Fire as high-elevation cold adaptation: An evaluation of fuels and Terminal Pleistocene combustion in the Central Andes

The use of fire constitutes an essential cultural adaptation to cold, and archaeological evidence for fire can be expected in high-latitude and high-elevation regions successfully inhabited by modern humans. At Cuncaicha rockshelter (4480 m above sea level, or masl) in the southern Peruvian Andes, evidence for fire is present from the earliest occupation, dating to the Terminal Pleistocene (similar to 12,500-11,200 cal BP). Yet, the site contains relatively few identifiable carbonized macrobotanical remains useful for identifying plants employed as combustible fuel. Based on a comprehensive review of nearly 40 early Andean archaeological sites above 2500 masl, little is known about fuels used for combustion. To understand fuel selection strategies at Cuncaicha, we conducted a combustion field experiment, evaluating the three highland plant taxa most likely to have been used as combustible fuels: Polylepis rugulosa (quenua) tree branches, Parastrephia spp. (tola) woody shrubs, and Azorella compacta (yareta) cushion plants. Temperature measurements informed on the combustion characteristics and efficiency of each fuel. We then compared the experimentally-produced fire residues to the geo-archaeological evidence from Cuncaicha. The resinous cushion plant yareta, endemic to the high Andes, may have been the primary fuel used at Cuncaicha based on the experiment outcome and the geoarchaeological evidence. Due to its high-temperature and complete combustion, yareta leaves little to no macrobotanical evidence, thus its identification at other Andean sites may require a multi-methodological approach. Because the geographic range of this plant corresponds with most early archaeological sites in the high Andes, yareta may have been a key resource enabling early settlement throughout the region.