Petrifying (tufa-forming) springs are freshwater springs in which calcium-rich groundwater deposits tufa (Lyons and Kelly 2016). Tufa is a highly porous calcareous rock formation, typical of karst environments. It forms primarily at springs, seepages, and stream channels from calcium-rich waters under ambient temperatures when CO₂ degassing, driven by changes in hydrodynamic pressure, water agitation, exposure to air, photosynthetic uptake, and evaporation, induces supersaturation and precipitation of CaCO₃ (Pentecost 2005; Heery 2007; Capezzuoli et al. 2014). Carbonate nucleation occurs on submerged surfaces, particularly on bryophytes, green algae and cyanobacteria, whose tissues become progressively encrusted, creating the structural framework for tufa deposits (Onete et al. 2014; Garner et al. 2025).

In addition to the hydrochemical conditions required for tufa deposition, its formation is largely controlled by biological activity, through which cyanobacteria, algae, and bryophytes trap and bind calcite crystals through secreted mucopolysaccharides, thereby promoting mineral precipitation (Janssen et al. 2016), while vascular plants further shape the development of deposits (Heery 2007; Onete et al. 2014). This process leads to the gradual “petrification” of plant tissues and other organic substrates, creating a complex and highly specialized biogenic habitat (Capezzuoli et al. 2014; Garner et al. 2025). The tufa formation may be small deposits around the bases of plants within the spring, attached or unattached coated particles (stones or plant fragments) or can comprise very large mounds and cascades (Lyons and Kelly 2016; Denyer et al. 2023).

Petrifying (tufa-forming) springs support highly specialized bryophyte- and fern-dominated communities, often including rare or threatened species adapted to the distinctive conditions of these systems (Heery 2007; Denyer et al. 2023). Due to their ecological specificity and rarity, they are listed as a priority habitat under Annex I of the European Union (EU) Habitats Directive (92/43/EEC) as habitat type 7220* “Petrifying springs with tufa formation (Cratoneurion)” (European Commission 2013). They are also recognised as groundwater-dependent terrestrial ecosystems (GWDTEs) under the Water Framework Directive (2000/60/EC), which requires the maintenance of the hydrological and chemical status of the aquifers that feed them (Schutten et al. 2011). Furthermore, this habitat is included in the European Red List of Habitats, classified as Vulnerable (C2.1.b Calcareous Spring and spring brook) (Janssen et al. 2016), reflecting its sensitivity to alterations in the hydrological regime and water quality.

The floristic core of habitat type 7220* corresponds to the alliance Cratoneurion commutati (class Montio-­Cardaminetea), comprising moss-rich vegetation of calcareous springs in the montane and subalpine regions of Europe (Mucina et al. 2016). This vegetation type is rare outside the Alpine Folding Zone, particularly in the Central European Highlands (Pentecost 2005). However, an ecological continuum between the Central European Cratoneurion and Mediterranean Adiantion vegetation has been described by several authors, both of which are dominated by bryophyte- and fern-rich communities on calcareous wet cliffs (Zechmeister and Mucina 1994; Spampinato et al. 2023).

In southern Europe, these communities are often assigned to the association Eucladio-Adiantetum (alliance Adiantion), characterized by Adiantum capillus-veneris and Eucladium verticillatum. Although the syntaxonomic relationship between temperate Cratoneurion and Mediterranean Adiantion remains debated, both are ecologically linked to lime-rich, permanently moist habitats and contribute actively to tufa formation. Mucina et al. (2016) emphasizes the marginal position of Cratoneurion commutati within the class Montio-Cardaminetea and propose its closer affinity to Adiantetea. Similarly, Zechmeister and Mucina (1994) report the absence of a clear phytosociological boundary between Adiantetea and Montio-Cardaminetea communities, supporting the interpretation of these vegetation units forming an ecological continuum across spring habitats.

Although Pedley (2009) provides an extensive synthesis of tufa in the Mediterranean region, Cyprus is not included among the documented regions. To our knowledge, petrifying springs and the associated EU priority habitat type 7220* have not been previously reported on the island. To address this, we conducted dedicated field surveys to investigate their potential presence and document their floristic, geomorphological, and hydrological characteristics. Specifically, this study aimed to identify, and map springs whose vegetation structure, floristic composition and active tufa-forming processes correspond to the characterisation of Annex I habitat type 7220* under Directive 92/43/EEC.

This study provides the first confirmed record of petrifying (tufa-forming) springs in Cyprus, corresponding to European habitat type 7220*. The documented stands of the association Eucladio-Adiantetum exhibit all the defining features of this habitat: discharge of calcium-rich groundwater, active tufa deposition, and dominance by bryophyte–fern assemblages with Eucladium verticillatum and Adiantum capillus-veneris. These taxa are diagnostic for Adiantion communities and are widely recognized as key builders of the tufa crusts (Zechmeister and Mucina 1994; Lyons and Kelly 2016; Denyer et al. 2023).

The coexistence of Eucladium verticillatum and Adiantum capillus-veneris, accompanied by Samolus valerandi and Pellia endiviifolia, reflects a transitional floristic composition between Central European Cratoneurion commutati and Mediterranean Adiantion. Similar Mediterranean expressions of petrifying springs have been reported in Sicily and Calabria (Puglisi et al. 2018; Spampinato et al. 2023). Therefore, the Cypriot assemblages represent the easternmost Mediterranean vicariant of habitat type 7220*, occupying analogous ecological niches under warmer and drier climatic conditions.

The dominance of Eucladium verticillatum, a principal tufa-generating moss, and its calcite encrustation confirm ongoing carbonate deposition. Pellia endiviifolia and Oxyrrhynchium hians are both linked to tufa-forming habitats in continental Europe (Dakskobler et al. 2014; Guitián et al. 2020), further strengthening habitat interpretation. Glime (2020) reported Eucladium verticillatum and Palustriella commutata as the most common species in petrifying springs in a pH range of 6.9–8.3. A similar group of plant communities of Irish petrifying springs of tufa cascades was described by Lyons and Kelly (2016), consisting of Eucladium verticillatum-Pellia endiviifolia, dominated by bryophytes, with affinities with Adiantion communities of damp cliffs.

Notably, Hydrogonium bolleanum, a rare and threatened bryophyte, largely confined to the Mediterranean region of southern Europe (Schröck et al. 2019; Puglisi et al. 2024), was detected at two localities. This species is typically associated with moist calcareous substrates such as flowing or dripping water habitats (Fiaschi et al. 2025). As a carbonate-encrusting bryophyte associated with biogenic rock formation, its occurrence further supports the active tufa-forming character and high conservation value of the investigated springs. The presence of such specialised bryophytes also highlights the role of these spring systems as refugia for moisture-dependent and habitat-sensitive Mediterranean taxa.

At the structural level, Eucladium verticillatum function as keystone acrocarpous cushion-forming bryophyte that can be practically described as synonymous with tufa formation. Their adpressed leaves and the dense colonies allow an efficient capillary retention of water and progressive carbonate encrustation. The high density and small size of bryophyte leaves provide a large surface area that promotes carbonate precipitation (Bates and Smith 2011). Pellia endiviifolia, the most frequently reported thallose liverwort in European tufa deposits, typically colonises zones of active precipitation, where it may become incorporated into carbonate. This species prefers low nutrient levels (Glime 2020). Ferns are often recorded in tufa but are usually absent from actively depositing zones. Adiantum capillus-veneris is widely recorded in shaded seepages at sites across Europe, Asia, and Africa (Pentecost 2005).

Petrifying springs are among the most fragile GWDTEs in Europe. Their persistence depends on the continuity of groundwater discharge, stable hydrochemistry, and microclimatic conditions. Even small hydrological changes can disrupt carbonate deposition and the survival of bryophyte communities (Lyons and Kelly 2016; Denyer et al. 2023; de Mars et al. 2024). The high abundance of carbonate-encrusted bryophytes in the investigated springs indicates currently favourable ecological conditions, as the species found are among the positive indicator species of petrifying springs (Lyons and Kelly 2016; Denyer et al. 2023), yet these systems remain extremely vulnerable to changes in hydrological regime, water chemistry, temperature, and seasonal variability (Sironić et al. 2023).

The challenges presented by the Mediterranean climate include a high level of natural stress due to seasonal fluctuations in climate and hydrology. Although seasonality (dry summers and wet winters) is highly predictable, marked interannual variability (dry and wet years) is not (Cantonati et al. 2020). As small, usually localised GWDTEs, petrifying springs are very sensitive to changes in hydrology. In Cyprus, their vulnerability is amplified by severe water scarcity, groundwater abstraction, and localized pollution from diffuse sources (WDD 2023). Similar threats and pressures have led to an unfavourable conservation status of habitat type 7220* in the Mediterranean biogeographic region during the 2007–2012 assessment period in Italy, France, and Spain (EEA 2025c).

Because this is the first documentation of habitat type 7220* in Cyprus, the habitat is not yet listed as a qualifying interest in any SAC. Where petrifying springs are designated as qualifying interests, Article 6 of the Habitats Directive imposes strict protection (European Commission 1992). Given their groundwater dependence and potential hydrological interconnections, any development affecting aquifer systems should be evaluated with exceptional caution. Formal designation, notably within the CY4000010 Chersonisos Akama and CY4000008 Koili–Mavrokolympos SACs-would substantially strengthen their legal protection and enable systematic monitoring. Site-specific conservation objectives should prioritize the maintenance of natural groundwater regimes, regulation of water abstraction, and continuous water quality monitoring. Catchment-scale management is essential, given the small size, localised extent, and hydrological sensitivity of these systems. Furthermore, mapping potential spring sites across the island may reveal additional occurrences of this habitat type, enabling a more accurate assessment of its conservation status. The NPWS (2019) provides a list of tangibles, quantifiable conservation targets relevant to the habitat type.

Beyond biodiversity conservation, petrifying springs offer additional societal value, contributing to geodiversity, environmental education, and sustainable geotourism, as demonstrated in established geoparks (Megerle 2021; Petrović et al. 2023; Çiltepe and Uzun 2024). In Cyprus, these geo-ecological features can become focal points for sustainable tourism.

This study provides the first documented evidence of petrifying springs with active tufa formation in Cyprus, corresponding to the EU priority habitat type 7220*. The vegetation is assigned to the association Eucladio–­Adiantetum, dominated by Adiantum capillus-veneris and Eucladium verticillatum, both of which are key diagnostic species of Mediterranean tufa-forming communities. Their presence, together with active CaCO₃ deposition, confirms the existence of a groundwater-dependent habitat on the island.

The presence of carbonate-encrusting bryophytes and the recording of species such as Hydrogonium bolleanum indicate sites of high ecological quality. However, the small spatial extent, hydrological dependence, and water stress conditions, render these habitats highly vulnerable to groundwater abstraction, water-quality degradation, and climate-driven hydrological change.

Further research is required to determine the full distribution of petrifying springs across Cyprus, which is likely to be broader than that currently documented. Additional tufa morphotypes (including cemented rudites, oncoids, and ooids) have already been identified, suggesting a complex and diverse carbonate system deserving continued investigation.