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E.S. Fernando: Vegetation of the Philippine Islands 3
material from the Philippine lslands from their earliest known geological history. Their
vegetation history, thus, remains poorly understood.
Vegetation
The natural vegetation of the Philippine Islands is generally a mosaic of different kinds of
forests (often called formations, Whitmore 1984a) which differ from each other in structure,
physiognomy and floristic composition. The primary vegetation (both dry land and wetland)
may be divided into 13 types following the scheme and nomenclature used by Whitmore
(1984a). The forest types described by Whitford (1911) have been adapted here with some
modifications. These have also recently been reviewed by Tan & Rojo (1988).
Similar formations can be recognized elsewhere in Southeast Asia on the basis of their
structure and physiognomy, but the differences in floristic composition can be substantial.
1. Tropical lowland evergreen rain forest
This is the typical tropical rain forest formation in the Philippine Islands. It includes the
dipterocarp and mixed-dipterocarp forests. This formation occurs from coastal flats up to C. 900
m elevation and is best developed in areas where rainfall is more or less uniform throughout
the year (as in the eastern parts of the archipelago) or where there is only a short dry season.
It is characterized by its richness in arborescent flora (Table 2). The Dipterocarpaceae forms
the major component of the forest and its emergents. Whitford (1909) has shown that the
relative density of dipterocarps, among trees exceeding 40 cm in diameter, varied from 3% on
Mindoro to 89% on Negros.
Variation generally occurs within the tropical lowland evergreen rain forest (Whitmore 1984a).
Whitford (191 I), indeed, recognized sociological units (also termed subtypes or associations)
within this formation in the Philippines. These are, however, often not readily distinguishable
because of the large number of species concerned and the difficulty of differentiating them in
the field. The change from one subtype to another is also usually gradual. The variation is
apparently correlated with elevation, topography, soil-water relations and dominant species
composition and perhaps even storm frequency.
This type of formation, dominant along the eastern parts of the archipelago, is battered yearly
by storms coming from the Pacific. Their canopy structure is often greatly moditied becoming
more diffuse and allowing more light to penetrate the understorey. This permits dense growth
of tangles of rattans (calamoid palms) and lianas, epiphytes, herbaceous plants on the forest
floor, arecoid tree palms, and seedlings and saplings of the emergents.
2. Tropical semievergreen rain forest
This formation includes deciduous trees in a mixture but with a tendency towards
gregariousness (Whitmore 1984a). It occurs in areas where there is yearly water stress of
some duration and perhaps bounds the zone of monsoon climates. 'There is, as yet, no exact
delimitation of this formation in the islands, but the deciduous "Yakal-lauan" and "Lauan-
apitong" subtypes described by Whitford (191 1) probably belong here as well as the semi-