Abstract
The forest-steppe ecotone of the eastern slope of the Andes in Central Western Patagonia (43°40'-49°15' S, Chile, South America) provides a unique area for assessing long and short term dynamics between humans and past environments. Central Western Patagonian was a demographically marginal zone inhabited intermittently and with low intensity by hunter-gatherers during the Holocene. This paper adopts a novel approach in order to assess the relationship between trends in the archaeological, pollen and charcoal records. The recognition of temporal and spatial scales in both archaeology and paleoecology is crucial for defining roles in paleofire records. The main goal of the paper is to assess the role of climate and human beings as potential ignitors of wildfires by acknowledging the scales in which they operate and the different roles either one played in paleofire trends. We investigated a case study in the Cisnes River Valley where the frequencies and magnitudes of fire episodes – reconstructed from macro-charcoal particles from the Lake Shaman intermoraine sequence – can be attributed to human action, while acknowledging the driving role of climate over broader time scales. The Lake Shaman charcoal record spanning the last 19000 cal years is compared to the archaeological record starting at 11500 cal years BP. After comparing paleofires, reconstructed from the charcoal record, with peaks and troughs in the radiocarbon record and archaeological evidence at local and site scales, we argue that this approach provides insights for assessing the timing and magnitude of human effects on the environment. We examine collation and correlation scenarios for comparative trends between the archaeological, pollen and charcoal records. The correlation of occupational events at the El Chueco 1 archaeological site and other sites along the Cisnes River Valley with the results obtained at Lake Shaman is suggestive of a combination of human agency and climate drivers in the occurrence of fires during most of the Holocene.
Highlights
Fire plays an important role in the global carbon cycle, in atmospheric chemistry, in large and small scale dynamics of terrestrial ecosystems and in biodiversity (Whitlock et al, 2007; Power et al, 2008)
Charcoal particles from the Lake Shaman sedimentary record were quantified by determining low frequency (CHAR base) and high frequency (CHAR peak) components, in order to segregate light-weight particles suspended in years without fires and/or transported by winds from long distances from charcoal particles directly derived from local fire episodes (Long et al, 1998; Whitlock and Larsen, 2001)
The Lake Shaman record shows the first macro-charcoal particles at 11,500 cal years BP (Figure 5), while fire-episode frequencies are characterized as absent before 12,000 cal years BP and absent to low before 10,500 cal years BP
Summary
Fire plays an important role in the global carbon cycle, in atmospheric chemistry, in large and small scale dynamics of terrestrial ecosystems and in biodiversity (Whitlock et al, 2007; Power et al, 2008). There is little doubt of the dominant role played by climate in fire ignition and maintenance at large spatial and time scales (Power et al, 2008). The timing of hominid fire use has been discussed, together with how it was used and controlled (Weiner et al, 1998; Stahlschmidt et al, 2015), there is little doubt that it plays a major role in modern human societies. Fire has been used for driving game, creating artificial temperatures, clearing underbrush, among other uses. For some of these purposes humans ignited open and forest vegetation, thereby establishing or maintaining fire-successional vegetation communities (e.g., Dincauze, 2000; Bliege Bird et al, 2012). Convincing scenarios of human agency in past fires are often elusive
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