Invasion of Rosa rugosa (Rugosa Rose) into coastal plant communities of Brier Island, Nova Scotia

Résumé

During August and September 2010, we surveyed the entire 20.4 km perimeter of Brier Island, Nova Scotia, for the invasive shrub Rosa rugosa (Rugosa Rose). This island in the outer reaches of the Bay of Fundy of Nova Scotia is geographically isolated and relatively undeveloped. Our objective was to determine the extent and mechanism of the invasion of R. rugosa into different coastal habitats to gain insight into the potential threat to native biodiversity from the unchecked population growth of this monopolizing, rank shrub. Over 300 colonies of R. rugosa with mean height over 1 m occupied 2089 m of the island perimeter within 10 m of the top of the beach. The mean distance between colonies was about 61 m and the maximum distance was 1927 m. At least 33 colonies formed almost impenetrable walls, each over 10 m in length, and 2 colonies occupied about 500 m² each. Rosa rugosa had greatest density on a sand–gravel beach on which 88 colonies occupied 22% of the area and 33% of the beach margin. Exponential growth of the population (inferred from aerial photographs from 1970, 1988, and 2000) may be due to the various systems of seed dispersal. Agents include primary (American Mink, Neovison vison, and Red Squirrel, Tamiascurius hudsonicus) and secondary (an unidentified rodent) biotic dispersers. Longer distance dispersal may include Coyotes (Canis latrans), off-road vehicles and deposition of fruits by currents and waves. The main sites of seedling establishment are native habitats, such as dune grass and seashore Seaside Plantain (Plantago maritima) zones, albeit modified by this exotic rose. Dispersal of colonies contradicts a hypothesis of dispersal from human habitation along roads and tracks to the coastal habitats. We conclude that R. rugosa is having a significant impact on marine coastal plant communities and has the potential to dominate windswept shrub habitats on coastlines of much of Nova Scotia.