Landscape changes in the southern Amazonian foreland basin during the Holocene inferred from Lake Ginebra, Beni, Bolivia

Abstract

Our study is located in northern Beni and aims to improve knowledge on regional landscape changes from the last 8600 years, based on pollen and charcoal analyses from a lacustrine sediment core from Lake Ginebra. Our results showed that gallery forest and lacustrine sediment were observed from 8645 until 3360 cal yr BP. After a change from a lacustrine to a swamp environment at 1700 cal yr BP, the Cerrados and the Mauritia swamp became installed 1000 years ago on our study site. The environmental changes we observed over the last 8600 years in the Ginebra record reinforce the evidence of a west–east climatic gradient with the persistence of rain forest throughout the Holocene on the western side and the presence of the Cerrados until the late Holocene on the eastern side. Moreover, the persistence of a wet forest in the early to mid-Holocene in southwestern Amazonia highlighted some local responses to the global trend that could be related to the distance from the Andes; while in the late Holocene, both an increase in insolation and strengthening of the South American summer monsoon system enabled the installation of a seasonal flooded savanna in northern Beni and of the rain forest in eastern Beni.

Relationship between pollination syndromes, pollen morphology and plant ecology in Quaternary deposits of the Cerrado

“…This reflects differences in pollen deposition between lakes and swamps. In addition, during wetter intervals both sites showed an increase in the concentration of medium-sized pollen grains, which was more evident in VGE-17 than in LFB1, even if the concentration of small-sized pollen grains appeared to be higher than that of medium-sized pollen grains during the three dry intervals (Escobar-Torrez et al 2023). The fact that LFB1 displayed lower pollen concentrations during wetter intervals was expected, particularly as the influence of the river on the lake is minimal or non-existent (Xu et al 2016).…”

“…In both cores, pollen deposition changed depending on water availability, although in different ways. In the case of LFB1, an increase in the accumulation of terrestrial pollen was linked with a reduction in aquatic plant pollen deposition, which was interpreted as a reduction in the lake water level that had allowed terrestrial vegetation to advance toward the coring site, thus increasing terrestrial pollen deposition (Escobar-Torrez et al 2023). In VGE-17, a reduction in terrestrial pollen deposition was observed as water level-related pollen taxa deposition decreased too (indicating the Mauritia palm swamp had dried out) toward the top of the core; conversely, when water availability increased (probably as a result of a wider drainage), the swamp was replaced by arboreal elements (gallery forest), as observed at the bottom of the core.…”

“…Currently, the lake's maximum water column is 2–3 m, and macrophytes ( Nymphaea , Sagittaria , Eichhornia ) are observed starting from the shore and continuing toward the center of the lake. The pollen record from the first 3 m of the LFB1 core was evaluated, representing pollen taxa assemblages for the last 5000 cal yr BP (Escobar-Torrez et al 2023).…”

“…The paleoecological and paleoclimatic interpretations of these two pollen records have been presented elsewhere (Escobar-Torrez et al 2023). Here, we focus solely on the depositional aspects of the pollen assemblages.…”