On the special botanical character of the Leuser Park and vicinity, with Emphasis on the High Mountain Blang Vegetation of Northern Sumatra

‘Blang’ is the Gayo name for the extensive, open, grassy, lowland savanna land of their area in Aceh, N Sumatra. By analogy, the open areas with heath-like vegetation high in the mountains are called ‘mountain blang’. There are two somewhat intergrading types: a wet and a dry one. They are believed to have been caused by regularly burning since immemorial times by hunters, but our explanation is that they have (at least largely) developed for edaphic reasons, i.e. are due to prevailing climatic conditions on very poor, leached-out and almost impermeable kaolinitic soils. Their extension was possibly enlarged by occasional frost and burning, which may account for the sometimes, but not at all always, sharp demarcation with the surrounding stunted forest. The wet-type blang probably is maintained by the absence of woody species which cannot stand the permanent water-soaked conditions of the peat soil under the boggy vegetation. It is advanced here that the mountain blangs, although in total they may cover only a few square kilometres, merit the status of a high-ranking vegetation formation of their own, next to the subalpine ericoid forest, rather than being included in the latter as accepted for the whole of Sumatra. This is supported by: 1. its floristic composition, including a number of ‘northern’ as well as ‘eastern’ elements and a remarkable number of very local endemic species on the old, largely non-volcanic N Sumatran mountains, compared to those over base rock of volcanic origin as found on the high mountains of the rest of the Barisan Range, possibly in connection with isolation by the relatively recent volcanic Toba eruptions; 2. the singular physiognomy of the high mountain blang vegetation, located on a number of high mountains in restricted areas in N Sumatra; 3. the edaphic, non-anthropogeneous origin, both of the dry and the wet types of the blang.