Impact of mid- to late Holocene precipitation changes on vegetation across lowland tropical South America: a paleo-data synthesis

Abstract

A multi-proxy paleo-data synthesis of 110 sites is presented, exploring the impact of mid- to late Holocene precipitation changes upon vegetation across Southern Hemisphere tropical South America. We show that the most significant vegetation changes occurred in southwest Amazonia and southeast Brazil, regions reliant on precipitation derived from the South American summer monsoon (SASM). A drier mid-Holocene in these regions, linked to a weaker SASM, favored more open vegetation (savannah/grasslands) than present, while increased late-Holocene precipitation drove expansion of humid forests (e.g., evergreen tropical forest in southwest Amazonia,Araucariaforests in southeast Brazil). The tropical forests of central, western and eastern Amazonia remained largely intact throughout this 6000-year period. Northeastern Brazil’s climate is “antiphased” with the rest of tropical South America, but a lack of paleo-data limits our understanding of how vegetation responded to a wetter (drier) mid-(late) Holocene. From this paleo-data perspective, we conclude that ecotonal forests already close to their climatic thresholds are most vulnerable to predicted future drought, but the forest biome in the core of Amazonia is likely to be more resilient. Of greater concern are widespread deforestation and uncontrolled anthropogenic burning, which will decrease ecosystem resilience, making them more vulnerable than they might be without current anthropogenic pressures.

Upland Lakes of the Carajás Region: Origin and Development through Time

“…This contradicts a long set of paleoclimate studies in the Carajás region, that indicates dominance of montane savanna and SDF during the mid-Holocene under drier climate conditions (Absy et al, 1991;Sifeddine et al, 2001;Cordeiro et al, 2008;Hermanowski et al, 2014;Guimarães et al, 2016, Reis et al, 2018Guimarães et al, 2018b). Assumptions about the Holocene pollen assemblage of Carajás only reflect canga vegetation with small signals from HETF, then reflecting local changes on the plateau itself and making difficult any regional scale vegetation changes (Smith and Mayle, 2017), must be viewed with caution. Smith and Mayle (2017) authors based their assumptions on the modern pollen rain of the Violão Lake (Guimarães et al, 2014), while the modern pollen rain of the Amendoim Lake shows the opposite, with predominance of the pollen signal from HETF (Guimarães et al, 2017).…”

“…Assumptions about the Holocene pollen assemblage of Carajás only reflect canga vegetation with small signals from HETF, then reflecting local changes on the plateau itself and making difficult any regional scale vegetation changes (Smith and Mayle, 2017), must be viewed with caution. Smith and Mayle (2017) authors based their assumptions on the modern pollen rain of the Violão Lake (Guimarães et al, 2014), while the modern pollen rain of the Amendoim Lake shows the opposite, with predominance of the pollen signal from HETF (Guimarães et al, 2017). Thus, it depends on the topographic position of each lake, wind direction among others factors (Guimarães et al, 2018a).…”

A 7000‐year history of changing plant trait composition in an Amazonian landscape; the role of humans and climate

“…Watling et al . ; Smith & Mayle ). To enhance our functional understanding of forest responses to environmental changes, we can make use of plant traits (Violle et al .…”

Impacts of Holocene and modern sea‐level changes on estuarine mangroves from northeastern Brazil

“…The DTM considers only the substrate surface, without the vegetal covering . This software can then quantify the areas to be flooded according to projected rates of sea level rise (Schweikert, 2018). Triangulation of these points produced the first estimate of the DTM.…”

“…Based on these DTMs, Global Mapper can measure areas within a specified distance according to a topographic gradient. This software can then quantify the areas to be flooded according to projected rates of sea level rise (Schweikert, 2018).…”