Relationships between the distribution of co-occurring Salicaceous species and soil texture of their habitats were studied in the floodplain of the Ishikari River, Hokkaido. Four river morphological zones were distinguished. The delta zone was characterized by a homogeneous, fine soil texture which contained gley-spots, and in these extremely moist conditions Salix subfragllis was dominant. The river meandered greatly in the intermediate zone, and here S. sachalinensis was dominant. The largest number of Salicaceous species occurred in the alluvial fan zone, where soil texture was spatially heterogeneous. Populus maximowiczii was found only in the valley zone. An estimation of niche relationships among nine Salicaceous species and Alnus hirsuta revealed both broad niche species(S. sachalinensis and S. pet-susu)and narrow niche species(S. gracilistyla and P. maximowiczii)to be present. The largest niche overlap was found between S. sachalinen-sis and S. pet-susu, which are taxonomically closely related. The nine Salicaceous species and A. hirsuta were divided into three species groups by the group-averaged clustering method using a niche overlap index.
It is well-known that several mountains in central and northeastern Honshu, Japan, lack coniferous forests in their subalpine zones. In order to clarify the factors determining this phenomenon, the development of subalpine coniferous forests, the snow accumulation depth and the extent of subalpine area were surveyed in the Jo-etsu Mountains and their vicinity. Generally, the subalpine coniferous forests were poorly developed in mountains with heavy snowfall, but were well extended on mountains or peaks in mountain regions with larger extents of subalpine area. These facts suggest that on each mountain the extent of subalpine coniferous forests has changed in close relation with the extent of the subalpine area and the accumulated snow depth condition. This has continued throughout the climatic changes during the Postglacial Age, especially the Postglacial Warm Period, when the extent of coniferous forests was markedly reduced.
Annual production rates(by dry weight/number)of pollen, male flowers, seeds and cones in three natural stands, A, B and C(100-200 years old), and an artificial stand D(50 years old)of Sugi(Cryptomeria japonica D. DON)of Japan Sea Type were measured by litter traps and analyzed. Production rates of pollen dispersed into the air were estimated from enumeration of fall rates of open male flowers per hectare and dry weight/number of pollen grains per flower sample before anther opening. Pollen production rates in 1981-1986 were in the range of 3.4-430kg/ha・yr and 0.43×1012-49×1012 no./ha・yr, and the mean values of four stands over the seven years' period were 63kg/ha・yr and 6.6×1012 no./ha・yr, which were nearly equal to those described in Japanese red pine and Siebold walnut stands. In accordance with the numerical ratio of pollen to seed production, two types of dry matter production over reproductive organ are distinguished ; one being a high proportion(60-70%)of male parts to the total dry matter production, and the other, a low proportion (40-50%). Of the numerical ratios of pollen grains to seeds and male flowers to seeds, the former is about four times higher than the latter, which had no relation to mast and lean years. Stands A, B and D were classified into the former type, and C into the latter.
The vegetational zonation of sandy and shingly coasts in the southern Kii Peninula (Honshu), southern Shikoku and southeastern Kyushu was studied in relation to depositional topography. The vegetation was divided into five zones. The first zone (Z1) is associated with tidal drift annual plants, and the second (Z2) consists of small herb communities dominated by Carex kobomugi or Calystegia soldanella. The third zone (Z3) is demarcated by dominant growth of Ischaemum anthephoroides, and the fourth(Z4)by Vitex rotundifolia. The last zone (Z5) is the coastal scrub community. On sandy coasts, dune and beach ridge differ in their zonal patterns and their topographical development grade. As dune height increases, Z3 becomes narrower and Z4 starts near the shoreline. On the beach ridge Z3 is absent. On shingly coasts the vegetation occurs from near the shoreline, especially on the large shingle beach ridge. The relationship between the zonation of coastal vegetation and topography is discussed.
From 1978 to 1980,two population of Henosepilachna niponica feeding on wild thistle (Cirsium spp.) were studied in different habitats, Sawai and Kashio at Ohshika village, Nagano Prefecture, by construction of life tables and mark-recapture of adults. The life histories of the two populations were seasonally synchronous with the phenology of the host plant and population densities never reached a level where food shortage occurred. Both populations were characterized by high mortality(95-97%)during the immature stages due to egg cannibalism by adults, and predation by polyphagous arthropods on eggs, larvae and pupae. The reproductive rate(=no. of newly emerged females per overwintered female)during the three-year study period was low in both populations, that in Sawai(0.9-1.8)being more stable than that in Kashio(1.3-5.4). According to key factor analysis, the variation in number of eggs laid per female was the major factor responsible for the variation in reproductive rate seen in Sawai. No clear tendencies were evident in Kashio. The reason for this difference in variation pattern between the two population was obscure. The variation in number of eggs laid per female also seemed to play an important role in stabilizing population densities in both populations.