Hydrochemical regime of fen and bog in north Japanese mires as an influence on habitat and above‐ground biomass of Carex species

Abstract

Summary The gradient relations proposed by Wheeler & Proctor for NW European mires were tested for six Carex species common in north Japanese mires. Hydrochemical properties of their preferred habitats were compared with above‐ground biomass data. Canonical discriminant analysis showed that soil water pH was the strongest discriminant between habitats of the Carex species, with total dissolved nitrogen (TDN) concentration also contributing, independently of pH. Two major patterns were apparent in the distribution of Carex species: pH determines a bimodal distribution into fens with pH > 5.0 and bogs with pH < 5.5, whilst TDN captures the variation in above‐ground biomass within both fen and bog, but does not differ significantly between them. Concentrations of Ca and Mg were low throughout the pH range. The floristic gradients associated with base richness seen in Euramerican mires do not therefore apply in north Japanese mires, where periodic flooding with neutral water removes the acid fractions in fens, and is the major determinant of pH. Thus, pH is the best variable for distinguishing between fen and bog, as the poor fen‐rich fen classification is inappropriate for non‐calcareous north Japanese mires.