Vegetation and hydrogeology along the distribution range of Centaurium somedanum, an endemic plant of mountain calcareous springs

Abstract

Calcareous springs support bryophyte-dominated habitats relevant to biodiversity and conservation, but not much is known about the ecology of vascular plants restricted to these environments. Here, we investigate vegetation and hydrogeological patterns within the distribution of Centaurium somedanum, a threatened vascular plant endemic to mountain calcareous springs in the Cantabrian range (Spain). We studied the hydrogeological characteristics of the spring systems where this species occurs and identified three types of springs: (a) springs with active travertine deposition in small valleys, (b) springs in rock fall avalanches and (c) springs fed by calcareous water close to geological faults. Vascular plants and bryophytes co-occurring with the study species were sampled in 1-m2 plots to identify major vegetation types and to assess the relationships between species composition and topography. The presence of C. somedanum was associated with vegetation of calcareous spring fens (Caricion davallianae) in geological faults, tufa concretions (Adiantion) in active travertines, and another vegetation type of calcareous flushes (Pinguiculion) that was found in all of the spring types. C. somedanum shows a wider ecological range than other vascular plants of calcareous springs, occupying micro-habitats with similar cover of bryophytes but different from the cover of vascular plants. Although these plant communities are primarily dependent on the hydrology of springs, the variation in species composition is also correlated to the slope and solar radiation at the micro-scale. Our study demonstrates how a vascular plant with a calciphilic character may adapt to tufa-forming niches along the spring-flush-fen gradient, thus allowing it to occupy a wide range of habitats at different altitudes and geohydrological conditions.