COS 56-4 - First record of past fire temperature reveals new insights into human landscape modification in the tropics

Abstract: Charcoal recovered from sedimentary deposits provides direct evidence of two of the three different aspects of the fire regime: past fire frequency and severity, but past fire intensity has, until now, remained elusive. Here we present the first comprehensive record of a complete past fire regime change and provide new insights into the changing pattern of how the Chachapoya used fire to manipulate Andean montane forests over the last 2000 years. We used Fourier Transform Infrared Spectroscopy (FTIR) to generate wavelengths (spectra) of charcoal fragments recovered from a sedimentary record of Lake Condores, Peru. The spectra were matched with measurements derived from a database of known plant species and burned at known temperatures.

Our results showed that fire intensity (burn temperatures) corresponded with changes in land use and precipitation. The dominance of mid-temperature fires throughout the record shows that our FTIR analysis can detect slash-and-burn types of land use, a practice that had been common in a landscape that was used for maize cultivation, as the area around Lake Condores. High-intensity fires aligned with or preceded strong drought events and resulted in the most intense forest clearance and an increase in open ground vegetation in the fossil pollen record. Fire severity, frequency and intensity decreased with a wetter climate when the Chachapoyas built a mausoleum and began using the site for ceremonial purposes, completely changing their use of Lake Condores. During this period, many forests that were previously opened began to recover. Our reconstruction of fire intensity at Lake Condores demonstrates that while charcoal abundance measurements provide insight into the spatial extent or amount of biomass burned within a fire, additional measurements (such as with FTIR analysis) are needed to assess the way people managed past landscapes and the way landscapes changed through time.