India showing the area under forest covers as percentage of the total land area. It gives the geographical distribution of various soil types found in the Indian subcontinent.
As for most other disciplines of biology, the earliest contributions to Indian ecology were made by British and European scientists and forest officers, notably Dudgeon. Bharucha seems to have been the first Indian ecologist to apply the phytosociological concepts developed in Europe to the study of vegetation of India, and accordingly can be called as the father of ecology in India. R. Misra and G.S. Puri went to England, received their training under the eminent British ecologist W.H. Pearsall, and did good work in England during the 1930s.
Upon return to India, the former established active centres of plant ecology in Saugar (Madhya Pradesh) and Varanasi (Uttar Pradesh) and produced a large number of Ph.D. students mostly on some aspects of autecology, synecclogy, and phytosociological studies of forests and grasslands.
G.S. Puri mainly worked at the Forest Research Institute in Dehradun and made valuable contributions to our understanding of vegetation, especially forests. He later migrated abroad and is now settled in England. Another active school of plant ecology is situated in Pondicherry and it has produced valuable work in phytogeography and vegetation mapping.
In recent years, some important contributions have also been made to our knowledge of production ecology in relation to grasslands, forests and crop ecosystems (see Pandeya, 1971; Coupland, 1979). Some of the more important contributions of Indian workers are briefly summarized below.
In Madhya Pradesh, the forests are dominated by teak and sal and have variable floristic and physiognomic diversities depending on such factors as topography and human influence. The work of G.S. Puri on Himalayan forests has demonstrated a high degree of correlation between forest type and geological formation. In the case of sal forests in Uttar Pradesh, it has been suggested by R. Misra that there is a higher investment in canopy development in the younger trees, while the older trees tend to accumulate more of bole and less of root biomass.
The Forest Research Institute, Dehradun has made intensive studies on sylviculture, management and artificial as well as natural regeneration of teak forests in the states of Madhya Pradesh, Karnataka, Tamil Nadu, Maharashtra, Andhra Pradesh, Kerala, Gujarat and Rajasthan (see Seth and Kaul, 1978). Teak (Tectona grandis) forests cover about 9 million hectares in India, of which about half is in Madhya Pradesh.
Teak grows best in areas where annual rainfall ranges between 1200-4000 mm, the average minimum temperature is 13-17°C and the average maximum temperature is 39-43°C. It avoids waterlogged or excessively dry habitats and prefers hilly terrain on traps, basalt and other base-rich rocks. It grows poorly, if at all, on noncalcareous rocks. The optimum pH for its growth ranges between 6.5-7.5.
Very little critical research work seems to have been done on such ecological aspects of teak forests as productivity and biomass estimations, water balance and nutrient cycling. Virtually nothing is known about nutrient inputs through precipitation, soil weathering, dust, and nitrogen fixation, or for outputs through run-off and harvesting.
No work seems to have been done on the contribution of understorey vegetation or on the rates of litter decomposition and nutrient release. However, some work has been done on its diseases, parasites and pests, and on the effect of forest fire. Teak regenerates after fire by sprouting, and is fairly fire-tolerant.
P. S. Ramakrishnan has made valuable study of slash-and-bum agricultural practices (“Jhum” cultivation) in Shillong and neighbouring areas. In the central and western Himalayas, Singh et al. (1984) observed the replacement of oak forests by pine forests following fire outbreaks. Unlike oak, pine is fire- adapted.
The surface fires which occur once every few years, cause substantial nitrogen losses in pine forests. Deforestation, burning and cutting all tend to exterminate the oak forests, which is replaced by pine. The reverse case of pine being replaced by oak has not been observed in these areas. One possible explanation for this may be the greater nutrient-conserving ability of pine as compared to that of oak.
Pandeya and associates (see Pandey a, 1971) made useful quantitative analyses of biomass production correlations of natural sal and teak in reserve forests in the River Narmada upper catchment area.
Based on their work on a dry deciduous forest near Varanasi, Singh and Misra (1978) estimated the amounts of nitrogen, phosphorus and potassium in litter fall in this forest.
Preliminary findings of a MAB research project on structure and functioning of forest ecosystems in Chandraprabha Sanctuary near Varanasi revealed that the total plant biomass in this area is highest (94-1031/ ha) in the natural forest, followed by Tectona plantations (1021 t/ha) and savanna (6-8 t/ha).
The corresponding figures for the net primary production in the absence of grazing are 14, 10, and 13 t/ha/yr for the forest, plantation, and savanna respectively. (For comparison, the production in dryland agriculture is only about 2.5 t/hr/yr. As compared to the forest, the ungrazed savanna shows a higher efficiency of capturing sunlight energy (about 0.9 per cent) and annually withdraws greater amounts of nutrients from the soil (207 kg/ha nitrogen, 20 kg/ha phosphorus, and 179 kg/ha potassium). About 40 per cent of the production and the nutrients taken up seem to be retained in perennial parts in the forest and most of these components are recycled annually in savanna.
A comparison of forest and savanna in respect of nutrient balance (input through rainfall and output through runoff) indicates that the forest annually loses more of calcium, potassium and sodium than the savanna. Whereas the phosphorus balance in the two cases is fairly similar, the forest tends to have a higher nitrogen balance as compared to savanna (Singh and Misra, 1978).
Choudhri and his associates studied the ecology of plant communities of saline lands in the Indo-Gangetic plains (Choudhri and Varshney, 1979). At high pH values of the soil, poor aeration and lower nutrient availability tend to inhibit seed germination or establishment of many species. However, certain facultative glycophytes can adapt to the saline-alkaline soil by delayed seed germination, early wilting, depression in growth, and decreased productivity.
K.P. Singh’s recent researches on primary production and nutrient cycling have generated valuable measure of stability and functioning in Indian deciduous forests and derived savanna and cropland ecosystems. He has used fresh approaches to understand the root-soil interactions in forests and agroecosystems, and the ecological responses of grasses and weeds.
He has also quantified (a) forest nitrogen cycle, and (b) biomass and nutrient dynamics of fine roots of trees. He has successfully shown better nitrogen conservation in forest than in savanna, and relatively slower nutrient cycling but a fairly efficient nutrient use in the deciduous forest.
Brij Gopal (New Delhi) has contributed to the ecology and management of wetlands and aquatic weeds, particularly Eichhornia, Marsilea and Typha. He has furthered our knowledge of primary production, nutrient dynamics and community dynamics in relation to changing water regimes in wetlands.
M.S. Dash (Burla, Orissa) has contributed to the understanding of the population biology and energetics of soil oligochaetes and their role in ecosystem functioning. He has worked on energy flow modelling and interrelationships of soil fauna and flora. He has also shown that earthworms can be effectively utilized in waste recycling, for raising frogs and chicken and for cultivating mushrooms.
R. Gadagkar (Bangalore) has worked on the structure and evolution of insect societies. He has demonstrated behavioural caste differentiation in primitively eusocial wasps. He also showed pre-imaginal caste determination in a primitively eusocial wasp.
Tripathi and his associates have made valuable contribution to our knowledge of population ecology and weed-crop interactions (see Tripathi, 1968, 1977; Tripathi and Harper, 1973). While studying the population interaction between crops and weeds, Tripathi observed that Asphodelus tenuifolius is a more successful competitor of wheat than is Euphorbia dracunculoides.
The latter, however, competes more successfully with gram (Cicer arietinum). He postulated that the degree of competition largely depends upon the similarity of forms of the individuals competing for available resources. He also reported that the competitive ability of the common weed A. tenuifolius against wheat crop was much greater as compared with its competitive ability against gram. His observations have indicated that the intensity of competition between crop plants and weeds increases with the delay in emergence of the latter.
The factors that determine the outcome of competition between crops and weeds have also been recently enumerated by Tripathi (1977).
A study of interference between populations of Agropyron repens and A. caninum raised from tillers and from seeds revealed that 4. repens, which is a serious weed in many temperate regions, has a competitive edge over the shade-loving A. caninum irrespective of whether their populations are raised from tillers or seeds.
Tripathi and Harper (1973) reported that the mortality in monocultures was greater than in mixed populations possibly because the constraints of resource limitation tend to be less severe when the individuals involved in competition differ in their requirements.
In an account of the dynamics and regulation of plant populations, Tripathi and Dwivedi (1978) have emphasized the need for identifying the factors and agents that cause mortality and influence the rate of reproduction through seeds and vegetative units.
The population dynamics of a serious ruderal weed, Eupatorium odoratum, have been studied and it was observed that only about 1.4 per cent of the new seedlings of the weed are left as survivors in field populations annually, and the important factors contributing to this large-scale reduction in population size may be the associated plant species, adult plants of Eodoratum itself, litter accumulation on ground surface, certain pathogens, and such environmental factors as low temperature, moisture stress and low light intensity.
R. S. Tripathi and Gupta (1980) compared the response of two closely related sympatric fodder grasses Bothriochloa pertusa and Dichanthium annulatum in Gorakhpur (northern UP) to increasing density and herbage removal. At high grazing pressures, D. annulatum suffers a greater setback in its growth than does B. pertusa.
According to Tripathi and Gupta, the increased density may regulate the population sizes of the two grasses through reduced seed output and decreased potential of vegetative reproduction as indicated by reduced tiller production in both the species and the reduction in rhizome production by D. annulatum.
R.S. Tripathi studied the population dynamics and population regulation of the exotic weed, Galinsoga spp., in pure and mixed stands, with special reference to the effects of density and soil nitrogen levels. Tripathi and Yadav (1987) likewise contributed to the population dynamics of two species of Eupatorium in relation to burning.
C.K. Varshney has made valuable contributions on primary processes, ecosystem analysis, resource survey, air pollution (especially S02 pollution) and impact analysis. Varshney and Garg (1979) and Varshney and Varshney (1981) studied the responses of plants and pollen to S02.
With the establishment of integrated life sciences departments in Rajkot, Madurai, Simla, Dibrugarh, Jammu, Shillong, Bhopal, Indore, Surat and some other places, some important projects on integrated ecology have been started recently and valuable high quality work is expected to emanate from these schools in due course of time.