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ŠUMARSKI LIST 9-10/2023 str. 21     <-- 21 -->        PDF

investigated for the first time in Croatia by Trinajstić (1987) on the island of Unije near Lošinj and on the islet of Veli Pržnjak near Korčula. The association has been described for some islets in the Zadar archipelago (Pandža & Milović 2017). Phoenician juniper macchia covers large surface areas throughout the entire southern coastal region of Croatia (Kovačić et al. 2001; Pandža 2004).
On the island of Rivanj 3 phytosociological relevés of the Myrto communis-Quercetum ilicis vegetation of the Fraxino orni-Quercion ilicis alliance were produced (Tab. 6, Fig. 3, Claster B). As shown in Table 6, a total of 20 species were recorded (relevés present 9-14 species, in average 12 species per relevé). Similar results were obtained through the analysis of floristic relevés from the island of Rava (Pandža 2008): in 11 phytosociological relevés there are 13 species per phytosociological relevé in average. As for the three phytosociological relevés from the island of Brač, 22 species (13 species per phytosociological relevé) were recorded by Trinajstić (1990). Regarding coverage the woody elements of the Quercetea ilicis class prevail: Pistacia lentiscus, Arbutus unedo, Viburnum tinus, Rhamnus alaternus, Phillyrea latifolia and Laurus nobilis in relevé 1. The macchia is thick and impassable so the number of companion species is quite small and their coverage insignificant. This association is common in the warmer and drier areas along the eastern Adriatic coast and islands (Horvatić 1963).
The Aleppo pine forests belong to the Pinetalia halepensis order that used to belong to the Quercetea ilicis class (Škvorc et al. 2017), but the Pinetalia halepensis order has been singled out as a separate class termed Pinetea halepensis (Bonari et al. 2020). Two phytosociological relevés were made (Tab. 7, Fig. 3, Cluster D) one of the islet of Sestrica Mala and the other on the island of Rivanj. In both relevés the Pinus halepensis species dominates within the tree layer where as the Pistacia lentiscus species dominates within the shrub layer. In addition to the Lentisk Pistache, species of the Quercetea ilicis class were also identified in the shrub layer. The Aleppo pines species on the islet of Sestrica Mala have been planted by lighthouse keepers. The pine trees have been spontaneously spreading towards the dock in the southwest. On the island of Rivanj the Aleppo pine vegetation grows on small areas and for the time being there is no significant spontaneous expansion of the pine vegetation into the surrounding natural vegetation, except in the case of fire. The association is widespread along the Adriatic coasts (De Marco et al. 1984; Trinajstić & Kamenjarin 2001).
CONCLUSIONS
ZAKLJUČCI
Rivanj Island has 346 vascular plant taxa. The total number of taxa represents about 6.71% of the Croatian vascular flora. There are 84 taxa under cultivation. The total flora of the island of Rivanj numbers 430 taxa. The flora has a Mediterranean character. It is dominated by plants with a Mediterranean floral element (42.77%) and the life forms are dominated by therophytes (43.93%). Four endemics and four endangered taxa were recorded in the vascular flora of Rivanj, of which Lathyrus ochrus is critically endangered. The flora includes five taxa from the orchid family (Orchidaceae). The above-mentioned taxa mostly occur in open habitats (grasslands and olive groves) that disappear due to the overgrowth of macchia. As succession processes advance, open habitats decrease, the number of species decreases, and thus decreases the total biodiversity of the island. In 2019 and 2020, the investigation of the shrubs and forest vegetation on the island od Rivanj and the Sestrice islets was conducted. A total of 30 phytosociological relevés were produced (tab. 5–7). Based on these relevés five associations (Erico arboreae-Arbutetum unedonis, Myrto communis-Pistacietum lentisci, Pistacio lentisci-Juniperetum turbinatae, Myrto communis-Quercetum ilicis and Pistacio lentisci-Pinetum halepensis). Since Horvatić’s investigations (1961–1962) the island has been depopulated (cutting and grazing ended) resulting in a strong natural progression towards primary forest vegetation. There are evergreen holm-oak woods, which can be considered as the potential vegetation type (Myrto-Quercetum ilicis).