DISENTANGLING THE LAST 1000 YEARS OF HUMAN–ENVIRONMENT INTERACTIONS ALONG THE EASTERN SIDE OF THE SOUTHERN ANDES (34–52°S LAT.)

NANAVATI, WILLIAM; WHITLOCK, CATHY; EUGENIA DE PORRAS, MARIA; GIL, ADOLFO; NAVARRO, DIEGO; NEME, GUSTAVO

Madison

Congreso; 2022 AMQUA Biennial Meeting; 2022

The American Quaternary Association

Researchers have long debated the degree to which Native American land use altered landscapes in the Americas prior to European colonization. Human-environment interactions in southern South America are inferred from new pollen and charcoal data from Laguna El Sosneado, Mendoza Province, Argentina, and their comparison with high-resolution paleoenvironmental records and information from archaeological and ethnohistorical research along the eastern Andes of southern Argentina and Chile (34-52°S). Prior to the last 500 years, the late-Holocene vegetation and fire history from Laguna El Sosneado was characterized by grass- and shrubsteppe with moderate-to-high fire activity. Fire activity at Laguna El Sosneado decreased at ~1280 CE, preceding an increase in shrubs at the expense of grass cover at the onset of the cool Little Ice Age (~1400-1700 CE). Little Ice Age cooling in this dry region should have favored fire by generally increasing effective moisture and, as a result, fuel loads, but the charcoal record suggests the opposite. A shortage of ignitions may have been a limiting factor for fire activity at this time, either as a result of land abandonment, a change in land use, or fewer convective storms. The appearance of nonnative taxa after ∼1750 CE coincided with increased trade between local Native American groups and Spanish Colonial settlements, as well as cattle, sheep, and horse pastoralism throughout the region. The comparison of similar high-resolution records of the last 1000 years and interdisciplinary research along the eastern Andes indicate that humans, by altering ignition frequency and the availability of fuels, variously muted or amplified the effects of climate on fire regimes. For example, fire activity at the northern and southern sites was low at times when the climate and vegetation were suitable for burning but lacked an ignition source. Conversely, abundant fires set by humans and/or infrequent lightning ignitions occurred during periods when warm, dry climate conditions coincided with ample vegetation (i.e., fuel) at midlatitude sites. Prior to European arrival, changes in Native American demography and land use influenced vegetation and fire regimes locally, but human influences were not widely evident in the paleoecological record until the 16th century CE, with the introduction of nonnative species (including Rumex acetosella, Plantago lanceolata, and Eurasian livestock), and then in the late 19th century CE, as Euro-Americans targeted specific resources to support local and national economies. The complex interactions between past climate variability, human activities, and ecosystem dynamics at the local scale are overlooked by approaches that infer levels of land use simply from population size or that rely on regionally composited data to detect drivers of past environmental change.