Disentangling the last 1,000 years of human–environment interactions along the eastern side of the southern Andes (34–52°S lat.)

Abstract

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 and their comparison with high-resolution paleoenvironmental records and archaeological/ethnohistorical information at other sites along the eastern Andes of southern Argentina and Chile (34–52°S). The records 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 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 until the 16th century, with the introduction of nonnative species (e.g., horses), and then in the late 19th century, 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.

The historical and archaeological evidence for Southern Cone human–environment interaction

“…But this explanation, focused on horses, cannot apply to the spread of Rumex acetosella and other nonnative species of plants, as well as increases in fire activity recorded at Río Rubens in ∼1590–1640 CE (360–310 cal y BP) mentioned by Nanavati et al. ( 1 ). This evidence precedes the known dispersal of horses to South Patagonia by centuries, and the importance of this record has not yet been completely explored.…”

“…The comparison of the pollen and microcharcoal information from Laguna El Sosneado, Mendoza, with other high-resolution records from southern South America is very informative ( 1 ). Particularly, the good use of the abundant archaeological information from Mendoza highlights the important fact that humans appear as agents of modification of fire regimes, particularly since the 16th century CE.…”

“…In general, this is a very difficult period to deal with using archaeological information (see below), but Nanavati et al. ( 1 ) identify the introduction of nonnative animals, mainly the horse, as an important agent of environmental change. The precise year of the introduction of horses is not well known, but they were seen in northern Patagonia at the beginning of the 17th century CE ( 2 ).…”

“…In PNAS, Nanavati et al. ( 1 ) study the available high-resolution pollen and microcharcoal columns for the last 1,000 y along a latitudinal transect in Patagonia. The result is a serious effort to understand the degree of alteration of landscapes by the human use of fire and the introduction of nonnative plants.…”

“…Nanavati et al. ( 1 ) show that the human imprint on the landscapes is not always evident, and—more important—is not exclusively dependent on population size. What population increase does is to augment the number of localities where pertinent information can be searched.…”