Rosa rugosa as an invader of coastal sand dunes of Cape Breton Island and mainland of Nova Scotia.
Rosa rugosa is described for the first time as an invasive species associated with coastal sand dunes in Atlantic Canada. Our surveys of 24 beaches on western Cape Breton Island and the mainland of northern Nova Scotia from Cheticamp to Fox Harbour showed that 11 of the dune systems (ca. 45%) were colonized. This was more prevalent in Cape Breton where R. rugosa occurred on 9 of 13 systems, whereas only 2 of 9 mainland systems were colonized. Four dunes (three in Cape Breton) were considered heavily colonized with 0.4-8.8% of the dune area with cover of R. rugosa. These beaches had 12-42 independent clumps with almost monospecific stands over 90% cover. In general, heavily colonized beaches were found adjacent to communities where extensive domestic planting and hedges of R. rugosa occurred and where escapes onto roadsides had occurred. In most colonized beach systems, rhizomes from clones extended 1-5 m to produce younger shoots. The absence of Ammophila breviligulata, Lathyrus maritimus and Myrica pensylvanica, from the interior of many clumps of R. rugosa suggests that native dune communities are being negatively impacted. This exacerbates dune integrity already compromised by impacts of sea level rise.