Hůrka u Hranic National Nature Reserve

The Hůrka u Hranic (Hůrka hill near Hranice) NNR lies on the right bank of the fault valley of the Bečva river between the railway station in Teplice nad Bečvou and the town of Hranice na Moravě in the Olomoucký kraj – Olomouc Region. The protected area was declared in 1952 on an area of 37.45ha to protect the flora, fauna and karst phenomena – especially the Hranická propast – Hranice Abyss, which is the deepest abyss in the Czech Republic (depth 289.5m – measured in 2008).

The territory lies on the contact between the Devonian limestones, which lie under the southern section of the reserve, and the Culm (Lower Carboniferous) shales, greywackes and conglomerates. This variety of geological basements is reflected in the variety of plant communities in the reserve, although the limestone area has much richer vegetation than the rest of the reserve. Remnants of the natural forest stands, with near-natural tree species composition and shrub and herb layers which reflect the locality type and conditions have been preserved here. The forest stands include central European hornbeam-oak woods and beechwoods but we can also find vegetation here which is close to the forest steppe and steppe communities of xerothermal regions. Nearly 380 vascular plant species and more than 130 moss species have been recorded in the reserve so far. The tree layer is dominated by hornbeam (Carpinus betulus), pendunculate oak (Quercus robur), sessile oak (Quercus petraea), small-leaved lime (Tilia cordata), maples (Acer sp.) and ash (Fraxinus excelsior), with beech (Fagus sylvatica), silver fir (Abies alba) and Scots pine (Pinus sylvestris) in places. Non-native elements in the forests include the Weymouth pine (Pinus strobus), false acacia (Robinia pseudoacacia) and Norway spruce (Picea abies). Uncommon plant species which grow in the section with a limestone basement include the oxlip (Primula elatior), Hacquetia epipactis of the Apiaceae, white helleborine (Cephalanthera damasonium) and the martagon lily (Lilium martagon). The rare relict fern – hart´s tongue (Phyllitis scolopendrium) has survived on the floor of the dry section of the abyss. Rare mosses which grow in the reserve include the beard moss Didymodon sinuosus, common striated feather-moss (Erynchium striatulum) and the pocket moss Fissidens arnoldii – which has its only locality in Moravia in the Hranice Abyss.

The abyss and its surroundings are also the most interesting part of the reserve from a zoological standpoint. More than 20 types of organisms have been identified in the apparently dead water in the pool in the abyss. All of these organisms have been found at the correct levels according to the stratification of the water column. The animals which have been found near the water surface are representatives of species from various kinds of waters, with a predominance of spring area animals. The deeper water layers are only inhabited by small crustaceans which typically live in underground karst waters. These uncommon members of our aquatic fauna include the arthropod – Bryocamptus typhlops, the scud – Niphargus tatrensis and Acanthocyclops venustus of the Cyclopidae. The pseudoscorpion Chthonius heterodactylus was also recorded for the first time in the Czech Republic in the Hranice Abyss. This Carpathian endemic species was later found in other parts of the NNR. However, the most significant find of recent years is the discovery of the rove beetle Atheta spelaea for the first time in the Czech Republic. This rare element of the central European cave fauna is on the northern edge of its range at Hůrka u Hranic. This small beetle seeks out bat droppings and other organic remnants, on which it hunts smaller invertebrate animals in the Rotunda suchá cave. This dry cave can only be reached by cave-divers as its entrance lies in the pool in the abyss, although the bats can reach it through a crack in the wall of the abyss. A unique summer colony of greater mouse-eared bats (Myotis myotis) can be found in the Rotunda suchá cave and a further 13 species of bats (Chiroptera) hunt in and around the abyss during the vegetative season. Jackdaws (Corvus monedula) and kestrels (Falco tinninculus) also nest on the rocky walls in the abyss.

The Hranice Abyss and the nearby Zbrašovské aragonitové jeskyně NNM (Zbrašov Aragonite Cave) both developed as a result of hydrothermal karstification processes. The abyss was opened up by the abrasive effects on the limestone by the warm acidic waters rising up from inside the massif along fissures leading to the surface.

The top of the hill offers stunning views into the depths of the abyss with its vertical rocky walls. The visible “dry” part of the abyss is 69.5 metres deep but an enormous space full of mineralized water continues below the surface of the pool and nobody has yet reached the bottom of the abyss. The Polish diver Krzysztof Starnawski reached a depth of 181 metres in 2000. A probe released by divers in 2006 went down to 220 metres below the water surface making a combined depth of the abyss of 289.5 metres. The Devonian limestones are up to 1000 metres in thickness here and when we consider that the abyss was carved out by hydrothermal processes, where the karstification took place in an upward direction, the Hranice Abyss is potentially much deeper than the depth which has been discovered so far.

Folk legends which tell of the supernatural origins of the Hranice Abyss date back many centuries. The first written record of the abyss comes from Tomáš Jordán of Klausenburg, who described the abyss in detail in his “Book of Medicinal or Mineral Waters in Moravia” in 1627 as a rugged hill and this made the Hranice Abyss the first karst feature in the Czech Republic to be recorded on a map.

Visitors can follow a themed trail which was built in 1998 and leads from the Teplice nad Bečvou railway station to the wide mouth of the abyss or enter the reserve from the opposite direction from the campsite in Hranice.

The large number of trees which were felled by a windstorm in the summer of 2008 will offer a unique opportunity to monitor the natural renewal and regeneration of the forests in the reserve.