A mid‐Holocene environmental change in Amazonian savannas

Abstract

In South America, savanna vegetation occupies a discontinuous area. Similarly, within Brazilian Amazonia, disjoint savannas occupy large areas of Amapá and Roraima states, and are also found in Humaitá (Amazon State) and Alter do Chão (Pará State) (Salgado-Labouriau, 1997). ABSTRACT AimThe main goal of this study was to investigate how climate and human activities may have influenced ecotonal areas of disjoint savannas within Brazilian Amazonia.Location Eastern Brazilian Amazonia, Amapá State. MethodsThe fossil pollen and charcoal records of two lakes in Amapá (Marcio and Tapera) were used to provide a Holocene palaeoecological history of eastern Amazonian savannas. Detrended correspondence analysis was used to enhance the patterns of sample distribution along the sediment core.Results Even though sedimentary hiatuses were recognized in the sediment cores from both lakes, a marked change in vegetation from closed forests with swamp elements to open flooded savanna at c. 5000 yr bp was evident from the pollen record. Charcoal analysis revealed a pattern of increased accumulation of charred particles coincident with the establishment of savanna vegetation, suggesting higher fire frequency near the lakes. Because the timing of the sedimentary hiatus overlapped with the highest Holocene sea level, which would have increased the local water table preventing the lakes from drying out, we infer that both lakes used to depend heavily on flood waters, and the sedimentary gap was caused by reduced discharge from the Amazon River, due to a dry period in the Andes, when precipitation levels markedly decreased between 8000 and 5000 yr bp. The lack of Andean pollen (probably river transported) in the sediment record after this event and the existence of similar records near the study site make this interpretation more appealing. The resumption of sedimentation in Lake Marcio, contemporaneous with falling sea level and increasingly wet conditions in the Andes after 5000 yr bp, indicates that Holocene sea-level variation did not play an important role in maintaining lake levels. Main conclusionsThe study site recorded long-term occupation by preColumbian peoples. However, it is still unclear whether these disjoint savannas have an anthropogenic origin. Even though locally dry environmental conditions were inferred from both records, there is no evidence of a mid-Holocene dry climate in eastern Amazonia. Instead, the Amapá record indicates a connection between Andean climate and eastern Amazonia, demonstrating the need for a better understanding of the impacts and magnitude of climate changes.

A Holocene environmental record reflecting vegetation, climate, and fire variability at the Páramo of Quimsacocha, southwestern Ecuadorian Andes

“…Sediment hiatuses can indicate a complete drying out of the sediment. Hiatuses for the mid-Holocene have for example been reported from two shallow lakes (Lago Marcio and Lago Tapera) in the eastern Amazon basin region (De Toledo and Bush 2007). Here, the authors suggest they are mainly due to the low stand of the Amazon River during that time.…”

Niche modelling and landscape genetics of Caryocar brasiliense (“Pequi” tree: Caryocaraceae) in Brazilian Cerrado: an integrative approach for evaluating central–peripheral population patterns

“…This is usually attributed to environmental components, such as seasonal precipitation, fire regime, soil fertility and drainage, as well as historical fluctuations due to climate changes (Oliveira-Filho and Ratter 2002;Ledru 2002). Because of the intrinsic association between a species' range and the ecological characteristics at the biome level, it is expected that part of the genetic variation could be explained by shifts at these scales and would be linked with Pleistocene climate fluctuations that affected the limits of Cerrado, Amazon and Atlantic forest in the last 10,000 years (see Toledo and Bush 2007;Caetano et al 2008). Although these fluctuations can help understand phylogeographic patterns within the species and eventually its origin from other species (probably in the Amazonian region), they are probably not strongly related to clinal and central-peripheral patterns discussed here.…”

Gran Sabana fires (SE Venezuela): a paleoecological perspective

“…Furthermore, dry climates could only favor the occurrence of fires but cannot ignite them, whereas humans can do both things as they use to do nowadays in the Gran Sabana. In paleoecological records of the Neotropics, it has been suggested that the occurrence of phases of continuous and high fire incidence can be interpreted as a proxy for human settlements even in the absence of other land use signals, such as cultivated plants de Toledo and Bush, 2007). Moreover, recent GS studies about modern pollen depositional rates have highlighted the absence of cultivated plant signals in this region, including locations where agriculture was developing, so the direct human impact in pollen records can easily go unnoticed (Rull, 2007(Rull, , 2009aLeal, 2010).…”