Plant community ecology of petrifying springs (Cratoneurion) - a priority habitat

Aims: To investigate the floristic and abiotic characteristics of the Habitats Directive priority habitat 'Petrifying springs with tufa formation (Cratoneurion)'. Location: The island of Ireland, north-western Europe. Methods: Vascular plants, bryophytes and abiotic variables were recorded in a field survey of 186 relevés (4 m²). Relevés were assigned to groups based on species composition, using fuzzy clustering and Indicator Species Analysis. Eight plant communities were described. Results: Group 1 Eucladium verticillatum-Pellia endiviifolia Tufa Cascades, of steep slopes, are related to Continental Eucladietum verticillati and Adiantion communities. Group 2 Palustriella commutata-Geranium robertianum Springheads and Group 3 Brachythecium rivulare- Platyhypnidium riparioides Tufaceous Streams and Flushes are woodland communities related to the Equiseto telmatejae-Fraxinetum and the Pellio endiviifoliae-Cratoneuretum commutati. Groups 1 to 3 fall broadly within the Brachythecio rivularis-Cratoneuretum forest spring vegetation type. Group 4 Palustriella commutata- Agrostis stolonifera Springheads are intermediate between Groups 1 to 3 and Groups 5 to 8. Group 5 Schoenus nigricans Springs, Group 6 Carex lepidocarpa Small Sedge Springs and Group 7 Palustriella falcata-Carex panicea Springs are transitional to Caricion davallianae small-sedge fen communities. Group 8 Saxifraga aizoides- Seligeria oelandica Springs are ecologically distinctive, species-rich assemblages confined to montane cliffs, with a restricted distribution in upland limestone regions, containing a number of nationally and internationally rare taxa. Of our eight groups, Groups 7 and 8 have the closest affinities with Cratoneuretum falcati spring communities. Abiotic variables differ significantly among the eight groups. Slope, macronutrient levels and shading by tree canopies are highly significantly related to the main axes of variation in the floristic data. Species diversity is inversely related to phosphate levels. Group 8 communities are irrigated by water of the highest pH and lowest solute concentrations. Conclusions: Our eight groups characterise variation within the habitat, elucidate ecological gradients with related habitats and facilitate conservation of this ecologically distinctive habitat.