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A floristic study of the islet of Ošljak, Zadar Archipelago (North Dalmatia)

The islet of Ošljak on the eastern Adriatic coast is a part of the Zadar Archipelago in the North Dalmatia. It is situated in the Zadar Channel between the city of Zadar and the island of Ugljan. The islet has an area of 0.34 km2 , with a coastline length of 2.25 km, and a maximum altitude of 89 m a.s.l. The lithology consists of highly permeable Cretaceous and Paleogene limestones. The climate is Mediterranean, with mild and rainy winters and hot summers (Csa type of the Köppen–Geiger climate classification system). In this Eu-Mediterranean zone, climazonal vegetation of holm oak (Quercus ilex L.) represents special value and a particular asset. In 1985, the islet was declared as the Significant Landscape. On the higher altitudes, macchia and the abandoned arable areas occur. On the eastern slopes, the Aleppo pine (Pinus halepensis Mill.) stands are developed. The Aleppo pine was planted especially after World War II. The flora of Ošljak is almost unknown. The oldest data date back to the early 19th century, when Host (Host in Visiani 1826) reported 15 plant taxa. Visiani (1842-1852) in Flora Dalmatica lists three other taxa: Arthrocnemum macrostachyum Moric.) C. Koch, Prasium majus L. and Teucrium flavum L. Until now, plant taxa list is not completed. The study was carried out from 2016 to 2022 in different seasons. Altogether, 350 taxa were recorded on the islet. Among them, several are endemics (Rhamnus intermedia Steud. et Hochst, Tanacetum cinerariifolium (Trevir.) Sch. Bip., etc.) and endangered taxa (Lathyrus ochrus (L.) DC. ; Critically Endangered taxon) and Salsola soda L. ; Vulnerable taxon). Several orchids (Orchidaceae) were also found, i.e., Limodorum abortivum (L.) Sw., Ophrys bertolonii Moretti, O. liburnica Devillers et Devillers-Tersch. and Serapias parviflora Parl. The present study offers a contribution to the knowledge of the insular vascular flora, a description of the vegetation units, and phytogeographical comments. The floristic data have been used to analyze life-form and chorological spectra and to assess species- area relationship, the occurrence of islet specialists and to assess the risk of alien plant invasion.

Croatia, eastern Adriatic, floristic survey, islet, vascular plant richness

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