Abstract
The main results of a study of pollen representation in surface soils from different plant communities in the upland savannas of Guayana were presented. The representation of savanna herb pollen mainly belonging to the Poaceae and Cyperaceae was high in open communities such as fernlands, grasslands and Mauritia palm swamps, but decreased as vegetation structure became more closed and woody; from savanna-forest borders to secondary forests and lastly, evergreen montane forests; mimicking the gradient of vegetation openness observed in living plant communities. Thus, the proportion of savanna herb pollen in herbaceous communities: swamps, fernlands and grasslands, reached over 80% and arboreal pollen contributed less than 10%. This ratio changed in savanna-forest borders where savanna herb pollen decreased to 60% or less and the proportion of arboreal pollen rose to 30% or higher. Lastly, in forest soils, pollen abundances from trees (Dimorphandra, Protium, Schefflera), shrubs (Miconia and other Melastomataceae) and lianas contributed higher than 60% of the pollen sum, even in open gallery forests and fallows. The lack of pollen from cassava, the main crop in the forests of the region, at these sites was remarkable. The ordination of sediment samples from 4 records from the Late Holocene with respect to the soil surface samples studied, showed that the characterization of pollen rain was useful for identifying long-term compositional and structural changes in the sedimentary records, thus providing objective indicators for the interpretation of past vegetation structure.
Highlights
Several paleocological studies have been carried out in the upland savannas of Guayana, in Southeast Venezuela, over the last few years [1,2,3,4,5,6,7]
The representation of savanna herb pollen mainly belonging to the Poaceae and Cyperaceae was high in open communities such as fernlands, grasslands and Mauritia palm swamps, but decreased as vegetation structure became more closed and woody; from savanna-forest borders to secondary forests and lastly, evergreen montane forests; mimicking the gradient of vegetation openness observed in living plant communities
The necessity of improving the paleoecological interpretation of data from the neotropical lowlands, uplands and highlands, has led to an increasing number of pollen rain studies, some of the most notable being the study of pollen representation in soils from Costa Rican ecosystems by reference [11], studies done on pollen rain along altitudinal gradients [12,13,14,15,16] and those undertaken by references [17,18] in coastal communities
Summary
Several paleocological studies have been carried out in the upland savannas of Guayana, in Southeast Venezuela, over the last few years [1,2,3,4,5,6,7]. The interpretation of palynological data has been supported by few pollen rain studies (see for example references [8,9]). Since the main goal of paleoecological studies in the region is to understand the factors influencing the apparently anomalous coexistence between evergreen forest and treeless savannas, the palynological characterization of forest, savannas, and the transitional communities between them is strongly required. Many important plant associations in the Guayana uplands have not been characterized from the palynological point of view, including gallery forests and montane forests on welldrained soils, which represent more than 70% of regional plant cover [10]. Published analyses of pollen production-dispersal in tropical rainforests, deciduous forests and sa-
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