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A CONTRIBUTION TO THE ECOLOGY OF THE
UPPER GANGETIC PLAIN
By Winfield Dudgeon,
Ewing Christian College, Allahabad.
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Introduction.
There is little published information about the ecological relations of the vegetation of the Upper Gangetic Plain. In their monumental survey and summary of the vegetation of India, HOOKER AND THOMSON (4) have little to say of this area. They state that there are no forests except at the base of the Himalayas, and that uncultivated tracts are usually covered with loose "bush-jungle". As every writer must do, they call attention to the markedly periodic climate. SCHIMPER (10) concludes that a rainfall below 90 cm. per annum produce "xerophilous scrub", while above that amount produces "xerophilous woodland". Allahabad has a mean annual rainfall of very nearly 90 cm., but the connection of the vegetation with some type of a Schimper climatic climax is not so obvious.
The Upper Gangetic Plain, comprising roughly the United Provinces, is a very distinct ecological area. Eastward it passes into the much more humid climate of Bengal; southward it merges into the hilly regions of the Vindhias, where the climate is similar but the vegetation is distinct; westward it passes into the drier Panjab; and northward it is abruptly limited by the Himalayas. The rainfall diminishes westward, and increases northward and rapidly eastward. The climate is continental, with great range between winter and summer and between day and night.
This study is restricted to a small area about ten miles in radius with Allahabad at the center. Such a restriction is chosen because I am more familiar with this limited area, and because it is quite representative of the much larger area of the Upper Gangetic Plain.
Physical features of the area.
Allahabad is situated at 25° 26' N. Latitude and 81° 52' E. Longitude, at the southern edge of the great plain of the Ganges and Jamna Rivers, at their junction. The Meteorological Observatory is 319 feet above mean sea level, and this may be taken as approximately the level of the surrounding plains. The soil (9) is all alluvial, deposited within recent geological times. It ranges from sand, through a mixture of sand and clay, to fine clay. The older alluvium often contains deposits of calcium carbonate in irregular nodules, locally called
