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The Pleistocene Changes of Vegetation and Climate in Tropical South America

T. van der Hammen
Journal of Biogeography
Vol. 1, No. 1 (Mar., 1974), pp. 3-26
Published by: Wiley
DOI: 10.2307/3038066
Stable URL: http://www.jstor.org/stable/3038066
Page Count: 24
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The Pleistocene Changes of Vegetation and Climate in Tropical South America
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Abstract

Palynological studies in the Northern Andes have shown a gradual upheaval of the Cordillera during the Late Pliocene and the creation of the high montane environment. A long sequence of glacial and interglacial periods has been recorded from the Pleistocene. The successive appearance of new taxa, by evolutionary adaptation from the local neotropical flora and from elements immigrated from the holarctic and austral-antartic floral regions, can be followed step by step. For the Last Glacial to Holocene sequence the contemporaneity of the changes of temperature with those recorded from the northern temperate latitudes could be proved by 14 C dating During the coldest part of the Last Glacial the tree line descended to c. 2000 m altitude, i.e. 1200-1500 m lower than where it lies today. During the period from c. 21,000 to c. 13,000 B.P. the climate was, moreover much drier. Even taking the greater aridity into account, the lowering of the temperature during the coldest part of the Last Glacial may have been 6-7⚬ C or more. The lowering of the temperature in the tropical lowlands during glacial times may have been c. 3⚬ C. The temperature gradient must, therefore, have been steeper than it is today. In the coastal lowlands of Guyana and Surinam glacial-interglacial eustatic movements of sea level have been recorded. Pollen diagrams show in this area a considerable extension of savannas during glacial periods with low sea levels. In the inland savannas of the Llanos Orientales of Colombia and the Rupununi savanna of Guyana, several periods of grass-savanna and of savanna-woodland alternate during the Late Pleistocene and the Holocene; lower and higher lake levels corroborate the conclusions that these are caused by changes in the effective precipitation. One of the driest periods in the Rupununi seems to correspond to the time immediately before c. 13,000 B.P. Pollen data a series of samples from Rondonia, in the southern part of the Amazon basin, have shown that in that area grass-savannas replaced the tropical forest during a certain interval of Pleistocene age. From the above it appears that in considerable parts of the South American tropics a much drier climate prevailed during certain parts of the Pleistocene. A major dry period seems to have occurred during the later part of the Last Glacial, when the glaciers in the northern latitudes and in the Andes were reaching their maximum extension. These changes of climate and vegetation are of considerable importance for the explanation of speciation patterns and the recent distribution of plant and animal taxa.

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