This is the lowest vegetation belt of Illyrian province. The entire area is characterised by temperate continental climate with agreeable summer temperatures and abundant summer precipitation.
Querco-Carpinetum illyricum is one of the major and most significant climazonal forest community in this belt and it also belongs to the Carpinion betuli illyrico-podolicum alliance and the Fagetalia order. The Querco-Carpinetum illyricum flourishes on lowland terrains with gentle slopes, on moderately podsol, zonal soil with neutral of slightly acid reaction. By its floristic structure which is characterised by a large number of species, this community has basically middleeuropean character. Nonetheless, among its constituent elements there is a great number of old, relic, illyrian-balkan species.
However, most of the area of this vegetation belt former forest stands of communities Querco-Carpinetum illyricum are cleared out and their habitats , due to agreeable climatic, edaphic relief conditions turned into agricultural superficies of all kinds. These are mostly arable fields and partly meadows and pastures which in general belong to the order Arrhenatheretalia and partially to Brometalia erecti order.
Within this belt, on lime-poor , deeper and leached soil as well as on silicates grows the acidophyllous forest community Querco-Castanetum illyricum of the Quercetalia robori petraeae order. On the place where such forests used to be after they retreated, developed heather which belongs to the community Genisto-Callunetum illyricum.
The great significance for this belt have the specific flood and bog communities. The vegetation of woodlands and shrublands of these areas belongs chiefly to Populetalia albae order. Among the flood and bog communities the most significant is the Genisto elatae-Quercum roboris community together with the following communities: Carici brizoides-Alnetum glutinosae, Alnetum glutinosae-incanae, Salici-Populetum, Leucoio-Fraxinetum angustifoliae. After the retreat of these woodlands and shrublands on the places where they used to be develops the vegetation of flood and bog meadows and pastures which mainly belong to the Deschampsidietalia and Molienetalia orders and partly to Phragmitetalia and Arrhenatheretalia orders.
In some parts of Croatia, within the lower vegetation belt of Illyrian province on calcareous and dolomite locations which are not suitable for the development of the climazonal community Querco-Carpinetum illyricum, grows the special forest community Querco-Ostryetum carpinifoliae. According to its floristic structure this community has a Mediterranean-montane character and therefore it enters the Ostryo-Carpinion orientalis alliance.
On the basic soil of this area grows essentially the Erico-Ostryetum community
