Réserve naturelle régionale des grottes de la côte de la Baume: Mapping the Protected Karst Landscape

The protection history of these caves dates to a period before regional nature reserves existed in this form. Following the 2002 "Démocratie de proximité" law, competence for certain nature protections was transferred to the French regions, and the earlier status of Réserve naturelle volontaire was abolished. Three cave sites of importance for bats lost their protected status as a result.

In response, the former Franche-Comté region, working closely with CPEPESC Franche-Comté, studied the feasibility of building a network of new regional nature reserves specifically for bat caves and their habitats. This effort resulted in the classification of seven reserves, of which the Grottes de la côte de la Baume is one. The site's formal registration as a Réserve naturelle régionale dates from the deliberation of 17 November 2017, while the manager, CPEPESC Franche-Comté, was officially appointed by orders of 12 October 2015 and 22 December 2017.

Beyond the RNR designation itself, the site already benefited from earlier protections. It has been listed as a ZNIEFF type I area for the reculée de Vaux-sur-Poligny since 2009, and the cliff sections are covered by a prefectoral biotope protection order for the limestone cornices of the Jura dated 5 July 2013. The cliffs were included in the Natura 2000 cave network site for Schreibers' bent-winged bat from 2015. In 2019, after a period of consultation, a unified management plan covering the entire cave network was adopted unanimously by the permanent commission of the Bourgogne-Franche-Comté Regional Council, setting conservation objectives for a first five-year period.

The reserve lies on the flank of a reculée, a steep-sided dry valley typical of the limestone plateau of the Jura. These formations were carved by river erosion that cut back into the plateau, leaving behind near-vertical cliff faces and amphitheater-like half-valleys. The cliffs below the caves of the côte de la Baume show this character clearly, with exposed rock walls, coarse scree slopes, and forested ledges that climb toward the plateau above.

The slope faces roughly north, which keeps it cooler and moister than the surrounding plateau. This combination of shading, rockfall, and the build-up of fine humus on stable ledges creates the conditions for distinctive mountain-slope forest communities, particularly scree-slope ash woodlands. Lewis the surrounding vegetation has been left untouched for more than twenty years, the cliff base and the accumulating scree are steadily returning to a more natural, uneven state. The resulting visual texture is one of mixed woodland, rocky outcrops, and exposed cliff, framed within an unusually narrow protected perimeter.

The forest on the reserve's slope hosts habitat types that are considered priority features under the European Habitats Directive. In particular, the cool-faced scree slopes support a form of ash forest rich in hart's-tongue fern (Scolopendre), a fern that thrives in humid, shaded, rocky conditions.

These hillside woodlands have not been actively managed for more than twenty years, and as a result they show structural diversity typical of maturing natural forest, with fallen deadwood, layered canopy, and varied regrowth on unstable ground. The combination of cliff, scree, and layered canopy produces transitions between rock habitat, open slope, and closed woodland within a very short distance. This high habitat diversity in a compact area is what allows the reserve to support such a wide range of bat species alongside woodland flora and cliff-nesting birds.

Bats are by far the most important wildlife group on this site. Fourteen species or species groups are recorded as using the caves across different seasons. The caves function as winter hibernation sites, spring and autumn transit roosts, and summer maternity sites for different species.

The Schreibers' bent-winged bat (Miniopterus schreibersii) uses the cavities during the spring and autumn transit periods, with gatherings that can reach around 200 individuals. The Greater horseshoe bat (Rhinolophus ferrumequinum) maintains a maternity colony of roughly 150 individuals in one cave, while the nearby cave is used as a winter hibernation site by the same group. Several other horsehoe and mouse-eared bat species, including Geoffroy's bat and other members of the Vespertilionidae family, also hibernate in these cavities. Across the wider cave network, six bat species are designated as conservation priorities: Schreibers' bent-winged bat, lesser mouse-eared bat (Myotis blythii), Mediterranean horseshoe bat (Rhinolophus euryale), greater horseshoe bat, lesser horseshoe bat (Rhinolophus hipposideros), and Geoffroy's bat (Myotis emarginatus), most of which appear on this site.

Above the bats, the cliffs provide nesting habitat for peregrine falcon (Falco peregrinus), a species that depends on undisturbed rock ledges for breeding. Because of this, cliff-nesting raptors are also factored into the reserve's seasonal protection rules.

The reserve's main conservation role is to maintain a functional, protected network of bat caves across the Bourgogne-Franche-Comté region. The Grottes de la côte de la Baume is one of seven linked sites in this scheme, and the network's overall objective is to preserve enough roosting and breeding habitat to keep six priority bat species viable. The presence of so many species on a single small cliff indicates how heavily these cave networks carry the regional bat population.

The site enjoys multiple overlapping protection layers. The RNR designation under the 2017 regional deliberation provides the core regulatory shelter. A prefectoral biotope protection order for the limestone cornices of the Jura covers the cliff face and particularly protects nesting birds from disturbance between mid-February and mid-June. The caves form part of the Natura 2000 Special Area of Conservation known as the Réseau de cavités à Minioptère de Schreibers, which extends the cave-level protection to the wider regional network. A ZNIEFF type I designation has covered the broader reculée de Vaux-sur-Poligny since 2009, providing an additional scientific inventory layer.

To protect sensitive cave-dwelling species, public access to the Grotte de la Rivière de la Baume is permitted only from 1 June to 31 October, while access to the Trou de la Baume is permitted only from 16 October to 14 April, a rotation that also keeps cave visitors away from the most vulnerable periods of hibernation and maternity. About seventy planned actions across the cave network target these priority bat species while also ensuring that the surrounding forest and cliff habitats remain in good condition.

The reserve is a remarkably compact site that packs together several layers of conservation interest: two natural caves used by at least fourteen bat species or species groups, a cliff face used by nesting peregrine falcons, and a maturing scree-slope ash forest that qualifies as a priority habitat under the European Habitats Directive.

It is also a clearly structured example of how French regional nature reserves are used today: a small surface area, tightly defined around cave mouths and cliff habitat, protected by overlapping statutory tools and managed under a single coordinated plan that links it to six other caves in the same network. For visitors interested in karst landscapes, cliff scenery, or the quieter side of wildlife conservation, this site offers a striking example of how caves can sit at the center of a carefully built protection strategy.

Public access to the two main caves follows a seasonal rotation designed to protect bats. The Grotte de la Rivière de la Baume is open to the public between 1 June and 31 October, while the Trou de la Baume is open between 16 October and 14 April; outside these windows both caves are closed. The cliff portions of the reserve are also subject to restrictions on certain activities between 15 February and 15 June to safeguard nesting cliff birds.

For general enjoyment of the surrounding landscape, the warmer months offer easier walking conditions through the wooded slope, while mild autumn days frame the cliffs and the entrance area in lively colors. Anyone curious about the site should be aware that cave interiors are only open during specific seasonal windows and that the broader reserve is a quiet protection zone rather than a developed visitor attraction.