Mohelenská hadcová step NNR covers an extensive complex of xerothermal communities of serpentinite rocky steppe, thermophilous grasslands and serpentinite pinewoods and is a unique territory from a number of viewpoints. The territory has been protected since 1933. The physical and chemical properties of the serpentinite rock, together with the ruggedness of the relief and the variations in microclimatic conditions have led to the unusually varied vegetation, flora and fauna communities which are found here. The specific character of the serpentinite basement has influenced the formation of some of the morphological peculiarities of the flora and fauna in the reserve, especially the nanism (dwarfed growths).
The NNR is a rocky and predominantly south-facing amphitheatre on the left-side valley slopes above the Jihlava river and the neighbouring peneplaned plateau which lies 150 metres south of the village of Mohelno in the south-east of the kraj Vysočina – Bohemian-Moravian Highlands Region. The buffer zone includes the rocky headland on the right bank of the Jihlava river – the so-called Čertův ocas – Devil’s Tail and the surrounding slopes around a sunken meander. The reserve covers an area of 50.34 ha at elevations of 260 – 384 metres above sea level, with the buffer zone covering a further 8.89 ha. The NNR lies in the parish of Mohelno and the buffer zone is in the parish of Dukovany.
The basement is formed predominantly of serpentinite, which was formed by regional metamorphism of basic rocks. The serpentinite consists of minerals of the serpentine group, especially antigorite and chrysotile with a high magnesium and iron content. Coarse-grained gabbro also accompanies the serpentinite. The serpentinite body near Mohelno is enclosed in granulites of the Náměšť – Krumlov massif. Parts of the granulites are recrystallized and such minerals are close in character to gneisses. The etchplain of the Znojemská pahorkatina hilly land is broken up by the deeply incised meanders of the Jihlava river valley with frost-riven cliffs on the serpentinite and talus aprons. The Čertův ocas (Devil’s Tail) rocky headland lies on the right bank of the river. In places the serpentinite is covered with Pleistocene loesses and loess loams which also include calcareous nodules (“cicváry”). The majority of the surface of the serpentinite body lacks a covering of weathering products. Boulder fields, boulder streams and serpentinite rock formations are found on the valley slopes. On the plateau above the valley the serpentinite is weathered with a thin soil cover. The granulite breaks down into sand-dominated elluvium, on which eutric cambisol has formed. On the lower parts of the slopes this passes into accumulated forms of cambisol of higher thickness and lower sand content. In localities where loesses cover the serpentinite, luvisols also occur. High concentrations of cobalt, chrome and nickel have been measured in the soil, reflecting the presence of these metals in the serpentinite.
The differing ecological conditions in each part of the territory are reflected in the different types of vegetation which grow there. Communities of the Asplenion serpentini alliance can be found in rock clefts and fissures with the serpentine spleenwort (Asplenium cuneifolium) which is strictly bound to a serpentinite basement and the cloak fern Notholaena marantae, which grows here in an exclave on the northern boundary of its range (it is only known from further north in Český kras PLA – The Bohemian karst). Communities of the Alysso-Festucion pallentis can be found on the steep rocky slopes with the dominant fescue - Festuca pallens, accompanied by the feather-grass Stipa dasyphylla, hairy greenweed Genista pilosa, mountain alyssum (Alyssum montanum), the moon carrot Seseli osseum, the toad flax Linaria genistifolia, the wild garlic Allium flavum, the viper’s grass Scorzonera austriaca and the spurge Euphorbia seguieriana subsp. minor. Growths of the dwarf sedge (Carex humilis) predominate on gentler slopes with a deeper soil profile and are accompanied by the clover Dorycnium germanicum, the feather-grass Stipa capillata, the moon carrot Seseli hippomarathrum, hoary ragwort (Senecio erucifolius), the pink Dianthus pontederae and goldilocks aster (Aster linosyris). Open communities of spring therophytes can be found on small areas with early star of Bethlehem (Gagea bohemica). Short-stemmed grasslands of the Festucion valesiacae alliancecan be found on the upland plateau, where the predominate species are the fescues Festuca pseudovina and Festuca valesiaca as well as another serpentinophyte – the thrift Armeria vulgaris subsp. serpentini and the accompanying species are purple mullein (Verbascum phoeniceum) and spiked speedwell (Pseudolysimachion spicatum). The potential forest vegetation of the territory would be serpentinite oakwoods (Asplenio cuneifolii-Quercetum petraeae). However most of the current forest stands, which developed by secondary succession and artificial planting are completely dominated by Scots pine (Pinus sylvestris) with only small numbers of sessile oak (Quercus petraea). The undergrowth is dominated by barberry (Berberis vulgaris). Rare species in the herb layer include mountain pennycress (Thlaspi montanum), which grows on the Čertův ocas (Devil’s tail) rocky outcrop across the river in the buffer zone and the moor-grass Sesleria albicans. Notable flora of lower plants, mosses and lichens can be found on the serpentinite rocks and rare lichen species which can be found here include Acarospora suzai, Lecanora leatokkaensis, Harpidium rutilans and Lichinella stipatula.
The invertebrate fauna in the reserve is unique and exceptionally rich. Detailed research began in the 1930s and has brought many interesting findings. The spiders, ants and other invertebrate groups have been studied in detail. Among the very rare thermophyte spider species which are found here are Ozyptila kotulai, Xysticus marmoratus and many more. More than 60% of the ant species in the Czech Republic live here and especially steppe and thermophyte species such as Plagiolepis vindobonensis and Camponotus aethiops are represented. Other notable Hymenoptera include the mammoth wasp Scolia hirta. The beetle populations are also notable and the ground beetles Cymindis axillaris, Cymindis humeralis and Platyderus rufus can be found here with the jewel beetle Buprestis octoguttata on the pines. One of the rarest grasshoppers which are found here is the bush cricket Ephippigera ephippiger and the rare ant-lion Distoleon tetragrammicus also occurs here regularly.
The butterfly populations on the steppe have been studied in detail and from several hundred species which have been recorded here, it is not easy to choose a few representative species. Among the most valuable butterflies here we can mention the forester moth (Jordanita chloros), the burnet Zygaena laeta, the geometrids: middle lace border (Scopula decorata), broom-tip (Chesias rufata), barred tooth-striped (Trichopteryx polycommata), the moths Ashworth’s rustic (Xestia ashworthii), rosy minor (Mesoligia literosa), the Arctiid moth Cycnia luctuosa and others. The moth - Ateliotum hungaricellum lives here on its north-western range-edge and other small butterflies which occur here include the pyralid moth Mecyna trinalis, the Tortricid moth Eucosma tundrana, the Gelechiid moth Sophronia ascalis, Scythris paullella and Adela dumeriella. In recent years the previous occurrence of the rare burnets Zygaena punctum and Zygaena cynarae and several other butterfly species has not been confirmed. The ant Strongylonathus bulgaricus and some relict spider species have also not been recorded here recently. On the contrary, current entomological research has uncovered many new insect species for the territory, but also for the whole Czech Republic.
The sunny slopes are the biotope of the common lizard (Lacerta agilis), smooth snake (Coronella austriaca) and especially the emerald lizard (Lacerta viridis), which has a relatively large population here and reaches its furthest penetration into the Bohemian-Moravian Highlands. The slowworm (Anguis fragilis) can be found in the open forest and the dice snake (Natrix tessellata) lives by the river below the steppe. The bird populations include the eagle owl (Bubo bubo) and predominantly thermophyte birds such as the wryneck (Jynx torquilla), hoopoe (Upupa epops), barred warbler (Sylvia nisoria) and the linnet (Acanthis cannabina). A small population of European souslik (Citellus citellus) lives in the reserve.
Mohelenská hadcová step NNR lies in a region which has probably been used continuously for agricultural purposes since Neolithic times. As the reserve is relatively close to the village and unsuitable for other agricultural purposes, it was used as a common pastureland. Cattle, sheep and goats were grazed on the steppe at various times. Photos from the first half of the 20th century show how intensive this grazing was – as they show a steppe “wasteland” with distinct evidence of erosion caused by grazing. After the territory was protected it was left unused for a long period, which also led to secondary succession by tree species (especially Scots pine) and grass biomass accumulated on the upland plateau. At the end of the 1980s a management plan was prepared and authorised and systematic work to remove the opportunistic pines and thin out the shrub growths began. Sheep grazing as a management technique was reintroduced on the plateau in 1997. Great efforts have been made, and are still being made, to remove the unsuitable false acacia (Robinia pseudoacacia). The reserve is open to the public by way of marked trails and a themed nature trail.