Abstract
Deteriorations of vegetation and hydrochemical environments were examined in the Hirosato restoration area on the margins of Kushiro Mire, where agricultural land use and a drastic increase of alder forest have influenced the ecosystem for the last past halfcentury. The vegetation was classified into seven types, where the meadow types dominate in the pasture area and the alder or fen types are distributed in the mire area. A following Canonical Correspondence Analysis shows two major results: 1) A vegetation gradient from the mire area to the pasture area corresponding to the obvious lowering of the groundwater level, 2) A vegetation gradient from the fen types to the alder types in correspondence to the lowering of the groundwater level and to the decrease of phosphorous concentration coupled with the increase of nitrogen concentration in soil water. The intense decrease of the groundwater level in the pasture area due to the diversion of the neighboring river has probably changed the mire vegetation into meadow vegetation, indicating that serious deteriorations have been introduced artificially. In the mire area, the distribution of the alder forest was mostly affected by hydrological regime in flooding, yet artificial influences could not be specified.
