Geographical differences in the habitat of forb species occurring in Japanese beech (Fagus crenata) forest zone

Abstract

The habitat differences for vascular plant species, particularly for forbs, between the Pacific Ocean side (POS) and the Sea of Japan side (SJS) were investigated in the Japanese beech (Fagus crenata) forest zone. Some of the beech forest communities contain many forb species in the herb layer. Distributions of these communities themselves are restricted in POS; however most of the constituent forb species or their varieties are distributed also in SJS. Thus, in SJS, we can expect that these forb species will be growing in some communities other than beech forest. The community floristic composition and the habitat of vascular plant species were surveyed using phytosociological methods and description of topographic condition (165 releves were collected in total). Four micro-landform units were distinguished, i.e. 1) gentle crest slope, 2) side slope, 3) valley and 4) side slope in a small valley. Releves were collected for each micro-landform unit and the habitat of vascular plant species was compared between POS and SJS. As a result of this comparison, eight species groups were distinguished from their habitat patterns. The habitat differences for vascular plant species were observed as a species group which grew on gentle crest slope and side slope in POS where beech forest are established, and grew only on valley and side slope in a small valley in SJS where beech forest are absent. These species groups contained many forb species. Consequently, absence of forbs in beech forest in SJS may not be caused by an absence of forbs in SJS, but by habitat shift of forbs from beech forest (gentle crest slope and side slope) to other habitats in SJS.