Dune Restoration Introduces Genetically Distinct American Beachgrass, Ammophila breviligulata, into a Threatened Local Population

There is mounting concern over the source and genetic history of plant propagules used for habitat restoration because introduced genotypes may destabilize remnant local populations through competition and introgression. We examined whether introduced dune grass, Ammophila breviligulata, from Michigan is genetically distinct from a threatened local Minnesota population by comparing local and nonlocal genotypes in well-established stands in the field and in experimental common gardens. Both observational and experimental studies suggest that Michigan plants differed genetically and had an advantage over local plants in terms of vegetative spread and sexual reproduction. Well-established restoration populations composed of Michigan plants produced fertile culms that were 1.8 times taller than Minnesota plants and more than twice as fecund. Introgression is unlikely, however, because Minnesota genotypes flowered on average 6.7 weeks earlier than Michigan plants and only 20% of Minnesota pollen remained viable after 4 weeks. In the common gardens, Michigan plants from two sources were larger in size, grew faster, and flowered more frequently than Minnesota plants. Plant surveys across the study area suggest that nonlocal genotypes have spread beyond documented restoration areas and into local stands, particularly in foredunes. Even if gene flow between local and nonlocal plants is limited due to differences in flowering phenology, Michigan genotypes may out-compete plants in the threatened Minnesota population through greater vegetative and sexual reproduction. The fitness consequences of this change in the genetic composition of the local population have yet to be determined.