MOVEMENTS OF VEGETATION DUE TO SUBMERSION AND DESIC- 

 CATION OF LAND AREAS IN THE SALTON SINK. 



By D. T. MapDougal. 



DESERT BASINS AND REVEGETATION. 



Extensive basins occur in various parts of North America, Australia, Africa, and Asia, 

 in which the climatic and hydrographic conditions are such that the lowermost parts of 

 the depressions are at times occupied by bodies of water which may disappear or show 

 wide fluctuations of level or volume. Alternations of this kind are followed, of course, 

 by the annihilation of the terrestrial species, as lakes are formed or as they increase, and 

 by the revegetation of emersed areas laid bare by receding waters. It is fairly evident 

 that occurrences of this kind have taken place in the great basins of Nevada and Utah, 

 in the Oteri and other depressions in New Mexico and Arizona, in the Pattie Basin in 

 Mexico, and in the Cahuilla Basin in southern California. 1 In some the alternations date 

 far back in geologic time and many thousands of years must have elapsed since the last 

 change occurred. In others, such as the Pattie and Cahuilla Basins, the transformations 

 follow each other rapidly, and although they may have begun far back in time, yet they 

 continue up to the present. 



The evidences of differences in level at which bodies of water have stood in the lower- 

 most parts of inclosed drainage systems during historic times are indisputable, and con- 

 sideration of the facts obtained from the study of these basins and of the records of long- 

 lived trees leads to the conclusion that the variations in the level of some lakes without 

 outlets in North America were connected in a direct way with variations in major climatic 

 factors. Such variations woidd have great influence upon the movements of plants about 

 the world, but would lie beyond the scope of this discussion. 2 



The chief biological interest of the present paper centers in the fate of organisms over- 

 whelmed by floods, in the physical changes which follow emersion, and in the biological 

 mechanism of reoccupation of sterilized areas as they emerge from the water, episodes 

 which must have been duplicated in their main features innumerable times in the history 

 of the surface of the earth. Many of the important features of distribution of plants and 

 animals at the present time may be due to antecedent facts of this character. 



Opportunities are not common for studies of this kind and for analysis of the means 

 and manner by which living things move onto a sterilized area or into a sterilized medium. 

 Krakatau, an island in the Indian Ocean, was devastated by a volcanic eruption in 1883 

 which destroyed practically all of the higher plants growing upon it. The place was 

 visited by botanists in 188G, 1897, and 190G, and brief analytical studies were made of 

 the establishment and constitution of the flora at these widely separated dates. Little 

 attention could be paid, however, to the successions or to the progress of physical condi- 

 tions upon which the dissemination and establishment of seed-plants depended. 3 



1 Gilbert, G. K., Lake Bonneville. Misc. Doc. House of Representatives, first session, Fifty-first Congress, 1889-90. 

 Russell, I. C., Geological History of Lake Lahontan. Misc. Doc. House of Representatives, first session, Forty-ninth 



Congress, 1885-86. 

 Gregory, J. W., The dead heart of Australia, London, 1900. 

 ' See Huntington, E., The fluctuating climate of North America. The Geographical Journal, vol. XL, pp. 264-280, 



392-411, 1912. 

 J Ernst, A., The new flora of the volcanic island of Krakatau, translated by A. C. Seward, 1908. 

 Campbell, D. II., The new flora of Krakatau. Amer. Naturalist, vol. xlii, August 1909. 



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