Clonal structure and diversity of Cryptomeria japonica along a slope in a cool-temperate, old-growth mixed forest in the snowy region of Japan

Abstract

To clarify patterns of clonal growth along a slope for Cryptomeria japonica (L.f.) D. Don, which can regenerate by layering resulting from snow pressure, we analyzed the spatial genetic structure with respect to slope position and in relation to stem size in a cool-temperate, old-growth mixed forest in the snowy region of Japan. For the genetic analysis, five polymorphic microsatellite markers developed for C. japonica were used. Spatial autocorrelation analyses revealed a significant positive association of ramets (trees) with the same genotype as the result of clonal growth at around <6 m regardless of slope position for understory trees (≥50 cm stem length and <10 cm diameter at breast height (DBH)). This clonal patch size almost corresponded to the clustering scale for overstory trees (≥10 cm DBH) belonging to the same genet. For understory trees in three subplots established along a slope, the size distribution of ramets within a clone (genet) followed an inverse J-shaped distribution without small ramets being distributed peripherally. These results suggest that each clone of C. japonica is maintained continuously in a relatively restricted area where it establishes, regardless of slope position, which could contribute to the high clonal and genetic diversity of C. japonica in this forest.