What causes the vegetation types on Mount Bloomfield, a coastal tropical mountain of the western Philippines?

Mount Bloomfield has been shown to have several vegetation types, including medium stature forest on greywacke, small stature forest on serpentinized peridotite, and scrub and Gymnostoma woodland on dunite. The causes of the large physiognomic and floristic differences among these vegetation types have been investigated by soil chemical analyses, soil physical studies, and by a phytometer experiment involving the crop plant Zea mays. There was no relationship between maximum tree height and the soil chemical factors analysed (P, K, Ca, Mg, Ni) but there was a directly proportional relationship between maximum tree height and soil water retention. The phytometer experiment supported the idea that there is no acute soil toxicity in spite of the high soil Ni and Mg/Ca quotients recorded in this study. It is concluded that soil water retention, perhaps in combination with fire, is the major cause of stature differences among the vegetation types and together with soil chemistry is an important determinant of floristic composition.