New records of the invasive alien Rosa rugosa (Rosaceae) in the Archipelago Sea National Park, SW Finland

Rosa rugosa Thunb. is an invasive alien species in Europe with negative ecological effects on biodiversity. In Finland it occurs especially in the coast and in the archipelagos of the Baltic Sea, where it replaces native plant species and causes overgrown of rare and threatened habitats, like sand beaches and seashore meadows. This study contributes new records of Rosa rugosa stands within the Archipelago Sea National Park and its surroundings in SW Finland. In total, the shores of 665 islands or skerries were inventoried systematically during the field studies in 2017 and 2018. We found 96 new occurrences of R. rugosa. The median size of new stands was 4 m2 and total they covered 698 m2 area. The most common habitat was stone shore (48 stands), but also shore meadows were also typical habitats (22 stands). Altogether 301 stands are now found from the study area. Distribution, stand sizes and habitats of naturalized R. rugosa are essential information for performing the control work of this invasive species. It is likely that dozens of stands are still undiscovered from the National Park area