15,000-yr pollen record of vegetation change in the high altitude tropical Andes at Laguna Verde Alta, Venezuela |
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Authors: | Valentí Rull, Mark B. Abbott, Pratigya J. Polissar, Alexander P. Wolfe, Maximiliano Bezada,Raymond S. Bradley |
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Affiliation: | aDepartament de Biologia Animal, Biologia Vegetal i Ecologia, Universitat Autònoma de Barcelona, C1-215, Bellaterra, 08193 Barcelona, Spain;bDepartment of Geology and Planetary Science, University of Pittsburgh, Pittsburgh, PA 15260-3332, USA;cDepartment of Geosciences, University of Massachusetts, Amherst, MA 01003-5820, USA;dDepartment of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada AB T6G 2E3;eDepartment of Earth Sciences, Universidad Pedagógica Experimental Libertador, Caracas, Venezuela |
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Abstract: | Pollen analysis of sediments from a high-altitude (4215 m), Neotropical (9°N) Andean lake was conducted in order to reconstruct local and regional vegetation dynamics since deglaciation. Although deglaciation commenced 15,500 cal yr B.P., the area around the Laguna Verde Alta (LVA) remained a periglacial desert, practically unvegetated, until about 11,000 cal yr B.P. At this time, a lycopod assemblage bearing no modern analog colonized the superpáramo. Although this community persisted until 6000 cal yr B.P., it began to decline somewhat earlier, in synchrony with cooling following the Holocene thermal maximum of the Northern Hemisphere. At this time, the pioneer assemblage was replaced by a low-diversity superpáramo community that became established 9000 cal yr B.P. This replacement coincides with regional declines in temperature and/or available moisture. Modern, more diverse superpáramo assemblages were not established until 4600 cal yr B.P., and were accompanied by a dramatic decline in Alnus, probably the result of factors associated with climate, humans, or both. Pollen influx from upper Andean forests is remarkably higher than expected during the Late Glacial and early to middle Holocene, especially between 14,000 and 12,600 cal yr B.P., when unparalleled high values are recorded. We propose that intensification of upslope orographic winds transported lower elevation forest pollen to the superpáramo, causing the apparent increase in tree pollen at high altitude. The association between increased forest pollen and summer insolation at this time suggests a causal link; however, further work is needed to clarify this relationship. |
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Keywords: | Palynology Paleoecology Paleoclimatology Holocene Neotropics South America Andes Venezuela |
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