Recent clonal reproduction of Cryptomeria japonica in a snowy region revealed by a survey of small-sized ramets

Clonal reproduction may contribute to population maintenance in areas where disturbance caused by snow limits tree recruitment. To understand the importance of clonal reproduction in the population dynamics of canopy tree species, it is necessary to determine the frequency of clonal reproduction in the early stages of seedling establishment. We found 106 ramets, including “small-sized” ramets of less than 5 cm in diameter at breast height, aggregated within 4 patches in a 70 × 50 m plot and also identified 20 genets among these ramets with the use of nuclear microsatellite markers. The size structure of the ramets revealed an inverse J-shaped distribution, suggesting that continuous recruitment of new ramets occurs. However, the number of intermediate-sized ramets (around 10 cm DBH) at the present study site was small, suggesting that most new ramets die while they are still small by pressure from heavy snow. Of the 20 genets, 12 included one or more small-sized ramets, which indicated recent recruitment. Of the 12 genets, 3 included only a single small-sized ramet, which suggested seedling recruitment, whereas the other 9 included multiple ramets (39 small-sized ramets in total), which indicated clonal recruitment. The frequency (9/12) and number (39/9) of recent clonal recruits suggest that clonal reproduction effectively maintains the population of Cryptomeria japonica in snowy regions.