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The Lowland Floral Element on the Summit of Cerro Guaiquinima and Other Cerros of the Guayana Highland of Venezuela

1980; Wiley; Volume: 7; Issue: 3 Linguagem: Inglês

10.2307/2844634

1365-2699

Julián A. Steyermark, G. C. K. Dunsterville,

Plant and animal studies

Cerro Guaiquinima is one of the largest of the sandstone table mountains (tepuis) of the Venezuelan Guayana. The relatively abundant vegeta- tional cover with an especially high percentage of tall forest, together with a rather level topography and deficiency of rock outcrops are outstanding features. The summit attains an altitude of 1680 m above sea level, but in some parts drops to 700 m, a record low level for the summit altitudes of the major table mountains. The phanerogamic flora encountered on the summit consists of a mixture both of elements characteristic of and endemic to the summits of the sandstone table mountains as well as a considerable proportion (21.6%) of the flora of low altitudes. The relatively low percentage (9.5%) of the endemic phanerogamic flora of the summit provides further evidence that the summit floras of these sandstone mountains often harbours less than 50% of the total flora. Vertical upward movement of the flora from the lowlands is postulated on the basis of either (1) present-day dispersal along available migration routes by means of the low passes extending to the summit from the Rio Carapo and other affluents tributary to the Rio Paragua on the south and west flanks of Cerro Guaiquinima, or (2) upward migration during one of the warmer interglacial stages of the Pleistocene Epoch, when warmer and/or more humid climate pre- vailed. The relatively high percentage of the lowland flora encountered on the summit supports the view that a considerable vertical movement is involved in this dispersal, and negates the contrary view that no significant dispersal move- ments have occurred between species on the summits and those in the contiguous lower levels of the mountains.