The Jánský vrch NNM covers the flattened ridge of the Jánský vrch Hill which lies close to the village of Korozluky and not far from the town of Most in the Ústecký kraj – Ústí nad Labem Region. The protected area covers an area of 11.9ha on the western edge of the České středohoří Mountains PLA and was declared in 1951. The subject of the protection is the occurrence of rare xerophilous and thermophilous communities on a calorific basalt rock basement.
The hill is built of effusive basaltic rocks. Beds of porcelanite and burnt clays of the Most Strata can also be found in the near surroundings of the protected area.
The geological basement together with the slope angle and exposition provide the conditions for the occurrence of xerophilous and thermophilous plant species. The oat-grass Helictotrichon desertorum grows here as a relict from warmer times and is on the western fringe of its distribution here. This continental element has the centre of its distribution on the steppes of southern Russia and Turkmenistan. We can also find the feather-grass Stipa joannis, St. Bernard’s lily (Anthericum liliago), spring pheasant’s eye (Adonis vernalis), the milk-vetch Astragalus excapus, purple mullein (Verbascum phoenicum) and the small Bohemian pasque flower (Pulsatilla pratensis subsp. bohemica) on the ridge. The most valuable botanical localities are the steppe meadow and the small steppe enclaves within the wood. The wood itself acts as a buffer zone because its species composition is a long way from the natural condition.
The fauna on Jánský vrch Hill has not been fully researched, and the only inventory concerns the butterflies. Endangered species which are bound to forest-free areas or forest steppe were recorded here, including the red-underwing skipper (Spialia sertorius), blue-spot hairstreak (Satyrium spini) and the black-veined white (Aporia crataegi).
The forest stands are heavily modified, consisting of domestic and introduced tree species. They are significant in that they form a buffer zone around the most valuable parts of the territory and help to isolate them from the nearby built-up area of the village of Korozluky.
The territory requires regular maintenance work including removal of false acacia (Robinia pseudoacacia) and bladder senna (Calutea arborescens). The area would be in better condition if the previous methods of cultivation, such as sheep grazing were renewed. The fringes of the monument suffer from being close to the buildings in the village and the ways in which the local farmers utilise the landscape.