Environment drives spatio-temporal patterns of clonality in white spruce (Picea glauca) in Alaska

Wuerth, David; Eusemann, Pascal; Wilmking, Martin; Roland, Carl

Many plant species reproduce by cloning, if environmental conditions are unfavorable for sexual reproduction. To test the alternative hypotheses whether cloning is an “exit strategy” or caused by selection, clonal growth in white spruce (Picea glauca (Moench) Voss) was investigated in three stands in Alaska, each consisting of a core (closed forest) and an edge (treeline) plot. A total of 2571 trees were mapped and genotyped with 11 SSR markers. The proportion of clonal trees follows a moisture gradient and was lowest in the dry Interior basin (4.5%), followed by the sites at the Alaska Range (9.0%) and Brooks Range (21.7%). At the two latter sites, clonal growth was more frequent in the edge plot. A comparison among 960 aged trees revealed that clonal growth becomes more likely with increasing age and continues over the life span of a tree. Genetic data do not indicate any genetic predisposition for cloning. Most likely, clonal growth in white spruce takes place via layering and depends on environmental conditions. Since performance of the trees, and therefore likely plant reproductive success, is lower in plots with a high proportion of clones, selection for clonal growth seems to be highly unlikely.