An 8700-year record of the interplay of environmental and human drivers in the development of the southern Gran Sabana landscape, SE Venezuela

Abstract

The vegetation of the southern Gran Sabana (SE Venezuela) consists primarily of a treeless savanna with morichales ( Mauritia flexuosa palm stands), despite the prevailing climate being more favorable for the development of extensive rainforests. Here, we discuss the results of our 8700-year paleoecological reconstruction from Lake Encantada based on the analysis of pollen, algal remains, charcoal, and geochemical proxies. We use the findings to assess a number of hypotheses that seek to explain the dominance of savanna vegetation and consider the relative importance of factors such as climate, fire, and erosion on the landscape. The reconstruction of vegetation changes suggests the following trends: open savanna with scattered forest patches (8700–6700 yr BP), forest-savanna mosaic (6700–5400 yr BP), open savanna with forest patches (5400–1700 yr BP), and treeless savanna with morichales (1700 yr BP–the present). We conclude that the interplay between climate and fire and the positive feedback between the presence of grasses and increased fire frequency played a major role in the vegetation dynamics from the early to middle Holocene (8700–6700 yr BP). The synergistic action between reduced fires and wetter conditions appears to be a determinant in the development of rainforest around 6700 yr BP. Despite higher available moisture at ~5400 yr BP, the savanna expanded with the increased frequency of fire, potentially driven by human land-use practices. We also propose that the interplay between fire and erosion created forest instability during the middle and late Holocene. The current southern Gran Sabana landscape is the result of the complex interplay between climate, fire, erosion, and vegetation.