Vegetation changes in the Neotropical Gran Sabana (Venezuela) around the Younger Dryas chron

Abstract

The occurrence of the Younger Dryas cold reversal in northern South America midlands and lowlands remains controversial. We present a palaeoecological analysis of a Late Glacial lacustrine section from a midland lake (Lake Chonita, 4.6501 8N, 61.0157 8W, 884 m elevation) located in the Venezuelan Gran Sabana, based on physical and biological proxies. The sediments were mostly barren from $15.3 to 12.7 k cal a BP, probably due to poor preservation. A ligneous community with no clear modern analogues was dominant from 12.7 to 11.7 k cal a BP (Younger Dryas chronozone). At present, similar shrublands are situated around 200 m elevation above the lake, suggesting a cooling-driven downward shift in vegetation during that period. The interval from 11.7 to 10.6 k cal a BP is marked by a dramatic replacement of the shrubland by savannas and a conspicuous increase in fire incidence. The intensification of local and regional fires at this interval could have played a role in the vegetation shift. A change to wetter, and probably warmer, conditions is deduced after 11.7 k cal a BP, coinciding with the early Holocene warming. These results support the hypothesis of a mixed origin (climate and fire) of the Gran Sabana savannas, and highlight the climatic instability of the Neotropics during the Late Glacial.

Forest–savanna–morichal dynamics in relation to fire and human occupation in the southern Gran Sabana (SE Venezuela) during the last millennia

“…There is some archeological evidence consisting of pre-Hispanic remains (spearheads and bifacial worked knives) similar in style to others that are about 9000 yr old found in other Venezuelan localities (Gassón, 2002;Rostain, 2008). In addition, palynological evidence indicating the occurrence of intense and extensive fires during the Younger Dryas (around 12,400 cal yr BP), suggested a potential early human occupation of the GS as one of the potential factors for fire occurrence (Montoya et al, 2011), but a definitive assessment is not yet possible.…”

“…The lake is within a treeless savanna landscape, surrounded by scattered morichal patches. In the absence of a known local name for the lake, it will be called Lake Chonita for the purposes of the present study, to be consistent with previous studies developed at the same site (Montoya et al, 2011). The core (PATAM1 B07; 4.67 mlong) was obtained in the deepest part of the lake (3.13 m water depth), using a modified Livingstone squared-rod piston core (Wright et al, 1984).…”

Mauritia flexuosa palm swamp communities: natural or human-made? A palynological study of the Gran Sabana region (northern South America) within a neotropical context

“…5). This is among the earliest burning evidence found in northern Sotuh America (Montoya et al, 2011c) although these fires could not be attributed to any known cause. As stated above, evidence for human occupation during that time is also lacking (Gassón, 2002).…”

“…In the other sites, Mauritia and its pollen was absent for different reasons. The localities called Ariwe and El Oso were above the upper distribution boundary of this palm species but Mapaurí, Colonia and El Paují were below 1000 m elevation and the absence of Mauritia in these sites is still a matter of discussion (Rull, 2007;Montoya et al, 2011c;Leal et al, 2013). The summary pollen diagrams obtained in these localities show that Mauritia pollen had been absent during the Lateglacial and most of the Holocene, and did not colonised these sites until the last ~2000 years (Fig.…”

New Insights From Pre-Columbian Land Use and Fire Management in Amazonian Dark Earth Forests

“…Palms (e.g., Mauritia, Attalea, Astrocaryum, Euterpe, Elaeis, and Oenocarpus) and fruit bearing trees (e.g., Agavaceae, Caryocar, Byrsonima, Theobroma cacao, and Lecythidaceae [i.e., Bertholletia excelsa]), are among some of the most enriched species, exhibiting higher concentrations on ADE soils (Clement et al, 2003;Junqueira et al, 2010;Levis et al, 2018). Additionally, numerous paleoecological studies in non-ADE forests attribute the late Holocene increase in edible palms (e.g., Mauritia) to human cultivation and fire management (Montoya et al, 2011c;Rull and Montoya, 2014).…”