大雪山北部東斜面の森林限界高度における気温状況 Air Temperature Conditions at the Forest Line Level on the Eastern Side of the Northern Daisetsuzan Mountains, Central Hokkaido, Northern Japan

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北海道中央部に位置する大雪山の北部東斜面の森林限界(標高1700m)で気温観測を行った.その結果,森林限界の年平均気温は,1995年に-1.9°Cであった.また,平年値に近い1995年暖候期の気温から求めた温量指数は18.3°C・月であり,吉良が示した森林限界め温量指数15°C・月を上回る.観測点付近の温量指数15°C・月の高度は標高1823mと推定される.一方,この森林限界とほぼ同高度にある大雪山中央部の風衝地(標高1710m)では,年平均気温が森林限界よりも1.0°C低く,不連続的永久凍土帯の気温に相当する.また,温量指数は13.8°C・月であり,15°C・月の高度は標高1658mと推定され,温量的にもこの風衝地は高山帯とみなせる.ほぼ同高度にある両地点で見られた気温状況の違いは,積雪や植生など地表面付近の気温支配要因の差によるものと考えられる.

In Japanese mountains, the altitude of the forest line is often controlled by factors, such as thermal conditions, prevailing wind, and superficial deposits. The vegetation above the forest line of high Japa-nese mountains is characterized by the <i>Pinus pumila</i> community which essentially belongs to the upper part of the forest zone. The vegetation is different from that of high European mountains which are characterized by conifer krummholz. From this vegetational point of view, the existence of the alpine zone in vertical distribution such as in high European mountains is sometimes not the same as in Japan. The area above the forest line in high Japanese mountains, however, nearly corre-sponds to the periglacial area. Therefore, when natural phenomena in the upper part of the forest line of high Japanese mountains are studied from the viewpoint of climatic geomorphology, it is impor-tant to clarify the controlling factors and the current climatic conditions of the forest line.<br> In this study, air temperature observations were carried out at the forest line of 1, 700 m a.s.l. (Ginsen-dai observation site) on the eastern side of the northern Daisetsuzan Mountains, and the air tempera-ture at the wind-blown site of 1, 710m a.s.l. (Takanegahara observation site) on the main ridge run-ning north to south, about 7km SSW of the Ginsendai observation site, was also observed for the pur-pose of comparing the air temperature with that of the former site. The results of air temperature observations in 1993, 1994, and 1995 at the forest line, Ginsendai, are shown in Table 1. The annual mean air temperatures were -1.8°C in 1994 and -1.9°C in 1995. The mean air temperatures in the coldest month in 1993, 1994, and 1995 were -14.9°C, -17.9°C, and -16.0°C, respectively, and those in the warmest month were 12.5°C, 14.8°C, and 12.6°C, respec-tively. The monthly mean air temperatures from June to September in 1995, which were higher than the standard temperature (5°C) and were almost normal, gave a warmth index (WI) of 18.3°C •months at the forest line. This WI value exceeds 15°C •months of Kira's WI for the forest line in Japan.. The al-titude of WI 15°C •months around the observation site is estimated at 1, 823m a.s.l. This result sup-ports the proposal that the forest line of the Daisetsuzan Mountains is controlled not by thermal condi-tions but by other factors such as the prevailing westerly wind in winter or superficial deposits.<br> The results of air temperature observations from October 1992 to September 1993 at Ginsendai and Takanegahara are shown in Table 3. The mean annual air temperature at Takanegahara, a wind-blown site, was -3.0°C, lower than that at Ginsendai at the forest line by 1°C, which suggests that the thermal conditions of Takanegahara correspond to those of the discontinuous permafrost zone. The WI at Takanegahara is estimated 13.8°C •months, and the altitude of WI 15°C •months is 1, 658 m a.s.l. These thermal conditions indicate that Takanegahara clearly belongs to the alpine zone. The present forest line is situated at about 1, 500m a.s.l. around Takanegahara. Although both observa-tion sites are located at almost the same altitude, there is a conspicuous difference in thermal condi-tions between the two. This is considered to be caused by the difference in the controlling factors of tem-perature, such as snow cover and vegetation cover, on the ground surface which are influenced by the landform and prevailing wind conditions.<br> Around the main ridges such as Takanegahara strong prevailing winds in winter caused the alti-tude of the forest line to be lowered. Consequently climatic conditions equivalent to that of the alpine zone in terms of thermal condition are produced on the main ridge, where periglacial phenom-ena are distributed widely.

収録刊行物

  • 地理学評論. Ser. A  

    地理学評論. Ser. A 71(8), 588-599, 1998-08 

    The Association of Japanese Geographers

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各種コード

  • NII論文ID(NAID)
    10002222309
  • NII書誌ID(NCID)
    AN1016484X
  • 本文言語コード
    JPN
  • 資料種別
    SHO
  • ISSN
    00167444
  • NDL 記事登録ID
    4532747
  • NDL 雑誌分類
    ZG1(歴史・地理)
  • NDL 請求記号
    Z8-571
  • データ提供元
    CJP書誌  CJP引用  NDL  J-STAGE 
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