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Vol. 14 (1997) No. 2 p. 105-117




The vegetation structure and soil properties of mixed deciduous broadleaf/conifer forest were studied on Mt. Horoiwa (376 m altitude), eastern Hokkaido, Japan. 154 grids (1 ha : 100 m×100 m) were set out on an aerial photograph of the study area, and their vegetation was classified into three types by ratio of conifer ; broadleaf, mixed broadleaf/conifer and conifer forests. Further, the topography of the grids was categorized into ridge, valley and slope, and the aspect of slopes was determined in 8 directions. Broadleaf or mixed broadleaf/conifer forests and conifer forests were primarily distributed in valleys or on slopes facing north, north-east or east and on ridges or slopes facing south, south-west or west, respectively. In 18 quadrats, DBH of trees (over 2 m in height) were measured, and phytosociological measurements were carried out on the vascular plants on the forest floor (below 2 m in height). Two communities were recognized on the basis of similarity in relative dominance of trees, and on species composition of the forest floor : broadleaf-dominated forest and conifer-dominated forest. The former community was distributed on the slopes facing north, north-east or east ; the latter was on the slopes facing south, south-west or west. Soil types of the broadleaf-dominated and the conifer-dominated forests were identified to B_D type (mesic brownish forest soil) and B_B type (xeric brownish forest soil), respectively. Synthetic indices of habitat fertility were provided using the soil chemical properties of horizon A, which showed a tendency to become gradually reduced in xeric habitats (i.e., ridges or slopes facing south, south-west or west). Soil chemical properties showed clear differences between the two community types. In particular, a close relationship between the relative dominance of conifers (mainly Abies sachalinensis) and habitat fertility was recognized.

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