To examine the factors influencing the formation of plant zonation in a brackish marsh, vegetation and soil characteristics were investigated at 5-m intervals from the shore of the brackish Lake Obuchi, located in northern Japan. Two-way indicator species analysis (TWINSPAN) broadly classified the sites into
Phragmites australis-dominated,
Juncus yokoscensis-dominated, and
Miscanthus sinensis and
Cirsium inundatum-dominated vegetations. Vegetation boundaries were distinct and the order of vegetation arrangement corresponded with the distance from the shore of Lake Obuchi, which indicated the existence of plant zonation. Species diversity increased in the order of
P. australis-dominated <
J. yokoscensis-dominated <
M. sinensis and
C. inundatum-dominated vegetation. Electrical conductivity (salinity index) in the soil was the highest in
P. australis-dominated vegetation. Inorganic N conc entration in the soil tended to increase in the order of
P. australis-dominated <
J. yokoscensis-dominated <
M. sinensis and
C. inundatum-dominated vegetation. These results suggest that, concerning on the zonation around the brackish Lake Obuchi, species distributions in the area nearer to the shore are determined by tolerance to salinity.
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