Kaluža NNR covers an area of 57.03 ha at elevations between 320 and 482 metres above sea level in the parishes of Lesní Albrechtice and Žimrovice, which lie to the south of the city of Opava in the Moravskoslezský kraj – Moravian-Silesian Region. The subject of the protection is the natural herb-rich beechwoods and talus and ravine forests in the environmental complex of the Moravice river valley in the eastern part of the Nízký Jeseník mountain range. The reserve includes a wide variety of forest types, but the herb-rich beechwoods cover the largest area.
The NNR includes the upstream slope of a sunken meander on the Moravice river as well as the neighbouring etchplain of the Nízký Jeseník mountain range. On the surface on the whole area of the reserve the Hradec – Kyjovice Formation of the Nízký Jeseník culm can be found. The terrain surface is covered with stone-loam elluvia and colluvia of varying thicknesses. The steep, west-facing concave slopes are covered by acidic skeletal cambisols, although talus ranker can also be found on small areas.
The territory covers a large complex of preserved natural beechwoods and fir-beech stands in which the poor, acidic beechwoods of the 4th vegetation level (Luzulo-Fagion) are interspersed with the herb-rich beechwoods of the 5th vegetation level (Dentario enneaphylli-Fagetum, Melico-Fagetum and Festuco-Fagetum associations). In all of the beechwood types which are found here, beech (Fagus sylvatica) is the dominant tree species. On the rocky, western slopes in the Moravice river valley where the stands transform into oak-hornbeam with maple and lime (Tilio-Acerion alliance) there are larger numbers of sycamore (Acer pseudoplatanus) and with more Norway maple (Acer platanoides) and small-leaved lime (Tilia cordata) in places.
On the upper parts of the slope with poorer substrates, which are covered with beechwoods of the Luzulo- Fagetum association, we can also find a higher representation of silver birch (Betula pendula) in the tree layer. The presence of Norway spruce (Picea abies) and European larch (Larix decidua) in the tree mixture in parts of the reserve is evidence of insensitive forestry intervention in the past. The composition of the herb layer in the reserve reflects the variety of local conditions which are determined by the relief and is a reliable indicator of the phytocenological category to which each individual area of the beechwoods belongs. Among the rare and endangered species which grow here are the nine-leaved toothwort (Dentaria enneaphyllos) and martagon lily (Lilium martagon).
A detailed inventory of the fauna in Kaluža NNR has not been carried out yet. Beetles which can be found on the dead trunks of old, deciduous trees, especially beeches, include lesser stag beetle (Dorcus parallelopipedus), the stag beetles Platycerus caraboides and Sinodendron cylindricum, rose chafer (Cetonia aurata), the chafer Potosia cuprea, the bee beetle (Trichius fasciatus), noble chafer (Gnorimus nobilis), the chequered beetle Tillus elongatus and the cardinal beetles Pyrochroa coccinea and Schizotus pectinicornis. On the meadows by the Moravice river (below the reserve) some rare butterfly species have been recorded, including scarce large blue (Maculinea teleius) and purple-shot copper (Lycaena alciphron).
The whole territory of the reserve is covered with predominantly natural beechwoods of medium and old stand age (with a younger understand in places). The forest stands include a low proportion of spruce (approximately 5 – 15%) but fir is missing here. Forestry intervention is aimed towards gradual elimination of the spruces and supporting the natural rejuvenation of the beeches and other deciduous trees by leaving the dead trees in place. Dead and dying spruces are gradually removed from the forest stands and firs are planted here.