We surveyed the distribution of vegetation and substratum of the ground surface on the depositional landform developed by some debris flows in a subalpine area of the Oku-Nikko region, Central Japan, and discussed the effect of subsequent movement of debris flow deposits on succession of vegetation. The substratum of the ground surface was divided into three types according to the difference in deposited materials : 1) BS-type, consisting of boulder with sandy soil matrix, and retaining the features of debris flow deposits ;2) B-type, consisting of boulder without matrix, and suffering erosion ; 3) S-type, consisting of sandy materials transported by water flow. This depositional landform contained some depositional surfaces formed by past debris flows. However the three types of deposits were located in order of B, BS, S (B in the upper part of the depositional landform, down to S), and not corresponding to the age of depositional surfaces. This reflects the subsequent movement of debris flow deposits through the different depositional surfaces. There were young forests dominated by Alnus matsumurae, Pterocarya rhoifolia, and Salix sachalinensis which are regarded as the primary phase, or old forests of A. matsumurae and P. rhoifolia with juveniles of Tsuga diversifolia in the B-type deposit areas. Abies veitzcii forest, more than 55 years old, was dominant in the BS-type deposit area. Furthermore, S. sachalinensis was dominant in the area buried by S-type deposits. This distributional pattern is considered to be developed by the subsequent movement of debris flow deposits which affect on the speed and direction of succession on the depositional landform. In the B-type areas, the pioneer stage of succession occurs repeatedly due to the destruction of the site by erosion, however, these areas have potentiality to proceed T. diversifolia forests. In the BS-type area, which had been stable since a major debris flow more than 55 years ago, succession proceeded to A. veitzcii forest. In the S-type areas, only S. sachalinensis survived deposition, while conifer trees failed to invade.
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.
A phytosociological survey was carried out on Zelkova serrata forest in Aomori Prefecture. Based on the floristic composition, the following three associations were recognized. The distribution pattern of the three associations is closely related to the precipitation level, the temperature and total snowfall. Parabenzoino praecocis - Zelkovetum is distributed only in the eastern part of this prefecture, i.e. around Hachinohe city and Sannohe town, where precipitation and snowfall is less than in other parts of the prefecture. Cacalio bulbiferae-Zelkovetum is distributed widely in Aomori Prefecture. This association is found in areas where the annual precipitation and snowfall are higher. Aceri glabri-Zelkovetum serratae is found on windy sea-facing slopes, where it is warmer than other areas, with the annual mean temperature over 10℃. The floristic composition of these associations was compared with that of Zelkova serrata forests investigated by other researchers. The northern limit of distribution of these Zelkova serrata forest associations is Aomori Prefecture.