Dendrological characteristics of the Trsteno Arboretum.
The Trsteno Arboretum, managed by the Croatian Academy of Sciences and Arts, is a former land estate with gardens, old olive groves and natural vegetation. It is a protected site of natural and cultural goods of the Republic of Croatia. The history of its land estate can be traced back to the year 1494, while the Arboretum itself was established in 1948 over 28 ha. It has been 65 years since the first list of plants in the Arboretum was drawn up. In order to determine the current wealth of woody taxa, the plants were documented during 2017 and 2018. A dendrological analysis was made and the present richness of the woody plants was compared to the literary data from the middle and the end of the 20th century and the beginning of the 21st century. Currently, the Arboretum contains 317 woody taxa, of which 233 are species, 8 subspecies, 2 varieties, 10 hybrids and 64 cultivars (Table 1). The taxa belong to 179 different genera from 82 families. The gymnosperms are considerably less represented with 19 taxa, and the rest are angiosperms (298 taxa). Slightly more than a quarter of the species and subspecies are autochthonous in Croatia and are predominantly Mediterranean species. The Trsteno Arboretum is the only littoral arboretum in Croatia which supports important collections that preserve and represent the Croatian dendroflora. As a guardian of biodiversity, the Arboretum has an important educational and scientific role for both Croatian and foreign visitors. The majority of the exotic species and subspecies, that is, those which occur exclusively outside the European continent, are of Asian origin (64 species), followed by the species from the area of America (45 species), Africa (14 species) and Australia (6 species). There is a large number of particularly valuable taxa that are unique to or rarely present in Croatia, such as Acacia cyclops A. Cunn. ex G. Don, A. karoo Hayne, Albizia amara (Roxb.) B. Boivin, Callitris preisii Miq., Casuarina cunninghamiana Miq., Persea indica (L.) Spreng., Retama sphaerocarpa Raf., Schinus weinmannifolius Engl. and Vitex negundo var. heterophylla (Franch.) Rehder. Besides the particularly valuable individual examples of some species, the Arboretum also boasts collections that include species, hybrids and cultivars of various genera. Since the first plant list was drawn up, new taxa have continuously been introduced into the Arboretum, making it wealthier and more diverse in species than 65 years ago. This was achieved by enriching the collections of particular genera, but also by revising previous documentation, which brought to light numerous old cultivars, such as those in the genera Olea, Citrus, Aloe, Pelargonium and others. The genus Olea is represented by a collection of 15 old autochthonous olive cultivars from the area of Dubrovnik, and the genus Citrus with 10 autochthonous and 8 more recent citrus cultivars. This is a valuable contribution to the preservation of the genofund of historical autochthonous Croatian cultivars. Over the past 65 years, the total number of taxa has increased from 226 to 317. The number of taxa which have survived in the Arboretum until the present day is 148, meaning that of the present 317 taxa, slightly less than half were in the Arboretum 65 years ago. Of the 226 taxa present in 1953, 74 taxa have disappeared from the Arboretum as a result of a number of different factors, including the climate, growing conditions, fires, but also diseases and pests. The majority of the changes occurring in the Arboretum since 1953 took place before 1998. For future maintenance and development of the Arboretum in the sense of regenerating the taxa that have disappeared or introducing new taxa, the facts mentioned above should be of particular concern. Exotic plants from warm regions of other continents are generally well adapted to the site conditions in the Arboretum, but they sometimes perish owing to extremely low temperatures lasting for several days. The eight oldest living trees in the Arboretum were planted in the period between 1858 and 1871: Ginkgo biloba L. (1858), Tilia americana L. (1858), Taxus baccata L. (1859), Diospyros virginiana L. (1859), Wisteria sinensis (Sims) Sweet (1861), Ginkgo biloba L. (1861), Platanus orientalis L. (1868) and Cedrus libani A. Rich. (1871). The Trsteno Arboretum is the only Croatian arboretum that is managed by a scientific institution - the Croatian Academy of Sciences and Arts, and it fulfils all the requirements set before a historical arboretum in the modern world.