Charcoal chronology of the Amazon forest: A record of biodiversity preserved by ancient fires

Abstract

The Amazon region holds a wide variety of ethnic groups and microclimates, enabling different interactions between humans and environment. To better understand the evolution of this region, ancient remains need to be analysed by all possible means. In this context, the study of natural and/or anthropogenic fires through the analysis of carbonized remains can give information on past climate, species diversity, and human intervention in forests and landscapes. In the present work, we undertook an anthracological analysis along with the 14 C dating of charcoal fragments using accelerator mass spectrometry (AMS). Charcoal samples from forest soils collected from seven different locations in the Amazon Basin were taxonomically classified and dated. Out of the 16 groups of charcoal fragments identified, five contained more than one taxonomic type, with the Fabaceae, Combretaceae and Sapotaceae families having the highest frequencies. 14 C charcoal dates span ~6000 years (from 6876 to 365 yr BP) among different families, with the most significant variation observed for two fragments from the same sampling location (spanning 4000 14 C yr). Some sample sets resulted in up to five different families. These findings demonstrate the importance of the association between anthracological identification and radiocarbon dating in the reconstruction of paleo-forest composition and fire history.

Does soil pyrogenic carbon determine plant functional traits in Amazon Basin forests?

“…Some preliminary charcoal dating results of three studied plots may confirm this variability in return times and spatial patterns: an eastern Amazonia plot had fire estimates of 1134 years before present (BP) (charcoal in 10-20 cm) and 1620 years BP (30-50 cm); a northern Amazonia plot, 989 years BP (32 cm); and a south edge plot, a range of 96 years BP (10-20 cm), 806 years BP (20-30 cm), and 1372 years BP (150-200 cm). Other recent AMS results from the same region show a larger return interval in fire records for some sites, *6000 years (from 6876 to 365 years BP: Goulart et al 2017). Previous studies of soil charcoal have also shown a spatially localized and heterogeneous signature of fire on Amazon forests (McMichael et al 2012(McMichael et al , 2017.…”

Pyrogenic organic matter from palaeo-fires during the Holocene: A case study in a sequence of buried soils at the Central Ebro Basin (NE Spain)

“…However, reported a difference in the composition of charcoal with ageing and Kaal and Rumpel (2009) found that PyC is affected by degradation processes in the soil, particularly the less intensely charred biomass. On the other hand, Goulart et al (2017) have pointed out that the interpretation of the results of the radiocarbon dating of charcoal fragments should be done with caution, since the age determination is less accurate in charcoal generated from long-lived trees than in that from young plants.…”

“…This can be also used as a palaeoenvironmental source of information (Conedera et al, 2009;Knicker, 2011), including for the reconstruction of past vegetation (Figueiral and Mosbrugger, 2000) as well as for radiocarbon dating (Bird and Ascough, 2012). In this last case, the age of wood should be considered in the interpretation of the results, since the growth layers in long-lived trees can add years to age determination (Goulart et al, 2017). The pattern of lipid distribution in soils has also been used to detect soils affected by fires in geological times, especially when fire does not produce large amounts of charcoal (Eckmeier and Wiesenberg, 2009), e.g., in the case of non-woody vegetation fires (Figueiral and Mosbrugger, 2000).…”

Fire Effects on Understory Forest Regeneration in Southern Amazonia

“…In the Brazilian Amazon, fire effects on tropical forests were first studied in the 1980's due to concerns of land clearing from wildfires (Uhl et al, 1981(Uhl et al, , 1982. While evidence of past fire has been reported for some old-growth Amazonian forests from charcoal radiocarbon dating and estimates of soil pyrogenic carbon storage (Sanford et al, 1985;Goulart et al, 2017;Koele et al, 2017), it is unclear whether past fire led to the selection of fire-adapted traits among Amazon forest tree species (Massi et al, 2017). If plant communities were adapted to past fires in Amazon forests, current burning would impact these differently (Brando et al, 2012).…”