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Topographical Zones

 

The vertical distribution of vegetation zones varies geographically both with distance from the equator, soil types and with local and regional climate. In this work the following broad altitudinal zonation terms are used. They are based on major broad altitudinal forest habitat divisions found in Borneo. These were the original biotopes covering all of Borneo:

 

i.       Lowland: sea level to below 600m
ii.      Hill or lower montane from c. 600 to c. 1500m
iii.     Upper montane c. 1500m to c. 2000m
iv.     Subalpine 2000-3000m
v.      Alpine >3,000m

 

A more detailed breakdown of the habitats and zones in which specimens have been collected is given in the Checklist section.

 

Roughly the five zones above correlate with the vegetation zones discussed by Whitmore (1990) and Ashton (2003), where lowland forest vegetation gradually gives way to a lower montane forest flora between 600-1200m and to upper montane forest above 1500m (other things, like soils, being equal, the larger the mountain, the higher the transition zones). On massive Mt Kinabalu, the highest point in Borneo, the tree diversity increases with altitude, reaching a maximum between 600-1300m. This is possibly caused by peaks in the lower or upper ranges of species. See also Kitayama (1992, 1995), Grytnes & Beaman (2006) and Grytnes et al., (2008). However because of the extensive lowland deforestation this probably underestimates the number of species at lower elevations (<1200m) (Ashton, 1992; 2003). Beck & Chey (2008) documented a pronounced diversity peak in Geometridae at c.650m asl but were unable to correlate this with increased faunal overlap as a single explanation of observed patterns. They tentatively conclude that temperature (i.e. energy limitation) is the best explanation for decreasing diversity towards high elevations, but did not find a compelling explanation of lowered diversity near sea level. There is evidence that lepidoptera distribution zones are extending upwards on Mount Kinabalu (I-Ching Chen et al., 2009), possibly associated with regional warming.

 

The absolute altitudes for transition between vegetation types vary considerably and there is no distinct transition between lowland forests and upper montane (moss) forests. However Ashton (2003) recognises a distinct lower montane forest ecotone [hill forest] at 900-1200m. Fagaceae spp. and Lauraceae spp. appear, becoming more common, as one ascends to the upper montane forest. The transition from lower montane to upper montane varies with the size of the mountain. For a small, exposed peak like Gg. Silam near Lahad Datu in E. Sabah, it is possible to find upper montane, mossy forest (at least on ridges), at a relatively low level. Conversely, on Mt. Kinabalu, upper montane forest becomes evident at around 1700m.