Compared to the lower forest area (2.1.1), the lower mountain vegetation belt, regarding the climatic conditions, is characterised by a notable decrease in temperature and increase in humidity. And the decrease in temperature, which rises as the height gradually increases, causes the shortening of the vegetation period. Both the lower and the upper boundary of this belt depend on various factors such as: geographical position, exposition, geomorphological conditions, structure of basic soil etc.
Regarding the vegetation, in the first place and most significant are mesophyllous beech and fir forests developed on basic, neutral or lightly acid base as the climazonal communities of the area.
They mostly belong to the south-eastern alliance Fagion Illyricum. The primary community of this alliance is the Fagetum illyricum community (mountain beech forest), which has a large number of separate distinctive species and is extremely differentiated in the horizontal as well as the vertical direction of its growth.
Apart from the basophyllous-neutrophyllous and lightly acidophyllous forest communities of the Fagion illyricum alliance various extremely acidophyllous communities of deciduous and coniferous forests which partly belong to the Quercetalia-Piceetalia and Luzulo-Fagion alliance and partly to Vaccinio-Piccetalia and Piceion excelse alliance grow in the mountain belt of Illyrian province on great heights.
Very interesting and economically important fir forests which belong to the Blechno-Abitetum community grow on silicates and other non-calcareous soils of western Croatia and have a large importance in Gorski Kotar area. The peculiar Picetum croaticum montanum community should be mentioned as a special type of fir forests in this mountain belt.
Except the fore mentioned communities in the mountain belt there are also basophyllous pine forests or Erico-Pinetalia order.
Though the mountain belt of this vegetation belt is mostly inhabited, forest vegetation is almost everywhere more or less influenced by man. Many forests are cleared long ago and in the area where they used to be grow various meadows and pastures. Calcareous earth is characterised by vegetation of meadows and pastures which largely belong to Brometalia erecti order, and from which in places under the influence of fertilising, develop certain communities of the Arrhenatheretalia order.
Silicate and other lime-poor superficies are characterised by completely different meadow and pasture vegetation, which belongs to Calluno-Ulicetea class. Those are partly vast heathers and partly acidophyllous meadows on which you can find Nardus stricta grass. In karst area of this belt, in moist, humid sink-holes grows in places a special vegetation of high herbaceous vegetation which belongs to Adenostyletalia order.
