Invasion of Rosa rugosa in Danish coastal dunes
The invasive shrub Rosa rugosa (Rosaceae) constitutes a considerable threat to coastal dunes of North-Western Europe because it suppresses natural vegetation of high conservation value. R. rugosa is a shrub originating from China and Japan which became a popular garden plant in Europe at the beginning of the 20th century due to its tolerance to wind, poor soil conditions and salt. In Denmark where the species is most problematic, R. rugosa was widely planted in the 1950s when summer cottages along the Danish coastline became popular.
All R. rugosa patches superior to 0.01 m² have been mapped in an area of 2364 ha of semi-natural dunes of Northwestern Denmark. This study revealed that R. rugosa was found in all the major vegetation types, but was most common in white dunes, and less abundant in grey and brown dunes. This is explained by the fact that white dunes in the area studied have a higher pH and are slightly richer in soil nutrients than inland dunes. For this reason the white dunes represent more suitable habitats for R. rugosa than grey and brown dunes, as R. rugosa is not limited by wind, salt spray and moving sand layers. As a result of both natural and anthropogenic processes, it was observed that the invasion of coastal dunes by R. rugosa was associated with the coastline, roads, paths, and houses. Seeds and vegetative fragments of the plant are transported by water and wind, and thus most propagules may be deposited close to the coastline.
With respect to habitat stress, R. rugosa is most common along protected coasts of the Baltic Sea and in inner fjords in Denmark where salt concentrations are lower. Thus, the higher abiotic stress of the North Sea coast may delay invasion by R. rugosa.
Sources
Halfdan Jørgensen R, Kollman J (2009) Invasion of coastal dunes by the alien shrub Rosa rugosa is associated with roads, tracks and houses. Flora 204, 289-297