RECENT MALACOFAUNA

There is a relatively rich mollusc fauna in Witkowe Rocks, including 58 species (Tables 1–2). The malacofauna identified in the wooded zones was abundant and included 48 species, among which shade-loving taxa were predominant. Almost 70% of the species identified belonged to this group (Fig. 7). The most numerous families were Clausiliidae, Zonitidae, and Helicidae. Noteworthy is the presence of several species that are rare for the southern part of the Kraków-Częstochowa Upland, such as Acicula parcelineata, Discus perspectivus, Ruthenica filograna, and Vitrea subrimata. Mesophilous taxa constitute the second important component of the analysed fauna. There are both species typical of medium-humidity habitats (Cochlicopa lubrica, Punctum pygmaeum, Clausilia dubia) and humid environments (Succinella oblonga, Arianta arbustorum), although the former are more numerous. Open-country species were of marginal importance and were represented only by Vallonia pulchella and V. costata (Fig. 7). The malacofauna found in grasslands and/or on the walls of limestone rocks was much less diverse and included 25 taxa (Tables 1–2). Its most prominent component was species typical of open, often strongly sunlit habitats. This includes both species preferring grass biotopes (V. pulchella and V. costata, Pupilla muscorum) and those living on exposed limestone surfaces (Pyramidula pusilla, Chondrina clienta, Pupilla sterrii). In addition, there were mesophilous taxa of dry habitats (Cochlicopa lubricella) and moderately moist habitats (C. lubrica, P. pygmaeum). Besides Alinda biplicata and Laciniaria plicata, shade-loving species and forms requiring more moist habitats were scarce (Fig. 7).

Fig. 7

Lithology of deposits filling small karst forms, subfossil, and recent malacofauna. E – ecological groups of molluscs, MSI – malacological spectrum of individuals, MSS – malacological spectrum of species, Pr – lithological profiles, Sm – samples

Table 1

Malacofauna in profiles of sediments filling small karst forms at Witkowe Rocks: RF – recent fauna of shaded zones, RO – recent fauna of grasslands and rocky walls, A–D – molluscan assemblages described in the text, E – ecological groups of molluscs (after Ložek (1964), Alexandrowicz S. W. & Alexandrowicz W. P. (2011), Juřičková et al. (2014a)): F_F – shade-loving forest species, F_B – shade-loving light forests species, F_H – shade-loving wet forests species, O – open-country species, M_D – mesophilous species of dry habitats, M_I – mesophilous species of semi-wet habitats, M_H – mesophilous species of wet habitats, H – hygrophilous species. ZG – zoogeographical groups of molluscs (after Alexandrowicz S. W. & Alexandrowicz W. P. (2011)): Hl – Holarctic species, Pl – Palearctic species, Ep – European species, Me – Central-European upland species, Ma – Central-European mountain species, En – North-European species, Ee – East-European species, Eb – Balkan species, Em – South-European species, Ew – West-European species, Ba – Boreal-Alpine species

Table 2

Diversity of subfossil and recent malacofauna in the area of Witkowe Skały: Ws-I – Ws-VI – profiles, RF – recent fauna of shaded zones, RO – recent fauna of grasslands and rocky walls, F – shade-loving species, O – open-country species, M – mesophilous species, H – hygrophilous species, CLS – cold-loving species (Semilimax kotulae, Columella columella, Vertigo arctica, Vertigo geyeri), N – number of species/specimens

LITHOLOGY OF SEDIMENTS

The lithological sequences filling small karst forms were characterised by a thickness ranging from 25 to 60 cm. The fills analysed are relatively homogeneous in terms of lithological formation. The most common sediment type is yellow, sometimes ash-grey or brown silt. Within them, sharp-edged blocks of Jurassic limestone appear. Individual profile intervals may differ in the number of rock fragments (in some places, limestone blocks appear sporadically, and in others, they are very numerous with a small amount of silty matrix) and in the size of the fragments (diameters vary from 2–3 cm sometimes reaching up to 10 cm). In addition to numerous mollusc shells, bones of small vertebrates also appeared in the sediments analysed. The lithological characteristics of the individual profiles are presented in Fig. 7.

SUBFOSSIL MALACOFAUNA

Studies of the subfossil mollusc fauna carried out in six profiles (Ws-I – Ws-VI) identified 54 land snail species represented by almost 7,000 specimens (Tables 1–2).

As in the case of the present-day malacofauna, shade-loving taxa are the most abundant (34 species; about 63% of the fauna) (ecological groups F_F, F_B, and F_H). Taxa with high environmental and thermal requirements (Discus perspectivus, D. rotundatus, R. filograna) and snails preferring cooler climates (D. ruderatus), as well as cold-loving forms (Semilimax kotulae) are present here. Noteworthy is the presence of several species that are not recorded alive in the Kraków-Częstochowa Upland. This group includes Argna bielzi, Eucobresia nivalis, S. semilimax and Vestia turgida. These taxa have only been found in Quaternary sediments from the southern part of the Kraków-Częstochowa Upland (e.g. Alexandrowicz S. W. 1983, 1987, Alexandrowicz W. P. 2004, 2021, Pawłowski et al. 2008). Open-country species, including those that live on exposed rocks or in grassland (ecological group O), are represented by eight taxa (15% of the fauna). Due to the significant degree of shading of Witkowe Rocks, this group is a relatively minor component of the assemblage. It is more numerous in only two samples. Particularly noteworthy is the occurrence of the cold-loving species Columella columella. The mesophilous species (ecological groups M_D, M_I, and M_H) include 11 taxa (20% of the fauna). It mainly comprises widely distributed snails with high ecological and thermal tolerance. Noteworthy is the occurrence of a cold-loving taxon – Vertigo arctica. Hygrophilous snails (ecological group H) are represented by only one cold-loving taxon: Vertigo geyeri (Fig. 7, Tables 1–2).

DIVERSITY OF THE MALACOFAUNA OF SMALL KARST FORMS

The profiles analysed can be divided into two groups. The first one includes the profiles Ws-I, Ws-II and Ws-III. The malacofauna found here is characterised by low taxonomic diversity (the number of taxa in individual samples usually does not exceed 20), as well as relatively low specimen abundance (the number of specimens in samples is up to 250 at most, although it is usually lower) (Tables 1–2). The ecological structure of the fauna in all samples representing profiles Ws-I, Ws-II, and Ws-III is similar. Shade-loving taxa, among which the high numbers of D. ruderatus and A. arbustorum are notable, are predominant. However, the most distinctive feature of the fauna analysed is the abundance of cold-loving taxa. This group includes V. arctica, V. geyeri, C. columella, and S. kotulae. Among these taxa, only S. kotulae occurs today in the Kraków-Częstochowa Upland, and it is a relict form (e.g. Riedel 1988, Wiktor 2004, Stworzewicz 2008, Pawłowski et al. 2008). The others are known only from Quaternary sediments associated with the Last Glacial, Late Glacial, and Early Holocene. They have been found at numerous sites near Kraków, including those dated using the radiocarbon method (e.g. Alexandrowicz S. W. 1983, 1987, Alexandrowicz W. P. 2004, 2021).

The remaining three profiles (Ws-IV, Ws-V, and Ws-VI; samples Ws-14 – Ws-27) contain fauna of a different composition. The malacofauna here is much more diverse in terms of species composition (the number of species in samples usually exceeds 20 and often even 40 in a sample) and more abundant (the number of specimens in samples can exceed 1,300) (Tables 1–2). In terms of ecological composition, shade-loving snails are predominant. There are numerous taxa with high thermal requirements: D. perspectivus, D. rotundatus, R. filograna, and Aegopinella pura. However, no cold-loving species exist (apart from the relict S. kotulae). In the two samples Ws-22 and Ws-23 (Ws-V profile), snails of open-country, living on rocks (Pupilla sterrii, P. pusilla, Ch. clienta) and in meadows (V. pulchella, V. costata), are abundant. The ecological structure of the malacofauna found in the fills of the small karst forms at Witkowe Rocks is shown in Fig. 7.

MOLLUSC ASSEMBLAGES

Analysis of the similarity dendrogram (Fig. 8) revealed the existence of four faunal assemblages within the overall mollusc fauna, which differ significantly in species composition as ecological and zoogeographical structure.

Fig. 8

Cluster analysis of subfossil malacofauna from deposits filling small karst forms at Witkowe Rocks: A–D – molluscan assemblages described in the text, Sm – samples

Assemblage A. This type of fauna is found in the bottom parts of profiles Ws-I, Ws-II, and Ws-III. The presence of cold-loving taxa (V. arctica, V. geyeri, C. columella, and S. kotulae) is a distinctive feature of this assemblage. Their proportion in individual samples is significant and varies between 55 and 85%. This assemblage is characterised by low species diversity, and in addition to the four taxa mentioned above, only shade-loving taxa with high thermal tolerance appears in relative abundance (A. arbustorum and D. ruderatus), the proportion of which in the assemblage may reach up to 40%. Only single specimens represent other species.

The ecological structure of the assemblage is characterised by a high proportion of shade-loving species of up to 50%. This group, however, is dominated by molluscs preferring light forests and shrubland zones (ecological group F_B), while the proportion of typically woodland forms is low (Fig. 9). Mesophilous taxa, particularly typical of moist habitats, play a distinct role as well. It is worth paying attention to the moisture-loving snails (Fig. 9). The zoogeographical structure indicates a high proportion of Central European taxa, both upland and mountainous (around 50%). However, the most distinctive feature of the fauna under scrutiny is the abundant representation of North-European and Boreal-Alpine snails, accounting for about 40% of the assemblage (Fig. 9).

Fig. 9

Ecological and zoogeographical structure of subfossil and recent fauna from Witkowe Rocks: A–D – molluscan assemblages described in the text, E – ecological structure, F – shade-loving species, O – open-country species, M – mesophilous species, H – hygrophilous species (for explanations of other ecological groups see Fig. 7 and Table 1), ZG – zoogeographical structure, HP – species of wide geographical range, ME – Central-European snails, MO – European taxa of narrow geographical range (for explanations of other zoogeographical groups see Table 1)

Assemblage A indicates a dominance of lightly shaded habitats (light forest and shrubland zones) and a cold climate.

Assemblage B. This fauna is found in the higher layers of the Ws-I, Ws-II, and Ws-III profiles. Its distinctive feature is the large proportion of D. ruderatus, which is the most important component of this assemblage, with its proportion reaching 50%. The assemblage is complemented by psychrophilic species (V. arctica, V. geyeri, C. columella, and S. kotulae), but they are noticeably less abundant than in assemblage A (representing up to 10% of the fauna). Taxa with high thermal tolerance are common, among which A. arbustorum and Vertigo substriata are most abundant. There are relatively few snails with higher thermal requirements.

Shade-loving taxa play a dominant role, accounting for more than 50% of the fauna. Compared to assemblage A, a spike in the occurrence of forest snails (ecological group F_F) with a concurrent decline in the importance of ecological group F_B is visible (Fig. 9). A high proportion of mesophilic species, up to 40% of the assemblage, persists. In contrast, hygrophilous snails are not present (Fig. 9). Compared to assemblage A, the zoogeographical structure of assemblage B is entirely different. Widely distributed Palaearctic and European taxa are prominent. At the same time, the proportion of North-European and Boreal-Alpine taxa is significantly lower (Fig. 9).

Assemblage B is typical of a coniferous forest environment growing on relatively moist soil and a cool climate.

Assemblage C. This type of fauna was recognised in profiles Ws-IV, Ws-V, and Ws-VI. It is characterised by high species diversity. Species of lower tolerance to cold temperatures (D. perspectivus, D. rotundatus, R. filograna, Ae. pura), are common here. Mesophilous snails are a substantial component of this fauna, while open-habitat species are only a minor addition.

This assemblage is characterised by the dominance of shade-loving snails, representing up to 80% of the fauna. Of particular prominence are taxa typical of deciduous and mixed forests. Among the mesophilous forms, taxa typical of habitats with average moisture levels predominate (Fig. 9). The zoogeographical structure is marked by a high proportion of Central European snails, especially mountain forms. The abundance of the species mentioned above is typical of the present-day fauna inhabiting the forested areas of the Kraków-Częstochowa Upland (Šteffek et al. 1990, Pawłowski et al. 2008, Stworzewicz 2008). The presence of thermophilous Balkan and South-European taxa is also a distinctive feature (Fig. 9).

Assemblage C is characteristic of a forest environment with a high proportion of deciduous trees and a relatively warm climate. Regarding species composition and ecological and zoogeographical structure, this assemblage shows strong similarities to the fauna of contemporary forested zones within Witkowe Rocks (Fig. 9).

Assemblage D. This fauna was found in only two samples (Ws-22 and Ws-23) in the uppermost part of the Ws-V profile. The dominant component of the assemblage is open-habitat taxa. Here are both snails typical of exposed and strongly insolated limestone walls (P. sterrii, P. pusilla, Ch. clienta) and open grassland biotopes (V. pulchella, V. costata). The proportion of open-country species is very high, reaching 80% (Fig. 9). Snails representing other ecological groups are less important. Among the mesophilous species, noteworthy is the presence of forms preferring open and dry habitats (Euomphalia strigella, C. lubricella) (ecological group M_D). The assemblage is completed by shade-loving and mesophilous snails of environments with medium moisture levels, and their total contribution does not exceed 20% (Fig. 9). The assemblage is dominated by widely distributed taxa (75% of the fauna), especially Holarctic snails. On the other hand, the presence of thermophilic Balkan and Southern European snails should be highlighted, while Central European forms play a minor role. Regarding species composition and ecological and zoogeographical structure, the analysed assemblage shows strong similarities to the present-day malacofauna inhabiting forestless zones in the Witkowe Rocks area (Fig. 9).

SEDIMENT STRATIGRAPHY AND ENVIRONMENTAL ASPECTS

The stark differences in the taxonomic composition and ecological structure among these assemblages indicate that the sediments containing them were deposited during different climatic phases.

Assemblage A, which is dominated by cold-loving taxa plus species with low thermal requirements, shows remarkable similarity to the Early Holocene malacocoenoses from the southern part of the Kraków-Częstochowa Upland (e.g. Alexandrowicz S. W. 1983, 1987, Alexandrowicz W. P. 2004, 2021, 2022, Krajcarz et al. 2020, Wilczyński et al. 2020). Based on the composition of this fauna, it is also impossible to preclude its association with the Late Glacial, particularly with its slightly warmer Allerød phase. In this case, however, the comparative materials are much scarcer, and the sediments containing malacofauna of this age have only been documented on a handful of sites (Alexandrowicz S. W. 1983, Alexandrowicz W. P. 2004, 2022, Wilczyński et al. 2020). There is no doubt, however, that assemblage A represents a period of cold climate and an environment of thin, light forest growing on calcareous, relatively moist ground. Such habitats were dominant in the southern part of the Kraków-Częstochowa Upland both during the Allerød phase and the beginning of the Holocene (Alexandrowicz S. W. 1983, Alexandrowicz W. P. 2004, Madeyska 1995, 1998) (Fig. 10).

Fig. 10

Stratigraphy of deposits and environmental changes of Witkowe Rocks during Late Glacial and Holocene. AG – age (thousands of years), ST – stratigraphy (after Walker et al. 2019), MA – stratigraphical range of molluscan assemblages, MF – malacofauna (selected index species), A–D – molluscan assemblages described in the text, EN – environmental changes

Assemblage B, characterised by the abundance of D. ruderatus, the presence of species with high ecological tolerance as well as cold-loving taxa, shows significant similarity to the so-called ruderatus-fauna (Dehm 1967), an assemblage considered indicative of the Early Holocene. Malacocoenoses of similar taxonomic composition and structure have been reported from numerous Quaternary profiles throughout central and western Europe (e.g. Gedda 2006, Meyrick 2002, Limondin-Lozouet & Preece 2004, 2014, Limondin-Lozouet 2011, Alexandrowicz W. P. 2013, Alexandrowicz W. P. et al. 2014, Juřičkova et al. 2014b, Horáčková et al. 2015, Horsák et al. 2019, Granai et al. 2020), including many sites of calcareous tufas and fluvial deposits in the southern part of the Kraków-Częstochowa Upland (Fig. 10) (e.g. Alexandrowicz S. W. 1983, 1987, Alexandrowicz W. P. 2004, 2021), indicating uniform environmental conditions prevailing in the area. Similar faunas have also been found in the fills of large caves around Kraków (e.g. Alexandrowicz S. W. et al. 1992, Cyrek et al. 2000, Wilczyński et al. 2012, 2020, Szymanek et al. 2016, Krajcarz et al. 2020, Alexandrowicz W. P. 2022). The ecological structure of the fauna under scrutiny indicates that at the time of the deposition of the sediments, the area of Witkowe Rocks was covered by a dense forest with a high proportion of conifers and relatively moist ground and cool climate with marked continental features predominated.

Malacocoenoses with composition and structure corresponding to assemblages A and B have not yet been found in sediments filling small karst forms in the Upland. In Poland, such sites have only been reported in the Podhale Basin and the Pieniny Mountains (Alexandrowicz W. P. 1997, Alexandrowicz S. W. 2001, Alexandrowicz W. P. & Rudzka 2006, Skoczylas-Śniaz & Alexandrowicz W. P. 2022). Similar sites have been found in the Czech Republic and Slovakia (Ložek 1972, 1980, 1981, 1989, 2000). From this point of view, the profiles in Witkowe Rocks representing the Early Holocene (or even Late Glacial) should be considered very valuable. The main reason for such rare finds of fills of small karst forms containing malacocoenoses of this age is the low resistance of these sediments to erosional processes. Unlike in large caves, where deposition takes place over long periods punctuated by relatively short erosion phases, small karst forms, due to their shape, undergo repeated periods of deposition and erosion over short intervals of time (on the order of several hundred years). As a result, the accumulated sediments are entirely or almost completely removed in the subsequent erosion episode. Consequently, in most small karst forms, only the youngest fills accumulated over the last few hundred years are preserved. Studies of similar sites in the Kraków-Częstochowa Upland lead to similar conclusions (e.g. Alexandrowicz S. W. 1992, 2000, Alexandrowicz W. P. 2000, Alexandrowicz S. W. & Alexandrowicz Z. 2003).

Regarding specieas composition, assemblages C and D are similar to the malacocoenoses now inhabiting Witkowe Rocks. Thus, it can be assumed that the fills of small karst forms containing it are related to the youngest Holocene, probably representing the last few hundred years, as stated above. Assemblage C represents a mixed forest environment with a significant proportion of deciduous trees. Assemblage D is characteristic of open habitats with intense sunlight and dry grassland or rocks. Observations of contemporary and Late Holocene subfossil assemblages in the southern part of the Kraków-Częstochowa Upland indicate that the two assemblages mentioned above frequently inhabit adjacent areas. There are significant differences in their species composition and microhabitat condition structure mainly due to slope exposure (the slopes facing south tend to have D-type fauna, and the slopes facing north tend to have C-type fauna) and slope morphology (the rocky slopes are dominated by petrophilous taxa and the grassy slopes by meadow taxa). The fact that both types of malacocoenoses occur within single profiles (in the case of Witkowe Rocks, the Ws-V profile) indicates that a significant change in environmental characteristics has occurred during sediment deposition. These changes can be caused by human interference (deforestation) or local natural factors (e.g. fires, mass movements, windfalls). There are no traces of anthropogenic processes in the Witkowe Rocks area, so the change in the characteristics of the malacocenoses in the Ws-V profile is related to natural factors. In contrast, there are clear signs of human activity on many other inliers in the Jerzmanowice area (Alexandrowicz S. W. & Alexandrowicz Z. 2003) (Fig. 10).

Given that around 90 species of land snails are recorded in the southern part of the Kraków-Częstochowa Upland (Riedel 1988, Wiktor 2004), the malacofauna of Witkowe Rocks is relatively rich.