Ever since it's Renaissance beginnings up to modern times, today's area of Arboretum Trsteno is marked by a natural and cultural (anthropogenic) component. The natural part of the Arboretum is recognized by its natural and cultivated vegetation and the cultural part by its gardens and buildings.
In their intertwining both components show "how man perfected wildlife" and achieved a harmonious, pleasant and culturally and historically valuable environment. Despite earthquakes, fires, wars, and lack of funds for a thorough restoration and high quality maintenance programme, the five-century-old land estate complex with the features of an Arboretum has managed to survive. Current and planned activities aimed at renovation and improvements are a contribution to the permanent preservation and sustainability of Arboretum Trsteno.
In terms of geography, most of the Arboretum is located on a plateau where there is a Renaissance-Baroque garden with a summer villa and ancillary buildings, a historicist garden on Drvarica, an olive grove, a natural downy oak forest (Quercus pubescens Willd) and areas for forestry experiments on the site of a former vineyard. A very steep, rocky terrain descends to the sea and a stream flows along the eastern border of the Arboretum, as well as along its central part.
Phytogeographicaly, Trsteno lies in the southern area of the Eumediterranean vegetation zone of the Mediterranean-littoral vegetation belt of the Mediterranean vegetation region. A mixed forest of holm oak and flowering ash (Fraxino orni- Quercetum ilicis Horvatić /1956/ 1958) is developing in this area. Nine plant communities of greater cover and three fragmentarily developed communities were identified. Said communities belong to forest, grassland, weed and ruderal vegetation, halophytic vegetation of coastal reefs and to vegetation of walls and rocks. The most common is the forest vegetation which covered about three quarters of the Arboretum before the fire in the year 2000. In the western part these were stands of Aleppo pine and cypress developed on the basis of garrigue, which have returned to their original plant formation after the fire through natural regeneration. In the eastern part of the Arboretum forest vegetation was developed with laurel as the predominant species, where it also covers most of the Renaissance garden. The phenomenon of mixing of species of the Eumediterranean and sub-Mediterranean vegetation zone is observed here as a distinctive feature of the vegetation of the Arboretum. The south-eastern part of the Arboretum forms a very steep and rocky slope with distinctly Eumediterranean garig vegetation and fragments of extra zonal vegetation of the Ionian-Aegean zone, as one of our few localities of woody spurge (Euphorbia dendroides L.).
The pronounced diversity of the vegetation cover of the Arboretum is manifested not only by the presence of twelve plant communities on only 25.61 ha, but also by the presence of numerous plant species. New dendroflora research conducted in the Arboretum in 2018 identified 317 wood taxa (233 species, 8 subspecies, 2 varieties, 10 hybrids and 64 cultivars) which belong to 179 different genera from 82 families. The gymnosperm has 19 taxa and the angiosperm has 298 taxa. The Arboretum is a significant collection of dendroflora with 84 indigenous, mostly Mediterranean woody species and subspecies. Of the species and subspecies that grow in nature exclusively outside the European continent 64 are Asian species, 45 are American, 14 African and 5 Australian. The Arboretum also houses valuable collections of olive cultivars, citrus trees, grapevine cultivars, palms, yuccas, aloae, cacti, bamboos and woody geraniums.
The first recorded inventory of plant taxa in the Arboretum was conducted in 1953 when 226 taxa were identified. In 2018 317 taxa were recorded in the Arboretum, which indicates an increase of 91 taxa. The Arboretum has preserved 148 taxa that have been there since 1953.
The oriental plane tree (Platanus orientalis L., trunk diameter 565 cm, height 36 m), cypress (Cupressus sempervirens 'Stricta', height 35 m), Aleppo pine (Pinus halepensis Mill., height 35 m) and American lime tree (Tilia americana L., trunk diameter 110 cm, height 35 m) stand out between the large and old trees.
The richness of the plant world, as well as the richness of the biocenoses, is not of original origin here but was created over five centuries as a result of the coordinated "cooperation" of man and nature. Nature has provided a wealth of ecological factors and man has invested much effort, work, and knowledge. Over the centuries man gradually changed the characteristics of the terrain, considering and respecting the natural laws of stone, soil and water. Although man has removed natural vegetation and planted and cultivated species in its place, he worked in harmony and balance with ecological factors and created new ecosystems which he maintained through his work, supported by nature.
