TROPICAL RAIN FOREST ECOSYSTEM

Rain forest is a complex community whose framework is provided by trees of many sizes. In this book the term forest canopy is used as a general one to describe the total plant community above the ground. Within the canopy the microclimate differs from that. outside; there is less light, humidity is higher, and temperature is lower. Many of the smaller trees grow in the shade of the larger ones in the microclimate that these produce. Upon the framework of the tree and within the microclimate of the canopy grow a range of other kinds of plants: climbers, epiphytes, strangling, plants parasites, and saprophytes (Withmore, 1975).

The trees and most of the other plants are rooted in the soil and draw nutrients and water from it. Their fallen leaves, twigs, branches, and other parts provide ; food for a host of invertebrate animals, amongst which termites are often important, and for fungi and bacteria. Nutrients are returned to the soil via decay of fallen parts and by leaching from the leaves by rain-water. It is a feature of tropical rain forest that most of the total nutrient store is in the vegetation; relatively little is held in the soil.

Within the forest canopy, especially in lowland forest, there live a large range of animals, vertebrates and invertebrates, some eating plant parts, same eating other animals. Complex interrelationships exist between plants and animals, for example, in relation to pollination of flowers and dispersal of fruits. Some plants, so-called myrmecophytes, provide shelter for ants in modified organs. Many plants, it is now believed, produce chemicals noxious to many insects and in this way attempt to protect themselves from being eaten.

The whole organic community and its immediate physical and chemical enviroment together make up tile ecosystem (Tansley 1935) of the rain forest. If part of the forest is destroyed plants (and attendant animals) recolonize the gap, others invade in competition with them; there is a secondary succession of seral plant communities, until eventually a community similar to the original is restored. This is called the climax. On bare land surfaces, for example, that created in 1963 by the eruption of Gunung Agong in Bali, a primary succession, or prisere, occurs leading also to the climax.

Over a sufficiently large area the climax itself is in a state of dynamic equilibrium. There is no net increase in the biomass of living plants and animals; deaths are more or less balanced by replacements. This is true on time-scales comparable to a man's life-span, and may he so too over a few centuries. But on a long, secular scale there may be change in the geographical range of species following alterations In climate such as have occurred during the Pleistocene period, and there are hints of this having happened. On a still longer time-scale new plants and animals have evolved and come to influence the ecosystem.

The synusiae

A synusia is a group of plants of similar life-form which fill the same niche and play a similar role in the community of which it forms apart (Richards 1952); that is, it is a partial life-form community.
Synusiae provide a good means for analyzing complex plant communities. Richards (1952) has introduced a convenient practical classification for the synusiae of tropical rain forest:

A. Autotrophic plants (with chlorophyll)
1. Mechanically independent plants.
(a) trees and treelets;
(b) herbs.
2. Mechanically dependent plants.
(a) climbers;
(b) stranglers;
(c) epiphytes (including semi-parasitic epiphytes).