Distribution and Habitat Preferences of the Invasive Alien Rosa rugosa (Rosaceae) in Archipelago Sea National Park, SW Finland

Rosa rugosa Thunb. is an invasive alien plant which was introduced from East Asia to Europe in the 19th century. Over the decades it has spread along the Finnish coast, including the archipelagos of the Baltic Sea. The shrub grows particularly along sandy beaches, stony shores and seashore meadows. There it leads to serious changes in coastal ecosystems and replaces native plant species. This paper presents the distribution and habitat preferences of R. rugosa in and near Archipelago Sea National Park in SW Finland. We identified 205 stands in the study area, 58% of them in protected areas. Systematic inventories do not cover the whole study area, so it is likely that dozens of stands remain undiscovered. Stands of the species were concentrated on the outer islands, where the archipelago’s most characteristic flora and fauna occur. Data on the shore type and area of all stands were collected. The total area covered by R. rugosa was 7277 m2 before control work started in 2008. The largest stand occurred on Örö Island, covering ca 2500 m2 before its eradication, and the median size of all stands was 6 m2. Five of the six largest stands were on sandy beach, but stony shore was the most common habitat type.