Island population structure of Norway spruce (Picea abies) in northern Sweden

Picea abies, which is predominantly sexual, has been reported to propagate vegetatively through layering in a cold harsh climate, although this has not been demonstrated genetically. Using 105 amplified fragment length polymorphism markers, we analyzed 117 trees of Norway spruce from seven islands in Lake Hornavan in Lapland, northern Sweden. These islands differ in size, time since last wildfire disturbance, and vegetation successional age. A total of 96 distinct genotypes were identified among the 117 samples, and the average gene diversity was 0.37. Genetic differentiation among islands was high, F ^st = 0.19. Drift, founder effect, small population size, infrequent sexual reproduction, and low seedling establishment would have contributed to the high F^st. Layering was found on five of the seven islands, giving an average clonal composition of 18%. A total of 11 clones, each consisting of two to five closely clustered ramets, were detected. Interestingly, layering was more common on the small islands that have not been disturbed by fire for over 1000 yr than on the larger islands with more recent fire disturbance. Our results indicate that island size and ecological conditions related to fire disturbance history on each island are important for the observed patterns of population structure.