Ascherson and Graebner, 1908-1913; Pula and Volosko, Schneider, 1906; Cres, Hirc, 1916; Kvarner, Hayek, 1924; Cres and Rab island, kanjon Rječine, Lovrić, 1981), as well as from Dalmatia (Richter, 1897; Adamović, 1911; Hayek, 1924, 1927). Later, Trinajstić (2006) suggested that in fact all Q. pseudosuber individuals reported from Croatia belong to Q. suber and concluded that the taxon Q. crenata is not present in Croatian flora. However, our results provide clear evidence that Q. crenata individuals do occur in Croatia and confirm similar findings of previous studies (Lovrić, 1981; Cristofolini and Crema, 2005; Perinčić, 2010; Simeone et. al., 2009, 2013; Schirone et. al., 2015). For example, more recently Q. crenata was recorded in Zadar, nevertheless it was cultivated in the Vladimir Nazor Park which dates from the end of the 19th century (Perinčić, 2010; Nikolić 2017). Thus, it remains an open question whether this taxon could have been established in Croatia naturally or has been man-mediated. Based on similar findings of Q. suber and Q. crenata individuals on the eastern side of the Adriatic sea, several authors hypothesized that Q. suber first originated in the Eastern Mediterranean (probably surviving in the Balkan Peninsula), expanded westward and finally got extinct in the East Mediterranean (Bellarosa et. al., 2005; Simeone et. al., 2009; Schirone et. al., 2015). Under this hypothesis, Q. suber and Q. cerris would have been naturally co-occurring until a recent past, possibly giving rise to occasional hybridizations. However, up to date this scenario has not been generally accepted due to lack of strong scientific evidence and is a subject of ongoing debate (c.f. Magri et al., 2007).
The two “green oak” individuals included in this study did not show identical genetic patterns, indicating a different descent. If we assume an hybridogenic origin, the phylogenetic position of Q. × viridis from Rijeka, clustering among Q. crenata individuals from Slovenia and Trentino (Northern Italy) and Q. suber (Figure 3, Figure 4) suggest that, at least for the region of Istra and Kvarner, it is plausible to infer a natural origin of this tree, since both parental species (Q. cerris and Q. suber) grow in this area since, at least, four generations (Trinajstić, 2006). On the other hand, it is highly unlikely that the “green oak” from Islam Latinski (Zadar) is a natural hybrid of the two parental species, since Q. suber is absent from the surrounding area and the nearest known cork oak trees grow on the island of Rab (cca 90 km away), where they were planted at the beginning of the 20th century (Šurić, 1933), thus after the “green oak” individual was already established. Placement of this green oak individual in the phylogenetic relationships with Q. crenata from Latium in Italy indicates a possibility that this particular oak originated from this region where Q. crenata is particularly widespread. It was likely planted in the village of Islam Latinski a long time ago since long distance pollen dispersal from Q. crenata and /or Q. suber from Central Italy does not seem highly probable. However, extinction/progressive rarefaction of its wild, close-by relatives that were part of a common, little differentiated gene pool is also probable, and more extensive samplings would be clearly needed to accurately establish autochthony or the provenance origin of this important tree.
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