Factors affecting the vertical distribution of Betula platyphylla var. japonica and Betula ermanii on Mt. Neko in Nagano Prefecture, Japan
2010
Jiro, Otsubo, IDEA Consultants, Inc., Tsuzuki, Yokohama, Kanagawa, Japan | Shigeru, Mariko, University of Tsukuba, Tennodai, Tsukuba, Ibaraki, Japan | Ichiroku, Hayashi, University of Tsukuba, Sanada, Nagano, Japan
Betula platyphylla var. japonica and Betula ermanii segregate vertically at an elevation of approximately 1,850 m on Mt. Neko in Nagano Prefecture, Japan. B. platyphylla var. japonica and B. ermanii were the dominant species below and above this altitude, at which the mean-annual and growing-season air temperatures were 4℃ and 14.1℃, respectively. Based on a modification of Kira's warmth index which employs cumulative temperature represented as ℃ day, leaf unfolding in both species was observed to be initiated at 58℃ day and 169℃ day, respectively. In 1996, leaf unfolding was initiated on 18 May in B. platyphylla var. japonica (+/-6 days) and on 5 June in B. ermanii (+/-8 days), shortly after the last frost which occurred on 5 May 1995 above 1,850 m; below this elevation there was no risk of frost at the time. At elevations above 1,850 m, the unfolded leaves of B. platyphylla were damaged by late frost, while B. ermanii escaped injury because the leaves were still protected by winter buds. The optimum temperature for seed germination in both B. platyphylla and B. ermanii was 30℃. Temperature alternation from 10 to 30℃ and moist storage of seeds at 4℃ (stratification) prior to incubation increased germination rates in both species. The seedlings of B. ermanii had a greater survival rates than those of B. platyphylla var. japonica when planted above 1,850 m. Comparisons of the timing of leaf unfolding and the latest frost at a site appeared to be the main factors affecting the vertical distribution of these species.
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