Plants as indicators of hydrological quality in sedge-moss fen ecosystems

Mesotrophic sedge-moss-dominated fen ecosystems develop only under favourable hydrological conditions, the most important of which is stable groundwater discharge through permeable undecomposed peat layers. As a result of anthropogenic hydrological changes and landscape transformation, these ecosystem types, once widespread in temperate Europe, are now rare and conservation or restoration measures are required to maintain them. The success of conservation and restoration of these ecosystems is highly dependent on the ability to maintain or restore favourable hydrological regimes and soil properties. The assessment and monitoring of hydrological and soil habitat quality can be time consuming, costly and technically challenging. The concept of indicator species combines the ecological requirements of species with the possibility of using them as indicators of averaged, often long-term environmental conditions. However, selecting indicator species in a way that allows their widespread use is only possible if a sufficiently large and diverse dataset linking species occurrence with measured environmental conditions is available. In our study, we used vegetation data combined with hydrological and soil data collected from 46 plots within 23 fens located along a transect of more than 500 km across the northern part of Poland. On this basis, using the so-called Huisman-Olff-Fresco models, we selected species of vascular plants and bryophytes that could be indicators of stable groundwater discharge (low amplitude of water level fluctuations) and unchanged soil conditions (low bulk density of peat). The list of these species only partially overlaps with previously published lists of indicator species for sedge-moss fen vegetation known from the literature, and can be used for a rapid and inexpensive assessment of the degree of change in abiotic conditions within fen ecosystems.