SEEDLING ESTABLISHMENT OF POLYGONUM-CUSPIDATUM AND POLYGONUM-WEYRICHII VAR ALPINUM AT HIGH-ALTITUDES OF MT FUJI

Seedling establishment of Polygonum cuspidatum (Seib. et Zucc.) and Po lygonum weyrichii (F. Schmit) var. alpinum (Maxim.), dominant early-su ccessional species in a volcanic gravel area on Mt Fuji, Japan, was co mpared for current-year seedlings at 2500 m a.s.l. The rate of surviva l in the first winter after germination at 2500 m was 2% and 24% for P . cuspidatum and P. weyrichii seedlings, respectively, and correlated with the upper distribution limit of each (2500-2600 m for P. cuspidat um; 3200-3300 m for P. weyrichii). The critical size for survival was 12 mg dry weight for overwintering current-year seedlings of both spec ies. At 2500 m, the percentage of seedlings that attained the critical size for survival at the end of the first growing season was 19% and 85% for P. cuspidatum and P. weyrichii, respectively. Growth curves in dicated that the larger-seeded characteristic of P. weyrichii contribu ted to larger end-of-season size and resulted in higher rate of seedli ng survival at 2500 m, compared with smaller-seeded P. cuspidatum. Cur rent-year seedlings of P. weyrichii, at least up to 3250 m, attained t he first year annual growth critical for overwintering and therefore f or successful seedling establishment, due to the large-seeded characte ristic. At the top (3770 m) beyond the upper distribution limit of P. weyrichii, most seedlings raised artificially failed to attain the cri tical size for survival in the first growing period due to the reduced growing period. Failure of seedling establishment would thus appear t o restrict the distribution of the species at altitudes higher than 33 00 m.