Growth and survival of current-year seedlings of Polygonum cuspidatum at the upper distribution limit on Mt. Fuji.

Seedling establishment of Polygonum cuspidatum Sieb. et Zucc. colonizing in a volcanic gravel area at 1,400 m and 2,500 m altitude on Mt. Fuji was compared. At the upper altitudinal limit (2,500 m) the average dry weight of seedlings at the end of the first growing season after germination was 24 per cent of that at 1,400 m. The proportion of seedlings, which survived the winter, was significantly (P<0.005) higher at 1,400 m than at 2,500 m. Seedlings in the range of 0-10 mg DW could not survive winter at any altitude. The survival rate increased with increasing seedling dry weight up to 100 per cent in seedlings with sizes more than 40 mg DW at 1,400 m. Seedlings from 2,500 m with sizes below 2 mg DW did not form perennation buds and were found to die before winter. Smaller seedlings in the range of 2-20 mg DW, even if they had buds, did not survive in the-15°C freezing resistance experiment. Larger seedlings (40-100 mg DW), which were grown in pots at 1,400 m and transferred to 2,500 m, survived winter those like as at 1,400 m. The difference in mean seedling dry weight between at 1,400 m and at 2,500 m was attributable to the difference in the length of the growing season and not to a different relative growth rate. It appears that there is a critical amount of annual dry-matter production necessary for full freezing resistance and winter survival capacity and therefore for successful seedling establishment.