Current state and historical notes on sand dune flora of the Bulgarian Black Sea Coast

This study is the first overview of the floristic diversity of Bulgarian coastal dunes in terms of the presence of typical psammophytic or non-psammophytic plant species. It also aims to reveal changes in sand dune flora over time, based on own samples and existing data from previous studies. Our original floristic data was extracted from 154 phytosociological plots sampled in 12 large dune systems during 2017. All available literature sources were compiled to derive a list of vascular plants recorded for Bulgarian coastal dunes between 1905 and 2016. Due to the different scientific approaches applied in previous publications we split the studies into three periods over time: (I period: 1905 1950; II period: 1951–1990; III period: 1991–2016), and separate lists were also prepared for each. All vascular plants were assigned to one of five groups, according to their general habitat preference: 1) psammophytes, 2) weeds and ruderals, 3) grass- and shrubland plants, 4) forests plants and 5) alien (including invasive) species. The full species list comprises 501 taxa, and the highest number of species was compiled from publications after 1990. Across all periods and studied dune complexes, grass- and shrubland plants were most abundant, while other non-psammophyte species groups showed low presence. A comparison of data from 2003 and 2015 showed that species richness of psammophytes decreased over time, which is in contrast to the average number of weeds and ruderals, and particularly to species richness of grass- and shrubland species. Our results show that a core group of characteristic psammophytes remains constant through all study periods. Alien (including invasive) species still are limited in abundance but there is an alarming recent increase in their numbers. We believe that our synthesis will be of use for further floristic inventories of Pontic sand dunes.