This is the highest belt of forest vegetation of mountain areas in the Illyrian province which covers the area above the upper border of the belt of submontane forests. On relatively short mountains juniper is the highest belt of vegetation all together. Regarding the general climate-ecological conditions of the juniper belt, significant are low average annual temperatures and relatively cold and short summers. Therefore is the vegetation period relatively short too. Besides that in this belt a great importance carry the strong winds as well as the long snow period.
The juniper itself has the characteristics of the low-lying, lodged "forest", or shrub where the greatest importance has the Pinus mugo. Pinus mugo belongs, within the Vaccinio-Piceetalia order to a separate alliance Pinion mughi. The community Pinetum mughi illyricum has the greatest importance in the mountains of the western Croatia. This community develops in various facies and development phases which belong to the two main subasociations: Pinetum mughi illyricum typicum and Pinetum mughi illyricum fagetosum. Besides these main associations in the juniper belt there are some other phytocoenological related communities of woody and mountain plants such as Rhodoreto-Juniperum shrublands, Erico-Fagetum and Salicetum grandifoliae shrublands.
On the huge area of this belt grow different communities of mountain swards, rock rifts, steep limestone rubble etc. which according to their phytocoenological structure mostly belong to various vegetation units of the mountain belt above the upper forest border.
