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In this essay we will discuss about physical geography. After reading this essay you will learn about: 1. Definition of Physical Geography 2. Scope of Physical Geography 3. Branches.
Essay on Physical Geography
1. Essay on the Definition of Physical Geography:
Physical geography is one of the two branches of geography viz., physical geography and human geography. In fact, the study of physical aspects of the earth represents the core of spatial science i.e., geography. Most of geographers have pleaded for bifurcation of geography into physical and human geography but it is rather unwise to ignore biotic aspect of the biospheric ecosystem of the earth and hence there should be trifurcation of geography into physical geography, human geography and biogeography.
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Physical geography in terms of its meaning and definition, scope (subject matter) and methods of study has undergone sea-change in the past few decades. In the beginning, physical geography was defined as the study of only physical environment (namely reliefs, air and water) of the earth e.g., ‘the study of physical environment by itself is physical geography which includes consideration of surface relief of the globe (geomorphology), of the seas and the oceans (oceanography) and of the air (meteorology and climatology) (Arthur Holmes).
Physical geography was considered as the agglomeration of different branches of earth sciences or natural sciences viz., sciences of atmosphere (meteorology and climatology); science of seas and oceans (oceanography); science of solid earth (geology); science of soil (pedology); science of plants (botany) and science of landforms (geomorphology).
Arthur Holmes further remarked that ‘physical geography is simply the study of unification of a number of earth sciences which give us a general insight into the nature of man’s environment. Not in itself a distinct branch of science physical geography is a body of basic principles of earth sciences selected with a view to include primarily the environmental influences that vary from place to place over the earth surface’.
It may be pointed out that presently physic geography is not only the agglomeration and unification of earth sciences as referred to above but it also studies the patterns of interactions between human activities and physical environment.
As a distinct branch of geography physical geography studies the spatial patterns and spatial relationships of environmental components of the globe in regional context, it also studies the causes of regional patterns of such spatial relationships, simultaneously it incorporates the explanation of spatial and temporal changes of environmental components and causes thereof.
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It is evident that the focus of the study of physical geography is the biosphere (life layer) comprising the envelope of land, air and water around the globe which supports the life of all biota (plants and animals) on the earth surface.
Thus, we include the study of all such physical elements and factors in physical geography which provide suitable habitats for the living organisms of the biosphere (plants and animals including man). It may be mentioned that the quality of biosphere is determined by the physical environment, the quality of which in itself is determined by the interactions between endogenetic forces (coming from within the earth) and exogenetic forces (originating from the atmosphere i.e., denudational processes which include the processes of erosion and weathering).
The solid earth’s surface (crust) provides different types of habitats to living organisms of the biospheric ecosystem. Different reliefs (tectonically originated) are created (like mountains and hills, plateaus, lakes, plains etc.) on the earth’s surface by endogenetic forces which introduce diversity in the habitats.
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The outer solid crustal surface also provides nutrients to the biosphere. On the other hand, atmosphere provides essential elements (namely carbon, hydrogen, oxygen, nitrogen etc.) to the biosphere and gives birth to different types of climate on the earth’s surface.
The exogenetic processes originating from the atmosphere on one hand help in the circulation and exchange of heat between the atmosphere and the earth’s surface, on the other hand they create different types of landforms through their denudational works and these landforms in turn further introduce diversity in the habitats produced by endogenetic forces. Thus, physical environment affects life forms (plants and animals) of the biosphere while man also modifies and changes physical environmental conditions through his economic activities.
2. Essay on the Scope of Physical Geography:
It is evident from the foregoing discussion on the nature of physical geography that the detailed consideration of four components of the earth viz. lithosphere, atmosphere, hydrosphere and biosphere, are included in physical geography wherein characteristic features of these components are studied spatially and temporally.
First, the origin, age and structure of the interior of the earth, isostasy and evolution of continents and ocean basins are studied in-order to understand the characteristic features of the aforesaid four components. The study of forces or movements of the earth, both endogenetic (originating from within the earth) and exogenetic (originating from the atmosphere) becomes significant to understand the interactions between these two forces and resultant features.
In fact, endogenetic forces (termed as constructive forces) coming from within the earth, create reliefs of varying dimensions on the earth’s surface (e.g. mountains, folds, faults, volcanic cones etc.) which provide habitats for living organisms of the biospheric ecosystem on the one hand, and present initial reliefs for the interplay of exogenetic forces originating from the atmosphere, termed as destructive forces (denudational processes e.g., fluvial, marine, glacial, aeolian, periglacial etc. processes and weathering agents) on the other hand. The study of evolution of continents and ocean basins and their drifting (continental drift as evidenced by plate tectonics) helps in the understanding of evolution and dispersal of plants and animals.
The characteristics, origin and distribution of constructional reliefs namely mountains, faults, folds etc. are thoroughly investigated. The distribution, characteristics and origin of vulcanicity and landforms resulting therefrom are studied as physical features and natural hazards which adversely affect both human being and plants and animals.
The study of features resulting from the interactions between endogenetic and exogenetic forces involves the discussion of mode of denudational processes (weathering and erosion), hetherto termed as geomorphic processes, their mechanism of operation (machanism of erosion, transportation and deposition by running water-river, groundwater, sea waves, wind, glacier and periglacial agent) and resultant landforms.
The study of hydrospheric component involves the consideration of reliefs of the ocean basins (continental shelves, submarine canyons, continental slope, deep sea plains, ocean deeps etc.); thermal characteristics of ocean water; salinity (composition of seawater, sources and distribution of oceanic salinity); ocean deposits; ocean tides; ocean currents and coral reefs and atolls (their distribution and origin, coral bleaching etc.).
The study of atmospheric component includes the discussion of composition and structure of atmosphere, elements of weather and climate, insolation and heat balance, terrestrial radiation balance and anthropogenic factors causing imbalance, air temperature, air pressure and winds (permanent or planetay winds, seasonal and local winds), characteristics and origin of monsoon, humidity and precipitation, airmasses, frontogenesis, cyclones and anticyclones, world climate etc.
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The study of biospheric component involves the consideration of components of biosphere (both abiotic and biotic), soil system, ecological production and energy flow in the biospheric ecosystem, circulation of elements in the ecosystem, biogeochemical cycles, evolution, dispesal and extinction of plants and animals, biomes and man, ecosystem stability and man, man and atmospheric environment (global radiation balance, ozone depletion, greenhouse effects and global warming), man and environmental processes, main- induced soil erosion and sedimentation, environmental degradation and pollution, extreme events, hazards and disaster, environmental planning and management, global environmental problems and international co-operations.
It is evident from the aforementioned discussion that the scope of physical geography includes the consideration of systematic study of physical environment as well as the study of interactions between man and physical environment.
Major changes have taken place in the subject matter and methodology of physical geography due to following factors:
(1) Universal desire to make physical geography more meaningful and applicable for human welfare and to integrate it more intimately with human geography in-order to redefine and to keep the discipline of geography intact and to make it more relevant to society.
(2) More attention of man towards natural hazards and disaster and greater emphasis on the evaluation of adverse impacts of human activities on physical environment and environmental problems resulting therefrom and remedial measures therefor.
(3) Greater emphasis on instrumentation and measurement of operation of different geomorphic processes and mathematical analysis of data derived through field and laboratory studies.
(4) More attention towards the study of certain aspects of physical geography e.g. ecosystem and ecological stability and instability, hydrology, plate tectonics etc.
(5) Recent trends of increasing emphasis on micro-temporal scale (i.e., graded and steady state time scale) in place of macro-temporal scale (i.e., cyclic time involving geological time i.e., millions of years) and on shorter microspatial scale (10 to 100 km2) in place of large or macro-spatial scale (mega scale, millions of square kilometres) in the study of geomorphic and environmental processes to make such study more relevant to society in-order to solve immediate environmental problems.
3. Essay on the Branches of Physical Geography:
The discipline of physical geography has evolved through successive stages of its development in terms of methodology and approaches to study. After taking its birth in the philosophical ideas and reports of ancient thinkers, philosophers and historians of the ancient seats of civilization and culture e.g., Greece, Rome and Egypt, the science of physical environment attained its present status wherein different components were added from time to time.
Previously physical geography concerned with only three components i.e., lithosphere, hydrosphere and atmosphere but biosphere has been recently added to this discipline. It is desirable that the historical development of four distinct branches of physical geography e.g., geomorphology, oceanography, climatology and bio- geography should be discussed separately dealing with lithosphere, hydrosphere, atmosphere and biosphere respectively.
i. Geomorphology:
Geomorphology is a significant branch of physical geography. The term of geomorphology stems from three Greek words i.e., ge (meaning earth), morphe (meaning form) and logos (meaning discourse).
‘Geomophology may be defined as the scientific study of surface features of the earth’s surface involving interpretative description of landforms, their origin and development and nature and mechanism of geomorphological processes which evolve the landforms’.
The subject matter of geomorphology is organized on the bases of:
(i) Dimension and scale of relief features (landforms),
(ii) Processes that shape the landforms, and
(iii) The approaches to the geomorphic studies.
The systematic study of landforms requires some fundamental knowledge of geology as the genesis and development of all types of landforms primarily depend on the materials of the earth’s crust (rocks) and partly on the forces coming from within the earth.
Certain principles of structural and dynamic geology are included in geomorphic studies. Theoretical geology helps in understanding the nature of landforms and, therefore, the origin of different types of reliefs like mountains, plateaus, faults, folds, continents and ocean basins cannot be properly understood because it helps in understanding the denudational landforms which develop on them.
Endogenetic forces particularly diastrophic and sudden (vulcanicity and seismic events) should be taken note of as these introduce irregularities on the earth’s surface which generate variety in landforms. First order relief features include continents and ocean basins while mountains, plateaus, plains, faults, rift valleys etc. are included in relief features of the second order.
Micro-level landforms developed on second order relief features by exogenetic denudational processes (both erosional and depositional landforms) e.g., running water, groundwater, sea waves, wind, glacier and periglacial agents, are included in the categories of relief features of third order.
‘The rapidly evolving discipline of geomorphology has undergone sea-change in methodology and approaches to the study of landforms and related processes since 1945 when R.E. Horton introduced quantitative methods for the analysis of morphometric characteristics of fluvially originated drainage basins’. The present status of geomorphology is the result of gradual but successive development of geomorphic thoughts postulated in different periods by innumerable philosophers, experts and geoscientists in the subject and outside the subject.
In the ancient period some ideas of landforms were presented by philosophers and historians of Greece, Rome and Egypt e.g., Herodotus (485 B.C.-425 B.C., he named depositional features at the mouth of a river as delta and propounded that ‘Egypt is the gift of Nile’), Aristotle (384 B.C.-322 B.C., he described the features developed on limestones, origin of springs and streams), Strabbo (54 B. C.-25 A.D., according to him the size of delta varies depending on the nature of rocks of the region through which the river makes its course) etc. No significant development of geomorphology could take place during Dark Age (1st Century A.D. to 14th Century A.D.) as a lull prevailed in the development of geographical knowledge with the fall of Roman Empire.
The long continued academic silence of 1400 years was suddenly broken by the emergence of catastrophism which believed in the quick and sudden origin and evolution of all animate and inanimate objects in very short period of time and thus new pages of peculiar and fantastic concepts were added to the treasure of geomorphological and geographical literature.
The age of catastrophism was dominated by the concept of sudden occurrence and evolution of all types of features but this concept was soon rejected by the advocates of uniformitarianism. The emergence of age of uniformitarianism resulted in the outright rejection of the concept of catastrophism and gradual cyclic nature of earth’s history was postulated by James Hutton (1726-1797 A.D.) in the 18th century.
His concept of uniformitarianism was based on the basic tenet ‘that the same geological processes which operate today operated in the past and therefore the history of geological events repeats in cyclic manner.’ His concept of ‘present is key to the past’ aimed at the reconstruction of past earth history on the basis of the present. He was the first geologist to observe cyclic nature of earth’s history. He also propounded the concept of ‘no vestige of a beginning: no prospect of an end’. His two disciples John Playfair (1748-1819 A.D.) and Charles Lyell (1797-1873 A.D.) further developed and propagated the concept of uniformitarianism.
Geomorphology became an independent discipline and a major branch of geology at the beginning of the 19th century when the development of geomorphic thoughts took place at regional level and two distinct schools of geomorphic thoughts can well be identified e.g. (1) European School and (2) American School.
European School was characterized by significant contributions in the fields of recognition and identification of Pleistocene Ice Age and glaciation, glacial erosion, marine erosion, fluvial processes and erosion, arid and karst landscapes. Louis Agassiz (1807- 1873 A.D.), Jean de Charpentier, John Playfair, Venetz, Esmark etc. made significant contributions in the development of glacial geomorphology. Jean de Charpentier and Louis Agassiz postulated the concept of continental glacier and ice ages while James Geikie published his book ‘The Great Ice Age’ in 1894.
According to him an ice age involving longer geological period is comprised of distinct several glacial periods separated by warm interglacial periods. A. Penck and Bruckner identified four glacial periods during Pleistocene Ice Age (Gunz, Mindel, Riss, Wurm) which were separated by three warm interglacial periods. Sir Andrew Ramsay (1833-1905 A.D.) made significant contributions in marine geomorphology while J. Walther, Passarge etc. developed aeolian geomorphology. W. Penck postulated the concepts of cycle of erosion and slope replacement through his ‘morphologishe analyse.’
American School is credited for making maximum contributions in the field of geomorphology. In fact, the last two decades of 19th century and first two decades of 20th century (i.e., from 1875 to 1920) are considered as ‘golden age’ not only of American geomorphology but also of world geomorphology because it was this period when for the first time general theory of landscape development was propounded by W.M Davis and landform analysis attained its final shape.
The concept of sequential changes of landforms through successive developmental phases in terms of time based on the basic tenet of time-dependent concept of Davisian model of geographical cycle of erosion became the core of landform analysis and guideline for geomorphologists and geologists not only in North America but world over. Powell, Gilbert, Dutton and Davis made significant contributions in the field of subaerial denudation.
Major J.W. Powell (1834-1902 A.D.) postulated the concept of limit of maximum vertical erosion by streams to which he proposed the term base level, which is determined by sea level. G.K. Gilbert (1843- 1918 A.D.) propounded the concept of dynamic equilibrium and introduced quantitative methods of the analysis of landforms W.M. Davis (1850-1934 A.D.) is given credit to synthesize and integrate hitherto scattered ideas of American geomorphologists to present them in coherent and well defined framework.
Davis is given credit for postulation of first general theory of landscape development which is in fact a synthesis of his three major concepts viz. ‘complete cycle of river life’ (1889), ‘geographical cycle’ (1899) and ‘slope evolution’.
He emphasized progressive development of erosional stream valleys through the concept of ‘complete cycle of river life’ while sequential changes of landscapes through time involving historical evolution of lands forms (time-dependent series of landforms) or cyclic development of landforms were highlighted through the concept of geographical cycle.
The beginning of the 20th century was heralded by methodological revolution in geomorphological studies brought by W.M. Davis and his followers at home (U.S.A.) and geographical cycle was variously termed, popularised and applied by his followers world over e.g., normal cycle of erosion, geomorphic cycle, humid cycle etc. His concept of geographical cycle was later on applied with all other processes by Davis and his followers e.g., arid cycle of erosion, glacial cycle of erosion, marine cycle of erosion, karst cycle of erosion, periglacial cycle of erosion etc.
Davis’ concept of historical evolution of landscape became the pivot for the development of classical concept of denudation chronology and erosion surfaces in U.K. British geomorphologists made their independent identity and there emerged an entirely different school of geomorphology which laid emphasis on the chronological (historical) study of landscape development in historical perspective better known as denudation chronology based on the concept of palimpsest.
The Davisian model of geographical cycle met with strong criticism and rapid and erosionless upliftment became the crux of criticisms by the opponents of cyclic concept of landscape evolution particularly by German geomorphologists. W. Penck, through his ‘morphological analysis’ and ‘morphological system ‘, attempted to reconstruct and interpret past events of crustal movements on the basis of exogenetic processes and morphological characteristics and postulated the concept of time independent landscape evolution.
A new branch of geomorphology in the form of climatic geomorphology was developed in France and Germany based on basic tenet that ‘each climatic type produces its own characteristic assemblage of landforms’. Sauer (1925), Wentworth (1928), Saper (1935), Friese (1935), Budel (1944,1948), L.C. Peltier (1950), Tricart and Cailleux etc. made significant contributions in this field.
Post-1950 geomorphology has undergone seachange in methods and approaches to the study of landforms, conceptual framework, paradigm and thrust areas of study. The recent trends in the field of geomorphological studies since 1950 include increasing criticism of Davisian model of cyclic development of landforms, concerted efforts for the replacement of cyclic model by non-cyclic (dynamic equilibrium) model, descriptive geomorphology (qualitative treatment of landforms) by quantitative geomorphology, inductive method of landforms analysis by deductive method, introduction of models and system approach, emergence of process geomorphology, climatic geomorphology, applied geomorphology, environmental gemorphology, shift from larger spatial scale (mega geomorphology) and longer temporal scale to smaller spatial and shorter temporal scale (micro- geomorphology) etc.
The decade 1950-60 was devoted more for the quantitative study of landforms and processes and the consideration of geomorphic theories occupied a back seat. The rejection of Davisian concept of ‘cyclic model’ culminated in the postulation of ‘dynamic equilibrium theory’ of landscape development by J.T. Hack, R.J. Chorley and others but the conceptual vacuum caused by the rejection of Davisian model could not be filled up even by dynamic equilibrium model. Recently, a few alternative geomorphic theories have been postulated e.g. ‘geomorphic threshold model’, ‘tectonic geomorphic model’ (M. Morisawa), episodic erosion model’ (S.A. Schumm) etc.
The most outstanding contribution to the advancement of geomorphological knowledge has been replacement of ‘form geomorphology’ by ‘process geomorphology’ and postulation of ‘functional theory’ in place of ‘evolution theory’ and emergence of environmental geomorphology’ as a new branch of geomorphology. As regards Indian contributions to geomorphology four centres of geomorphology have developed at Allahabad university, Calcutta university, Poona university and Central Arid Zone Research Institute (Cazri), Jodhpur.
ii. Oceanography:
About three-fourth of the globe (70.8 per cent) is covered by hydrosphere. Out of the total surface area of the globe (509,950,000 km2) lithosphere and hydrosphere cover 361,060,000 km2 and 148,890,000 km2 respectively. The study of hydrosphere (oceans and seas) is called oceanography which includes the consideration of description and analysis of physical and biological aspects of hydrosphere.
According to J. Proudman fundamental principles of dynamics and thermodynamics are also studied in relation to characteristics of ocean water and biological aspects. The science of oceans i.e., oceanography includes marine geology, marine geomorphology, physical oceanography, chemistry of ocean water and bio-oceanography.
The origin of ocean basins (continental drift and seafloor spreading), structure of crust and mantle, characteristics of ocean deposits and characteristics and origin of marine landforms are studied in marine geology and geomorphology. Physical oceanography includes the consideration of physical properties of ocean water (e.g., temperature, pressure, salinity, density, compressibility, viscosity, water masses and their distributional patterns) and dynamics of ocean water (e.g. sea waves, currents, tides, tsunamis etc.).
Recently, marine meteorology is also included in oceanography wherein atmospheric conditions over ocean water are studied. Bio-oceanography includes the study of the characteristics, evolution, distribution and dispersal of marine organisms.
The study of seas and oceans dates back to the ancient period of before Christ though early descriptions were based on empirical observations of individuals.
The long period of 1200 years from 1000 B.C. to 2nd century A.D. is divided into 3 phases of development of knowledge of marine environment:
(1) Early period of 500 years from the age of Homer (1000 B.C.) to the age of Hecatius includes the knowledge of Mediterranean sea based on individual voyages,
(2) Period of the study of tides by Pytheas (4th Century B.C.), a contemporary of Alexander; detailed description of land and sea by Strabbo (54 B.C.-25 A.D.) and measurement of ocean depths upto 1000 fathoms near Sardinia by Posidonius, and
(3) Presentation of the map of the world and Indian Ocean as closed sea by Ptolemy (2nd Century A.D.), dark age continued from 2nd century A.D. to 14th century when no significant contribution could be made in the science of oceanography.
The period from 15th to 16th century is called Great Age of Discovery and Exploration because efforts were made to discover and explore new areas. Columbus discovered America and Vasco de Gama reached India and Magellan circumnavigated the globe during this period.
The map presented by Ortelius in 1570 gave new knowledge about the distribution of land and seas. Significant contributions were made in the fields of origin of coastal geomorphology, theoretical base of tides, ocean currents and sea waves during this period of renaissance.
The study of seas and oceans began on theoretical basis since 17th century and mathematical methods and scientific principles were used for the interpretation of empirical knowledge and description. Ocean tides became the focal theme of study. Detailed studies were carried out regarding the mapping of ocean depth, variation in horizontal and vertical distribution of salinity, pressure of ocean water, ocean tides and currents on the basis of investigation of these variables in Gibralter Strait.
Newton presented his theory of the origin of ocean tides. In spite of such attempts the period of 17th and 19th century remained a period of inactivity in this field because of greater emphasis on physics, mathematics and astronomy.
The study of the subject again received attention with the exploration of South Pacific Region by Captain James Cook (1728- 1779). Marsigli for the first time presented the description of regional oceanography based on his studies of bottom relief, temperature, salinity, water pressure, tides and currents of Mediterranean Sea.
The development of the science of oceanography gained currency in 19th century.
This period is divided into three stages of the development of knowledge of oceanography as follows:
(1) Period of Edward Forbes (1815-1854):
Forbes was a marine biologist. His contributions to the development of oceanography included the study of sea animals upto the depth of 230 fathoms near Great Britain, Hebrides and Mediterranean Sea, study of bottom reliefs of some parts of the Atlantic Ocean; discovery of sites of 18 submerged ancient cities near Lycian coast; distribution of marine life in the Aegean Sea; preparation of map showing world distribution of marine life etc.
(2) Period of Challenger Expedition:
Wayville Thompson (1830-1882) made significant contributions in oceanography through his different expeditions’ viz. Lightening (1868), Porcupine (1869, 1870) and Challenger (1872-76). He explored the depth of oceans from Faroes in the north to Gibralter in the south through his first two expeditions while Challenger expedition was undertaken to study the bottoms of the oceans all over the world wherein he covered the distance of 1,10,400 km (69,000 miles) of the oceans and accomplished dredging at 362 centres.
The results of this great expedition (pertaining to bottom reliefs, sea water temperature, marine deposits etc.) were published in a book entitled Voyages of the Challenger-the Atlantic in 1877. He also studied the formation and origin of coral reefs and presented a world map of the distribution of pelagic deposits.
John Murray (1841 -1914) laid the foundation of modern oceanography. His major contributions based on Triton (1882) and Challenger Expedition (1872-76) include discovery of submarine ridge of Wayville Thompsons Ridge located to the northwest of Scotland; study of planktons, deposits on seabottoms, formation and origin of coral reefs; formulation of theory of the origin of atolls; determination offish zones and mud lines and presentation of map of ocean deeps of the Atlantic- Ocean.
(3) Post-Challenger Period:
Louis Agassiz made detailed study of Florida Reefs and Keys. He studied different aspects of ocean from Florida to Sans Francisco around south American coast. Alexander Agassiz, son of Louis Agassiz undertook coastal surveys covering a distance of 1,60,000 km (1,00,000 miles) through Black and Albatross Expeditions.
His major contributions include location and origin of Gulf Stream between Newfoundland and Florida, studies of coral reefs near Bahamas and Cuba, Bermuda and Florida, Great Barrier Reef of Australia, Fizi Islands, and Maldives etc. He rejected the Darwinian theory of subsidence of the origin of coral reefs and atolls. According to him atolls and barrier reefs are formed due to biological, mechanical and chemical processes.
Several expeditions were launched to study different aspects of seas and oceans in the first half of the 20th century e.g., Gazelle Expedition in the North Atlantic Ocean, Fishing Commission and Albatross Expedition in the East Pacific Ocean, Meteor Expedition in the South Atlantic Ocean, Michael Sars Expedition in the South Atlantic Ocean, Carnegie Expedition in the Pacific and Indian Oceans, Discovery (2nd) Expedition in Southern Seas (1950-51), Challenger Expedition and Danish Expedition in Southern Seas etc.
Several renowned oceanographers namely Nansen, Amundsen, Pettersson, Shepard etc. enriched the science of oceanography through their elaborate studies of different aspects of oceans and seas. F.B. Taylor and A.G. Wegener postulated the concepts of continental drift to account for the origin of continents and ocean basins. In the 1960s Hary Hess (1960) propounded the concept of sea floor spreading which further validated the hypothesis of continental drift.
With the postulation of plate tectonic theory the riddle of origin of ocean basins, bottom reliefs of the oceans, displacement and drifting of continents and ocean basins could be successfully solved. Recently, new information about marine environment and marine ecology are forthcoming through the institutes of oceanography, ocean departments and ocean expeditions established and funded by several countries and organizations like Naval Hydrographic Office, the Coast and Geodetic Survey, the Scripps Institute of Oceanography (U.S.A.) ; the Geophysical Institute, the Hydrographic Biological Commission in Scandinavia; the Marine Biological Association of U.K.; the Oceanographic Institute in Paris; Institute of Oceanography in Canada and Russia etc.
The first co-operative work for the study of Indian oceans was initiated with the launch of the International Indian Ocean Expedition (IIOE) comprising 20 countries and 38 research ships in 1960. Naval Hydrographic Office (at Dehra Dun) and the Department of Ocean Development (Goa) have been assigned the task of investigation of Indian ocean and all aspects of its marine environment.
It may be pointed out that recently the study of oceanography has gained currency because the economic and strategic importance of seas and oceans is increasing very fast. Thus, more attention is paid towards applied oceanography which includes the consideration of delineation, mapping, exploitation, utilization and management of marine biotic and abiotic resources.
Marine ecology and marine ecosystem have become the focal themes of oceanography. There is a need to introduce and develop ‘economic oceanography’ (resource oceanography) as a new branch of oceanography.
iii. Climatology:
The gaseous envelop surrounding the earth is called atmosphere while the science dealing with the study of the atmospheric components and characteristics is called meteorology and climatology. Climatology includes the systematic and regional studies of the atmospheric conditions i.e., weather and climate. Weather refers to the sum total of the atmospheric conditions in terms of temperature, pressure, wind, moisture, cloudiness, precipitation and visibility of a particular place at any given time.
In fact, weather denotes short term variations of atmospheric conditions and it is highly variable. On the other hand, climate is defined as aggregate weather conditions of any region in long- term perspective. According to Trewartha ‘climate represents a composite of day to day weather conditions and of the atmospheric elements, within a specified area over a long period of time.’
According to Critchfield ‘climate is more than a statistical average; it is the aggregate of the atmospheric conditions involving heat, moisture, and air movement. Extremes must always be considered in any climatic description in addition to means, trends, and probabilities’. According to Koeppen and De Long, ‘climate is a summary, a composite of weather conditions over a long period of time; truly portrayed, it includes details of variations, extremes, frequencies, sequences of the weather elements which occur from year to year, particularly in temperature and precipitation.
Climate is (thus) aggregate of the weather’. G.F. Taylor has maintained that ‘climate is the integration of weather, and weather is the differentiation of climate. The distinction between weather and climate is, therefore, mainly one of time.’ According to Critchfield climatology is that science which studies the nature of climate, the causes and interpretation of its spatial variations and its association with the elements of natural environment and human activities.
There are three distinct branches of climatology e.g.:
(1) Physical climatology,
(2) Regional climatology, and
(3) Applied climatology.
Physical climatology deals with the interpretation of factors responsible for the spatial and temporal variations of exchange of air circulation, heat and humidity.
It studies various elements of weather namely insolation, temperature, air pressure, wind, evaporation and humidity, precipitation, fogs, visibility etc. Different climates are formed due to combinations of these weather elements.
The occurrences of different combinations of these weather elements are accomplished through different processes and mechanisms. Thus, these processes of exchange of heat, humidity and momentum between atmosphere and earth’s surface are also studied thoroughly. It is, thus, evident that physical climatology studies the factors and processes of regional variations of climatic conditions.
Regional climatology includes the study of types, distribution, pattern and characteristic features of world climates.
Regional climatology is studied in three ways on the basis of spatial scales viz.:
(1) Macro- climatic regions,
(2) Meso-climatic regions, and
(3) Micro-climatic regions.
Applied climatology studies the application of climatic knowledge to solve various problems faced by human society e.g., global warming and climatic changes.
It studies the interactions between climate and biosphere i.e., how does climate influence and control plants and animals including man and in turn how does man modify climate by introducing advertent and inadvertent changes in the physical environment and by making certain weather modifications e.g., cloud seeding and induced precipitation.
Further, applied climatology includes the study of variability of climate, climatic changes, air pollution, climate and comfort, climate and health, climate and society, extreme weather events (e.g., floods, drought etc.) and their impacts, climate and agriculture, climate and manufacturing industries, climate and recreation, climate and urban planning, weather forecasting, climate and transport and communication, weather modifications etc.
Human biometeorology, which studies the reactions of human bodies to the changes in the atmospheric environment, has gained currency recently. It lays emphasis on to ‘establish how much of the overall biological variability is the result of changes in weather, climate and season’.
The study of climate is also divided into three categories based on influences of climatic environment on human health and behaviour on different spatial scales viz. microclimate, ecoclimate and geoclimate.
According to M. Bates (1966) three levels of climatic environment affect human behaviour viz.:
(1) Microclimate, which represents weather conditions surrounding an individual organism;
(2) Ecological climate or ecoclimate, which represents weather elements of the habitats of the organisms, in the case of man the habitat may be his house and working places like factory, office, mine, agricultural farm, pasture etc. and
(3) Geographical climate or geoclimate, which represents weather conditions of larger areal unit and longer temporal span.
iv. Biogeography:
Biosphere is a life supporting layer which surrounds the earth and makes plants and animal life possible without any protective device. The organic world or biosphere is that part of the earth which contains living organisms-the biologically inhabited soil, air and water’. According to A.N. and A.H. Strahler (1977) all the living organisms of the earth and the environment to which these organisms interact make biosphere.
Thus, the biosphere consists of all the living organisms (the biotic component), energy (the energy component) and physical environment (abiotic component) and there are continuous interactions between living organisms and physical environment and among the living organisms themselves.
The average thickness of biosphere or life supporting layer consisting of land, air, water, soil and rock is about 30 km. The upper limit of biosphere is determined by the availability of oxygen, moisture, temperature and air pressure which are necessary for the existence of organisms.
Decrease in oxygen, temperature, moisture and air pressure with increase in height in the atmosphere limits the upper boundary of the biosphere. Though the NASA has discovered the presence of bacteria upto the height of 15 km in the atmosphere but the lower layer of the atmosphere upto a few hundred metres accounts for most of the living organisms because favourable environmental conditions are available for the growth and development of living organisms in the lower part of the atmosphere.
The depth of the biosphere over the land is upto the depth of deepest roots of trees or the depth upto which can live the burrowing organisms or the depth at which lie the parent rocks. The biosphere extends upto greater depth in the oceans. The existence of life has been detected upto a depth of 9,000 m in the deep oceanic trenches and deep sea plains.
The study of biosphere is called biogeography, which includes the consideration of physical environment, soil, animals and plants. ‘Biogeography as the term indicates, is both a biological and a geographical science. Its field of study is the biologically inhabited part of the lithosphere, atmosphere and hydrosphere- or, as it has become known the biosphere’.
Since the living organisms of the biosphere are studied in botany, zoology, biochemistry and geography with different view-points and focus and hence there are variations in the meaning and scope (subject matter of study) of biogeography in the aforesaid disciplines.
If a geographer studies the distribution patterns of plants and animals of the biosphere in spatial and temporal contexts and attempts to analyse the processes and factors which are responsible for such spatial and temporal variations, the biologists limit themselves to the study of physiological, morphological, behavioural and functional aspect of an individual organism.
A geographer besides studying the distributional patterns of community of plants and animals also emphasises two more aspects viz.:
(1) Intimate interrelationships between the abiotic and biotic components, and
(2) Reciprocal relationship between man and biosphere.
It may be pointed out that the discipline of biogeography cannot be exclusive domain of either biology or geography as its boundary is overlapping not only with these two subjects but also with other subjects. J. Tivy (1982) has aptly remarked, ‘the geologist, climatologist, pedologist, geomorphologist as well as the botanist, zoologist, geneticist and geographere all ‘cultivate’ or ‘crop’, as the case may be, particular parts of this very large and varied field (biosphere): and in doing so they are, to a greater or lesser extent, essential to as well as being dependent on, an understanding of biogeography’. Thus, the meaning, subject matter and approach to study vary according to the interest and objective of the investigator.
The primary goal of a geographer is to present a vivid picture of spatial patterns of distribution of plants and animals, their temporal variations and processes and causes thereof. Margaret Anderson defined biogeography as the essence of ‘biological relations between man (considered as animal) and the whole of his animate and inanimate environment’.
Since plants and animals are major components of biogeography and hence the subject is divided into two branches viz.:
(1) Plant geography, and
(2) Animal geography but in geographical studies plant geography is given more attention while animal geography or zoogeography occupies back seat.
This is because of the fact that the study of distribution pattern of animals becomes difficult due to mobility of animals, very micro-forms of animal species and very high variability in their behaviour while the study of distribution patterns of plants becomes easy due to their static nature and their aggregation in static community. Simultaneously, plants represent most of total biomass of the world (say biosphere).
In comparison to animals plants depend more on physical environment of their habitats, they are more affected by their environment and in turn they also affect their environment. Plants provide food to all animals including man because they are primary producers and become most valuable resource to human society.
It may be pointed out that though biotic components of the biosphere are most significant aspect of the study of biogeography but abiotic components’ involving land, air and water are also studied in this discipline. Land or lithospheric component includes (from smaller to higher) elements (iron, nickel, oxygen, nitrogen, hydrogen, carbon etc.), minerals (hematite, dolomite, felspar etc.), rocks and soils, micro landforms (relief features of 3rd order viz. erosional and depositional landforms produced by exogenetic denudational processes like running water-fluvial process, groundwater, sea waves-marine process, wind-aeolian process, glaciers and periglacial process), meso-landforms (relief features of 2nd order produced by endogenetic forces namely, mountains, plateaus, faults, folds etc.) and macro-landforms (relief features of 3rd order e.g. continents and ocean basins).
The atmosphere is a significant component of the biospheric ecosystem because it provides all the gases necessary for the sustenance of all life forms in the biosphere. It also filters the incoming solar radiation and thus prevents the ultraviolet solar radiation waves to reach the earth’s surface and hence protects it from becoming too hot.
The atmospheric component includes the consideration of the composition and structure (troposphere, stratosphere, mesosphere, thermosphere-ionosphere and exosphere) of the atmosphere and the elements of weather and climate (insolation, temperature, air pressure, winds, humidity and precipitation, airmasses, frontogenesis and fronts, cyclones and anticyclones etc.).
The water or hydrospheric component is very important component of the abiotic or physical components because it is very essential element for all types of life in the biosphere. Water plays very important role in the circulation of nutrients in the various components of the ecosystems and it makes biogeochemical cycles effective in the biosphere.
The water components consist of surface water, subsurface or groundwater and oceanic water. Surface water of the earth surface is found in static state (e.g., water of lakes, ponds, tanks, reservoirs etc.) and in dynamic (in motion) state (e.g., surface runoff, streams, springs etc.). The groundwater is found in the pore spaces of regolith known as aquifers. The oceanic water or hydrosphere covers about 71 per cent of the total surface area of the globe.
On the basis of size and location the hydrosphere is divided into oceans, seas, small enclosed seas, bays etc. The hydrospheric component includes the consideration of origin and characteristics of botom reliefs (continental shelves, continental slopes, deep sea plains, deeps, submarine canyons etc.), temperature, salinity, ocean deposits, waves and currents, coral reefs and atolls because these determine different types of habitats of marine organisms.
Biotic components of the biosphere consist of 3 subsystems e.g. plant system, animal system including man and micro-organisms. Of these three subsystems plants are most important because these alone produce organic matters which are used by themselves and by animals including micro-organisms either directly or indirectly. Plants also make the cycling and recycling of organic matter and nutrients possible in different components of the biospheric ecosystem.
The study of plant component includes the consideration of classification of plants, major divisions of plant kingdoms, plant system, plants and their environment, structure and composition of plant communities, evolution, distribution, dispersal and extinction of plants etc. The study of animal component includes the consideration of classification, distribution, dispersion and extinction of animals.
The development of biogeography is closely linked with biological sciences (botany, zoology and ecology) which have themselves come out of the earth sciences and natural history as is aptly remarked by J. Tivy, ‘biogeography is firmly rooted in the biological sciences on whose data, concepts and methods the geographer is obliged to draw and whose developments have inevitably influenced his particular interest in and approach to the biosphere’.
Thus, the history of the development of biogeography is traced from biological sciences. In fact, the development of biological sciences and thus biogeography began with the contributions of early explorers and naturalists like Carl von Linne, Alexander von Humbolt, Edward Forbes, Joseph Hooker, Louis Agassiz, Alfred Wallace, Charles Darwin etc. Initially, different aspects of plants (e.g., classification, taxonomy, evolution etc.) were given more significance.
The development of two basic concepts for the explanation of biological diversity and anomalies in the distribution of different types of plant and animal species on the basis of information of plants and animals gathered by early explorers and naturalists made revolution in biological sciences and biogeography mainly plant geography together.
These two basic concepts were:
(1) The concept of adaptation of species to their physical environmental conditions, and
(2) Concept of natural selection and survival of the fittest.
It may be mentioned that these two basic concepts became the basis of Darwinian Theory of evolution arid origin of species in 1859. In fact, the Darwinian theory of origin of species, propounded by Charles Darwin, is related to the concept of progressive evolution of species (gradual speciation).
Charles Darwin (1859) postulated the principles and mechanisms of evolution of species by the process of natural selection wherein the heritable variations in the populations (here population means a community of individuals of sexually reproducing species) form the basis of evolution of species.
The process of natural selection simply means that a few of the advantageous qualities inherited from the parents of a species by a few populations of that species are such that these qualities enable a few individual members of that species to survive in their environment and to become adapted to the physical environmental conditions.
On the other hand, some individual members of the species lack in the advantageous qualities because these could not be inherited by them from their parents. In such cases the individuals which possess the advantageous qualities which are useful for their adaptation to their physical environmental conditions eliminate those plants and animals which do not possess those advantageous qualities.
In the early stages of the development of biogeography two aspects were more emphasized viz., taxonomic aspect and ecological aspect. The classification (taxonomy) of plants, their nomenclature and distribution, dispersion and evolution of individual plants became the centre of investigation and study by botanists whereas geographers attached more importance to the ecological aspects (relationships between plants and physical environmental factors) and geographical factors responsible for spatial variations in plant species.
In fact, ‘plant geography has made and continues to make important contributions to the elucidation and assessment of the relative importance of the factors which determine floristic (plants) distribution’. Plant geographer, as influenced by the Huttonian theory of uniformitarianism based on two concepts of ‘present is key to the past’ and ‘no vestige of a beginning and no prospect of an end’ (as propounded by Scottish geologist James Hutton), also attempted to study the influences of past events and environmental conditions on present distribution of plants.
Plant geographers were more influenced by the ecological concepts of interactions between biotic components (plants and animals including man) and abiotic (physical) environment and among the biotic components themselves. Ecology, in a very simple term, is a science that studies the independent, mutually reactive and interconnected relationships between the organisms and their physical environment on the one hand and among the organisms on the other hand.
Though the term ‘oecology’ (oekologie or oecologie, oiko=home) was first coined and used by German biologist, Ernst Haeckel in 1869, a few conceptual terms were already proposed to reveal relationships between organisms and their environment, for example, ‘ethology’ by French Zoologist, Isodore Geoffroy St. Hilaire in 1859 (for the study of relations of the organisms within the family and society in the aggregate and in the community); lexicology by British naturalist St. George Jackson Mivart (for the study of relations which exist between organisms and their environment) etc.
Since then the scope of ecology and its objectives have expanded enormously with the development of ecological concepts and thoughts consequent upon growing interest in man-environment relationships due to increasing pressure on natural resources to sustain and enhance economic development.
The field and the scope of ecology have changed during various phases of methodological development of the subject. In the beginning ecology was exclusively associated with biological sciences e.g. botany and zoology and hence plants and animals were studied separately.
This approach led to the emergence of plant ecology and animal ecology. The second approach of the study of relationships between organisms and physical environment (i.e. ecology) was based on habitats in terms of their physical characteristics (e.g. topography, soils, insolation and temperature, water, minerals, weather and climate etc.). This approach of ecological study led to the development of habitat ecology. The third approach to ecological studies is to study either individual organisms or groups of organisms of a particular ecosystem.
This approach led to the development of autecology and synecology. Autecology is the study of relationships of individual species to its environment while synecology is the study of complex interrelationships of groups of organisms known as biological communities because organisms (plants, animals and micro-organisms) affect each other in reciprocal manner and interact with habitat or natural environment.
Synecology was further divided into population ecology, community ecology, biome ecology, ecosystem ecology etc. Though synecology is given more attention in biogeography but autecology also does not lose its relevance. It may be mentioned that biogeography became more concerned with the ecological studies of plants than animals. In fact, plant geography was also referred to as ecological plant geography.
Simultaneously, plant geography was replaced by more specific term of vegetation geography so as to differentiate it from botany. In fact, ‘the study of vegetation geography, however, developed nearly a century before the recognition and acceptance of ecology as an academically respectable branch of the biological sciences’.
Climate was accepted as a significant ecological variable during 18th and 19th centuries, consequently attempts were made to divide vegetation of the world into vegetation zones on the basis of climatic conditions. For example, C.H. Merriam divided the world into life zones on the basis of climatic parameters mainly temperature in 1894. A.W.F. Schimper attached reasonable importance to climate while dealing with various aspects of vegetation in his famous book entitled ‘Plant Geography on a Physiological Basis’.
The vegetation-climate relationship also reflected in the classification of world climates by W.K. Koeppen (1918) and divisions of the world into natural regions by A.H. Herbertson (1905). It may be mentioned that by this time vegetation was taken (studied) as static component of the biosphere. In other words, vegetaion was studied at a given time and no attempt was made to study its changing form with time i.e. its dynamic aspect (temporal changes in vegetation) was altogether ignored.
Thus, with the march of time other factors were also taken into consideration which could control and determine the nature of vegetation. Consequently, the importance of time in influencing dynamic aspect of vegetation gained currency and the process of succession was introduced in the study of vegetation geography which gave a new direction to biogeography.
‘Succession’ simply means the entire process of directional and sequential changes of either plant community (groups of plants adapted to a particular habitat) or the whole ecosystem through time. The sequence of successional development (changes) of vegetation community is called ‘sere’. In other words, the transitional stages of sequential changes from one vegetation community to another vegetation community are called ‘sere’.
The succession of vegetation community in any habitat of an ecosystem is classified into two types on the basis of temporal changes in the environmental conditions of that habitat viz. autogenic succession (due to changes in the environmental conditions effected by vegetation itself) and allogenic succession (due to variations in physical components of habitats e.g., global climatic changes, rapid rate of siltation of lakes, ponds etc., accelerated rate of erosion of the region concerned, upliftment or subsidence of ground surface etc.).
F.E. Clements introduced genetic approach to the study of vegetation community and gave more emphasis to time factor to strengthen dynamic nature of vegetation geography. He further enriched and elaborated the concept of ‘succession’. After elaborating two processes of succession (e.g., primary and secondary succession) he propounded the concept of ‘climax’ to indicate last stage of successional development of vegetation community.
Primary succession refers to the developmental sequence of vegetation in those bare areas where there were no vegetation and animals earlier whereas secondary succession refers to the developmental sequences of vegetation in those areas which had vegetation cover earlier but now have been rendered nude or bare, due to destruction of vegetation (either partly or completely) either by natural processes (like lava flow, prolonged drought, glaciation, natural widespread forest fires, severe storms, catastrophic floods etc.) or by human interferences (like intentional burning of vegetation, massive land use changes, mass felling of trees, overgrazing etc.).
It may be pointed out that such disturbed ecosystems or habitats still contained mature soils and some original vegetation and therefore the initial stage of ‘sere’ of secondary succession of plant community is quite different from the initial stage or sere of primary succession which starts on a bare rocky surface, having no earlier plants and animals. The end product of the process of succession of vegetation community was given the term of climax succession, climax vegetation, climatic climax etc.
A.G. Tansely defined the ‘climax’ on the basis of main dominant factor which controls the maximum growth of vegetation of habitat.
According to him the climax should be identified as:
(1) Climatic climax (when climate is the most dominant factor),
(2) Edaphic climax (when soil is the most dominant factor),
(3) Relief climax (relief being the most dominant factor),
(4) Anthropogenic climax (human activities being the most dominant factor), and
(5) Biotic climax (biotic factors being the most dominant factors) etc.
It may be pointed out that the concept of succession and climax stage as propounded by Henry Cowles and F.E. Clements denoting development of successive stages of vegetation evolution in terms of time was in conformity with Darwin’s theory of evolution of species and William Morris Davis’ concept of cycle of erosion.
Similarly, time concept was also used for the explanation of pedogenesis and developmental stages of evolution of soils. It may be mentioned that there began a major shift from larger spatial and longer temporal scales to smaller spatial and temporal scales in geomorphology, pedology and climatology in the beginning of the 20th century but biogeography was still seized by zonal approach and the concept of climatic climax which laid more emphasis on major vegetation zones in association with soil zones at world level and evolution of vegetation communities involving geological time scale.
But soon there began a shift in research methodology in biogeography due to new emphasis on field study, collection of vegetation data from smaller areas and laboratory experimentation, with the result data and information obtained through controlled areas and experiments in the laboratories enabled the investigators to examine empirical hypotheses and modify earlier hypotheses.
During this course of new emphasis there emerged two aspects of detailed study namely plant sociology and ecological energetics.
Secondly, two distinct schools of ecological studies emerged at world level e.g.:
(1) The American School (led by F.E. Clements) and British School (led by A.G. Tansely) of ecological studies which emphasized the study of habitats and vegetation communities and
(2) European School which gave more attention to the study of floristic composition of plant community.
The post-first world war period registered a sea- change in the subject matter and methodology in biogeography and ecology. The larger spatial scale involving larger areal extent was replaced by small spatial scale involving small areal extent for intensive study of vegetation. Secondly, the study of ecological relationship was preferred to vegetation taxonomy and ecosystem was accepted as a convenient ideal areal unit for ecological study.
Since 1970 the environmentalists, ecologists, conservationsists and planners became more and more aware about the process of environmental degradation and ecological imbalance caused by depletion of natural resources (both biotic and aboitic) due to their rapaciousi exploitation and irrational utilization by man. Consequently, the study of components, circulation of energy, circulation and cycling and recycling of nutrients, soil systems etc. in the biospheric ecosystems of various orders gained currency.
The systematic study of different aspects (e.g. classification, evolution, distribution, dispersion and extinction) of plant and animal systems and characteristic features of biomes is more emphasized. Simultaneously, the study of man-environment relationships and ecological equilibrium has become the focal theme of ecology and biogeography.
Recently, more and more attention is paid towards the study of processes and factors of environmental degradation and pollution, stability and instability of ecosystem and ecological in-balance.
Environmental planning and management involving remedial measures of environmental degradation and pollution, reduction in the impact of natural hazards and disaster, conservation and preservation of ecological resources etc. has become centre of ecological study.
Biosphere reserve (nature reserve) with three roles (e.g., logistic role, development role and conservation role) programme has been launched world over for the management of abiotic and biotic resources of the nature which has been least impacted by human activities.
Since 1970 numerous books have been published on ecological conservation and resource management e.g.:
Biological Conservation by D.W. Ehrenfield, (1970),
Conservation in Practice by A. Warren and F.B. Goldsmith (1974),
Grassland Ecology and Wildlife Management by E. Duffey (1974),
Conservation of Nature by E. Duffey (1970),
The Scientific Management of Animal and Plant Communities for Conservation by E. Duffey and A.S. Watt (1971),
Ecology and Environmental Planning by J.M. Edington and M.A. Edington (1977),
Environmental Conservation by R.F. Dasmann (1977),
Biological Management and Conservation by M.B. Usher (1973),
The Ecosystem Concept in Resource by G.M. Van Dyne (1969),
Environmental Geography by Savindra Singh (1991), etc.
The significant books on biogeography are Basic Biogeography, Biogeography-An Ecological and Evolutionary Approach, Biogeography-A study of Plants in the Ecosphere, Biogeography, Principles of Biogeography, and Geography of the Biosphere etc.
It may be concluded that physical geography has recently become more relevant to society because of increasing interest of geographers to strengthen the core of geography i.e., physical geography and greater emphasis on the study of spatial pattern of physical environment and complex interrelationships of its components which may be more relevant and conducive for regional planning and development.
In fact, environment has always been at the centre stage of geography but unfortunately it was overshadowed by tilt of geographers towards sociology and economics during 1960-1980 but now they have realised the risk of leaving their core subject i.e. physical environment and are now giving due importance to the study of physical geography.
The introduction and development of ‘environmental geography’ as a new branch of geography by Savindra singh (1989 and 1991) is a positive welcome step in this direction.