Vegetation of Southeast Asia Studies of Forest Types 1963-1965

In the silvicultural sense Dominant trees of a forest canopy are
those whose crowns are more than half exposed to full illumination,
while the crowns of Sub-dominant trees are less than half exposed to
full light. Trees whose crowns are entirely shaded are referred to
as Suppressed. This usage may thus be applied to the actual development
of an individual tree.
Isolated trees whose crowns rise above the general canopy ara a
constant feature of several types of tropical forests. They are
clearly Dominant in the silviculture! sense, but not in the ecological,
since they exercise no general controlling influence on the
forest. The terra 'Predominant' is sometimes applied to them.
Since this may imply a specially high degree of dominance, the term
'Emergent' is considered preferable. Emergent trees may be considered
collectively as forming a discontinuous or extra layer above the
general tree canopy.
Within an area of uniform climate, however, soil or other natural
factors may have been at work to prevent the development of the
typical climatic vegetation. . Here the essential habitat and lifeforms
of the dominants are determined by such edaphic or biotic
factors. Different Consociations and Associations which are influenced
by these factors and agree in life-form, are known as Edaphic
or Biotic Formations. A typical example of the former (edaphic) is
Mangrove forest, occurring in deltas and around the estuaries of
rivers in southeast and peninsular Thailand, along the coast cf Cambodia,
and Ilorth and oouth Vietnam.
Formations with characteristic life-forms and strikingly similar,
and are obviously influenced by similar climatic pattern, are formed
throughout tropical regions, no matter what part of the world they may
occur, Lon,