There are 35 active volcanoes in the region, with the western side steeper, and the eastern slide inclining to lowlands and plains.

Characteristic upper montane plants include conifers and trees in the myrtle family Myrtaceae.

The sub-alpine forest zone begins at higher elevations, and features grasses, heath, and bogs.

Ericaceous plants, including species of Rhododendron and Vaccinium, are common in the sub-alpine and upper montane forests.

Endemic birds include the red-billed partridge (Arborophila rubrirostris), Salvadori's pheasant (Lophura inornata), Hoogerwerf's pheasant (Lophura inornata hoogerwerfi), Sumatran ground cuckoo (Carpococcyx viridis), Schneider's pitta (Pitta schneideri), and Sumatran cochoa (Cochoa beccarii).