Vegetation and Climate of the Summit Zone of Mount Kinabalu in Relation to the Walker Circulation

Abstract

Mountains of the tropical Pacific are influenced by synoptic-scale air subsidence, which causes a temperature inversion and a distinct dry meteorological condition above the inversion. The inversion appears at a lower altitude in the eastern Pacific where descending air of the Walker circulation prevails. On the other hand, if or how the alpine ecosystem of the tropical mountains of the western Pacific is influenced by dry synoptic-scale air subsidence is not well documented. We studied the vegetation and climate of the summit zone of Mount Kinabalu (4095 m) of Borneo. The leaf-size spectrum and physiognomy of forest community changed abruptly along the slope approximately at 3200 m from microphyll to leptophyll, suggesting that dry climatological conditions influence the vegetation above that altitude. Mean daily vapor pressure deficits (VPDs), estimated daily potential evapotranspiration (ET0), and the ratio of 30-day total ET0 to 30-day total rainfall increased drastically during El Niño and the magnitude of the increase was greater in the summit zone than in the montane zones. Increased VPDs during El Niño were linked with katabatic winds in the summit zone. We suggest that such irregular dry spells caused by synoptic-scale air subsidence in El Niño years can be a major factor for the formation of xeromorphic vegetation of the summit zone of Mount Kinabalu.