Abstract
Alnus japonica and Ulmus Davidiana are the main constituents of Japanese swamp forests. Their presence in the forests are said to be arranged according to a gradient of humidity of the habitat from wet to mesic, with the intervening forest dominated by Fraxinus mandshurica var. japonica on less wet habitats.
In the present study, forest vegetation with their habitat conditions were surveyed intensively in a small tributary basin in a hilly area in Kawatabi, Miyagi Prefecture, in which a number of stands was found to be occupied by alder and elm forests (Figs. 1 and 2). The forest vegetation occurring on the valley floor were classified in terms of their species composition. Four communities were distinguished: Ulmus Davidiana community, Alnus japonica-Carex fulta comm., A. japonica-Sasa senanensis comm. and A. japonica-Miscanthus sinensis comm. The second community can be divided further into Filipendula kamtschatica type and Phragmites communis type (Table).
In addition to the humidity gradient, other essential differences were found in the landforms and subsurface materials between the habitat of alder and elm forests in this valley. Alnus japonica-Carex fulta community, which has a typical species composition and physiognomy of Japanese swampy alder forest, is found on a flood plain with standing water. While, Ulmus Davidiana community occurs on comparatively steep and rough mass movement deposits. The other communities occupy rather restricted areas.
