Establishment and genetic structure of Empetrum hermaphroditum populations in northern Sweden

In late successions of the boreal forest of northern Sweden the evergreen dwarf shrub Empetrum hermaphroditum forms an extensive cover and is believed to spread mainly vegetatively through layering. To analyse the process of population establishment and the relative importance of sexual vs asexual reproduction and the spatial clonal distribution of this species we selected one mainland and two island sites of different post-fire successional ages (145, 375 and 1720 yr since last fire, respectively). Using 61 polymorphic RAPD markers, we found 96 genotypes in a total of 133 samples. All three populations showed high levels of genetic variation. AMOVA analysis revealed that 33% of the total variation resided among sites, 26% resided among plots within sites and 41% was due to variation within plots. The youngest population had only 14% clonal fraction. In contrast, the oldest population had > 30% clonal fraction and many genets had dimensions of 10-40 m and were intermingled. It appears that E. hermaphroditum establishes by seeds to a larger extent than previously thought and that the clonal spread by layering is rather slow.