01H1

H. Inland rock habitats

Cave entrancess

Relationships with habitat classifications. EUNIS: H1.221 Continental subtroglophilic vertebrate caves, H1.231 Troglobiont invertebrate temperate caves, H1.24 Troglophilic invertebrate caves, H1.25 Subtroglophilic invertebrate caves; PAL. CLASS.: 65.25 Continental bat caves, 65.41 Troglobiont invertebrate temperate caves, 65.5 Troglophilic invertebrate caves, 65.6 Subtroglophilic invertebrate caves; HD 92/43: 8310 Caves not open to the public.

Conservation status. BDA, BC, HD.

Category. Vulnerable [VU – A1, 2 C1 D3 H2 I J L1].

General characteristics. The access to the caves can be both narrow crevices or entrances that are several tens of meters high and wide. Due to strong erosion processes resulting from the intensive impact of different atmospheric factors, the entrance to some caves can be larger than the profile of the underground galleries. The characteristics of the habitat are close to the ecotonic zone between surface and typical underground environment, where sunlight and photosynthesising organisms are absent. The temperature fluctuations are high and the light decreases progressively towards the inner part of the cave. There are several types of cave entrances: entrances of dry caves and abysses, sinkholes where rivers and streams disappear, and entrances of spring caves. The increased air humidity due to the air circulation from the inner parts of the caves creates favourable conditions for the development of hygrophytic mosses, ferns, etc. Very often, dead leaves and branches accumulate at the entrances of the caves, thus creating favourable conditions for the development of rich detritophilic invertebrate fauna. The habitat is inhabited by specific pariethal fauna, dominated by insects and arthropods (mainly spiders and scorpions). Winter accumulations of Culicidae individuals are typical. The entrances of the spring caves are inhabited by typical crenophilic fauna dominated by Mollusca, Copepoda, Amphipoda, Isopoda, Trichoptera, Diptera, Coleoptera, Hydracarina, etc. Pyrrhocorax graculus builds its nests close to the entrances of abysses, while Hirundo daurica and Apus species build their nests in the arcs of the horizontal caves. A number of bat species (Rhinolophidae - Myotis blythii, Myotis myotis, Miniopterus schreibersii, etc.) reproduce at the entrances of the caves.

Characteristic taxa.

Distribution in Bulgaria. The habitat is directly related with the 5470 existing caves and abysses that have been discovered and registered in Bulgaria at altitudes from about 30 m (the caves in the lower part of the karst valley of Batova River and other rivers flowing into the Black Sea) up to above 2650 m on the ridges of the karst parts of Pirin Mts.

Conservation importance. The entrances of the caves area very important habitat for some Horseshoe bats and vesperoid bats during their reproduction period when they can reproduce in colonies in the semi-dark arcs near the cave entrances. Some bat species and birds that are not strictly related to the caves also can fly into the cave entrances. From the end of August to the beginning of October some caves are visited by hundreds of bats that search for breeding places and social contacts.

Threats. Unregulated fencing and transformation of the cave entrances into sheep shelters or other agricultural places. The breeding of domestic animals causes the permanent presence of flies (Calliphora spp., Musca spp., Sepsis spp., etc.) and parasites that are not typical for the cave environment. The firm closing of the entrances in order to convert them into storage places, fungi-farms, dairies, water catchments, open to the public tourist places, etc. Tourists and shepherds often make fires at the cave entrances, hence they can destroy the caves, the bat colonies and the cave invertebrate fauna. Often the cave entrances can be destroyed by activities in the stone-pits. The cave entrances that are close to human settlements, tourist complexes and chalets can be polluted by household wastes. When the entrances are the places where aboveground rivers and streams disappear, household and industrial wastes penetrate in the underground environment.

Conservation measures taken. The habitat and the caves themselves are in Annex № 1 of BDA. The habitat is geographically and functionally integrated with the continental caves and all measures for their protection are valid also in this case. The habitat is a part of the territory of the caves that have been proclaimed as nature monuments or protected sites and is also within the borders of nature and national parks and sites of the European Ecological Network NATURA 2000.

Conservation measures needed. Proclamation of the caves with rich biodiversity as nature monuments, protected sites and NATURA sites. Elaboration of regulations for opening to the public of new caves with informative texts at their entrances. Adoption of management plans for the protected areas karts areas and caves. On-site control of the visits in the protected caves that are important places for the bats; final approval and implementation of the Cave Law.

References. Benda et al. 2003; Beron et al. 2006; Petkoff 1943; Schunger et al. 2004; Stoyanov 2001.

Authors: Boyan Petrov, Ivan Pandourski


Cave entrances (distribution map)