Réserve naturelle régionale du gouffre du Creux à Pépé: Karst Geography and Bat Habitats

The reserve's history is closely bound to a shift in French environmental law in the early 2000s. The 2002 "Démocratie de proximité" law transferred new competences to the regional level and caused the lapse of the voluntary nature reserve designation that several pre-existing bat caves had relied upon. Three sites of recognized importance for bats lost their protective status during this transition, creating an urgent conservation gap.

In response, CPEPESC Franche-Comté, working closely with the former Franche-Comté region, studied the feasibility of building a new regional network of reserves specifically dedicated to the protection of bats and their habitats. The outcome was the creation, between 2015 and 2017, of a network of seven regional nature reserves across the region, each centred on a cave system of recognized importance for chiroptera. The Réserve naturelle régionale du gouffre du Creux à Pépé was classified on 24 September 2015 as part of the first wave of this network.

CPEPESC Franche-Comté was formally designated as the manager of the network by prefectural and regional orders in October 2015 and December 2017. A unified management plan covering all reserves in the network was submitted to the regional scientific council for natural heritage and adopted unanimously by the permanent commission of the Bourgogne-Franche-Comté regional council on 27 September 2019. This plan set out nearly seventy actions focused on preserving the functionality of the cave roost network for six priority bat species over a five-year horizon.

The Creux à Pépé lies on the western flank of a compact Jurassic limestone anticline, a typical structural feature of the Jura range. The host rock belongs to the Bathonian stage of the middle Jurassic and forms solid limestone beds in which karstic dissolution has opened the sinkhole and its associated gallery system. The cave extends several metres into the hillside as a series of natural underground passages.

Above ground, the landscape is unusually compact. The sinkhole opens onto a patch of dry calcareous grassland built on a very shallow stony soil interrupted by frequent rocky outcrops. The thin soils prohibit deep rooting and keep the sward low and herb-rich, a classic signature of Mesobromion-type limestone grasslands in the French Jura. To the south, a dense hedgerow screens the reserve from agricultural meadows on adjacent farmland, functionally restoring part of the original woodland edge that once separated cave openings from open farmland.

The broader setting is one of rolling limestone country south of the Doubs river. From the reserve's elevated position, the land drops toward the Doubs valley and the Grotte d'Osselle, giving the site a clear visual relationship with neighbouring karstic features. The reserve's elevation places it within the collinean to submontane zone of the Jura foothills, where the climatic conditions are cool and humid enough to support both beech woodland and the dry grassland facies of southern exposures.

Ecologically, the reserve is best understood as a stack of overlapping habitats: a subterranean cave system, an above-ground calcareous grassland mosaic, and a woody edge boundary created by the southern hedgerow. These habitats are small but strongly differentiated, and each contributes to the reserve's conservation logic.

The botanical inventory completed in 2019 by the Conservatoire botanique national de Franche-Comté recorded 103 vascular plant species across the reserve. Among these, one species, the early purple orchid (Orchis mascula), is considered regionally noteworthy in Franche-Comté. Four distinct phytosociological associations were identified within the reserve's footprint, three of which are classed as community-interest habitats under European conservation frameworks: Mesobromion grasslands of the French Jura, beech woodlands with wood melick, and xerothermic woodland edges. The general typicity of these habitats is moderate, reflecting the gradual encroachment of woody species into the open calcareous sward.

Ecologically, the reserve functions less as an isolated patch and more as a step in a chain of bat-friendly caves. The dry grassland and hedge mosaic around the sinkhole provides foraging resources and acoustic navigation cover for bats moving into and out of the cave, while the cave itself offers a stable microclimate suited to hibernation and nursery colonies. This combination of underground and surface habitats within a single, tightly bounded reserve is the defining ecological signature of the site.

The reserve's wildlife interest is overwhelmingly focused on bats, for which it was specifically created. Seven bat species or species groups are currently recorded as using the cave. The most significant is Schreiber's bent-winged bat (Miniopterus schreibersii), a cave-dependent species of European conservation concern whose populations depend on networks of undisturbed underground roosts. The Creux à Pépé functions as a major spring transit site for this species, with approximately two thousand individuals recorded moving through the cave during the spring migration period, making it one of the largest known spring concentrations of the species in Franche-Comté.

The cave also serves as a hibernation site for the greater horseshoe bat (Rhinolophus ferrumequinum), a species highly sensitive to disturbance during winter roosting. The reserve's broader conservation planning covers six priority species across the network: Schreiber's bent-winged bat, the lesser mouse-eared bat (Myotis blythii), the Mediterranean horseshoe bat (Rhinolophus euryale), the greater horseshoe bat, the lesser horseshoe bat (Rhinolophus hipposideros), and Geoffroy's bat (Myotis emarginatus).

The 2019 management plan defines nearly seventy conservation actions across the network, ultimately aimed at preserving the ability of these species to use the cave at all stages of their annual cycle. Any disturbance to underground roosting bats can cause direct mortality or force colonies to relocate to less suitable sites, which is why human access to the cave is prohibited year-round.

The Creux à Pépé is a conservation site of unusually high legal density for its size. Beyond its 2015 classification as a regional nature reserve, it carries a ZNIEFF type I designation (since 2014), two separate Natura 2000 special area conservation designations, and a biotope protection order (APPB). The reserve also sits adjacent to the RNR of the Grotte de Chenecey, another site in the same bat-focused network.

Its conservation logic is twofold. First, the site protects a discrete and ecologically essential piece of habitat: a single sinkhole and its associated cave, in a region where accessible underground roosts are scarce and easily disturbed. By subsuming the cavity permanently under multiple layers of protection, the reserve removes a recurring threat, the loss of protection through gaps between legal instruments, that had previously affected three important bat sites during the regulatory transition of 2002.

Second, the reserve's protection extends to the surface habitats that frame the cave entrance. The dry calcareous grassland, the beech-melick woodland patches, and the southern hedge form a functional foraging buffer around the roost, and each is recognized under European habitat conservation frameworks. The 2019 unified management plan for the network addresses not only cave microclimate and access control but also the long-term management of woodland structure, shrub encroachment, and the conservation of notable flora. Together, these layered instruments make the Creux à Pépé a model of how a very small site can carry outsized regional conservation value.

The Creux à Pépé is integrated into the karstic landscape identity of the Doubs valley, a region celebrated for its abundance of caves and sinkholes. The reserve lies just above the Grotte d'Osselle, one of the longest-known caves in the Jura and a landmark of regional natural heritage. This proximity places the Creux à Pépé within a broader cultural geography in which caves are both ecological treasures and elements of local identity, important to regional tourism, education, and natural history.

The reserve also exemplifies a specific chapter of modern French environmental culture: the transition of grassroots bat protection into formal regional conservation. The work of CPEPESC Franche-Comté, with regional government support, transformed a small number of locally important caves into a structured network of legally recognized reserves between 2015 and 2017. This model, driven by local expertise and citizen science traditions around chiroptera, is itself part of the cultural context of the site.

The reserve highlights itself through the combination of a very small footprint and a very large ecological role. Its underground system hosts one of the most important spring transit colonies of Schreiber's bent-winged bat in Franche-Comté, with about two thousand individuals moving through the cave each spring. The cave also supports a wintering population of the greater horseshoe bat, and is used across the annual cycle by six priority bat species across the broader network.

Its surface area is small but botanically rich: 103 vascular plant species, including a notable orchid, and three community-interest habitat associations within Mesobromion grassland, beech woodland, and xerothermic woodland edges. The site is layered under an unusually dense set of protection instruments, from regional nature reserve status to APPB and Natura 2000 designations, and is consistently regarded as one of the cornerstone sites for chiroptera conservation in the Jura foothills.

The site's year-round restriction on public access to the cave rules out any form of cave-based wildlife encounter. That said, the surrounding limestone grassland and the broader Doubs valley landscape have a clear seasonal character. Spring is ecologically the most significant period here, marked by the mass transit of Schreiber's bent-winged bats through the cave and by the flowering of early orchid species on the dry calcareous sward, including the regionally notable Orchis mascula.

Late summer and early autumn illuminate the Mesobromion grassland as it dries, while winter brings quiet conditions in which the cave's bat hibernation populations settle in. For visitors interested in the regional bat conservation network rather than cave access, the most informative encounters typically occur through CPEPESC Franche-Comté's outreach programming and guided landscape tours of related sites in the Doubs and Jura foothills.