The industrially advanced and highly affluent countries such as USA, Japan, West Germany, UK, etc., are facing diverse environmental problems arising chiefly from industrialisation, urbanization, over-production and over- consumption policies. In these countries in general nutritious food is produced in abundance, the health services and medical facilities are highly satisfactory, people can buy good clothes and houses, they can drink clean water, can have high quality education and get good jobs. There is little, if any, poverty. In these rich countries, the major problem is how to handle the physical and social garbage or the waste products generated by industries and affluence.
In marked contrast to this situation, poverty is the chief cause of environmental problems in many underdeveloped or developing countries in Asia and Africa. The poor under-produce and under-consume. They live a life of semi- starvation. Health services, education, drinking water, housing, etc., are all very poor in quality. Unemployment is rampant. People in these countries wittingly or unwittingly damage the environment while trying to create wealth.
Such attempts are limited or thwarted by the ever increasing population pressure. This factor makes it virtually impossible for the poor people to marshal technology and organize society for production. It illustrates the marked disparity between the consumption of agricultural fertilizers (in this case, potassium) in the developing as against developed countries. The last few decades have seen a great upsurge of environmental consciousness in the industrialized world and an equally disappointing material progress or advancement in the standard of living in the less developed countries.
Hopefully, the pace of progress in the poorer countries may increase to some extent if the population rate declines in the next few years. It gives the status of populations in developed and developing countries, with projections to the year 2025. Many developing countries in the tropical zone are tending to drift towards an ecological disaster. This is not only due to man’s accelerating activity but also because of certain recent climatic changes in the dry regions of tropical Africa north of the equator and of India. There is a general trend toward excessive drought. It is accompanied by a southward shift of the climatic zones. This shift is apparently a result of long-term changes in the zonal circulation patterns of the atmosphere in the northern hemisphere (see Winstanley, 1973).
Until two decades ago, agricultural research in the developing countries used to be oriented mostly to meeting the immediate requirements of extant land-use practices. Ecological research was likewise confined mostly to general surveys of topography, habitat, biota, and vegetation. Few, if any, structural and functional analyses were made. In recent years a few useful and critical investigations along these lines have, however, been completed in India, Sarawak, Thailand, Queensland, Malaysia, Panama, Amazonia, and Puerto Rico.
Out of all these, the most comprehensive piece of ecosystem research ever accomplished in the tropics has been the study (by American ecologists) of irradiation resistance, structural and functional aspects of a semi-virgin tropical seasonal evergreen forest in Puerto Rico (see Odum and Pigeon, 1970). Three other noteworthy projects launched in tropical countries under the IBP were: (a) research on structure, productivity, stability, and nitrogen status of certain pastures and deciduous forests in Uttar Pradesh, India, mainly studied by scientists of the Banaras Hindu University; (b) a British-Japanese project on a tropical evergreen lowland forest in the Pasoh Forest Reserve, Malaysia; and (c) a German-Brazilian project to estimate the structure, biomass, and other aspects of a tropical evergreen lowland forest near Manaus in Amazonia. The actual accomplishments and achievements of these three projects so far have, however, been far less as compared to the useful information and data generated by the Puerto Rico project. Work done under the IBP projects has demonstrated that the ecosystem is not just a hypothetical concept but a working principle endowed with enormous potential for tackling environmental problems (Reichle, 1975).
Some important properties of ecosystems (structural, e.g., organization, components, diversity; dynamic, e.g.
, homoeostasis, stability, sensitivity; and strategic, e.g., optimization, efficiency, adaptation, and perturbation) have been well-analyzed under some IBP projects, especially in the USA, but the researches have also focused attention on such pressing and unanswered questions as: (1) Are ecosystems strategic in the sense that they evolve so as to optimize processes by maximizing the efficient use of energy, water, and nutrients? and (2) Do they tend toward self-perpetuation and homoeostasis, thereby assuring perpetuation? In the light of the special problems and ecological needs of the tropical countries, intensive research is urgently needed in the following areas: 1. Physiognomic and genetic structure as well as the ecophysiological efficiency of natural ecosystems; 2. Self-regulation of tropical ecosystems, both natural and managed; 3. Ecological significance of diversity; 4.
Effects of climatic changes on the functioning of ecosystem; 5. Effects of local and regional shifts (relocations) of energy, materials, and population on ecosystems; 6. Possible protection of ecosystems against damage; 7. Consequences of deforestation; 8. Measures and criteria of environmental quality; and 9. Economics of rational use of natural resources. Recent observations on tropical systems clearly suggest that communities with a rich array of species and a complex web of interactions (as e.g.
, tropical rain forest) may be more fragile than the relatively simple and robust temperate ecosystems. Another interesting conclusion is that the reproductive mechanisms of tropical rainforest animals and plants are more adapted to biological competition than to major environmental disturbances. A general attribute of the tropical ecosystems is that they tend to store nutrients in the vegetation rather than in the soil. Such attributes make these ecosystems less resilient to change than temperate forests. Notwithstanding their fragility, these ecosystems persist because perturbations in the humid tropical environment are fairly small and localized. One striking property of tropical forests is the multiplicity of species and strange morphologies (e.g., climbers, buttresses, etc.
) with the species occurring as a confused mixture. Nutrient-depleted humid tropical climax soils with a high degree of entropy carry stands of low entropy (i.e., high diversity) so as to maintain efficiently a stable state of the system.
In contrast, rich soils and extremely poor soils tend to carry stands of much lower diversity. Tropical forest ecosystems have several protective, regulative and productive functions. Chief examples of protective function include soil protection, conservation of CO2 and moisture, and shelter for plants and animals. Regulative functions involve absorption, storage, and loss of water, absorption and transformation of heat and light, and absorption, storage, and release of gases and minerals.
Three main types of productive function include: (1) efficient storage of energy in utilizable form in plant and animal biomass; (2) self-regulating and regenerative processes of wood, baric, leaf, and fruit production; and (3) production of several major and minor products, e.g., resins, oils, latex, alkaloids and tannins, etc.
Productivity in forests mainly depends on soil fertility. In most tropical forests, soils are fairly poor in nutrients. Luxuriant tropical forests survive on such nutrient-poor soils because there are several nutrient conserving mechanisms that maintain the essential elements within the biomass of undisturbed forests. In such forests nutrients are mainly stored in leaves, and listed below are some of the nutrient-conserving mechanisms involved: 1. Well-developed root mat and humus layers on the top of the soil surface play a key role in the recycling and conservation of nutrients. They act as an exchange column which prevents leaching of nutrients. 2.
Mycorrhizal fungi facilitate direct transfer of nutrients from decomposing litter to roots. 3. In tropical rain forest, sclerophylly and evergreen habit are also nutrient-conserving mechanisms. 4. Nutrients are often transported back from leaves into stems before leaf- fall. 5. Trees are suitably adapted to their oligotrophic habitat in that roots efficiently extract nutrients, tolerate a low-oxygen environment well, and are resistant to flooding.
6. Insect predation of leaves is usually rather low, probably because of presence of alkaloids and polyphenols in leaves; these secondary metabolites also help conserve nutrients since it is more economical for the plant to synthesize secondary compounds than it is to manufacture new leaves in the nutrient-deficient environment. 7. Termites help bring about nutrient redistribution in the forest. 8.
Certain bark lichens and blue-green algae may fix nitrogen. 9. Forests are generally deficient in nitrifying bacteria and maintenance of nitrogen in the ammonium form is an important nitrogen-conserving mechanism. A fairly efficient nitrogen-conservation process has been demonstrated in a dry-deciduous forest stand near Varanasi by Singh and Pandey (1978).
This stand is dominated by Anogeissus latifolia and Diospyros melanoxylon. Singh and Pandey have shown that of the annual uptake of nitrogen by the vegetation in this forest, about 45 per cent is released through litter fall and about 55 per cent is retained within the vegetation. About 90 per cent of nitrogen released in litter fall becomes mineralized in a year and added to the soil. They have also estimated that the output nitrogen from this forest is only about one-fifth of the total nitrogen input, and hence the system effectively conserves nitrogen. In another study of the same forest, Ambasht and Singh (1978) reported that about 60 per cent of the total annual net energy fixation is by the ground community and about 40 per cent by the trees themselves.
They estimated that about 25 per cent of the total energy fixed in the above-ground parts is transferred to the litter component which decomposes rapidly, releasing some 90 per cent of the energy within a year.