Factors Responsible for Rapid Diminishing of Endangered Grass Plant Elymus farctus subsp. boreoatlanticus in Phytocoenoses on Dunes Coast of Baltic Sea

Sand couch-grass Elymus farctus (Viv.) Runemark ex Melderis subsp. boreoatlanticus (Simonet & Guin.) Melderis is a species of psammophytic perennial grass which grows on low embryo dunes, less frequently on white dunes, on a sandy substrate which is rich in chlorides, with a neutral or alkaline pH. The occurrence of E. farctus subsp. boreoatlanticus was confirmed on the Polish Baltic coast only in six stands out of 20 quoted in the 19th century and at the beginning of the 20th century, and the species is classified as critically endangered (CR). One of the largest populations of that species is situated on the Wolin Island (the Baltic Sea, west coast of Poland). The population of this species was monitored between 2015-2017 in the habitat of initial white coastal dunes (Nature 2000 site, code 2110), where the sand couch-grass is a characteristic species of Honckenyo-Agropyretum juncei R.Tx. 1955 plant association. The results of the conducted research show that the main reason for the rapid decline of the population of Elymus farctus subsp. boreoatlanticus on the western coast of Poland is recreational use of beaches, which is growing in an uncontrollable manner and puts pressure on this habitat, followed by complete destruction of psammophilous and halophilous vegetation. In addition, impact from marine abrasion inhibits the development of white coastal dunes where E. farctus subsp. boreoatlanticus occurs, and intensive aeolian sand accumulation hinder the regenerative ability of shoots and significantly limit vegetative reproduction.