The Distribution of <i>Zelkova serrata</i> in the North-central Abukuma Mountains

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  • 阿武隈山地中北部におけるケヤキの分布
  • アブクマ サンチ チュウホクブ ニ オケル ケヤキ ノ ブンプ

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Abstract

Zelkova serrata is a tree species familiar to human beings, serving as building material or for the beautification of the landscape. Because of that it is sometimes very difficult to distinguish natural wood clusters of Z. serrata from man-made woods.<br> The north-central part of the Abukuma Mountains is characterized by gentle slopes like a peneplain. Z. serrata is scattered in the form of single trees or of patches, far from forest vegetation in the talus of ravines, which is considered typical of this species. The present paper discusses this remarkable pattern of distribution and clarifies its formative factors, especially from the viewpoint of edaphic conditions, and also throws some light on the possibility of human impacts influencing the habitat points.<br> The study area covers about 25 square kilometers in the north-central Abukuma Mountains. It was classified into three zones; zone M (monadnock zone) situated on the upper part; zone L (low-relief zone) on the lower part; and zone T (transitional zone) covering the middle part. Every tree with a diameter at breast height above 20 centimeters was surveyed, and its correlation with edaphic factors such as micro-landforms, springlets and surface material was investigated. Interviews were also carried with local inhabitants specializing in forestry.<br> The results are summarized as follows:<br> (1) Z. serrata occurs in several locations, such as inside of the natural or man-made forest, on the edge of the forest, and outside of the forest (for example, cultivated pasture). The evidence collected from interviews and documents about this region suggests that the origin of these Z. serrata is mostly the natural regeneration and not planting.<br> (2) From the viewpoint of edaphic conditions:<br> 1) More than about 65% of habitat points in each zone is related to springlets.<br> 2) In the M and L zones, more than about 70% of the surface of habitat points is occupied by unstable materials such as block or bedrock, gravel, and decomposed granite soil (transported type).<br> 3) The habitat points in zone M correspond mainly to ‘valley type-A’ and in zone L exclusively on ‘the toe of side slope of valley type-C.’ There is a similar environment (edaphic conditions) in both micro-landforms.<br> 4) In zone T, it is difficult to find a clear relationship between the habitat points and surface material and micro-landf orm factors.<br> Generally, the edaphic conditions in the study area are the same as in ravines.<br> The factor preventing the possible development of forest vegetation of Z. serrata is presumably a lack of sufficient extension of suitable land. It must be added that in zone L, in spite of the similarity of the edaphic conditions in two microlandforms of ‘valley type-A’ and ‘the toe of side slope of valley type-C, ’ Z. serrata rarely occurs in the former. This unnatural distribution may be caused by the different human impacts on each microlandform:the coppice administration has unfavorably influenced Z. serrata in ‘valley type-A, ’ while local custom has contributed to conserving this species on ‘the toe of side slope of valley type-C.’

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