Relationship between distribution of large-diameter stems and topography in approximately 65-year-old secondary forest in the Yambaru area of Okinawa Island

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  • Takashima Atsushi
    Yona Field, Subtropical Field Science Center, Faculty of Agriculture, University of the Ryukyus
  • Oshima Junko
    Faculty of Global and Regional Studies, University of the Ryukyus

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Other Title
  • 沖縄島やんばる地域の約65年生二次林における大径木の分布と地形の関係
  • オキナワトウ ヤ ンバルチイキ ノ ヤク 65ネンセイ ニジリン ニ オケル ダイ ケイボク ノ ブンプ ト チケイ ノ カンケイ

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Abstract

<p>Because large trees are considered to be important for conservation of subtropical evergreen forest, we surveyed the relationship between distribution of largediameter stems and topography, in a small watershed of secondary forest, approximately 65 years old, in the Yambaru area of Okinawa Island. The density of stems with a diameter at breast height ≥ 30 cm was 91.0 ha-1 for all species, of which 65.2% were Castanopsis sieboldii, 20.9% were Schima wallichii, and 6.4% were Quercus miyagii. The density of large-diameter stems was less than half that found in a previous study that surveyed a mature non-clear-cut forest in the Yambaru area. We divided the target watershed into three zones (ridge, midslope, and valley)according to topography, and compared the zonal densities and sizes of large-diameter stems. The density of large-diameter stems on the ridge was less than half that in the valley and on the mid-slope. The stem sizes of C. sieboldii and S. wallichii were larger in the valley than on the ridge. Our results indicate that, in approximately 65-year-old secondary forest in the Yambaru area of Okinawa Island, large stems distributed around the valley zone. In addition, the small number of old large-diameter stems that escaped past logging were left in the valley and on the mid-slope. Therefore, the valley and the mid-slope are important topographic zones that might play a key role in ecosystem management and biota conservation, even in secondary forests.</p>

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