Vegetation of Southeast Asia Studies of Forest Types 1963-1965

conditions favorable for the germination of its seeds and the eventual
development of the seedlings. These conditions are precipitation,
atmospheric and soil moisture, temperature, soil, light, air movement,
and very often association with certain other organisms. If the
variation of any one or more of these factors exceeds the tolerance
of the plant, its seeds fail to germinate or the seedlings may not
attain maturity. Therefore, each combination of envirorimental
characters makes possible the growth of certain species arid the exclusion
of others.
Each habitat has certain environmental factors which the vegetation
itself cannot change materially. Such factors are temperature
regulated by broad climatic conditions; rainfall influenced by
climatic and physical agencies; and wind regulated by location and
topography. However, these factors are but a part of the environment.
This is subject also to modifications brought about by the growing
plents themselves. Large plants intercept and reduce the amount of
light so necessary for the development of their own seedlings and
other small plants in the ground cover. They may also modify the
wind currents, increase the atmospheric moisture and thereby reduce
temperature. They modify the soil both physically and chemically by
means of their roots and by the accumulation of decaying material.
Thus, plants not only alter the environment but become a part of it.
That the physical and vegetation features of the environment are
interrelated in the development of plant life in any region is clearly
indicated when a habitat is disturbed. The destruction of the original
vegetation, whether by the action of man. or by forces of nature,
is usally followed by the development of a new formation of plant
life. Sites in a primary forest when felled are soon populated by
fast growing plants, usually entirely different from the original
growth. A teak forest in northern Thailand, when cutover, is soon
invaded by certain species of bamboo, and which later are difficult
to eradicate. However, the Mangrove woodland of Southeast Asia, and
of other tropical regions, is an exception to this rule, in that it
is an edaphic community, immersed at high tide and regenerates itself
soon after cutting.
Physiognomy; By this is meant all the characters which contribute
to the appearance and structure of a plant community. The physiognomy
of a forest depsnds upon the stature, spread, and life-form of the
species composing it. In a tropical forest, physiognomy includes
such features as the number of stories and the height of the respective
story in a particular forest type. We may distinguish horizontal
structure, or spacing, and vertical structure, which corresponds to
stratification. The canopy of the forest nay either be open or closed,
and the constituent trees may stand at certain distances apart. The
primary characteristic of all but the simplest communities is their
stratification. The layering or stratification of a forest may be
sharply or poorly defined. In the Rain or Moist Evergreen forest
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